What are the hazards of high-order harmonics to electrical equipment?

Voltage distortion in AC power systems causes unequal intervals between the firing pulses of the control angle in conventional converters, and through positive feedback, it amplifies the system voltage distortion, resulting in unstable rectifier operation. In inverters, continuous commutation failures may occur, preventing normal operation and even damaging commutation equipment.

For star-connected transformers, third-order and triplen harmonics can cause third-harmonic oscillation when the winding neutral point is grounded, the grid has large distributed capacitance, or shunt capacitors with neutral grounding are installed, greatly increasing transformer stray losses. In delta-connected transformers, these harmonics circulate as loop currents within the windings, causing overheating; furthermore, harmonic currents significantly increase both copper and iron losses in transformers.

In motors, high-order harmonic currents produce skin effect and magnetomotive-force eddy currents. As frequency increases, additional losses in the motor core and windings rise. During motor startup, torque pulsations easily occur, and interference torques generate significant noise. Since motors often carry heavy loads, the additional losses caused by high-order harmonics have a pronounced impact under heavy power load conditions.

Measuring instruments and meters are all designed under ideal conditions of a standard 50 Hz sinusoidal waveform. When the supply voltage or current contains high-order harmonic components, measurement accuracy is affected, and the normal operation of induction-type energy meters is impaired.

Large-amplitude low-frequency harmonic currents flowing through power lines couple magnetically into adjacent communication lines, causing interference. Under the combined effect of harmonics and the fundamental wave, telephone ringers may be falsely triggered, disrupting normal communication system operation and affecting voice transmission quality. Under certain conditions, this interference can even endanger communication equipment and personnel safety.

High-order harmonics severely affect relay protection and automatic devices in power systems, causing various types of malfunctions that threaten the safe operation of the power system.

In lighting systems equipped with starting ballasts and power-factor-correction capacitors, high-order harmonics can cause resonant overvoltages that damage ballasts and capacitors. High-order harmonics also distort images on televisions and computer monitors, cause screen brightness fluctuations, lead to overheating of internal components, and result in computer data errors.

High-order harmonics increase dielectric losses in capacitors, causing heating and shortened service life. After absorbing harmonics, capacitors may experience overcurrent, blowing fuses. When capacitors and inductive elements form a series resonance, harmonics are amplified, potentially burning out the capacitors.

Voltage distortion in AC power systems causes unequal intervals between the firing pulses of the control angle in conventional converters, and through positive feedback, it amplifies the system voltage distortion, resulting in unstable rectifier operation. In inverters, continuous commutation failures may occur, preventing normal operation and even damaging commutation equipment.