The degradation of power quality doesn't just disrupt the normal and secure power supply of the system; it also poses numerous threats to the power infrastructure, directly impacting both personal safety and economic efficiency. Consequently, this issue carries severe ramifications.
Defining Power Quality Issues
Power quality encompasses voltage quality, current quality, power quality, and more. The IEEE 22nd Standards Committee outlines several key power quality concerns:
Voltage Dip: A reduction in the effective value of voltage or current to between 0.1 and 0.9 of the rated value lasting from 0.5 cycles to 1 minute, while the system frequency remains nominal.
Voltage Interruption: Loss of voltage in one or more phases for a specific time frame (below 0.1 of the rated value). This can be classified into instantaneous outages (0.5 cycle to 3 seconds), temporary interruptions (3 seconds to 60 seconds), and prolonged outages (over 60 seconds).
Harmonics and Interharmonics: Sinusoidal voltages or currents whose frequencies are integer multiples of the fundamental supply frequency are known as harmonics, while those containing non-integer multiples are termed interharmonics. These are primarily generated by the nonlinear characteristics of power systems and electrical load equipment, such as induction motors, static inverters, cycloconverters, and arc equipment. Interharmonics can lead to flickering in lighting devices.
Voltage Fluctuation (Flicker): Regular or random changes in voltage amplitude within the normal range (90%-110% of the rated value), producing an illumination flicker of about 6-14 Hz. This phenomenon is referred to as flicker and is mainly caused by industrial loads like electric welders, rolling mills, and electric arc furnaces. Flicker is a subjective perception of lighting fluctuations and serves as a crucial indicator of voltage fluctuation impacts on electrical equipment.
Other power quality issues include voltage asymmetry, three-phase imbalance, overvoltage, undervoltage, etc.
Harmful Effects of Power Quality Problems
The decline in power quality not only affects the normal and secure power supply but also brings various risks to the power system, directly affecting personal safety and economic efficiency. Thus, power quality problems have severe consequences, manifesting in several ways:
Voltage Fluctuations and Flicker: This leads to unstable operation of electrical equipment, exceeding the allowable voltage range due to fluctuations. Moreover, voltage fluctuations during electric arc furnace steelmaking operations cause additional losses in rotating electric machines, reducing motor efficiency and lifespan.
Short-Term Voltage Interruptions: Common transients are often triggered by external factors like lightning or strong winds or internal equipment malfunctions. The increasing reliance on precision instruments and equipment controlled by computers and microprocessors makes them highly sensitive to power quality. According to an IBM market survey, 48.5% of computer data loss is attributed to power quality issues.
Harmonic Hazards: Harmonics increase transmission losses in the utility grid, reducing the efficiency of power generation, transmission, and usage. They also distort electrical instrument measurements, affect electrical equipment operation, and interfere with communication systems.
Reactive Power: Reactive power diminishes the efficiency of power generation and transmission equipment, increases equipment and line losses, and causes voltage fluctuations, severely affecting power quality.
Three-Phase Imbalance: This generates additional heat and vibrations in rotating motors, affecting safe operation and output. It also produces non-characteristic harmonic currents in semiconductor converters, leading to protection system malfunctions and increased interference in communication systems.
In conclusion, maintaining power quality is essential for ensuring reliable and efficient power supply. Addressing these issues requires comprehensive monitoring and advanced technologies to mitigate risks and ensure system stability.
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