There are a large number of "energy storage elements" in the power system, which are capacitors that store electrostatic energy and inductance that store magnetic energy. These components form a variety of oscillation circuits. During normal operation, these oscillation circuits are damped or shunted by the load, and generally do not produce serious oscillations. However, when a fault occurs, the system wiring method and parameters change, and resonance may occur. It often causes serious and long-lasting overvoltage; sometimes even if the overvoltage is not too high, some abnormal phenomena will appear, making the system unable to operate normally. Resonance can be divided into linear resonance, parametric resonance and ferromagnetic resonance.

linear resonance

In the system, the resonance phenomenon is formed when the natural frequency of the equivalent loop is equal to or close to the power frequency. The linear resonance overvoltage amplitude is limited by the loss (resistance) in the loop; at the same time, in some cases, due to the sharp increase in current at resonance, the ferromagnetic components in the loop tend to be saturated, so that the system automatically deviates from the resonance state and limits its overvoltage. voltage amplitude.

parametric resonance

The inductance parameters of some inductive components in the system will change periodically under certain circumstances. Under certain parameter combinations, resonance may occur.

ferromagnetic resonance

The inductance component with an iron core in the circuit will produce saturation phenomenon, and its inductance is no longer constant, but changes with the change of current or magnetic flux. This kind of circuit containing nonlinear inductance components will produce ferromagnetic resonance when certain conditions are met.

There are considerable opportunities for ferromagnetic resonance to occur in power systems. Domestic and foreign operating experience shows that it is the direct cause of some serious accidents in the power system. Common ferromagnetic resonances include PT disconnection resonance, transfer overvoltage, ferromagnetic resonance caused by electromagnetic voltage transformer and ferromagnetic resonance in series capacitor compensation line. Ferromagnetic resonance overvoltage is the most common resonance overvoltage and the most difficult to prevent.

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