Case analysis of abnormal ground current misjudgment of high frequency transformer core
The incident happened
On October 21, 2015, in a 220 kv substation in electric test, found that # 1 and # 2 main transformer core earth current were 181.8, 125.4 mA, test position at the bottom of the leakage current sensor, beyond the "priorities in shandong province electric power company substation equipment charged detection work out detailed rules for the implementation of" rule of iron core earth current is less than 100 mA.
Experiment personnel test is a problem with the clip-on ammeter, hence in protecting the room out the core earth current on-line monitoring data, the data show # 1, # 2 main transformer core earth current is respectively 191, 121 ma, the same values beyond the rules.
Therefore, it can be determined that there is no problem with the clamped ammeter, and the experimenter will test above the leakage current sensor. The ground current of the iron core of the main transformer #1 and #2 is 0.9 and 0.8mA respectively.
The reason analysis
The test data of the core ground current at the bottom of the leakage current sensor are in good agreement with the data of the on-line monitoring system, which indicates that the leakage current sensor is normal. The researchers examined the leakage current sensor unit, found that the transformer core grounding flat iron with tightly affixed to the leakage current sensor, the grounding wire flat iron and the touch sensors, sensor appearance of insulating varnish has wear and tear, exposure of the metal parts as shown.
Due to the contact between the flat iron of the ground wire and the metal part of the penetrating sensor, the test current of the tongs is included when the tongs are tested at the lower end of the sensor