THE POWER PLANT OF THE INDUSTRIAL PLANT

THE POWER PLANT OF AN INDUSTRIAL PLANT

An industrial plant like a brewery, cement plant, sugar milling plant or a wood-based industrial complex may in some instances elect to put up a self-generating plant to support its power requirements. In the country, these power plants are either diesel or steam power plants. The steam power plants are commonly fuelled by coal, or a combination of bunker oil & wood wastes or a combination of oil & sugar cane refuse called bagasse.

There could be four reasons for the concept, i.e.:

1) there might be no existing power supplier in the vicinity where the industrial plant is to be erected,

2) the local electric cooperative in the area may not be capable to supply the needed power,

3) process steam may be intensive where co-generation with power could be most economically attractive,

4) the cost of self-generation may be very much cheaper than utility’s PPA-laden power rates.

While it is true that power lines of National Transmission Corporation (TransCO) are now criss-crossing the countryside, tapping to a distant 230 KV line may not be cost-effective for a medium size plant of say 10 or 20 MVA. A 69 KV TransCO sub-transmission line may be deemed best but may not be available in the area when the plant was conceptualized. On top of this, a number of Independent Power Producers (IPP’s) are recently courting many industrial plants with Build Own Operate (BOO) or Build Operate Transfer (BOT) schemes - somehow offering rates which are lower than that of the utilities. The idea is to install medium size generating plant (distributed generation) close to the industrial plant to supply the power requirements of the manufacturing plant. If the IPP’s can offer lower power rates but still can produce profits, then self-generation may be attractive.

DESIGN REQUIREMENTS

The appropriate size of the power plant can only be answered as a result of a thorough study of the circumstances surrounding the conditions of the system. For instance, if the power plant in concept is only for emergency supply in the events of power outages by the utility, then, 80% of maximum demand capacity in two (2) or three (3) generating units may be the right size for the system condition in an ATS configuration. In small systems where power interruptions can be tolerated, one or two generating units serving the loads may be sufficient, again with an Automatic Transfer System or ATS.

For medium size systems to act as “Island Generation”, stringent requirements have to be met by the power plant in concept. The determination of the size of the power plant and the number of units may pass through a careful study of the behavior of the plant served as reflected by its load profile and load duration curve. For instance, an electrical engineer who fully understands the behavior & peculiarities of a brewery or cement plant load should be there during the conceptualization of such a project.

For large island generation systems, the more tough requirements are needed in the process of selecting of the sizes and number of generating units. Theory of Probability on forced outages of generating sets is to be employed and inputted into the computations. It’s only then that the number & sizes of generating units can be established.

Power Plant Engineering Design is an art that includes selecting and placing the necessary generating equipment so that a maximum of return will result from optimum capital investments & maintenance costs over the working life of the plant (Life Cycle Cost). Most industries that self-generate usually make use of bunker oil-fed diesel engines or steam generators. Power may then be co-generated with steam where bulk of the power produced may be configured to become “free” or “by-product” by using a combination of straight condensing with topping or back-pressure turbines.

Normally in Steam Power Plants, a few diesel-driven generators are also used in combination with steam turbine-driven mainstays for purposes of starts-up or alternate power supply in times where the boilers are in maintenance during weekends.

In any case, the selection of sizes and number of generating units in a well-designed “island power generating plant” for a medium sized industry should consider the following factors:

 Safety - this means safety in design and good workmanship in the execution or installation of the system components. A good design and workmanship will result to safety of personnel and property.

 Economics - this means resulting to the best choice of arrangement that would deliver the most cost effective first cost (P/kw), and operational costs (P/kw-hr) as well. Economics however does not mean not to include the necessary spinning and ready reserve units required in an island generation power plant.

 Maintainability - this means that the power plant can still meet load requirements even if part of the plant is under maintenance. In real life scenario, it always a fact for diesel power plants that one of the generating units is under maintenance at any given time. If ever one unit is under maintenance and the power plant can not serve plant requirements, then that plant is ‘not maintainable’. This is one area that the engineering manager and the finance manager are always in quarrel i.e., in interpreting costs.

 Reliability of Service - The reliability of the power system is measured by its ability to serve all power demands made by its customers without failure over long periods of time. For instance, a common criterion is to install sufficient capacity to prevent interrupting power to customers oftener than one day in a 5-year period on a long time average basis. The second criterion is the appropriate size of the generating units that must be placed in the power plant to satisfy the base units and reserve requirements. This is so because the loss of a large unit will render the power plant incapacitated of this large capacity.

Reliability means capital investments. New Reliability requirements are now expressed in terms of “Reliability Nines” (four to six nines) and they don’t come cheap. The demand for more reserves would increase the cost of power. Inadequate reserve causes great inconvenience and economic loss to the business, both to the power plant and the customer plant. It is thus for the engineer to assess the balance of these two extremes.

 Availability - “Operating Availability” is the statistical measure showing how physically ready the generating unit or plant is, in producing power whether needed by the system or not. It is a measure of overall unit or plant dependability. Availability Performance further shows the effects of forced outages and the unexpected glitches in operation & maintenance. If the power plant in concept has to operate like a utility company or an “island generation” where all the power requirements have to be supplied by the power plant, then the stringent requirements described above have to be met. This means that loss of power is not tolerated, i.e., to protect spoilage of the product that may prove to be too expensive.

PRINCIPLES IN POWER PLANT DIMENSIONING

The design engineer must consider the loads as seen by the power plant in terms of Load Profiles & Load Duration Curves. Having established them, the engineer is now in the position to design the shape of the power plant in concept.

But let us be reminded however, that the power plant has its own complexities where such complexities must be satisfied, to wit;

 What made power plant operation complex is the inherent variability of the loads and the power plant must be ready and serve the load in any eventuality.

 The production, delivery & sale of electricity all happen at the same time. The product of the power plant, which is “power”, is not completed until the instant it is needed and used, at the quantity exactly equal to the demand at that instant.

 There is no simple way to “warehouse” an extra supply of “Kilowatts” or Kilowatt-Hours” against some future period of extraordinary demand, yet it is certain that such a period will occur.

The above simply means that there must be power at any time the customer needs, and this power must be sufficient with spinning reserves. It means further that the power plant supply must always be significantly greater than the demand at the instant and at any instance, for that matter.

There are no hard and fast rules governing the sizing of the power plant. According to the Standard Handbook for Electrical Engineers, 13th Edition, “a design of a generating plant derived from probability calculations is still subjective. It is still the “han-ay sa pinsada” of the engineer that counts.

The electrical engineer of the industrial plant therefore has to consider all the important factors of a reliable power plant that would be best suited to his requirements”. However, experiences and practices of North American and Japanese power engineers can help shed light to this thought process. CESEEPS Power Book 2 (Medium Voltage Systems & Applications in Industries) could be a great help.

Doods A. Amora (July 2007)

MODERN MAINTENANCE MANAGEMENT PRACTICES

MODERN MAINTENANCE MANAGEMENT PRACTICES

by DOODS A. AMORA, PEE

BACKGROUNDER

What has Maintenance got to do with the global competitiveness of the electrical practitioner? This question cropped up because even in the modern times, maintenance is not understood universally…

For instance, in Germany, Sir John Peter Koss in the Beverage World International February 1999 Issue said, “THE FUNCTION OF MAINTENANCE STILL MEANS DIFFERENT THINGS TO DIFFERENT PEOPLE”. The issues & major problems as he continued are the following:

1) Inadequate Definition & Documentation of the Maintenance System,
2) Improper Organizational Structure,
3) Incompetent & Insufficient Personnel,
4) Insufficient Funding for Required Work,
5) Inconsistent Management Comprehension & Attitude.

At the other side of the globe, in America, Sir Jean-Pierre Wolff, a NETA member (interNational Electrical Testing Association), & Vice President of Electro-Test, Inc., Pleasanton, California in one of his EC&M articles said: “Common Maintenance problems can be summarized as follows:

a) Insufficient Proactive Maintenance,
b) Frequent Problem Repetition,
c) Erroneous Maintenance Work,
d) Unnecessary and Conservative PM,
e) Poorly Defined Rationale for PM Action,
f) Maintenance Program Lacks Traceability and Visibility,
g) Blind Acceptance of OEM Inputs, and,
h) PM Variability Between Like or Similar Units”

In the Philippines? Oh, sure, we have all the above!


INTRODUCTION

The challenge to survive the hard times of the new millennium has not spared the area of maintenance. It can be recalled that the decade of the 90's saw the manufacturing business sector in serious search for radical changes to catch up with the demands of world-class competition aggravated by the effects of the region's economic meltdown. With the dim economic recovery scenario, maintenance engineering is no longer an innocent bystander in the dead corner of plant environment but now seen as an active participant in dampening the effects of the national debacle.

Management experts say that the ingredients of today’s competitiveness are: quality, efficiency & productivity. To help attain this goal, several old inefficient plants in the 90's were replaced with high technology lines giving way to modern techniques and processes in manufacturing. On top of this, organizations were restructured to meet new synergistic requirements. Several companies in the country sought for ISO certification - showing to the world that these companies are at par with world class standards. The mood in the 1990’s therefore was modernization to meet global competition. But modernization is in fact going back to basics, again to: quality, efficiency and productivity.

Physical modernization does not exempt maintenance from modernizing itself. Old & obsolete concepts in maintenance are seen slowly fading out as we enter into the new millennium. For instance, many businesses realize that production alone is not a guarantee to survival. In the 70’s & 80's, the mood of manufacturing business was production, production, and yes, production. Somewhere along the way, we did what North American managers were preaching, "that high production volume (large lot size) is where profitability is”. The Japanese on the other hand, later reinvented the concept that “production can best be done in smaller lot sizes while instituting built-in process-to-process quality control to ensure perfect products at the end of the line”.

