The 33rd China International Exhibition on Electric Power Equipment and Technology
Shanghai International Energy Storage Technology Application Expo / Hydrogen Energy Expo
Power quality refers to the characteristics of the electrical supply at a given point in the power system, assessed against ideal sinusoidal voltage and current waveforms at the nominal frequency and voltage. Poor power quality manifests as voltage sags (brief reductions in voltage caused by faults or motor starting), voltage swells (brief overvoltages), harmonics (non-sinusoidal distortion caused by non-linear loads such as variable speed drives and power electronics), voltage unbalance (unequal voltages on three phases), flicker (rapid voltage fluctuations causing visible light flicker), frequency deviations, and transients (high-frequency voltage spikes from switching operations or lightning). Power quality problems cause equipment malfunction, reduced efficiency, overheating, and premature failure in sensitive industrial processes, data centres, and commercial buildings. The proliferation of power electronics in renewable energy inverters, EV chargers, and industrial drives is increasing harmonic distortion levels in distribution networks, making power quality management increasingly important.
5 Key Questions About Power Quality
The most common power quality problems in industrial facilities include: voltage sags caused by motor starting, fault clearing, or utility disturbances — affecting sensitive CNC machines, PLCs, and process control equipment; harmonics generated by variable speed drives, UPS systems, and rectifiers — causing transformer overheating, cable heating, and interference with communication systems; voltage unbalance from unequal single-phase loading — reducing motor efficiency and causing overheating; and transients from capacitor bank switching or lightning — damaging sensitive electronics. Power quality surveys using portable analysers are used to characterise the power supply environment and identify the dominant problems affecting a specific facility.
Harmonics are voltage and current components at integer multiples of the fundamental frequency (50 Hz in China), generated by non-linear loads that draw non-sinusoidal currents. Variable speed drives, UPS systems, LED lighting, and power supplies are major harmonic sources. Effects include: transformer overheating (harmonics increase iron and copper losses); cable overheating (skin effect increases resistance at harmonic frequencies); neutral conductor overloading (triplen harmonics add in the neutral); resonance between harmonic sources and power factor correction capacitors (causing amplified harmonic voltages); and interference with protection relays, meters, and communication systems. IEC 61000-3-2 and GB/T 14549 set harmonic emission limits for equipment connected to the public network.
Power quality mitigation equipment includes: passive harmonic filters (tuned LC circuits) that provide a low-impedance path for specific harmonic frequencies; active harmonic filters (power electronic converters) that inject cancelling harmonic currents in real time; static VAr compensators (SVCs) and STATCOMs that provide dynamic reactive power compensation to stabilise voltage; uninterruptible power supplies (UPS) that isolate sensitive loads from supply disturbances; voltage conditioners and dynamic voltage restorers (DVRs) that compensate for voltage sags; and power factor correction capacitors that reduce reactive power demand and improve voltage regulation.
The growth of renewable energy is affecting power quality in several ways: large-scale solar and wind farms inject harmonics and inter-harmonics from their power electronic inverters; variable renewable generation causes voltage fluctuations on distribution networks; the displacement of synchronous generators by inverter-based resources reduces system inertia, making frequency more sensitive to generation-load imbalances; and the proliferation of distributed rooftop solar creates bidirectional power flows on distribution networks designed for unidirectional flow, causing voltage rise and protection coordination challenges. Grid codes increasingly require renewable generators to provide reactive power support and ride through voltage disturbances to maintain power quality.
Power quality in China is governed by a series of GB/T national standards: GB/T 12325 (voltage deviation), GB/T 12326 (voltage fluctuation and flicker), GB/T 14549 (harmonics in public supply networks), GB/T 15543 (voltage unbalance), and GB/T 15945 (frequency deviation). These standards set limits for power quality parameters at the point of common coupling (PCC) between the utility and the customer. Equipment emission standards (GB/T 17625 series, harmonised with IEC 61000-3 series) limit the harmonic currents that individual equipment can inject into the network. Utilities are responsible for maintaining power quality within the limits at the PCC, while customers are responsible for ensuring their equipment complies with emission limits.
Key Takeaways
Power quality is a fundamental requirement for reliable industrial production, data centre operation, and commercial building performance. The proliferation of power electronics in renewable energy, EV charging, and industrial drives is increasing power quality challenges across distribution networks. EP Shanghai showcases the full spectrum of power quality measurement, analysis, and mitigation technologies from leading Chinese and international suppliers.
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