How Many Types of Overvoltages Can a Transformer in Operation Suffer?

During the operation of the power system, transformers are threatened by various overvoltages. If these overvoltage situations are not prevented and dealt with, they may seriously damage the insulation of transformers, affect their normal operation, and even lead to equipment damage.

Content

● Impact of Switching Overvoltages

Switching overvoltages mainly stem from switching operations in the system. For example, during no-load closing, high overvoltages will be generated in the transformer windings due to the electromagnetic transient process. Since there is residual magnetism in the transformer core, when the phase of the power supply voltage and the residual magnetic voltage is appropriate at the moment of closing, an overvoltage value far higher than the rated voltage will be superimposed. In addition, the operation of no-load switching lines can also trigger switching overvoltages. When opening no-load lines, energy conversion and oscillation will occur between the inductance and capacitance in the lines, generating high-frequency transient overvoltages. These overvoltages will propagate along the lines and act on the transformer, which may lead to partial discharges in the transformer winding insulation. Long-term accumulation will degrade the insulation performance and threaten the safe and stable operation of the transformer.

● Hazards of Atmospheric Overvoltages

Atmospheric overvoltages are mostly caused by lightning activities and can be divided into direct lightning strikes and shielding failure lightning strikes. A direct lightning strike means that lightning directly hits the transformer or nearby power facilities, instantaneously releasing huge energy and generating extremely high overvoltages. The amplitude of such overvoltages can reach millions of volts or even higher, which will directly break down the insulation of the transformer and cause serious faults such as short circuits in the transformer windings. Shielding failure lightning strikes occur when lightning bypasses the lightning protection wire and hits the conductor, and then introduces overvoltages into the power system where the transformer is located. Although the probability of shielding failure lightning strikes is relatively low, once they occur, they will also cause serious damage to the transformer because the generated overvoltages far exceed the insulation withstand level of the transformer and may lead to the breakdown of the insulation layer of the transformer and trigger power accidents.

● Risks of Resonant Overvoltages

Resonant overvoltages are generated when the inductive and capacitive elements in the power system resonate under specific conditions. When the system parameters match, for example, when the inductance of the transformer and the capacitance of the line form a resonant circuit, and under the action of external incentives (such as operations, faults, etc.), resonance may be triggered. During resonance, the voltage will rise sharply and may reach several times the rated voltage. These resonant overvoltages will make the transformer bear excessive voltage stress, accelerate insulation aging, and since the resonance may last for a period of time, the long-term action of overvoltages will gradually damage the internal insulation of the transformer and eventually lead to insulation breakdown, seriously affecting the reliability and service life of the transformer.

In Summary

In conclusion, transformers in operation may suffer from various overvoltage situations such as switching overvoltages, atmospheric overvoltages, and resonant overvoltages. Operation and maintenance personnel in the power system must fully understand the generation mechanisms and hazards of these overvoltages and take effective protection measures, such as installing lightning arresters, optimizing operation processes, and adjusting system parameters, to protect transformers from overvoltage damage and ensure the safe and stable operation of the power system.

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LuShan, est.1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase isolation transformers,electrical transformer,distribution transformer, step down and step up transformer, low voltage transformer, high voltage transformer, control transformer, toroidal transformer, R-core transformer;DC inductors, AC reactors, filtering reactor, line and load reactor, chokes, filtering reactor, and intermediate,high-frequency products.

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