Thus the concept of “zero defect” to the product and the concept of “zero breakdown” to process equipment became loud and very visible in the 90’s.

In the scene of plant maintenance, the concept that maintenance is nothing but a service unit has now been changed to the concept that “maintenance is a function of production, and conversely, production is a function of maintenance”.

Whether or not these new concepts are practicable is one question this paper seeks to answer.


HISTORY OF MAINTENANCE

The reason why the previous mind-sets and the need to shift to these new paradigms can be traced back to history…

Once upon a time, work for instance as in farming, was performed all by hand - without any machines or the benefit of technology. Some time later, tools were developed, and it then became very important to keep them intact and sharp otherwise the work can not be carried out efficiently. The demand for maintenance this time started to grow. Many years later, as electricity was invented then hastened by the Industrial Revolution of the West, production equipment started developing. The tools, implements and simple equipment at the beginning were not sophisticated enough such that a lot of people were required to keep production on stream. Production at this point was more or less, a handicraft.

Maintenance activities could not influence productivity so much (although it was important to keep the equipment running) because the quality and quantity of production were to a large extent decided by the skills of men and their capacity to work fast. All through a long period of time, from generation to generation, maintenance had been thought of as a service department - not a condition to production.

Times had changed. The quality and quantity of production now do not depend on man but on machines. With the increasing degree of automation and robotization in most manufacturing plants today, it is now appropriate to recall Mr. John Moubray a British expert on Reliability Centered Maintenance (RCM) when he said, "that product quality & quantity now depends on equipment". At the other side of the globe, Mr. Seiichi Nakajima, a Japanese guru on Total Productive Maintenance (TPM) preached: "that productivity, cost, inventory, safety, health and production output - as well as quality - now all depend on equipment”.

MISCONCEPTIONS ON MAINTENANCE

Some time in the 1990's, a survey was conducted in manufacturing plants in Cebu, to determine the mind-sets of personnel representing the cross-section of maintenance, operation and production workforce. Hereunder were the results with some comments and analysis:

1) "That Maintenance is an Expense, therefore a Necessary Evil"

That profit is the difference between revenue and expense. Minimizing expense is therefore maximizing profitability. This confirms the thoughts of Mr. William Bleuel of Barber Colman, Rockford, Illinois, when he wrote, “Each year, top management reviews the maintenance budget with an eagle’s eye towards making it as small as possible. Where this attitude prevails, maintenance would likely be given low priority. From this viewpoint, plant management usually takes a hard line that maintenance should be minimized”. This is what Mr. Thomas Alund, a Swedish maintenance consultant termed as “Cost Controlled Maintenance” - meaning that movements in a maintenance program are solely dictated by the money available in the budget.

The reason why maintenance is considered a cost-controlled activity is that engineers and technical men found it difficult to measure the investments on maintenance in total economic terms. It is very easy to find the cost of maintenance but difficult to quantify the results. Like an iceberg, where the biggest part is invisible under the water and only a small part visible above the surface. The visible part represents the direct maintenance expense while the invisible part silently denotes the various factors influenced by maintenance.

2) "That Good Maintenance is Repairing Broken Equipment Quickly"

The survey showed that "quick repairs on equipment" is a virtue. Restoring broken equipment back to operation in so short a time shows the mastery of maintenance men over their equipment. In any plant, there is always a guy – a technician, who always outshines his colleagues in troubleshooting equipment or system faults. Such guy, “Tarzan” the ‘trouble-shooter’ usually called out during the night has to come to the plant to make things going.

Tarzan is easily seen as the hero in the business. Because of this heroism, many Tarzans are promoted to supervisory positions but later found themselves in trouble handling managerial functions. Managerial skills are something else - a very different ballgame.

3) "That Production Group is the Adversary of Maintenance"

Observations in the past showed that production group oftentimes made maintenance the scapegoat and shock absorber whenever something in production went wrong. But it was also the same production people who always not grant maintenance sufficient time to maintain the equipment. Lording over during shifts, production people always make life of maintenance miserable.

4) "That Maintenance Men are Second Class Citizens in an Industrial World, Far Behind the Footings of their Counterparts in Production"

The belief was that, production is where revenue comes in. Production is making money while maintenance, the necessary evil. Hence, production groups are the favorites, maintenance the expense.

5) "That Maintenance Starts After the Equipment or Production Lines Have Been Commissioned"

Projects are someone else’s job. It’s not maintenance job anyway. Neither it’s production's job. But then, when the facility is in operation, people in the plant would start saying, “this should have been like this, and like that”.

6) "That It 's Very Difficult to Operate a PM System in a Plant"

“PM are nuisance activities. It only adds up workload to an already overloaded maintenance crew.” “Whether we like it or not, equipment will breakdown sooner or later. What's the fuss?”

These are just a few realities we gathered from the past perceptions on maintenance. These realities were not unique in the Philippines as they were also happening in advanced countries in Europe and the Americas.


MODERN CONCEPTS IN MAINTENANCE MANAGEMENT

As pointed out earlier, the name of the game in manufacturing today is automation & robotization. Why? Simply because in the global business arena, it is a must! John H. Zenger, a known American management expert in his book "Leading Teams" wrote, "In the 1960's, North America stood at the summit of world economic power. In those days, the order of the day for every manufacturing manager can be summarized by a sign that hung over his desk and that is: GOOD. FAST. CHEAP; PICK ANY TWO..!”

It means that:

"If you want quality and you want it fast, it'll cost you big bucks“.

"If you want it fast and cheap, no problem, but it won't be good enough to last through the winter“.

"If you want good quality at a good cheap price, that's fine too, but don't hold your breath for delivery. It'll probably take forever."

Then comes the customer’s cue to nod in wide-eyed agreement: "You always have to trade off one to get the other two“.

Today in the third millennium, a manufacturing company has to give out all the THREE, in order to survive fierce competition. In a customer-driven business environment, automation therefore becomes the answer to the need of efficiency & speed. Robotization where applicable, is the key to achieve large volume and uniform quality throughput especially in industries where human factor is too hazardous.

That in a nutshell, is why so many companies are putting themselves through so many agonizing internal changes, including the parting away of the traditional maintenance management styles. For until a manufacturing plant becomes "good, fast and cheap", it's an easy prey for any competitor that figures out how to deliver on all three.

In the past, responsibilities of maintenance are to concentrate only in making machines and equipment run in service to the production department. Today, maintenance is already included in the ownership of the quality and quantity of the products produced, because after all, it is maintenance’s job to make the process capability of the plant fit to produce such products.

Again, automation & robotization bring the equipment or machines to the center-stage. When we say equipment, it means maintenance. Maintenance now plays a much bigger role in production. Along with the shift in philosophies in maintenance, new concepts in modern management had been developed in Europe, among them are as follows:

ROLES OF MAINTENANCE IN MODERN MANAGEMENT

1) Achieve Target Production Outputs by Making the Process Equipment & Machineries Available,

2)Maintain Product Quality by Making Manufacturing Equipment Process Capable to Produce Such Product,

3)Implement Maintenance Services Imposed by Production Group,

4)Implement Systems & Routines to Sustain Equipment Effectiveness (e.g., PM),

5)Maintain Availability of Spare Parts & Materials,

6)Participate in the Conception & Implementation of Projects.

The first two roles of maintenance seem to be encroaching into productions group’s domain. But before anything else, a look at the roles of production in modern day management concept becomes necessary.

ROLES OF PRODUCTION IN MODERN MANAGEMENT

1) Achieve Target Production Outputs at Specified Quality Levels Through Process Efficiency (Zero Process Error), While Optimizing Utilization of Resources (man, machine, materials, method and time),

2) Operate, Clean, Align, Lubricate the Machines, Tighten Bolts, & Fix Simple Faults,

3) Monitor the Health Condition of Machineries & Equipment Leading to Imposition of Major Maintenance Schedules and the Eventual Preparation of the Plant for Maintenance,

4) Ensure Availability of Raw Materials and Finished Product Inventories,

5) Participates in the Conception & Implementation of Projects.

The first role of production focuses on process, practices and techniques in manufacturing. But items 2 & 3 can be perceived as maintenance functions. Seiichi Nakajima’s Total Productive Maintenance (TPM) confirmed this concept when machine operators in Japan became the first line of defense in the maintenance of the equipment. The new management concept in maintenance therefore runs like this:

“50% OF MAINTENANCE JOB IS PRODUCTION" &
"50% OF PRODUCTION’S JOB IS MAINTENANCE”

Radical as it may seem, but this can be aptly understood when applied to our own homes. Putting out a fire in our home is not supposed to be our job because it is the job of the city fire department. Extinguishing the fire as quickly as possible by the fire brigade speaks of its efficiency. But no amount of this type of efficiency can justify the job because in the first place, the fire should have not happened at all.

Exactly the same principle works in the plant. Modern Maintenance Management is not to repair broken equipment as quickly as possible because in the first place, it should have not happened at all. In other words, Tarzan must now be extinct because:

“GOOD MAINTENANCE IS NOT DOING THE WRONG WORK EFFICIENTLY”

There must be no fires. How to fight fires by preventing them to happen is from the very beginning the concern & responsibility of the “Taong Bahay”. Taong Bahay yes, are the production people.

