Requirements for Transformer Core Grounding Points

The transformer core must have only one grounding point, serving as the normal working grounding point, to limit the core potential and current flow. Absence of grounding or having multiple grounding points can lead to core failure, compromising the safe operation of the transformer.

Importance of Single Grounding Point

Electric Field Interaction

During transformer operation, an electric field exists between the charged windings and the oil tank, with metal components like the core and clamps situated in this field. Due to uneven capacitance distribution and varying field strengths, an ungrounded core develops a floating potential, leading to charging and discharging between the core and the ground or coil. This weakens the insulation strength of both the solid insulation and the oil. Grounding the core at one point eliminates the risk of a floating potential.

Risks of Multiple Grounding Points

Short-Circuit Formation

Grounding the core at multiple points creates a short-circuit ring around the working magnetic flux. This ring, influenced by the alternating magnetic field, generates significant short-circuit currents, which flow through the core, causing localized overheating. More grounding points result in more circulating current loops and larger circulating currents, depending on the position of the redundant grounding points. This increases the transformer’s iron loss and can cause severe overheating.

Damage to Silicon Steel Sheets

Overheating due to circulating currents can melt local silicon steel sheets, burning out the insulating paint film between adjacent sheets. Repairing this damage requires replacing silicon steel sheets, which is costly and time-consuming, affecting the power grid’s safe operation.

Consequences of Improper Grounding

Gas Generation

Ungrounded or multi-point grounded cores can produce large amounts of flammable gas due to overheating and discharge, potentially triggering light gas signals or heavy gas tripping the transformer switch, interrupting external power supply.
Therefore, to ensure safe operation, the transformer core and its fasteners must be well insulated, with only one reliable grounding point.