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Power, Reactive Volt-Amperes, Power Factor

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1 Author(s)
Fortescue, C.L. ; Consulting Transmission Engineer, Westinghouse Electric and Manufacturing Co., East Pittsburgh, Pa.

The relation between power, reactive volt-amperes, and power factor is discussed for sinusoidal electromotive forces and currents. Reactive volt-amperes is defined as the flow of stored energy into the circuit and is deduced from the stored energy cycle. It is shown to be a cyclic flow of power which is 90 deg in advance of the cyclic part of the dissipation or power input cycle which with the stored energy cycles is positive at all instants. This leads to the vector equation ??I?? + ???? derived for the equation of total inflow of energy given by Ri2 + d/dt (1/2Li2)or (Ri2 + L di/di i) for an inductive system or Ri2 + d/dt (1/2 q2/C) or (Ri + q/C) i for a capacitor system. Non-sinusoidal electromotive forces and currents are discussed and it is shown that there is no simple relation between the volt-amperes as obtained by voltmeters and ammeters and power as obtained by wattmeters and reactive power. The inflow of stored energy for double frequency fundamental can be obtained but it appears to bear little relation to the product of mean square volts and amperes and true average power. It is concluded that the ratio of power to mean square volt-amperes is a useful practical factor with non-sinusoidal waves encountered in practice but should not be used to define reactive volt-amperes. Polyphase power and reactive volt-amperes are defined. In a balanced system power is continuous and the instantaneous reactive volt-amperes are zero.

Published in:

American Institute of Electrical Engineers, Transactions of the  (Volume:52 ,  Issue: 3 )