But Mr. Nakajima’s TPM philosophy of “we operate, we maintain” does not really mean that full maintenance has to be accomplished by the operating personnel. In real life scenario, a person has to do maintenance of himself and to some degree performs some autonomy.

Personal maintenance activities like: taking a bath everyday, brushing of teeth, making oneself spic & span, eating the right food, daily exercises, etc. are just some maintenance activities that don’t need some neighbors to do it. To some extent, a headache, a stomach ache or muscle pains can be healed by self-medication, but then, if the problem needs an operation of the kidney or an organ transplant, or correction of an infection, definitely professional doctors are required to do it. In the same manner that annual physical/medical examinations can not be done by just anybody else except the doctors and their clinical staff.

Items 2 & 3 of the Roles of Production in Modern Plant Management, showed maintenance activities by the operators are limited to cleaning, lubricating, aligning, bolt tightening and finally, to fixing simple faults - all in the end view of preventing & controlling deterioration. Monitoring the health condition of the machines they tend, scheduling and preparation of the equipment for the eventual maintenance service are in modern management, obligations of the operating department. Teardowns are to be given to the surgeons - the maintenance department.

CONCLUSION

Modernizing maintenance management first needs top management’s re-thinking and realignment of beliefs. Seiichi Nakajima is telling us that if top management is not convinced of the true benefits of maintenance, then Total Productive Maintenance (TPM) can never take off. Modernizing maintenance must start from the top to bottom and includes all personnel in the plant. As a summary, among these beliefs are as follows:

 That Maintenance is Not a Necessary Evil But a Condition to Production,

 That Maintenance is 50% Production Job and Production is 50% Maintenance Job,

 That Maintenance Should be Seen as a Results-Controlled Enterprise”, Not a "Cost-Controlled Service Department in the Corner“,

 That Equipment Breakdown Should Not Happen at All, Because Good Maintenance is Not Repairing Broken Equipment But By Executing Planned Activities,

 That Production Group is Not the Adversary of Maintenance But Partners Sharing the Same Objectives,

 That Preventive Maintenance With Emphasis on Condition Monitoring is What We Need to make Maintenance More Effective,

 Systems Make Things Possible but It’s People Who Make Them Happen,

 That Honest-to-Goodness Maintenance is Needed to Achieve Good, Fast & Cheap products.

After all the modern concepts are understood, the next move is to define how maintenance performance must be measured. Basing on these measurements, attempts must be done to establish past performances. This will become the baseline reference. All future performances will be based on these baselines.

Target dramatic improvement as specific objective. Aim "zero downtime" first, later "zero breakdown".

Thirdly, is to overhaul existing maintenance management system with emphasis on planned maintenance imbedding the principles described herein this paper. This move normally needs changes in internal organizations.

Develop a new system and implement it in manual mode. It is important to feel the success or failure of the new system. This will also open up opportunities for changes and improvements. Implement changes before deciding to embark into computerization.

Next, is to computerize the entire system. Caution: Do not attempt to computerize your system when not ready. The last but not the least, management must look at maintenance as a new source of profit. A company with a good & effective maintenance program has a competitive edge over the others.

Remember:

In the past:
[COST + PROFIT] = [SELLING PRICE]

Today:
[SELLING PRICE] – [COST] = [PROFIT]

DAA/July 2, 2007

MAINTAINING MAINTENANCE

MAINTAINING MAINTENANCE

By Doods A. Amora, PEE

In the past, responsibilities of engineering maintenance had to concentrate only in making machineries & equipment run in service to production or operation departments. Today, maintenance is already included in the ownership of the quality and quantity of the products produced, because after all, it is maintenance’s job to make the process capability of the plant fit to produce such products. The many new concepts in modern maintenance management will then become as the bases in establishing the yardsticks in measuring performances in maintenance.

Quality maintenance is synonymous to quality product. This means that system equipment must be in tip-top condition, efficient, reliable and above all, available to service at any time they are needed. Quality maintenance in some plants is labelled as “Zero Production Downtime”, or in more strict fashion, others named it as “Zero Breakdown”. A “Zero Breakdown” policy can only be attained through a full time, whole-hearted and effective maintenance management, to include the commitment of top management. The key word here is “effective”. How effective the maintenance efforts are, is a question that every management should answer.

There are several ways in making a maintenance program in a plant. We say that a maintenance program is unique to every plant to fit different patterns of complexities in operation and to the different attributes of top level management policy towards maintenance. Some plants used to refer it as “Preventive Maintenance”, while others call it “Reliability Centered Maintenance” or others label it as “Total Productive Maintenance”. Whatever the program is, the objective is common - that is, to bring the plant to shape.

THE MAINTENANCE PERFORMANCE AUDIT

It is important to mention that most manufacturing plants in the country today do not have any visible indicators of the effectiveness of their own maintenance programs.

In many instances, maintenance crew used to content themselves in having successfully weathered major breakdowns which may have earlier required a round-the-clock work. With all the adrenaline flowing, we may call it as “Magdamag Type Maintenance”.

But there can never be quality maintenance in this case, because after the euphoria of its “heroism”, comes the tendency to relax and be complacent from the true attributes of maintenance. What happens next is what we call “Pa-Easy Easy Na Lang Maintenance” or “Waiting-for-Trouble” maintenance. In short, our maintenance attitudes seem to follow a biorhythm cycle - ‘sometimes up, sometimes down’. What if the maintenance referred to in this discussion, is that of an airliner? Something therefore has to be done by way of controlling the direction of maintenance towards consistent and sustained effectiveness. This is what this author called, “Maintaining Maintenance”. Have we ever thought of how to maintain maintenance?

Establishment of a maintenance performance standard is very much wanting if we are determined to monitor and eventually improve its performance. One way to do this is to look into the past by conducting a SYSTEM AUDIT on historical performance levels, where the objectives towards improving them are anchored.

As examples of maintenance audits, two common scenarios can be used as pilot areas, to wit:

 A Utilities/Support Plant which services the requirements of the production process, (a parallel configuration plant).

 A Production Plant producing the main product line, (a serial configuration plant).

THE UTILITY/SUPPORT PLANT

It is typical for support plants like steam, water treatment, refrigeration or power generating plants supplying utilities for production processes to have over its maximum duties, substantial sizes and number of reserve equipment necessary for the continuity & reliability of its operation.

Note that because of the installed spare units in a ‘support plant’, system outages leading to production downtime are always averted, as failure of one equipment could not necessarily affect the operation of a production line at the other side of the wall.

Most support plants are in parallel configuration, or in a few instances, a combination of parallel and serial set-up, while production lines are usually arranged in serial configuration. In the absence of any maintenance audit however, individual equipment maintenance status could not be made readily visible to top management and even by the maintenance group themselves, thus explains the complacency towards the ever-readiness of system machineries.

In a System Audit, the most important parameter that higher management should monitor is the “EQUIPMENT READINESS or AVAILABILITY FACTOR” or to a greater view, the “SYSTEM READINESS or SYSTEM AVAILABILITY FACTOR”. Measuring effectiveness of maintenance is to see how consistently ready the system equipment are, or how capable the support systems are in meeting the variable demands of operation or production. In other words, given a system with ample spare units, it would be unthinkable that if in the event of failure of one operating machine, the supposed back-ups could not be available for service for reasons that these equipments are undergoing maintenance or in a more horrible scenario, still waiting for spare parts to come.

THE PRODUCTION PLANT

One must appreciate that the scenario in a production or manufacturing line is quite different from that of a support plant described above. Most production lines are arranged in serial configuration such that a failure of one process equipment brings the entire plant to a halt as in the case of a Bottling Plant. The interruption means production downtime in terms of minutes or hours or in some cases, days. In these events, equipment breakdowns or maintenance failures are highly visible to top management owing to the loss of opportunity notwithstanding the shooting up of operating costs per unit product. A maintenance performance audit and monitoring is likewise necessary for standard setting, performance improvements and control. However, the standard parameters differ from that of a support plant.

SETTING-UP STANDARDS IN MAINTENANCE

With the discoveries following a system audit, it becomes necessary to set up standards of maintenance effectiveness on the basis of system availability or readiness. System Readiness in a way speaks of the capability of the system in a given time frame. It is also from this context that effective planning of maintenance activities and operations planning, as well must be based. Hence, in planning sessions where Maintenance, Operations & Production groups are in attendance, minimum set standards can be formulated based on critical scenarios.

HISTORICAL PERFORMANCE FITTED IN ESTABLISHED STANDARDS

Looking back to the historical performance gathered from the audit and making use of the established standards, charts will give insights on what happened to system availability or readiness within the subject years of the audit. From the charts, it would likely become evident that there are still much need for maintenance to improve particularly in systems which did not meet the minimum standards.

If and when the system readiness standards are attained through the concerted efforts of operations and maintenance groups, a smooth & uninterrupted plant operation can be assured. In effect, there is no substitute to planning in maintenance. But then, to properly plan the program, it is necessary for the operation group to be actively involved ensuring that a fair share of maintenance time and attention be given to each equipment. A Maintenance-Operation Master Plan becomes inevitable.

THE OPERATION–MAINTENANCE MASTER PLAN

With the standard properly established, what comes next is the conceptualization of a plant strategy in a yearly scope with the end view of injecting “just the right maintenance dose” to each major equipment of the plant. This means that the plan must not exceed the maintenance time allocated for each equipment.

