Suppose I know nothing about my load, only the voltage and current waveforms.
With this I can calculate apparent power (S), and real power (P) and use P and S to determine my reactive power (Q) for a cycle. However, the Q that is calculated could be positive (implying inductive load) or negative (implying capacitive load) for any given P and S.
Are there any simple tricks I could do with the voltage and current waveforms to determine whether Q is positive or negative?
I know I could see which peaks first, voltage or current, and that would tell me if the current is leading or lagging the voltage but that would involve keeping track of the max/min and just gets complicated. I'm wondering if there is an easier way to do this. I have available to me only the samples in a 60Hz cycle of the voltage and current. I also have sine/cosine vectors available, of which the sine vector is phase-locked with the voltage.
Best Answer
CIVIL stands for (amongst other things) Capacitor, I leads V and V leads I in an Inductor (L)
So, given that the displacement between voltage and current can only be 90 degrees max for a reactive load, look to see if the current rises through zero before the voltage waveform. If it is then it's a capacitive load. It's easier doing this than looking for peaks. Clearly you need to know the AC frequency and you need to be sampling at least 5 or 6 samples per cycle to accurately determine C or L type load.