Active Compensation

In the active compensation solution, the principle of compensation is the same, the only difference being that the output of amplifier A is connected in series with the secondary circuit. The amplifier has a gain of -α (reversing the phase of the voltage of 180 °).

By increasing the gain of the amplifier the errors are decreasing (in theory, infinitely). The structure of the equations shows that this form of compensation is a feedback circuit. Therefore, a serious limitation is the stability of the circuit, and since this stability is subject to the load characteristic as well, it is advisable to choose a relatively low value for the gain.

However, with a relatively low gain of, for example, α = 10, the errors will greatly decrease. To calculate the current transformer error it is necessary to know the current passing through the load impedance, Zc. The equivalent circuit of the secondary CT winding facilitates this calculation             ORC4SABHP37

The secondary winding equivalent circuit of a two-stage CT where V2 and V3 are the induced voltages in windings 2 and 3, respectively, and Z2 and Z3 are the internal impedances of the windings.