Application Of Instrument Transformer

The wiring of the instrument transformer shall comply with the connection principle: The first winding should be connected in series with the circuit under test while the second winding in series with all the instrument loads.

Select the appropriate ratio according to the measured current size, otherwise the error will increase. At the same time, the secondary end must be grounded to prevent the primary low-voltage side from channeling into the secondary low-voltage side, causing damaging to people and equipment, when the insulator breaks.

The secondary side is absolutely not allowed to be open, because once the circuit is open, the primary current will transform into magnetized current, causing the sudden increase of M and E2, resulting in excessive saturation and magnetization of the core which may heat severely and burn the coils. When the current transformer works normally, the secondary side is used to connect in series with the current coils, such as measuring instruments and relays. The impedance of the current coil is very small, making the secondary side close to short-circuit.

The installation site of the protection equipment for current transformer shall be the vacancies uncovered by the main protection equipment.

In order to prevent the busbar fault caused by the flashover of the pillar-type current transformer, the current transformers are usually stalled on the outlet of circuit breakers or the side of the transformers.

To reduce the damage of the internal failure of generators, the current transformer used to automatically adjust the excitation device shall be placed on the outlet side of the stator winding of generators. And the current transformer for the measuring instrument should be installed on the neutral point of a generator in order to facilitate the analysis on finding the internal faults before the generator incorporates into the system.

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