Working as a team, Operations & Maintenance Groups shall formulate the master plan. This is to capture the relevance, practicability & attainability of the plan. Moreover, this strategy will make up the complete faith & commitment to the program and the belief of their capabilities to accomplish what they themselves had planned. Again a Master Plan in forms of Charts may be created and are expected to reap the following benefits:

1) Planning out for a realistic maintenance budget for the year,

2) Procurement of indented spare parts can realistically be programmed viz-a-viz the maintenance service schedule,

3) Equitable share of operation of the system equipment will be realized,

4) Implementation of the master plan as one of the specific objectives (SO’s) of the concerned parties can be made as basis in performance appraisals, thereby eliminating subjectivity,

5) Availability of system equipment is ensured at any point in time.

CONCLUSION

Measuring the effectiveness of maintenance had been proven to have tremendous benefits to management. As a management tool, it provides ease in planning, directing, controlling and implementing maintenance strategies towards a well-defined objective. Results of Maintenance Performance Measurement System should be made available to the people in terms of Daily, Weekly, Monthly and Year-to-Date Charts posted on bulletin boards indicating their performance. The system will boost the morale of the individual as well as the teams challenged for improved performance. The will to achieve and to be counted as one, will become a bandwagon.

It might after all not impossible to achieve that elusive “Zero Breakdown” mark.

DAA/June 2007

THE NEW WAVE OF PROFESSIONAL ELECTRICAL ENGINEERS

Backgrounder: Recent developments brought me to edit and republish my article on similar topic which was posted in this blogsite some time last year.

THE NEW WAVE OF PROFESSIONAL ELECTRICAL ENGINEERS

By DOODS AMORA, PEE 1821

We have just been through with the April 2007 PEE Board exams… As we recall, we started this advocacy in Y2003 when I urged every promising REE to take the PEE licensure. Then we started with several hopefuls, but in the end -- only a few survived. ..

Although the candidates logged in their belts some 10, 15 years or more in actual experience of the profession, it took a series of training regimens in two years time to build-up enough confidence for the first five REE’s to venture out of the comfort of their shells and set sail through an open ocean - eventually ending up submitting themselves to the grueling PEE exams.

As of today, we have covered three (3) batches of eventful successes. To recall, in the September 2005 exams, five out five, then followed by two out of two in September 2006 and lately, three out of three REE’s in April 2007, a total of ten - all took the exams and successfully passed the PEE Licensure! The ten (10) New Wave PEE’s as we call them - 100%, no more, no less…!

THE SCENES BEHIND

The glorious trumpets were deafening - each note reverberating sweet tunes. But behind those exploits were unspoken but open secret tales of dedication, perseverance, even embarrassments…

Looking back at the very first rung of the ladder, we found ourselves groping in the dark how it is to become a PEE the RA7920 way. Then we realized that the molding of an REE to fit as PEE has to be in a ‘total change in personality’ approach; meaning - bearing competencies transcending not only in technical designing, but also from planning to project execution, from basic communications skills to effective lecturing, from system operation to plant management and more importantly, from a coy personality to a confident responsible engineer that a PEE should be.

The First Wave: The first batch of engineers went through frequent storms and icebergs that clogged the way, then we saw ourselves struggling at every challenge everyday, one episode at a time. That’s the only way. The sailing was rough - it wasn’t easy because in the actual face-off, you would not know what punch will hit you. And you have to cover vast areas of possibilities. Yet five out of fifteen original candidates for PEE’s persevered & survived the tough training episodes and thereafter saw land to seek shelter.

As we reminisce, battle-scarred yet we emerged victorious in our own small ways. Engineers Achilles Ponce of Mactan-Cebu International Airport, Ernie Abunda Jr of San Miguel Corporation–Glass Plant, Fred Mercado of UMMSI, Generoso Bayno Jr of APOCEMCO and Cesar Fernandez Jr of Taiheyo Cement Corporation eventually joined the companeros of PEE’s in this part of the country. We tried and succeeded. The proverbial ice was finally broken - that was September 2005… but history did not end there.

The Second Wave: The journey continued… while regaining strength for the next saga of the journey, the staccato of the engines of change kept throbbing on more relentlessly with power & energy. The fire was burning hot as the promising light beckoning from afar. At least, we already had the experience! We should be bolder, this time.

The tigers’ paws on guard in anticipation while the eagle’s watchful eyes probing into the still unclear wilderness. This time, seventeen hopefuls reported for duty, many of them veterans from the previous training. But then as the days went by, the flame of determination dwindled and flippancy caught several of them too fragile to continue. We wondered if this is a natural course of consequence, or ningas cogon..? Probably, yes… But six contenders somehow endured their wits but only two were readily-geared up to face the second battle in September 2006.

The time came. When the dust cleared, another canto had been captured. As the spoils of the second combat settled, two from this forum successfully made it! And two had been added to the list of new PEE’s in this loop, namely: colleagues Engr. Camilo Castro of Mactan-Cebu International Airport and Engr. Giardelo Guilas of General Milling Corporation. The feeling was superbly satisfying.

The Third Wave: Now refueled, our group was then again ready to embark into another uncharted chapter of the next battle. The four survivors of the training…? Only three were determined to face the April of 2007 arena, while one opted to hibernate in his tunnel, at least for the moment.

Tired but not spent. Weakened but not short of second wind. Still potent and sharp, this time wiser, more experienced… more determined.

Casualties so far? Zero…
Injuries? There were some setbacks, but everybody is standing upright…
Morale? Everybody is proud and smiling…

Engineers Jason Joule Troyo of Konsult Construction Corp., Willie Canizares of Cebu Power Exponents & Services Inc. and Franco Obierez of GTB Industrial Network Inc. finally braved the April 2007 heat into fruition and found themselves in the most demanding, most exciting and most exhausting PEE exams so far experienced. Yet their Technical Reports are highly praised and may even end up as model dissertations in the archives of National IIEE library. Needless to say, the only PEE passers in that examination – you guess it right, they are the only ones…!


HOW DO WE ACHIEVE SUCCESS?

The Fear Factor: The ‘Fear Factor’ as Engr. Noel Fernandez had always pointed out, is the biggest adversary. It is in fact the ‘handicap’ exemplified by the butterflies in one’s stomach that drive one player lose his wits during rounds of grueling combat inside a four walled ring, one against three authorities. As Willie Canizares said, “I felt I was well prepared for the oral exams, but it seemed everything in my mind vaporized when I entered the interview room. It was just good chance that I was able to recover sooner”. Therefore, the candidate must develop the necessary confidence to conquer the fear of the unknown. How? Practice, practice and practice…

Mentoring: After every success, the examinees are always quick in expressing their gratitude to their CESEEPS mentors who are at the same time their tormentors in training. Yes, success in a competitive game is usually won by team play and coaches do play big roles. However, success in one’s personal battle as in the board examinations is not won by coaches. It has to be won by the individual himself because he is not competing against others. He is in fact fighting against his own shadow.

Freddie Roach has made a lot of history. But his role is only limited, he can’t do anything once the player is already inside the ring. Once unleashed, it is the player’s diskarte that matters in solving the puzzles while alone. Let me tell you that our motivation as mentors is only to make our colleagues a much better technocrat in the dispensation of his responsibilities as an engineer. The decision to take the PEE Board Exams is by the individual himself.

Preparedness: The big difference however is preparedness and anticipation. As Achilles Ponce’s Technical Report states, “Looking through the future, there must be that so-called anticipation – and anticipation leads to preparedness as an answer to complete the loop. Surprisingly most of the time, preparedness derived from anticipation can only be discovered if we look back to past and historical performances. And past statistics usually become the answer and guide in future plans of actions”.

It is best to prepare and anticipate. But preparedness does not mean that we allow ourselves to lose track of the basics. It is the bedrock foundation of our competence. Once the basics are forgotten, the foundation will be weakened and the structure might crumble. Do not belittle these Code Basics because you will experience later that these basics after all will make someone a PEE. I am therefore inviting you all to focus on these basics.


WHY ‘NEW WAVE OF PEE’s’?

In our own definition, the new wave PEE’s are those who got their PEE status under the domain of RA7920. That makes RA184 PEE’s like me to belong to the old wave. During our time, we took written exams on the subjects: a) Mathematics, b) General Engineering, c) Electrical Engineering, d) Design & Construction and had to submit a Technical Report. The new wave PEE’s under RA 7920 have only to submit a Technical Report, take the Interview and defend his written report. By quick glance, it seems that the PEE licensure under RA7920 is much easier than its predecessor law. However, there is more to it than meets the eyes. Why is it that with the seemingly easier conditions now, there are only few PEE passers today as compared to the past? In reality, passing the PEE today is a huge job – it is to me, 10 times harder than before.


HOW TO BECOME A PEE?

As what I’ve been saying, there are only three ingredients in passing the PEE board exams and that is: work, work & work. As Franco Obierez puts it, “there is no such thing as something for nothing”. This means that nothing can be harvested if nothing had been planted. We need to work for it. And we mean hard work!

Of course, what constitutes hard work are the following:

Know your Engineering. The REE must re-engineer himself worthy in the PEE face-off. An engineer who thinks that ‘oido engineering’ can bring him success, he better think more seriously because he can never pass the PEE that way. Fact is that, the BSEE course plus experience is not enough. You might be an experienced engineer in a Power Plant or a Manufacturing Pant for 20 years but repetitive chores might have brought it down to an actual equivalency of only three years. You need to explore and be conversant of the other spectrums of the profession. Remember, the PEE license gives you the authority to practice the full scope of the profession. Thus the PEE interview anchors on all established principles of electrical engineering and not on “invented” practices without theoretical basis. The PEE candidate can not therefore escape engineering theories, because all good responsible practices came from proven engineering principles.

