The cause of voltage transformer explosion

The direct cause of the accident was the heating caused by the internal overcurrent. There are many possibilities of PT explosion, such as overvoltage, or poor product quality and other reasons.

There are three reasons for the explosion:

1. Insulation damage, primary to secondary or ground breakdown produces a large current;

2. Overcurrent, ferromagnetic resonance leads to saturation of the iron core, and the current rises sharply;

3. The secondary short circuit will also cause;

4. The ampere-second characteristic of the fuse is not good, and the fault overcurrent equipment cannot be cut off in time.

5.The secondary load of the voltage transformer is heavy, and the primary and secondary currents are large, so that the sum of the secondary side load current exceeds the rated value, causing the internal winding of the PT to heat up, especially when the voltage is higher than the rated voltage of the PT (6kV). The internal heating of the PT is more serious; moreover, the system is a neutral point non-effectively grounded system, so the primary side voltage is prone to skew during operation. When a high voltage appears in a certain phase, the phase PT is more prone to thermal expansion and burst.

Solution：

1) Add a damping resistor to the primary neutral point of the PT. This method has been widely used in China, and there are many manufacturers producing stereotyped products, and satisfactory results have been achieved in practical applications. For example, the RXQ series resonance eliminator produced by Xi’an Electric Porcelain Factory is connected in series between the neutral point of the PT primary winding and the ground. Made in a set. Its working principle is: under low voltage, the resonance eliminator has a high resistance value (up to several hundred thousand ohms), so that the resonance is not easy to develop in the initial stage. The linear resistance drops so that it does not affect the operation of the ground protection.

 

2) Fixed (or variable) damping is connected in parallel on the delta side of the PT opening, which is used for some substations or power distribution stations with low requirements.

Post time:
Jun-16-2023