What causes thermal failures in the core of an oil-immersed transformer?

What causes thermal failures in the core of an oil-immersed transformer?

Today we’ll discuss some types of thermal failures in oil-immersed transformers, specifically core failures. Core failures account for about 3% of all overheating failures, a proportion that warrants our attention. So, what are the most common transformer core failures? The most common is multi-point grounding faults in the core, followed by inter-laminar short circuits within the core.

Let’s explain the principle behind these failures: During normal operation, an oil-immersed transformer should only have one grounding point in the core. Multi-point grounding can induce different potentials at different grounding points in the magnetic field, forming circulating currents. These currents can cause localized overheating, leading to the decomposition of the insulating oil and potentially burning out the core, preventing the transformer from operating normally.

After understanding the principles, our manufacturer will explain the causes of multi-point grounding faults in transformer cores:

(1) Metal foreign objects left during core assembly and lead wire welding

(2) The yoke’s clamping pins touching the yoke

(3) During transportation or operation, vibration causes the clamp insulation to shift, resulting in contact between the core and the clamping parts.

(4) Negligence during infrastructure construction and installation, failing to remove the positioning pins on the transformer tank.

(5) Foreign objects such as nuts and bolts left in the transformer tank from installation.

(6) The pads between the upper and lower clamping parts and the iron wheel are damp or have sludge adhering to their surface, reducing their insulation performance.