Know your English. An engineer no matter how good he is in work but who is not good in his English is not a ‘good’ PEE candidate. Writing the Technical Report needs mastery of Technical English. The most difficult part of the PEE journey as admitted by most candidates is the actual writing of the report. It is therefore advised that if you are grooming yourself for the PEE board exams in the near future, you must have right now in your possession books on “Technical Report Writing”. Practicing the recommendations of these books now will help you express yourself technically comes the Technical Report preparation and the actual PEE interview.

Know your Drawings. A working knowledge in A-CAD or Visio software is a heavy advantage. However, what matters most is the mastery on how to construct complete & correct single line system diagrams in internationally accepted symbologies. Internationally accepted symbology doesn’t mean amalgamating ANSI and IEC symbols in one diagram. Most Single Line Diagrams that we saw used to be in this predicament and it only shows that the author doesn’t know his standards. If you intend to use ANSI, it should be ANSI all throughout. If IEC-based, it should be IEC all throughout. On top of these, several System Single Line Diagrams are incomplete thus; a system presented with lacking components can not in reality stand alone and won’t work! A lot of PEE candidates that I know need improvements in this department.

Know How to Answer Questions. Questions by the examiners need to be answered surely and confidently. Answers with pre-qualifying words, “I think…” won’t work, because a follow-up question like, “are you sure?” will send your structure crumbling. Do not lie or guess. If you don’t know the answer, honestly tell the examiners, you don’t have the actual experience. Moreover, do not think that the interview is only a question and answer affair. You may be required to write your calculations on the board. That’s why practice lecturing and repetitively drawing your system on the board will give you the taste of this competence.


NOW BACK TO BASICS

The danger of success is success itself – it’s intoxicating. We therefore need to always look back where we were before. “Ang taong hindi lumingon sa pinang-galingan ay hindi makakarating sa patutunguhan”. Looking back, we need to re-nurture the conviction of the principles we had been applying in the past several years. “If we rest, we rust. We shall never sit on our laurels. Our best is not enough. Our cup must never be full”. Do not mind the pressures imposed on you by the mentors. As I said, pressures in work are realities to live with, because we need it! Open a faucet and water flows from it. Why? Because there is pressure! Be a part of the team. Never be in the sideline, because if you are, you will be left behind.

Work is Force Times Distance: The tons of force exerted are nothing if you covered no distance. Passing the PEE Board is a vast mile covered. That is big work done!

To the new PEE’s, there's one fact in life that I would like you to keep in mind always. Just as life is temporal, life's setbacks are more recurring. The duration of these setbacks are a lot shorter than life itself. So don't allow these setbacks to spoil what otherwise is a life worth living. Your perseverance in turning around some of the extemporaneous setbacks in your interview performance was something not entirely surprising to me. It would have been surprising if it were someone else who did it. But knowing you and what you are capable of doing, you just have to do it because that's the stuff you are made of. Let me tell you this as part of your development and growth: I've known you people to be the kind of characters who eat personal challenges for breakfast, lunch and dinner. The problem as I see it is this: When those challenges disappear, you begin to starve. The biggest challenge therefore for you is how to keep looking at every situation as one that needs challenge. In other words, the challenge to challenge, and don't let mere words get the better of you.

You will therefore do your share in training others. It will be something of a work in a lifetime.

Doods A. Amora, PEE
May 8, 2007

A PROLOGUE TO FAULT CALCULATIONS (Part IV)

A PROLOGUE TO FAULT CALCULATIONS
(Last Part of a Series)

SELECTION OF EQUIPMENT

To recap, short circuits must therefore be quickly removed from the power system and this is the reason why protective devices such as circuit breakers and fuses are being placed there. To accomplish this, the protective devices must have the ability to interrupt the maximum short circuit current without injury; otherwise the injured breaker becomes the fault itself. The maximum value of short circuit current is frequently referred to as the “available short circuit current” or in some other terminology, the “available SC MVA”. The protective devices at any point of the system must be sized such that in any event of fault wherever they might be in the system, the associated upstream device closest to the fault must first interrupt the fault without disturbing others. The value of short circuit current is directly related to the size and capacity of the reference power source and is independent of the load current of the circuit being protected. The larger the capacity of the reference power source (e.g. larger transformer sizes), the greater the short circuit will be, while cable impedances along its path tend to lower them down.

Once the short-circuit levels are determined, the engineer can specify proper interrupting rating requirements, selectively coordinate the system and provide component protection. With personnel safety while minimizing equipment damage in mind, it is essential to use equipment with short circuit ratings greater than the available short circuit current that can occur at the equipment location. The 2005 National Electrical Code states that: “Art. 110.9 Interrupting Rating. Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment. Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted”.

When these requirements are applied to a circuit breaker, busway or to switchgear bracing, the maximum 3-phase fault current the breaker will be required to interrupt must be calculated. This current is applied as the short-circuit current available at the terminals of the protective device.

Distribution equipment, such as circuit breakers, fuses, busways, switchgears and MCCs have interrupting or withstand ratings defined by the maximum rms values of symmetrical current. In MV systems, as GE Publication GET-3550F say: “a circuit breaker can't interrupt a circuit at the instant of inception of a short circuit. Instead, due to the relay time delay and breaker contact parting time, it will interrupt the current after a period of five to eight cycles, by which time the DC component would have decayed to nearly zero and the fault will be virtually symmetrical.”

“Closing a breaker against an existing fault makes it possible to intercept the peak asymmetrical short-circuit current, which is greater than the rms value of the symmetrical current. Fault analysis must thus calculate and compare symmetrical and asymmetrical current values in order to select a protective device to adequately protect a piece of electrical distribution equipment. For this reason, equipment is also tested at a particular test X/R ratio value typical to a particular electrical apparatus, such as switchgear, switchboards, or circuit breakers, and is designed and rated to withstand and/or close and latch the peak asymmetrical current described above.” It is also for this reason that modern circuit breakers have built-in rms momentary rating equal to 1.6 times the symmetrical current rating for medium voltage circuit breakers and typically 1.25 times for low voltage circuit breakers.

Calculations seeking for maximum fault duties for purposes of establishing KAIC or MVA ratings of circuit breakers or switchgears must not be misinterpreted as applied to breaker trippings. As explained earlier, the KAIC or MVA rating of a protective device is intended to be over & above the actual fault currents flowing into it such that the same shall not disintegrate or injure itself in the course of interrupting such faults. That’s why in breaker KAIC sizing, it is important to know the maximum possible fault current at any condition because the interrupting ratings of the devices placed in the system must be capable of enduring the tremendous energy associated with faults.

‘Breaker Tripping’ in MV systems on the other hand is applied to ‘Protective Relaying’. Tripping points are settable and can be programmed, in fact, contrary to KAIC capabilities; minimum fault current values are sought in protective relaying. Arming up relays are programmed not at maximum fault currents ‘per se’, but on lesser fault values suited for its operation depending on the Time Current Performance Curve selected and the way the engineer wants them to perform. These settings also include varying degrees of overloads.

Therefore, a high interrupting capacity rated circuit breaker does not mean that it can not trip during low magnitude faults. Nor that it would only trip during high fault current condition. The relay trips the breaker according to how the relay is set. This is true to all power circuit breakers whether medium or low voltage.

For low voltage Molded Case Circuit Breaker applications, the principle of KAIC sizing remains in effect. The only difference is the absence of protective relays in MCCB’s. In MCCB’s, its built-in thermal element takes care of overload conditions as can be selected through its Continuous Current Rating while its magnetic trip element for faults.

DIMENSIONING THE CIRCUIT BREAKER

We have to establish and completely specify the KAIC or MVA ratings of circuit breakers. What then is KAIC all about?

To start with, each circuit breaker has three most important ratings – a continuous current rating, a voltage rating and an interrupting capacity (IC) rating. The IC rating is the maximum amount of current that the device will open safely to relieve a fault condition - without injuring itself. The ‘injury’ means the condition where after interrupting a fault, the breaker ceased to be operable - or worse, the breaker disintegrated because the fault current is too much for the breaker to handle. It must be remembered that breakers are placed in the system to protect the system itself. What if during a fault, it is the protective device that disintegrated? Isn’t it the design engineer’s lapses? Well and good, “the installation is operating for five years and no untoward incident like this happened, if it is my fault, why only now?”, says the engineer. Fine.., because in five years time there was no fault! It’s worthwhile to mention that breakers are not placed in the system for normal conditions; breakers are expected to perform its intended work during abnormal conditions. Abnormal conditions don’t just happen during the first energization event. They happen when the installations are going older where faults are lurking and loads are becoming more demanding.

New generation circuit breakers do not include anymore the “momentary rating” in its nameplates. The “momentary rating” (in answer to the asymmetrical current during the inception of the fault) as expressed in the old generation breakers refers to the greatest current that the device must withstand during the first half-cycle of the fault - where the transient contributions of the synchronous & induction motors in the system along with the DC component (which make the fault current asymmetrical) do occur.

It should not be understood that the momentary rating is already scrapped out. What was done was that the momentary rating is already built-in the KAIC symmetrical rating of the modern day protective device. In the interest of simplicity in the calculation and specification, the recent general procedure in breaker sizing is only to compute for the symmetrical fault current values and specify the KAIC ratings based on those values. New generation breakers do express in their nameplates the symmetrical KAIC or MVA but in reality, the momentary rating is already built-in (normally with the factor of 1.6 times the nameplate KAIC for high & medium voltage and 1.25 for low voltage circuit breakers).
.
Therefore, it is not enough to specify the Continuous Current Rating and Voltage Rating of the breaker but most importantly, the engineer must specify the KAIC ratings of these protective devices. This does not only cover the large breakers but must transcend to all breakers including the smallest branch circuits at the end points of the system.

