Oil Cooled Distribution Transformer Construction

The transformer is mainly composed of iron core, winding, oil tank, oil conservator, insulating bushing, tap changer and gas relay.

1. Oil Cooled Distribution Transformer Iron Core

The iron core is the magnetic circuit part of the transformer. During operation, hysteresis loss and eddy current loss will be generated to generate heat.

In order to reduce heat loss and reduce volume and weight, the iron core is made of cold-rolled grain-oriented silicon steel sheet with a high magnetic permeability of less than 0.35mm. According to the arrangement of the winding in the iron core, there are iron core type and iron shell type.

In large-capacity transformers, in order to ensure that the heat generated by the core loss can be fully taken away by the insulating oil during circulation to achieve a good cooling effect, a cooling oil passage is often provided in the iron core.

2. Oil Cooled Distribution Transformer Winding

Windings and cores are the core components of a transformer. Due to the resistance of the winding itself or the contact resistance at the joint, heat will be generated by I2Rt.

Therefore, the winding cannot pass a current higher than the rated current for a long time. In addition, when the short-circuit current passes, a large electromagnetic force will be generated on the winding and the transformer will be damaged. There are two types of basic windings: concentric and overlapping.

The main faults of transformer windings are inter-turn short circuit and short circuit to shell. Turn-to-turn short circuit is mainly due to insulation aging, or due to the overload of the transformer and the mechanical damage of the insulation during the short circuit.

The oil level in the transformer drops, so that when the winding is exposed to the oil level, an inter-turn short circuit can also occur; in addition, when there is a through short circuit, the winding is deformed due to the overcurrent effect, causing the insulation to be mechanically damaged, and an inter-turn short circuit will also occur.

When there is a short circuit between turns, the current in the short-circuit winding may exceed the rated value, but the current of the entire winding may not exceed the rated value. In this case, the gas protection operates, and when the situation is serious, the differential protection device will also operate.

The reason for the short circuit to the shell is also due to insulation aging or oil damp, oil level drop, or due to lightning and operating overvoltage.

In addition, when a through short circuit occurs, the winding is deformed due to overcurrent, and a short circuit to the casing will also occur. When the shell is short-circuited, the gas protection device and the grounding protection are generally activated.

3. Oil Cooled Distribution Transformer Fuel tank

The body (winding and iron core) of the oil-immersed transformer is installed in an oil tank filled with transformer oil, and the oil tank is welded with steel plates. The oil tank of medium and small transformers is composed of a tank shell and a tank cover. The body of the transformer is placed in the tank shell, and the tank cover can be lifted out for maintenance.