Application of Current Transformers

Calculate the excitation current of a protective CT of 50-5 A, 15kV nominal voltage, operating the nominal current. An overcurrent relay is connected to the secondary of the current transformer, which implies the choice of the nominal load of C100. In the design of the CT was adopted a magnetization of 500 ames-turns.

The secondary voltage at the current transformer terminals is limited by the saturation of the core, however, secondary high voltages may arise when the primary of the CTs is subjected to very high currents or a secondary load of a value higher than the nominal value is coupled of the CT scan.

When the sinusoidal flow wave is traversed by zero, the highest values ​​of overvoltage occur at this point, since at this point the maximum rate of variation of non-nucleus magnetic flux occurs.

Compute the secondary-induced electromotive force of a 200-5A current transformer supplying an induction-type overcurrent relay with the timed and instantaneous units set in tape 2 which derives in a total charge of (0.9 + . Determine the load and voltage on the secondary CT of the relay actuator, ie at 20 times the rated current.

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