Voltage transformer burned causes and protective measures - News - Global IC Trade Starts Here Free Products

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Voltage transformers are essential devices in electrical systems, typically consisting of a primary coil, a core, and insulation. They are commonly used for voltage measurement and protection. However, during the thunderstorm season, various faults can occur, such as lightning strikes on power lines or flashovers on porcelain insulators, which may lead to blown high-voltage fuses or even damage to the transformer itself.

One common cause is when a single-phase ground fault occurs on a 10kV outgoing line. In this case, the non-faulted phase's ground voltage on the primary side of the voltage transformer rises to normal levels, causing the core to saturate quickly. This saturation leads to a sharp increase in excitation current, which in turn causes the fuse to blow.

Another scenario involves a short circuit between turns or phases on the secondary side of the transformer. If the low-voltage fuse does not blow, the high-voltage fuse may still be damaged due to the sudden rise in excitation current.

Ferromagnetic resonance is another critical issue that can affect voltage transformers. This phenomenon occurs when the parameters of the power network—especially ferromagnetic components with iron cores—are not optimally combined. If a circuit breaker fails to close synchronously, and a no-load busbar with a transformer and a ferromagnetic voltage transformer is energized, it can trigger a short circuit between the high-voltage coil and ground. Ferromagnetic resonance can result in overvoltages exceeding 2.5 times the normal level, leading to insulation breakdown and equipment damage.

To protect voltage transformers from these issues, several preventive measures can be implemented:

• Strengthen substation monitoring and ensure that high-voltage fuses are not replaced by low-voltage fuses.
• Install a zero-sequence grounding automatic switch on the primary side of the voltage transformer to isolate the grounding line.
• Install a small air switch (3–5A) on the secondary side to prevent short circuits in the potential transformer.

By following these steps, the risk of failure and damage to voltage transformers can be significantly reduced, ensuring safer and more reliable operation of electrical systems.