The principle of transformer overvoltage generation
Transformers are electrical equipment for power grid voltage conversion and transmission of electric energy. They are the carriers of power grid to supply electricity to users. The safe and reliable operation of transformers is closely related to the lighting of thousands of households. However, overvoltage will be generated due to many reasons in the operation of power grid, and the insulation level of transformers is relatively weak. Among the reasons for transformer damage, overvoltage has the highest probability of damage. Overvoltage caused by some reasons in the operation of power grid will inevitably lead to damage of transformers. Its insulation level is mainly determined by lightning withstand voltage and power frequency withstand voltage.
Overvoltage refers to a sudden voltage rise that is dangerous to insulation. This abnormal voltage rise can reach several times the rated voltage of the equipment, which seriously threatens the safety of transformer insulation. If the overvoltage lasts for a long time, it will inevitably cause damage to the transformer. In order to ensure the safety of transformers in power grid operation, in addition to selecting high-quality transformers, reasonable and effective overvoltage protection measures should be set for transformers.
The overvoltage of power system can generally be divided into temporary overvoltage (power frequency overvoltage, resonance overvoltage, arc grounding overvoltage), operation overvoltage, lightning overvoltage, etc. Temporary overvoltage is mainly caused by single-phase grounding fault, resonance, etc. Resonance overvoltage is an overvoltage caused by the conversion of electric energy and magnetic energy under certain conditions when electrical equipment fails in the power grid or when the inductance and capacitance in the power grid are matched to form a resonant circuit due to frequent operation of the equipment. For example, the ferromagnetic resonance caused by the excitation inductance of the transformer and the capacitance to the ground will cause a higher overvoltage. Arc grounding overvoltage is an overvoltage caused by arc discharge at the grounding point due to a single-phase grounding fault in the system. Operation overvoltage is an overvoltage caused by the rapid release of energy due to the sudden change of the electromagnetic field energy caused by the sudden change of the power grid state, or the switching of large-capacity equipment, or the operation error of the equipment. It is mainly manifested in the disconnection and reclosing of unloaded lines and transformers. Lightning overvoltage is an overvoltage caused by the discharge of thunderclouds when a large number of positively charged thunderclouds in the atmosphere meet negatively charged thunderclouds. Lightning overvoltage can be divided into direct lightning overvoltage and induced overvoltage. Direct lightning overvoltage is caused by the discharge of thunderclouds directly to conductors such as equipment and components, while induced overvoltage is caused by the rapid change of electromagnetic fields.
