Trouble-shooting of through core current transformer

- Jan 15, 2020-

The through core current transformer is a common electrical device. Because of its simple wiring and easy installation, it is widely used in metering, testing, and protection circuits. However, a little attention during use can cause great errors. Inaccurate measurement, protection failure, and even electrical accidents are related to the ampere-turn capacity of the current transformer. Zh

Accident phenomenon

A certain electroplating plant in Hebei has three electric motors whose model specifications are YXXM-422kW, equipped with XXXX-0.5, 100/5, 300 amp current transformers, and the ammeter is 0-100A. In actual operation, it is found that the current value is always small, about 27A. The actual working current of the primary side measured with a clamp ammeter is 82A. The two obviously do not match, and the three motors are basically similar. One motor was replaced. The current transformers, secondary lines, and ammeters remain the same.

2. Accident Analysis

After careful analysis, we found a common law. The primary and secondary side detection and metering currents are nearly three times the difference. This caused our alarm. When we looked carefully at the transformer nameplate, we found that we ignored an important problem: the capacity of the ampere. It is 300 amp turns, so it should be wound three times for 100/5 lines, instead of the conventional one-turn core.

3. Accident Handling

The primary line was wound three times on the transformer, the detection current was 81A, and the primary line was measured with a clamp-type ammeter to 82A, which are basically consistent.

The so-called ampere capacity refers to the maximum rated current value when the single side of the current transformer is single-wired, that is, the product of the rated current and the number of core-turns.