<p style="text-align:justify"><span style="font-size:14px">As currents in power system are large, voltages are also high (11 kV, 66 kV, 132 kV, 220 kV etc.). These voltages are to be stepped down to a value (110 V) which can be fed to measuring instruments and protective relays. There are as many C.T.s required as are the number of transmission lines emanating from the substation. But in case of potential transformers, one P. T. per bus is required.</span></p>