The Impact of Harmonics on Electrical Equipment

I. Impact on Power Systems

Capacitors account for the largest proportion of reactive power compensation capacity in the power grid, with user-side capacitors accounting for approximately two-thirds of the total capacity. These capacitors are often designed with only reactive power compensation in mind, neglecting the actual power quality pollution at the installation location. Therefore, when the power quality indicators at the operating point are poor, it can easily lead to various accidents: for example, the compensation device may fail to operate normally, the capacitor's service life may be shortened, and protective fuses may blow. In severe cases, series and parallel resonance can occur, leading to harmonic overvoltage and overcurrent in the capacitors, and even causing explosions. Furthermore, the current management of user-side capacitors still uses average power factor as the assessment standard. Capacitors are rarely switched on and off flexibly according to the actual operating state of the power grid, and some even remain continuously connected. This reduces the voltage regulation margin of the power grid, making it difficult to effectively control power quality indicators such as voltage deviation.

II. Impact on Transformers

Harmonic currents increase the copper losses of transformers, leading to localized overheating, increased vibration, and increased noise. They also cause additional heating in the windings. If the excitation current of the transformer contains harmonic currents, it can cause the harmonic current in the inrush current to exceed the limit; under resonant conditions, these harmonic currents pose a serious threat to the safe operation of the transformer.

III. Impact on Synchronous Generators

Negative sequence currents and harmonic currents injected into the system from the user side will flow into the synchronous generator, causing additional losses, leading to localized heating of the generator and a decrease in insulation strength. At the same time, these currents will cause additional harmonic components in the generator's output voltage waveform, triggering torsional vibration in the synchronous generator rotor and shortening the equipment's service life.

IV. Impact on Circuit Breakers

Harmonics can interfere with the normal operation of the magnetic blow-out coils of some circuit breakers, reducing their breaking capacity and preventing them from interrupting fault currents with excessive waveform distortion. For medium-voltage circuit breakers, harmonic surge voltages and re-ignition may occur during current interruption, ultimately leading to burning of the circuit breaker contacts.

V. Impact on Automatic Control Devices

With the widespread application of digital control technology, the requirements for power quality of various precision loads are increasing. Power quality pollution mainly harms these automatic control devices in three ways: firstly, by introducing distorted signals into the equipment monitoring module; secondly, by interfering with the normal analysis and calculation of the equipment; and thirdly, by leading to incorrect output results. At the same time, it may also cause irreversible damage to precision motors, switching power supplies, and other hardware, interfere with equipment protection circuits, and trigger malfunctions.

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