Grounding requirements for clamp on current transformer and magnetic potential

- May 05, 2019-

When using the clamp on current transformer, it is necessary to select the appropriate ratio according to the current to be measured. Otherwise, the error will increase. When using the secondary side, the secondary side must be grounded. When it is damaged, the primary side high pressure breaks into the secondary low pressure side, causing personal and equipment accidents.

The secondary side of the clamp on current transformer is absolutely not allowed to open, because once the circuit is open, the primary current I1 becomes a magnetizing current, causing a sudden increase in φm and E2, causing excessive saturation magnetization of the core, causing severe heat or even burning the coil; After excessive saturation magnetization, the error is increased. When the current transformer is in normal operation, the secondary side is used in series with a current coil such as a measuring instrument and a relay. The current coil of the measuring instrument and the relay has a small impedance, and the secondary side approximates a short circuit.

The magnitude of the CT secondary current is determined by the primary current, and the magnetic potential generated by the secondary current is the magnetic potential that balances the primary current. If it is suddenly opened, the field electromotive force suddenly changes to a large value from a small value, and the magnetic flux in the core exhibits a severely saturated flat-top wave, so the secondary winding will be induced when the magnetic flux passes through zero. Very high apex waves, which can reach thousands or even tens of volts, endangering the safety of workers and the insulation of the instrument.