Instantaneous & Average Power

Instantaneous & Average Power

Instantaneous power is the power at any instant of time. In Ac circuit the instantaneous electric power is given by

P= VI

but these quantities are continuously varying. Instantaneous Power p(t) is the power, p(t)= u(t)*i(t). It is the product of the time functions of the voltage and current. 

This definition of instantaneous power is valid for signals of any waveform. The unit for instantaneous power is VA. 

Where; P(t) = 1/2 VmIm cos(ɸv-ɸi) + 1/2 VmIm cos(2wt + ɸv + ɸi)

Instantaneous power is at positive values if power is absorbed by the circuit. It will be on the negative values if power is absorbed by the source. 

Average power is the average of instantaneous power over one period. Defined as;

P = 1/2 VmIm cos(ɸv-ɸi) 

Characteristics

1. P IS NOT TIME DEPENDENT

2. ɸv=ɸi, purely resistive load

3. ɸv-ɸi = 90, purely reactive load.