What is the reason for the tv disconnection warning?

In the power system, TV disconnection means that the voltage transformer is disconnected.

TV disconnection can generally be divided into TV primary side (high voltage) disconnection and secondary side (low voltage) disconnection. No matter which side the disconnection is, it will cause The voltage of the TV secondary circuit is abnormal, which affects the correct operation of the relay protection device. (Recommended study: phpstorm)

If the primary side of the TV is disconnected, one situation is that all three phases are disconnected. At this time, there is no voltage on the secondary side, and the open triangle There is also no voltage;

One situation is asymmetrical wire breakage, that is, a certain phase is broken. At this time, there is no phase voltage on the secondary side of the corresponding phase, and there is no continuous line-phase secondary voltage. No change, the open triangle has voltage.

If the TV secondary side is disconnected, the TV opening triangle has no voltage, and the phase-to-phase voltage of the disconnected phase is zero.

Protective current transformer The protective current transformer mainly cooperates with the relay device. When a fault such as short circuit overload occurs on the line, it provides a signal to the relay device to cut off the faulty circuit to protect the safety of the power supply system.

The working conditions of micro current transformers for protection are completely different from those of measuring transformers. The protection transformers only start to work effectively when the current is several times or dozens of times larger than the normal current.

The purpose of the voltage transformer to transform voltage is mainly to supply power to measuring instruments and relay protection devices, to measure the voltage, power and energy of the line, or to protect the line when a line fault occurs. They are expensive equipment, motors and transformers, so the capacity of the voltage transformer is very small, generally only a few volt-amperes or dozens of volt-amperes, and the maximum does not exceed a thousand volt-amperes.

During normal operation, the three-phase voltage of the power system is symmetrical, and the sum of the three-phase induced electromotive force on the third coil is zero. Once a single-phase grounding occurs and the neutral point is displaced, a zero-sequence voltage will appear between the terminals of the open triangle to cause the relay to operate, thereby protecting the power system.

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