SYSTEM DIMENSIONING
(First of Two Parts)
(First of Two Parts)
SYSTEM RELATIONS
Let us step farther away and look at the forest. The industrial complex under a design concept needs to consider & integrate system voltages, voltage transformations; behavior of loads, load distribution, load growths, transformer KVA sizes, transformer connections, device & equipment sizes, grounding, switching schemes, and protection systems among others; that would serve best the manufacturing and/or industrial processes the plant is intended to. This integration usually ends up in the Substation that will eventually link the industry with the power distributor company.
This task is what is known in the industry as “System Dimensioning”. And the designer must see to it that the system to be built will last for years in the entire lifetime of the industrial plant.
The whole power system exists to serve the load. The behavior of the load therefore commands the shape of the power system. Incidentally, the character of the load is very capricious for which the electrical system has to readily react to load situations instant by instant to accommodate its peaks and valleys. It is worthwhile to mention that unlike any other systems in the planet, the production, consumption & sale of electricity all happen at the same time, at an instance. The design, installation and the operation of the system must therefore be best suited to the requirements of the load that varies from time to time.
To further illustrate, a few terminology needs to be understood, as follows:
Connected Load (CL) – the arithmetical sum total of the continuous nominal power consuming ratings of all equipment in a system. In Europe, it is known as “Installed Power or Installed kVA”. In real terms, all of this amount of power can not be used or consumed at any given time. Thus the “Installed Power” or “Connected Load” can not be reached.
Maximum Demand (MD) - the highest or peak load in a certain time frame of a system. It is also known as 15-Minute Demand KW or KVA. For instance in a system connected load of 1,000 KVA, if only 60% of maximum power found drawn as metered, then the same system has a Maximum Demand of only 60% or 600 KVA. IEC lingo termed it as “Maximum Utilized Power”. This is so because even in operating motors, the actual load of these motors can not reach the “Installed Power KVA” because they are not most likely operating at fully loaded condition all at the same time. The maximum demand usually is the demand kW reflected in monthly utility billings.
Average Load (AL) - the equivalent average load of a variable load in a certain time frame. As the actual load with respect to time could be seen as a “mountain range curve”, there exists an imaginary straight line equivalent to this mountainous curve. That straight line represents the average load. For instance, in a variable load for the month, the meter read-out is 1,000,000 kW-H, the Average Load for the month will be: AL = 1,000,000 kW-H /(30 days per month x 24 hr per day) 1,388.89 KW. This means that the actual variable load for the month is likened to a uniform 1,388.89 KW load all the time for 30 days. Normally, the average load can be derived from the kW-hr consumption of the period divided by the hours of the period. It thus can be likened that the plant has an average KW or MW at any given time for the subject period.
SYSTEM LOAD METRICS IN INDUSTRIAL APPLICATIONS
In order for the design engineer to further understand the meaning of the relevant design factors, the following is an attempt to provide more explanation using the experience of the author in brewery operations. Note however, that load metrics for different types of plants differ from each other. Load Metrics are reflections of the actual behavior of plants. It is now up to the plant engineer, to interpret and establish them into the real scenario of his plant. It is thus desired that the engineer should create his own statistics in his supposed field of expertise.
THE DEMAND FACTOR: Let us recall that Demand Factor is the ratio of the Maximum Demand or Peak Load over that of the Connected Load. For instance, for a connected load of 100 KW, if the actual peak load is only 50 KW, the Demand Factor is supposed to be 50%. If we say that the Demand Factor of a typical Beer Filtration Plant is 54.5%, could it mean that the plant is operating only half of its capacity? … Not quite!
For the sake of explanation, about 35% of the connected loads in a Beer Cellaring/Filtration Plant are destined not to operate during normal production days. These specific loads referred to as the CIP (Cleaning-In-Place) systems don’t run during production operation. They are meant to operate only when the system ceases to produce and cleaning/sterilizing of the equipment, pipelines, etc with caustic soda are required for every shutdown to prepare the system for another round of production schedule. These types of loads are the so-called “Non-Coincidental Loads”. The effect of non-coincidental loads in an operation is a good example how the demand factor takes shape for every type of operation. It must be appreciated that the CIP system in this example is included in the inventory of the “Installed KVA” but in reality doesn’t influence the size of the power center in concept. It must be understood therefore that demand factors depend on the mode & type of industrial plant operation. Again the engineer must define his own turf.
In like manner that in an industrial plant, there are a number of installed spare units as compressors, boilers and system auxiliaries. These are typical in Steam & Refrigeration Plants, where a number of installed spare units are included in the connected load inventory but are meant to operate only when needed – that is, in case of breakdowns of the operating units. Moreover, a running motor usually doesn’t operate at full load. Remember, the peak loads discussed here are real-time values captured by a demand meter, while the connected loads are based on nameplate ratings. Most motors in any industrial plant are in fact running at 75% to 90% load only – this further shapes the demand factor of a specific plant.
