In case of overload of three-phase transformer in operation, the current indication value may exceed the rated value, the indicator value of active and reactive power meter pointer increases, or the signal of "overload" of transformer, signal of "high temperature" and sound alarm may appear. If the personnel on duty find the above abnormal phenomena or signals, they shall handle them according to the following principles:
(1) Recover the alarm, report to the monitor and shift leader, and make records.
(2) Adjust the operation mode of transformer in time; if there is standby transformer, it shall be put into operation immediately.
(3) Adjust the load distribution in time and negotiate with the user to transfer the load.
(4) If it is normal overload, the allowable time can be determined according to the multiple of normal overload; if the time is exceeded, the load shall be reduced immediately; meanwhile, the monitoring of transformer temperature shall be strengthened, and the allowable temperature value shall not be exceeded.
(5) In case of accident overload, the allowable multiple and time of overload shall be carried out according to the regulations of the manufacturer.
(6) Conduct a comprehensive inspection on the transformer and its related systems. If any abnormality is found, it shall be reported to the company immediately for handling.
If the three-phase voltage of transformer is found to be unbalanced in operation, check the three-phase load first. If the three-phase load is unbalanced, the load shall be adjusted immediately to make it balanced.
For three-phase transformer with Δ /y connection, if the unbalanced degree of three-phase voltage is more than 5 volts, it may be short circuit between turns of transformer winding, and power supply and maintenance shall be conducted. For y/y connected transformers, the difference between three-phase to ground voltage is allowed to be 10% when under light load, but three-phase voltage balance should be made when heavy load is applied.
The polarity of the three-phase isolation transformer coil is mainly determined by the winding direction of the coil, and the polarity changes with the change of the winding direction. Polarity is one of the main conditions for the parallel connection of the transformer. If the polarity is reversed, there will be a large short circuit current in the coil of three-phase isolation transformer, and even the three-phase isolation transformer will be burnt.
Measure the primary coil lead out head A1 and secondary coil lead out head A1 of three-phase transformer. For safety, the most common way is to supply a DC power supply on the high voltage side of three-phase isolation transformer by DC method. Generally, 1.5V dry battery or 2-6v battery is generally used. At the moment of high voltage circuit connection, measure the direction of the pointer of DC current or voltage on the low voltage side. Add DC power supply between a-x-ray terminals, measure voltage between a-x-ray terminals. If the positive and negative of corresponding line ends are the same, the polarity is the same.
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