THE VALUE OF FAULT CALCULATIONS

The output of a fault calculation exercise will bear in the engineer’s frame of mind, the following realities. During fault conditions, i.e., three-phase faults, phase-to-phase faults, single line-to-ground faults whether bolted or arcing faults, the system behaves tremendously different from normal conditions:

1) During fault conditions, the system current behavior is to skyrocket to magnitudes in the KA levels at fraction of a second time condition where sub-transient reactances (not steady state) in the system prevail,

2) That during these conditions the protective devices must work as intended to,

3) That the protective device must not disintegrate or injure itself during these abnormal conditions and it is the responsibility of the engineer in providing such technical expertise in the design of the system in the first place,

4) That too much over-sizing or under-sizing of breaker KAIC ratings because of oversight is not supposed to be acceptable. Too much over-sizing results to tremendously large costs than what is needed while KAIC undersizing might result to disintegration of the breaker,

5) That lengths & sizes cables, sizes & impedances of transformers, fault duties of utility companies influence determination of the KAIC specifications of the breakers,

6) That the design engineer must perform a “Power System Study/Analysis” on the industrial plant he is supposed to be designing, especially in breaker KAIC sizing, protective relay settings and coordination/ discrimination,


MEDIUM VOLTAGE POWER CIRCUIT BREAKERS

Power Circuit Breakers for medium voltage application in the Philippines industries are in the 2.4, 4.16, 6.9, 13.8, 34.5 & 69 KV levels. These circuit breakers are in the forms of: Air, Oil, SF6 Gas or Vacuum types. Air & Oil Circuit Breakers are now obsolete while Vacuum Circuit Breakers are in the trend today – soon to replace the SF6 types which are lately found as non-environmentally friendly.

Vacuum Circuit Breakers at the time of this writing have reached the confidence level at the 25 KV Class while a few manufacturers claimed to have produced vacuum breakers at 36 KV levels. Leading electrical manufacturing countries in the world have been developing vacuum circuit breakers for applications at higher voltage classes with the intention that new generation vacuum breakers will replace the existing SF6 breakers in the immediate future. In the meantime, breakers at 36 KV, 69 KV and above have yet to contend with SF6 types.

LOW VOLTAGE CIRCUIT BREAKERS

The larger low voltage circuit breakers with trip units are known in the USA as "LV Power Circuit Breaker” while in Europe this type is called “Air Circuit Breaker”. LV Power Circuit Breakers are usually used in Power Transformers with low voltage secondaries. Consequently, Molded Case Circuit Breakers downstream the distribution feeders are recommended. Note the KAIC ratings of these circuit breakers on the manufacturers’ standard tables.

The Industrial Plant Systems Designer (IPSD) must know the fault duties of circuit breakers at any point of the system including the low voltage side. These fault duties will be pegged as the minimum KAIC ratings of the circuit breakers which will then be matched with standard ratings of circuit breakers available in the market. The engineer then has to specify the KAIC ratings in terms of standard sizes. The process may look easy in words but because of so many frame sizes & types with corresponding KAIC ratings in a continuous current rating of the breaker, the exercise is confusing than it may suggest. Before performing any fault calculation exercise, it is imperative to look at the ratings of modern-day molded circuit breakers. Note however that other manufacturers especially European–based have different KAIC ratings. It is therefore recommended to consult product journals/catalogs so that specifications will be done accordingly.

(End of Article)

A PROLOGUE TO FAULT CALCULATIONS (Part III)

A PROLOGUE TO FAULT CALCULATIONS
(Third of a Series)

TRUE-TO-LIFE STORY

In an effort to highlight system fault protection, it is deemed worthwhile to share a true-to-life story - the lessons learned from which, are worthy to recall:

In one afternoon of July 1999, four explosions in succession were heard over the whole plant area, the last of which was the loudest. One of the four XLPE 500 MCM phase “X1” (Phase “A”) main secondary conductors of the 5 MVA, 69KV/4.16KV Substation “B” developed an single-line-to-ground fault with the steel structure supporting the cables & the AVR by-pass switch. All the four events of faults did not trip the 69 KV SF6 primary circuit breaker that could have isolated the fault. The fourth fault eventually melted & cut-off the faulted cable while cutting a portion of the 8” steel channel member of the structure. In other words, the fault cleared itself when the faulted cable was cut-off - likened to the operation of a 500 MCM ‘fuse link’. Power from the Utility remained on line until plant personnel shut off the primary breaker. Utility System did not trip off because to the eyes of the utility it was only a throughfault. The nearest Utility breaker is some 25 kilometers away.

Each substation system was provided with GEC Alsthom top-of-the-line KCGG 140 phase overcurrent with residual ground relay at the primary circuit. Likewise, the transformer was provided with GEC Alsthom MBCH differential relay coupled with a lockout relay. The lock-out relay also accommodates signals on transformer over-temperature and over-pressure parameters that will trigger trippings of both the primary and secondary breakers. There was also a back-up ground fault protective relay 51G at the transformer neutral circuit. The system therefore was provided with millions of peso worth of protection equipment & devices the books could offer.

After the smoke cleared, subsequent investigation revealed the following:

 "The GEC Alsthom KCGG 140 Relay (50-51/50N-51N) for the primary circuit was found not ‘armed’ or ‘set up’. Parameters found were factory default values and therefore not “enabled”. Likewise, the tripping contact circuit was erroneously wired such that even if the relay worked, no breaker tripping could be realized.

 "The GEC Alsthom MBCH differential relay (87T) for transformer protection was tested and found OK, but the lockout relay (86T) did not trigger tripping because the lock-out relay dc power supply was incompletely wired. When the lock-out relay was finally made activated and simulated, no trippings of the 69 KV primary breaker and the main 5 KV secondary breaker happened. Again, the wirings were found erroneous.

 "The back-up ground protection (51G) was not set up as it was not correctly wired. If correctly wired and set up, this relay could have tripped the primary breaker and could have isolated the transformer should all other relays failed.

The subject plant is located somewhere in the southern part of the country. Built in nice quality aesthetics with recognition as ISO 9002 & ISO 14000 certified, the plant was made operational in 1995. However, it took four (4) years to discover the uselessness of the installed protective devices because of a simple reason, i. e., failing to arm the protective system into putting it to work when the need comes. A check with the other 5 MVA Substation "A" revealed the same condition as the faulted Substation "B". The rest is now history…

By sheer luck, there was a good thing that did not happen in the above story: the transformer was not burned, at least for the moment. Otherwise the transformer could have joined the archives of electrical disasters.

According to IEEE publications, damage to transformers brought by faults is cumulative. It means that in this case, there were already four faults that the transformer had been subjected to! Thanks, it did not give way in the fourth fault! But luck will surely run out. The engineer must not rely on luck, because the possibility of a disaster is always there - like a Sword of Damocles hanging over his neck.

In such a ground fault, how much destructive current was involved? Among others, this is what this paper seeks to answer.

POWER SYSTEM STUDY FOR EXISTING PLANTS

For existing installations where there are no visible fault calculation records, a Power System Study is necessary to establish the integrity of the power system. The value of Power System Study confirming correct ratings of circuit breakers leading to effective protective relaying can not be appreciated until a major fault occurred, after all - the protection system only comes to work during these abnormal times. Beyond a nice looking system, any industrial plant must review and see to it that the protection scheme is properly commissioned, set to predetermined performance levels, tested, simulated and live up to predictable expectations. The new Distribution Code and the new Grid Code of the Philippines require these commissioning chores.

Moreover, it seems that budgets for power system studies & commissioning most of the time, are forgotten or even not considered as necessary when it is in fact, the most important phase of a power system project. The truth of the matter is that commissioning the power system of a plant is never easy. It requires expertise & confidence acquired over long years of experience & practice. It also requires a battery of tests and test equipments that are not cheap, and the activity itself is NOT CHEAP.

In fact it needs a Power System Study to correctly set or arm the system protection devices. What happens next is that systems are energized with protective equipment & devices not commissioned to respond to abnormalities. Again, as long as when the system is energized, that’s it. Why mess with success? With lots of luck, the system operates for a few years, until an explosion is heard. Then, the electrical engineer will be brought to the center stage – grilled! Electrical Engineering is perceived by many as an easy job! No! Electrical Engineering is never easy! And nobody can substitute electrical engineers in his playing field.

(to be continued...)

A PROLOGUE TO FAULT CALCULATION (Part II)

A PROLOGUE TO FAULT CALCULATIONS
(Second of a Series)

THE NEED FOR FAULT CALCULATIONS IN DESIGN

Fault Calculations must precede any effort to procure system protection devices. This activity is supposed to be one major part of the design process, but is oftentimes skipped or omitted. Several provisions of the National Electrical Code, the Philippine Electrical Code & ANSI/IEEE Publications relate to proper system protection. Safe and reliable operation of the industrial plant based on these provisions mandate that electrical systems must be protected adequately & effectively.

While over-current protective devices (OCPD’s) are provided for overload protection for system components such as switchgears, busses, wires & cables, motor controllers, etc; it is also necessary as discussed earlier to place protection for more damaging events such as faults. To obtain a reliable operation and to assure that system components are protected from damage during abnormal events, it is necessary to first calculate the fault duties at various points in the electrical system while still on the drawing boards and adequate protective devices must subsequently be in place to anticipate these faults.

