Knowledge of transformer main protection and backup protection

The transformer is a stationary equipment in continuous operation, which runs more reliably and has fewer chances of failure. However, because the vast majority of transformers are installed outdoors, and are affected by the load during operation and the short-circuit fault of the power system, various kinds of faults and abnormal conditions will inevitably occur during operation.

1. Common faults and anomalies of transformers

Transformer faults can be divided into internal faults and external faults.

Internal fault refers to the fault that occurs inside the case, such as interphase winding short-circuit fault, one-phase winding inter-turn short-circuit fault, short-circuit fault between winding and iron core, winding line break fault, etc.

External faults refer to various inter-phase short-circuit faults between the external lead lines of the transformer and single-phase ground faults caused by flashover of the insulation bushing of the lead lines through the box shell.

Transformer failure is very dangerous. Especially when the internal fault occurs, the high-temperature arc generated by the short-circuit current will not only burn the insulation and iron core of the transformer winding, but also cause the transformer oil to decompose by heat and produce a large amount of gas, causing the transformer shell deformation or even explosion. Therefore, when the transformer fails, it must be cut out.

The abnormal situation of the transformer mainly includes overload, oil level reduction, overcurrent caused by external short circuit, high oil temperature of the transformer in operation, high winding temperature, high transformer pressure, and cooling system failure. When the transformer is in abnormal operation state, an alarm signal should be given.

2. Configuration of transformer protection

The main protection of short circuit fault: mainly includes longitudinal difference protection, heavy gas protection and so on.

Short-circuit fault backup protection: mainly compound voltage lock overcurrent protection, zero sequence (direction) overcurrent protection, low impedance protection and so on.

Abnormal operation protection: mainly overload protection, over-excitation protection, light gas protection, neutral gap protection, temperature oil level and cooling system fault protection.