Harmonics bring a wide range of adverse impacts to power grids, with the main risks outlined below:
1. Damages to Power Supply & Distribution Lines
(1) Compromised grid operational stability
Power distribution circuits and transformers rely on electromagnetic, induction or transistor relays for monitoring and protection. These protective devices are highly susceptible to harmonic interference, which can trigger false tripping or failure to respond to actual faults. This poses major threats to the overall safety and stable operation of the power supply network.
(2) Degraded power grid quality
Harmonics distort the sinusoidal waveforms of grid voltage and current. This distortion leads to reduced effective grid voltage and wastes available power capacity.
2. Damages to Power Equipment
(1) Harm to power capacitors
When harmonics exist in the grid, connecting capacitors to the circuit raises terminal voltage, and the current flowing through capacitors surges far more drastically. This boosts power loss inside capacitors and causes abnormal overheating. Combined with continuous electric field stress, high temperatures accelerate the aging of insulating materials. In severe harmonic conditions, capacitors may bulge, suffer dielectric breakdown, or even explode.
(2) Harm to power transformers
Harmonics raise both copper loss and iron loss within transformers. The extra power loss cuts down the transformer's usable rated capacity. Additionally, harmonics amplify transformer operating noise, sometimes creating harsh metallic humming sounds.
(3) Harm to power cables
Higher-order harmonics push up operating frequency. For large cross-section cable conductors, the skin effect becomes far more pronounced, raising the AC resistance of conductors. As a result, the maximum allowable ampacity of cables drops significantly.
3. Negative Impacts on End-User Electrical Loads
(1) Harm to electric motors
For asynchronous motors, harmonics introduce extra power losses and lower operational efficiency, which may lead to severe overheating. Negative-sequence harmonics create a reverse rotating magnetic field inside motors, generating counter-torque that acts as a braking force and cuts motor output power.
(2) Malfunction of low-voltage switchgear
Electromagnetic circuit breakers, thermal-magnetic circuit breakers and electronic circuit breakers are all prone to unwanted tripping caused by harmonic distortion.
(3) Electromagnetic interference with low-voltage signal & control systems
Harmonic radiation disrupts sensitive weak-current electronic devices.
4. Inaccurate Power Metering
Induction-type energy meters, the most widely used model, deliver unreliable and confusing readings under heavy harmonic distortion, leading to inaccurate power consumption measurement.
5. Physiological Impacts on Human Bodies
From a physiological perspective, human cells produce rapid electrical fluctuations when activated. If the frequency of grid harmonic electromagnetic radiation overlaps with the frequency of these biological electrical signals, it will interfere with the magnetic fields of the human brain and heart.
Sources of Grid Harmonics
Grid harmonics originate from three primary sources: low-quality power generation equipment, transmission and distribution infrastructure, and end-user electrical loads. Among the three categories, consumer-side loads generate the largest volume of harmonics.
Given the extensive risks posed by harmonics, targeted harmonic mitigation solutions are essential to improve power quality, reduce operational hazards, and prevent power system failures.