For all possible conditions, it is the responsibility of the system designer to design electric power systems with adequate control of short circuits as one major consideration. It is also the plant engineer’s responsibility to see to it that the protective relaying devices are armed to pre-determined settings either by himself or by consultants. As can be recalled, uncontrolled short circuits can cause service outages with accompanying production downtime and associated inconvenience, interruption of essential facilities, extensive equipment damage, personnel injury or fatality and a possible full-blown fire.

It is therefore important to de-mystify the stigma of faults and its counter-measures. Again, the system designer is responsible for the selection of the right equipment; and would generally have the task of calculating system short circuits. But alas… - procedures & techniques for these calculations are not generally available in one dissertation but are scattered among many publications & technical papers.

Fault Calculations also result to at least three very significant outputs which will become the bases of the following:

1) First: Proper selection of protective equipment ratings as circuit breakers or fuses that suit to system requirements;

2) Second: Realistic arming up of protective relays to trigger operation of circuit breakers once faults do occur;

3) Thirdly, Proper coordination of operation of these protective devices to effect selective interruptions of the only required breakers to trip faulted circuits without the hassle of rendering the other portions of the system powerless.

TYPES OF POWER SYSTEM SHORT CIRCUITS

Contributing sources of Short Circuit Currents into an industrial plant in focus include: Utility Generation thru the Industry Substation, Local Generation, In-Plant Synchronous Motors and Induction Motors. Capacitor discharge currents are normally neglected due to their short time duration.

In several forms or ways, short circuits can occur on a three-phase system. Again, for any type of faults, the protective devices must interrupt the faulted circuits while at the same time be able to withstand these faults.

a) THREE-PHASE BOLTED SHORT CIRCUITS

Three-phase bolted short-circuit describes the condition where the three conductors are physically held as if they were bolted together. In this condition, the impedance between these conductors or terminals is zero. This establishes a “worst case” condition, which results in maximum thermal and mechanical stress in the system. While ‘bolted short circuit condition’ seldom occurs (only in cases of errors in connecting buses or cables), it generally results in maximum short-circuit values and for this reason that the “basic short circuit calculation” in power systems is employed.

Subsequently, it is from these maximum values that the selection of fault duty ratings of circuit breakers, other protective devices and switchgear withstand ratings shall be based, busways included.

b) LINE-TO-LINE BOLTED SHORT CIRCUIT

From the three-phase fault calculation, other types of fault conditions can be obtained. The levels of line-to-line bolted short circuit currents in most three-phase power systems are approximately 87% of three-phase bolted short circuit currents, but this calculation is seldom required because it is not the maximum value, especially for establishing circuit breaker ratings. But then these values are needed as basis in relay settings or other purposes.

c) LINE-TO-GROUND BOLTED SHORT CIRCUITS

In solidly grounded systems, single line-to-ground bolted short circuit current in general, can be almost equal to the three-phase bolted short circuit current. Most of the time, SLG fault currents are lower than the 3Φ short circuit current due to the impedance of the ground return circuit and due to the non-zero-sequence current contribution from the motors which are usually ungrounded. Line-to-ground fault calculations are seldom necessary in solidly grounded low voltage industrial or commercial systems, but are needed in medium voltage systems for relay setting purposes.

In resistance-grounded medium voltage systems (common in 4.16 to 23kV) the neutral grounding resistor is generally selected to limit ground fault current to a value ranging between a few hundreds & a few thousand amps. Magnitudes of Line-to-Ground fault currents on these systems are controlled primarily by the resistor itself and a line-to-ground fault calculation using symmetrical components is generally required to size up the resistor.

d) ARCING SHORT CIRCUITS

In the real world, faults in many power systems tend to be arcing in nature. Statistics say that Single-Line-to-Ground Arcing Faults are the most frequent faults experienced in any power system.

Arcing faults are much lower level short circuit currents than the bolted ones at the same fault point. These lower levels of currents are due to the impedance of the arc ‘inserted’ into the circuit. Normally, arcing fault currents fall in the range from 40% to 50% of the bolted values.

(to be continued...)

A PROLOGUE TO FAULT CALCULATIONS

A PROLOGUE TO FAULT CALCULATIONS
(First of a Series)

GENERAL DISCUSSION

Experts say that, “continuity of operation in an industrial plant is as good as its electric power system. Its value speaks for itself the instant power is interrupted during production days or much more, during the visit of company officers. Even with the best design and top-of-the line materials available, the likelihood of a fault in power systems increases with age". According to experience, faults usually surface out after about five years operation of a brand-new plant. The industrial plant therefore must be designed to anticipate these faults, thus the need for fault calculations - the end objective of which is to design a plant sturdy enough to survive the disastrous effects of faults.

Electrical practitioners should be aware of the responsibility that an electrical system should not only be designed and constructed as a ‘safe system’ under normal service conditions but also during abnormal conditions. Its protection schemes designed & selectively coordinated as well, to insure continuity of service even during abnormal times. Abnormal conditions are always associated with electrical faults and a well-planned fault control system from the medium voltage level down to the last low voltage circuit is one where only the faulted circuit is isolated without disturbing any ‘unfaulted’ parts of the system. Although electrical systems are supposedly designed by responsible system designers to be free from short circuits as possible, but even with these precautions, the plant can not escape from faults because short circuits will surely do occur – perhaps not today but in the future.

It is worthwhile to mention that Fault Calculations may be easy to utility system engineers who may have been assigned in the ‘System Protection Department’ for years; but may be mystifying to operation or maintenance engineers in the industrial plant. Fault Calculations as a subject can not be understood nor mastered without constant practice & exposure to it over a long period of time. The task may seem overwhelming at least … at first, but constantly practicing a methodical step-by-step procedure can keep a novice engineer from getting tripped up…

IEEE says that power systems should be designed so that “protective relays operate to sense and to cause the quick isolation of faults in the end view of limiting the extent & duration of service interruptions. Because of their function, protective relays are the so-called "watchdogs or silent sentinels in a power system.” In medium voltage power systems, relays are considered as the “brains” while the breakers, the “muscles”. While smaller circuit breakers in the LV Systems are ‘electrical devices’, it should be noted that MV Power Circuit Breakers are not real electrical equipment. Being the muscles, they are in fact, ‘more of a mechanical device’ as the only electrical in them are the charging motor, tripping & closing circuits. Protective Relays guard the power system from the ever-present threat of damage caused by over-currents that can result to equipment loss, system failure and a much greater production loss.

But before attempting to set-up any system protection scheme, faults as complex phenomena must first be understood & their magnitudes calculated.

OVER-CURRENTS

An “over-current” as a widely-held phrase is either an overload or a short-circuit current. ‘Overload’ is defined as an excessive current in reference to normal operating current, but one which is confined to the normal conductive paths provided by the conductors & other components of the distribution system. On the other hand, as the name implies, a ‘short-circuit’ current is one which flows outside the normal conducting paths.

OVERLOADS

How ‘over’ are overloads? Overloads are usually between one and six times the normal current level. Generally, these are undisruptive fleeting surges that occur in events of motor or transformer starts-up. Such ‘transient overloads’ are normal events. Since they are of very brief duration; any temperature rise is trivial & has no harmful effect on the circuit components. In such cases, protective devices should not react to them.

Another form of overload is the ‘sustained overload’ that may have been caused by defective motors (such as worn motor bearings), overloaded equipment, or too many loads on a circuit. Such sustained overloads are destructive and must be disconnected by protective devices before they damage the distribution system or system loads. However, since they are relatively lower in extent compared to short-circuit currents, removal of the overload current within a few seconds is an acceptable practice. A sustained overload current if not cut-off results in overheating of conductors & circuit components and will cause deterioration of insulation, which may subsequently result in more severe damage such as short-circuits if not interrupted.

SHORT-CIRCUITS

While overloads do occur at somewhat modest levels, the ‘short-circuit’ or ‘fault current’ can be hundred times larger than the normal operating current. A high level fault may be 50,000 amperes and larger. If not interrupted within a matter of a few thousandths of a second, damage & destruction can become rampant. There can be severe insulation damage, melting of conductors, vaporization of metal, ionization of gases, arcing & fires. Moreover, high level short-circuit currents can develop huge magnetic-field stresses between switchgear buses that can reach destructive forces that even heavy bracing may not be able to keep them from being distorted beyond repair.

INTERRUPTING RATING

A protective device must be rated to withstand the destructive energy of short-circuits. If a fault current exceeds a level beyond the capability of the protective device, the device may rupture and disintegrate. The rating which defines the capacity of a protective device to maintain its integrity when reacting to fault currents is termed as “interrupting rating”. The interrupting rating of most branch-circuit molded case circuit breakers typically used in residential service entrance panels is 10,000 amperes. Larger circuit breakers used in industrial plants may have interrupting ratings of 18 kA or 60 kA or higher. In contrast, modern current-limiting fuses have an interrupting rating of 200 kA or 300kA and are commonly used as current-limiting devices.

SELECTIVE COORDINATION - PREVENTION OF BLACKOUTS

Note that proper coordination or discrimination of the operation of protective devices will prevent total system power outages or blackouts. When only the protective device nearest a faulted circuit opens and the larger upstream OCPD’s remain closed, the protective devices are “selectively coordinated” or in other words, “discriminated”. The word “selective” is to denote total coordination – meaning, isolation of a faulted circuit by the opening of only the affected circuit protective device. In other terminologies, this is also known as “fault control”.

(to be continued...)

