calculation of elctrical demand

calculation of elctrical demand - Session 2433 Electric...

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Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright © 2003, American Society of Engineering Education Session 2433 Electric Demand Calculations as a Critical Component of Power Distribution System Design and Analysis Ilya Grinberg, Petro Gogolyuk Buffalo State College/ L’viv Polytechnic National University 1. Introduction Calculation of electric demand is one of the most important procedures in design of a power distribution system (PDS) of any facility. Since demand is calculated at the very early stages of design, it significantly influences selection of the rest of the PDS elements as well as its technical and economical indices. Such parameters as capital investments and energy losses, to name a few, depend on the accuracy of demand calculations. If calculated demand is less than actual, additional energy losses, aging of insulation, and premature failure of PDS’s elements will result. On the other hand, inflated demand results in unjustified expenses and inefficient utilization of electrical equipment and wiring system 1,2 . 2. Basic Definitions Total Connected Load - the sum of the continuous ratings of the load-consuming apparatus connected to the system or any part thereof. The value of total connected load is a rather certain number because it is usually known. The sum of the continuous ratings of the load-consuming apparatus permits us to roughly estimate the upper limit of the rated demand (see below) of the group of consumers. The group’s connected real power is the sum of connected real powers of individual loads within the group. The group’s connected reactive power is the sum of connected reactive powers of individual loads within the group. = = + + + + = n i i con n con p p p p p P 1 , 3 2 1 ... (1) 123 , 11 ... nn con n con i n ii Qq q q q q P t g θ == =++++= = ∑∑ (2) where n is a number of connected loads and tg is a tangent of theta (angle between voltage and current).
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Proceedings of the 2003 American Society for Engineering Education Annual Conference & Exposition Copyright © 2003, American Society of Engineering Education Demand, or average load of an installation or a system is the load at the receiving terminals averaged over a specified interval of time. The load may be given in kilowatts (kW), kilovars (kVAR), kilovoltamps (kVA), or amperes (A). Demand of a group over a specified interval of time T is determined as: a av r av W P T W Q T = = ( 3 ) where P av and Q av are average active and reactive loads, W a and W r are active and reactive energy of all loads in the group; T – duration of the time interval. Active (or reactive) demand of a group equals to the sum of demands of individual loads of the group: 1 1 n av av i n av av i Pp Qq = = = = (4) where p av and q av are average active and reactive power of individual loads.
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This note was uploaded on 02/16/2011 for the course EE 472 taught by Professor Dr.ilyagrinberg during the Spring '10 term at SUNY Buffalo.

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calculation of elctrical demand - Session 2433 Electric...

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