(To be continued…)
DOODS A. AMORA, PEE
(August 17, 2007)
Let us step farther away and look at the forest. The industrial complex under a design concept needs to consider & integrate system voltages, voltage transformations; behavior of loads, load distribution, load growths, transformer KVA sizes, transformer connections, device & equipment sizes, grounding, switching schemes, and protection systems among others; that would serve best the manufacturing and/or industrial processes the plant is intended to. This integration usually ends up in the Substation that will eventually link the industry with the power distributor company.
This task is what is known in the industry as “System Dimensioning”. And the designer must see to it that the system to be built will last for years in the entire lifetime of the industrial plant.
The whole power system exists to serve the load. The behavior of the load therefore commands the shape of the power system. Incidentally, the character of the load is very capricious for which the electrical system has to readily react to load situations instant by instant to accommodate its peaks and valleys. It is worthwhile to mention that unlike any other systems in the planet, the production, consumption & sale of electricity all happen at the same time, at an instance. The design, installation and the operation of the system must therefore be best suited to the requirements of the load that varies from time to time.
To further illustrate, a few terminology needs to be understood, as follows:
Connected Load (CL) – the arithmetical sum total of the continuous nominal power consuming ratings of all equipment in a system. In Europe, it is known as “Installed Power or Installed kVA”. In real terms, all of this amount of power can not be used or consumed at any given time. Thus the “Installed Power” or “Connected Load” can not be reached.
Maximum Demand (MD) - the highest or peak load in a certain time frame of a system. It is also known as 15-Minute Demand KW or KVA. For instance in a system connected load of 1,000 KVA, if only 60% of maximum power found drawn as metered, then the same system has a Maximum Demand of only 60% or 600 KVA. IEC lingo termed it as “Maximum Utilized Power”. This is so because even in operating motors, the actual load of these motors can not reach the “Installed Power KVA” because they are not most likely operating at fully loaded condition all at the same time. The maximum demand usually is the demand kW reflected in monthly utility billings.
Average Load (AL) - the equivalent average load of a variable load in a certain time frame. As the actual load with respect to time could be seen as a “mountain range curve”, there exists an imaginary straight line equivalent to this mountainous curve. That straight line represents the average load. For instance, in a variable load for the month, the meter read-out is 1,000,000 kW-H, the Average Load for the month will be: AL = 1,000,000 kW-H /(30 days per month x 24 hr per day) 1,388.89 KW. This means that the actual variable load for the month is likened to a uniform 1,388.89 KW load all the time for 30 days. Normally, the average load can be derived from the kW-hr consumption of the period divided by the hours of the period. It thus can be likened that the plant has an average KW or MW at any given time for the subject period.
SYSTEM LOAD METRICS IN INDUSTRIAL APPLICATIONS
In order for the design engineer to further understand the meaning of the relevant design factors, the following is an attempt to provide more explanation using the experience of the author in brewery operations. Note however, that load metrics for different types of plants differ from each other. Load Metrics are reflections of the actual behavior of plants. It is now up to the plant engineer, to interpret and establish them into the real scenario of his plant. It is thus desired that the engineer should create his own statistics in his supposed field of expertise.
THE DEMAND FACTOR: Let us recall that Demand Factor is the ratio of the Maximum Demand or Peak Load over that of the Connected Load. For instance, for a connected load of 100 KW, if the actual peak load is only 50 KW, the Demand Factor is supposed to be 50%. If we say that the Demand Factor of a typical Beer Filtration Plant is 54.5%, could it mean that the plant is operating only half of its capacity? … Not quite!
For the sake of explanation, about 35% of the connected loads in a Beer Cellaring/Filtration Plant are destined not to operate during normal production days. These specific loads referred to as the CIP (Cleaning-In-Place) systems don’t run during production operation. They are meant to operate only when the system ceases to produce and cleaning/sterilizing of the equipment, pipelines, etc with caustic soda are required for every shutdown to prepare the system for another round of production schedule. These types of loads are the so-called “Non-Coincidental Loads”. The effect of non-coincidental loads in an operation is a good example how the demand factor takes shape for every type of operation. It must be appreciated that the CIP system in this example is included in the inventory of the “Installed KVA” but in reality doesn’t influence the size of the power center in concept. It must be understood therefore that demand factors depend on the mode & type of industrial plant operation. Again the engineer must define his own turf.
In like manner that in an industrial plant, there are a number of installed spare units as compressors, boilers and system auxiliaries. These are typical in Steam & Refrigeration Plants, where a number of installed spare units are included in the connected load inventory but are meant to operate only when needed – that is, in case of breakdowns of the operating units. Moreover, a running motor usually doesn’t operate at full load. Remember, the peak loads discussed here are real-time values captured by a demand meter, while the connected loads are based on nameplate ratings. Most motors in any industrial plant are in fact running at 75% to 90% load only – this further shapes the demand factor of a specific plant.
(To be continued…)
DOODS A. AMORA, PEE
(August 17, 2007)
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