POWER SYSTEMS

POWER SYSTEMS

It is being said that electrical power is somewhat like the air we all breathe. Power is just ‘there,’ meeting our every need, constantly. In an industrial plant for instance, it is only a matter of pushing a button and a 5,000 hp motor starts up - just like that! And nobody is thinking about it…

As one article in the internet puts it, “it is only during a power failure; when one walks into a dark room and instinctively hit the useless light switch, realizing how important power is in daily life. We use it for heating, cooling, cooking, refrigeration, light, sound, computers, entertainment… Without power, life can get somewhat cumbersome”. And production in manufacturing plants would come to a massive halt. Fact is that hitting the switch is actually invoking power from probably thousands of kilometers from a source passing through a maze of power distribution grids. Generally, the complete loop of an electric system may be composed of generation, transmission & distribution systems.

a) THE GENERATION SYSTEM

Generation of electric power is accomplished in a “power plant” where bulk power is produced through a system of prime movers coupled to generators turning out electricity. Generated voltages may vary from 4,000 to 24,000 volts (in most cases), or higher - depending on the size of the generating units. The prime movers may be in the form of internal combustion engines (ICE’s) or turbines (hydraulic, steam or gas). Generation in the Philippines is usually done by power producers such as the National Power Corporation (now known as Genco’s) and by Independent Power Producers known as IPP’s interconnected to common grids such as the Luzon, Visayas and Mindanao Grids.

For general discussion, generators can be classified as Turbo-Generators, Hydro-Generators, Industrial Generators or Induction Generators.

Turbo-Generators are driven by steam or gas turbines covering power outputs from a few MW up to the largest 1,300 MW steam turbine unit currently in existence. Information gathered by this author has it, that in two or three years time from now, the largest in the world will be the 1,600 MW 70-meter unit now being built by Siemens for a Finnish utility nuclear power plant. Operating at 3,600 rpm (2 poles) or 1,800 rpm (4 poles), these amazing machines are cooled by circulating air through shaft-mounted fans either drawn directly from external atmosphere or using an enclosed circuit having secondary air/air or air/water heat exchangers. For larger units typically in utility power plants of say 200 MW or larger, the rotor and stator cores may be cooled by circulating hydrogen and the stator windings by passing de-mineralized cooling water down the center of winding conductors.

Industrial plants however commonly use turbo-generators at sizes, 1,000 kW to 10,000 kW at 4,160v.

Hydro-Generators are driven by water turbines and are generally much slower than the steam or gas turbine counterparts. Depending on the available water head, these units are operating at 60 – 1,200 rpm. They have usually large diameters to accommodate a large number of salient pole pairs but with correspondingly short axial length. Generally such machines have vertical spindles with the generators mounted above the turbine. In the Philippines hydro-generators are usually found in utility power plants.

Industrial Generators are Diesel-Driven Generators widely used by industrial plants for standby power or for island generation. Standby power units at 1,750 rpm are typically the simple diesel fuel-fed units with ratings as large as 2,000 KW while island generation application engines are the more complicated bunker-oil fed units. Ratings of bunker-fed units may be up to 12 MW running at lower speeds of 300 – 700 rpm.

Operation with a Large System:

When the Industrial Plant decides to parallel their power plants with the grid, the following discussions are thus important:

When generators are connected to a large system as the grid, the action of the individual machine controls can not have significant effect on the system as a whole. Hence opening the throttle of the prime mover to increase power input to the machine can not affect system frequency but the power exported by the machine will be increased, while it continues to run at synchronous speed.

Similarly, increasing the machine excitation can not increase the voltage on the system but this simply increases the VARs exported by the machine to the system at the same time drifting the machine power factor further lagging. In the same way that reducing the machine excitation causes the power factor to move further leading however, reducing the excitation too far will cause the power factor to move more to the leading condition so that the machine could become unstable and pole-slip. Generally, to avoid any risk of pole-slipping leading power factor operation is limited to about 0.70 at zero load to 0.90 at full load. In the case of a generator connected to the system via a generator unit transformer, the change in reactive power and consequently the change in excitation are achieved by the operation of the on-load tap changer on the transformer.

b) THE TRANSMISSION SYSTEM

As learned from CESEEPS Power Books, power transformation may take place in several stages in sequence, starting at the generating plant where the voltage is raised to approximately 1,000 volts for every mile of transmission. Voltages are then progressively reduced to the voltage required for household, commercial or industrial use. A substation that has a step-up transformer increases the voltage whilst decreasing the current, while a step-down transformer decreases the voltage for domestic, commercial and industrial distribution.

Long distance transmission of energy over the feeders may take place at voltages as high as 500,000 volts. With sufficiently large load justifying the transmission, the farther the distance, the higher is the line voltage employed. Extra-High Voltages (EHV) reaching up to 1,200,000 volts are no longer uncommon in the United States, Sweden and Russia. In economic terms, this reduces conductor sizes while at the same time bringing down the line losses in transmission. However, more elaborate towers and higher insulation requirements are needed to accomplish this type of power conveyance.

The transmission line can therefore be considered as that part of the power system connecting one remote area with another remote area along with delivering bulk power over long distances. This is made possible by a system of towers carrying currents at high voltages. The towers usually of steel construction are now usually found crisscrossing the countryside. In Luzon Grid for instance, transmission voltages are accomplished at 500 KV, 350 KV, 230 KV and 115 KV. The Visayas Grid has 350 KV, 230 KV, 138KV, 115KV and occasionally 69 KV as sub-transmission lines while the Mindanao Grid at 138 KV and 69 KV. High Voltage DC transmission systems are now gaining popularity because of the tremendous economic advantage. The Philippines is no longer an exception, today the country has already this type of transmission at 350 KVDC.

Self power-generating industries normally omit the “transmission” component of the system because of the close proximity of the load centers from the power plant. In most cases, the distribution systems of the industrial plant also carry the function of transmission system.

c) THE DISTRIBUTION SYSTEM

The transmission lines end up at the proximate area of distribution. Electricity then is once more fed into substation transformers that reverse the process by lowering the voltage to some degree, normally in the Philippines at 69KV. Downstream of the system, another voltage transformation may still be necessary and be routed to various places for local distribution and utilization.

From the point of view of the power company, the distribution system is intended to cover a specific area such as towns, cities or directly to industrial plants usually through 60 footer wooden or concrete poles at 69 KV. These voltages may feed directly to large industrial plants while for towns or cities, another voltage transformation may be necessary to produce 13.8 or 23 or 34.5 KV. These feeders are usually called laterals.

In industrial plants, scenarios like self-generating power at 2.4 KV, 4.16 KV, 6.9 KV or 13.8 KV and distribute it directly to power centers which in turn transform the voltage to 480 V or 240 V are common installations in the country. Underground distribution or through over-head cable trays are likewise employed as common feeder management methods in industries.

d) THE SUBSTATIONS

The term ‘substation’ comes from the days before the distribution system became a grid. The first substations were connected to only one power station where the generators were housed, and were just ‘subsidiaries’ of that power station. Today, Substations carry several functions. They generally contain one or more transformers, and have switching, protection and control systems. In medium and large size substations, circuit breakers are used to interrupt any short circuit or overload currents that may occur on the network. Substations do not (usually) have generators, although a power plant may have a substation nearby. A typical substation will contain line termination structures, high-voltage switchgear, one or more power transformers, secondary switchgear, surge protection, controls & metering. Other devices such as power factor correction capacitors and voltage regulators may also be located at a substation.

Substations may be on the surface in fenced enclosures, or underground, or located in special-purpose buildings. Substations located within the buildings they serve are particularly a feature of high-rise buildings. Indoor substations are usually found in urban areas to reduce the noise from the transformers, and for reasons of appearance. Where a substation has a fence, it must be properly grounded (‘earthed’ in European terms) to protect people from high voltages that may occur during a fault in the transmission system.

Transmission Substations

A transmission substation is one whose main purpose is to connect together various transmission lines. The simplest case is where all transmission lines have the same voltage. In such cases, the substation contains high-voltage switchers that allow lines to be connected together or isolated for maintenance.

Transmission substations can range from simple to complex. A small "switching station" may be little more than a bus plus some circuit breakers. The largest substations can cover a large area with multiple voltage levels and a large amount of protection and control equipment.

Large transmission substations usually have complex configuration. Aside from the function of switching several incoming & outgoing circuits, redundancy as well as by-pass schemes are common in these types of substations. Set-up of circuit breakers and their related relaying, as well as arrays of HV switchers, surge arresters and disconnect switches make the system more complicated.

Bulk Distribution Substations

A distribution substation is one whose main purpose is to transfer power from the transmission system to the distribution system of some area. Note that it is uneconomical or impractical to directly connect electricity consumers to the main transmission network (unless they use huge amounts of energy, see Chapter 3 of this book). So the distribution station reduces voltage to a value suitable for connection to local loads.

The input for a distribution substation is typically at least two transmission or sub-transmission lines. Input voltage may be, for example, 115 kV or 138 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 13.8, 24, 34.5 and 69 kV depending on the size of the area served and the practices of the local utility. The feeders will then run overhead, along streets (or under streets, in a city) and eventually power the distribution transformers at or near the customer premises.

Besides transforming the voltage, the job of the distribution substation is to isolate faults in either the transmission or distribution systems. Distribution substations may also be the points of voltage regulation, although on long distribution circuits (several kilometers), voltage regulation equipment may also be installed along the line.

Complicated distribution substations can be found in the downtown areas of large cities, with high-voltage switching, and switching and backup systems on the medium-voltage side. More typical small distribution substations have a disconnect switches, one transformer, and minimal facilities on the secondary voltage side.