Why did the PT cabinet in a normally operating 10 kV substation suddenly explode?

Describe the situation so we can analyze it. There are issues with the quality of the transformer; overvoltage can cause an explosion.

There are too many. Here, as many as 5 sets of fireworks were set off in the year 2007. There are several reasons for this: 1) the voltage is too high, above 12 KV; 2) today’s PT manufacturers prioritize cost savings, which results in poor quality products. 3. A single-phase ground fault or arc grounding occurs in the external circuits; as a result of a single-phase ground fault, the phase voltages of the other two phases become line voltages, that is, 5.7 KV turns into 10 KV or even higher. In the case of arc grounding, the voltage can increase by 3 to 5 times the normal phase voltage, which makes it very likely for the PT to be damaged. 4. High-order harmonics: Products such as power cables, frequency converters, and soft starters in your company can also generate high-order harmonics. 5. Resonance caused by arc grounding or other reasons is also one of the most destructive methods of causing PT explosions. In summary, the third and fifth items present the highest probability of problems and are also the most difficult to resolve. Through two years of practical experimentation, I have managed to solve these issues to a large extent; now, after more than a year of operation, no explosion accidents have occurred. Solutions: 1. First, test for harmonics; if the source of harmonics is eliminated and the level does not exceed 3%, no action is necessary. 2. Install harmonic suppression devices on both the primary and secondary sides of the PT. On the primary side, a high-sensitivity resistor-type device should be used, which differs from traditional primary-side harmonic suppression devices in that it adjusts the resistance value based on the voltage with respect to ground, being infinite under normal conditions. 3. Replace the PT with one of 3.5 times the voltage rating; there are several manufacturers in China that produce such units well, and Hefei Kaili is one very professional company – it is better in this regard than other professional PT manufacturers in China. Let’s talk about these things first to see if they’re helpful to you. If they can’t solve the problem, get in touch with me and I’ll definitely help you resolve it

The secondary switch in the voltage circuit cannot be reliably disconnected in the event of a fault, which is largely due to the unreliability of the circuit breaker

The PT sparking may be caused by resonance; is there a problem with the resonance suppression device?