What kinds of tests should be carried out for transformers in operation?
In order to ensure the normal operation of the transformer, the following tests shall be carried out frequently:;
(1) Temperature test. The temperature is very important for the normal operation of the transformer. The regulations stipulate that the upper oil temperature shall not exceed 85C (i.e. 55C temperature rise). General transformers are equipped with special temperature measuring devices.
(2) Load measurement. In order to improve the utilization rate of transformer and reduce the loss of electric energy, the power supply capacity that the transformer can really bear must be measured during the operation of transformer. The measurement is usually carried out during the peak period of electricity consumption in each season, and is directly measured with a clamp ammeter. The current value should be 70~80% of the rated current of the transformer. If it exceeds the value, it indicates overload and should be adjusted immediately.
(3) Voltage measurement. The regulation requires that the voltage variation range shall be within ± 5% of the rated voltage. If this range is exceeded, the tap shall be used for adjustment to make the voltage reach the specified range. Generally, use a voltmeter to measure the terminal voltage of the secondary coil and the terminal voltage of the end user.
(4) Insulation resistance measurement. In order to keep the transformer in normal operation, the insulation resistance must be measured to prevent insulation aging and accidents. During the measurement, try to stop the transformer. Use a megger to measure the insulation resistance of the transformer. The measured resistance is required to be no less than 70% of the previously measured value. When using a megger, the low-voltage coil can be of 500 V voltage grade.