Inquiry Email Whatsapp

Hazards, causes, and types of multi-point ground faults in transformer core

1. The hazards of multi-point ground faults in the core

During normal operation of the transformer, the core cannot be grounded at multiple points. During normal operation of the transformer, there is an alternating magnetic field around the winding. Due to electromagnetic induction, there are parasitic capacitances between the high-voltage winding and the low-voltage winding, between the low-voltage winding and the core, and between the core and the shell. The live winding will be coupled through the parasitic capacitance. , causing the core to generate a floating potential against the ground. Since the distance between the core and other metal components and the winding is not equal, there is a potential difference between the components. When the potential difference between the two points reaches a level that can break the insulation between them, Spark discharge is generated, which is intermittent and has adverse effects on transformer oil and solid insulation in the long run.

To eliminate this phenomenon, the core and the shell are reliably connected so that they are at the same potential as the shell. However, when the core or other metal components are grounded at two or more points, the grounding point will form a closed loop, causing circulation and Local overheating will cause oil decomposition and insulation performance degradation. In severe cases, the core silicon steel sheet will be burned out and cause a major accident in the main transformer. Therefore, the core of the main transformer can only be grounded at one point.

2. Causes of core ground fault

Transformer core grounding faults mainly include short circuits of the grounding plate due to poor construction technology and design; multi-point grounding caused by accessories and external factors; burrs, rust, welding slag, and other factors caused by metal foreign objects left in the main transformer and poor core technology Cause grounding.

3. Types of core failures

There are six common fault types in transformer cores:

(1) The iron core hits the shell and the clamp. During the installation, due to negligence, the stable nails for transportation on the top cover of the fuel tank were not turned over or removed, causing the iron core to collide with the tank shell; the iron core clamp limb plate touched the iron core column; the silicon steel sheet warped and touched the clamp limb plate; the iron core was clamped under The cardboard between the piece's feet and the iron yoke fell off, and the feet collided with the silicon steel sheet; the thermometer seat cover was too long and collided with the clamp, iron yoke, and core column, etc.

(2) The steel seat cover of the core bolt is too long and short-circuited with the silicon steel sheet.

(3) There is foreign matter in the fuel tank, causing the silicon steel sheet to partially short-circuit. For example, a 31500/110 power transformer in a substation in Shanxi experienced multi-point grounding in the core, and a screwdriver with a sky handle was found between the clamp and the iron yoke; a 60000/220 power transformer in another substation The transformer hanging cover is inspired by a 120mm long copper wire.

(4) The core insulation is damp or damaged, such as sludge and moisture deposited on the bottom, the insulation resistance decreases, the clamp insulation, pad insulation, iron box insulation (cardboard or wood block) is damp or damaged, etc., resulting in high resistance multi-point grounding of the core.

(5) The bearings of the submersible oil pump are worn, and metal powder enters the oil tank and accumulates at the bottom, forming a bridge under the action of electromagnetic attraction, connecting the lower rail to the pads or the bottom of the tank, causing multi-point grounding.

(6) Poor operation and maintenance, and no scheduled maintenance.

We use cookies to ensure that we give you the best experience on our website. If you continue to use this site, we assume that you accept such use.