Hermetically sealed transformer is the electrical equipment that transforms voltage and transmits electrical energy in the power grid. It is the carrier that the power grid supplies power to users. Therefore, the safety of transformers is related to people’s living electricity. However, Sealed power transformers often have various faults during operation. One of the common problems is overvoltage.
Overvoltage refers to the phenomenon that the rms value of the AC voltage rises at the power frequency, exceeding 10% of the rated value, and the long-term voltage fluctuation is longer than 1 minute. The occurrence of overvoltage is usually the result of load switching, for example: Cut off a large capacity load or energize the capacitor bank (overvoltage caused by excess reactive power compensation).
Overvoltage refers to a sudden voltage rise that is dangerous to insulation. This abnormal voltage rises up to several times the rated voltage of the equipment, which seriously threatens the safety of the oil immersed transformer insulation. If the overvoltage duration Longer, it will cause damage to the transformer.
There are several reasons why a transformer generates an overvoltage:
(1) Atmospheric overvoltage The overvoltage induced on the transmission line by lightning strikes the transmission line or tower, or due to the discharge of thunderstorm clouds in the atmosphere.
(2) The overvoltage caused by the closing or closing of the circuit breaker on the transformer or line.
(3) Fault overvoltage An overvoltage generated by a single-phase short circuit or intermittent arc grounding in the system.
Regardless of the overvoltage, the time of action is very short, only a few tens of microseconds. The values of the operating overvoltage and fault overvoltage are generally 2 to 4.5 times the rated phase voltage, and the atmospheric overvoltage can be 8 to 12 times the rated phase voltage. With an overvoltage of 2.5 times or less, the transformer is generally capable of withstanding. More than 2.5 times, any overvoltage can damage the insulation of the transformer.
In order to ensure the safety of the oil-immersed transformer in the operation of the power grid, in addition to the selection of high-quality ZTELEC hermetically sealed transformer, it is necessary to set reasonable and effective over-voltage protection measures for the transformer.