Zl is a load which absorbs 4KVA with pf 09 lagging Find the

Z_l is a load which absorbs 4KVA with pf = 0.9 lagging Find the ideal-transformer turns ratio n. Find the P_l and Q_l values at the load. Find the value of C to correct the feeder pf to 1.0.

Solution

A capacitance CC has impedance

ZC=1jCZC=1jC

But note that

1j=j1j=j

so equivalently

ZC=j1CZC=j1C

A capacitor\'s impedance therefore has a negative imaginary part.

An inductor LL has impedance

ZL=jLZL=jL

and therefore has a positive imaginary part.

So if the load has a positive imaginary part then it behaves more like an inductor, and if it has a negative imaginary part then it behaves more like a capacitor.

If both inductors and capacitors are present then simply find the equivalent impedance of the load network. If the imaginary part of the equivalent impedance is positive then the load is inductive, if it is negative then it is capacitive, and if it is zero then it is resistive. An inductive load network has an overall higher impedance as the frequency increases even if there are capacitor(s) in the network, and a capacitive load network has an overall lower impedance as the frequency increases even if there are inductor(s) in the network.

It can be important to distinguish between the two cases in order to understand the frequency response of a circuit. For example, if a voltage amplifier has an inductive load then the amplifier will perform better at higher frequencies where the load has a higher impedance (the ideal load for a voltage amplifier is infinite in order to maximize the voltage gain). However, if the voltage amplifier\'s load is capacitive then it will perform better at lower frequencies since the load will then have a higher impedance at lower frequencies.