Why is it necessary to ground the transformer core? And why is it not advisable to use a multi-point grounding approach?

The core and its metal components generate different potentials due to their positions in the electric field. When the potential difference between two points reaches a level sufficient to break down the insulation between them, intermittent spark discharges occur. This discharge is intermittent, with the potential between the two points becoming equal after each discharge, causing the discharge to cease. Once a potential difference is reestablished, the discharge occurs again. This intermittent discharge can lead to the decomposition of transformer oil and potential damage to solid insulation, resulting in accidents. To prevent such occurrences, the core and other metal components (such as clamps and winding pressure plates) must be connected to the oil tank and grounded to ensure they are at the same potential (zero potential). If there are through-core screws on the core, they are effectively at the same potential as the core due to capacitive coupling, and separate grounding is not necessary.

Currently, a common grounding method involves placing a copper strip between the core laminations. Although there is insulation film between the core laminations, the entire core can still be considered grounded capacitively.

If the core is grounded at two points, it is equivalent to creating a short circuit on both sides of the core, resulting in a certain amount of current flow. This current leads to local overheating, increased losses, and may even cause the grounding strips to fuse, creating a suspended potential in the core, which is not allowed.

Therefore, the core must be grounded, and it should be done using a single grounding point.

LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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