I. Definition
Power quality refers to the quality of electric energy in the power system, in which the ideal electric energy should be a perfectly symmetrical sine wave. In practical applications, due to the influence of various factors, the waveform of electric energy may deviate from this ideal state, resulting in power quality problems. These factors include but are not limited to voltage fluctuations, frequency deviations, harmonic distortion, etc. in the system, which will affect the waveform of electric energy. Therefore, querying and solving these problems aims to make the electric energy waveform close to the ideal sine wave to the greatest extent possible, so as to ensure the stable operation of the power system and the high-quality supply of electric energy.
II. Indicators of Power Quality
- Voltage deviation: For voltage levels of 35kV and above, the allowable voltage variation range is ±5% of the rated voltage value; for voltage levels below 10kV, the allowable voltage variation range is ±7%.
- Frequency Deviation: The rated frequency of my country’s power system is 50Hz, and the allowable frequency deviation during normal operation is ±0.2~±0.5Hz.
- Waveform: To ensure the quality of electric energy, the voltage is required to be a sinusoidal waveform, but due to the presence of harmonics, the voltage waveform will be distorted.
- Harmonics and Interharmonics: Harmonics are caused by the nonlinear characteristics of power systems and power load equipment, while interharmonics refer to sinusoidal voltages or currents with frequencies that are non-integer multiples of the fundamental wave.
- Voltage fluctuations and flicker: Voltage fluctuation refers to the regular change of voltage within the envelope, while flicker refers to the visual effect of voltage fluctuation on lighting.
- Three-phase voltage unbalance: The allowable value of normal voltage imbalance at the common connection point of the power system is 2%, and shall not exceed 4% for a short time.
- Overvoltage and undervoltage: Overvoltage refers to a voltage duration of more than 1 minute and an amplitude of 1.1 to 1.2 times the rated value; undervoltage refers to a voltage duration of more than 1 minute and an amplitude of 0.8 to 0.9 times the rated value.
- Voltage cut: A periodic voltage disturbance with a duration of less than 0.5 cycle, mainly caused by the current switching from one phase to another when a power electronic device has a momentary short circuit between the two phases involved.
III. The Influence of Power Quality on Power Equipment
- Affect the normal operation and life of power equipment
- Affect automatic control devices
- Affect the accuracy of power metering
- Affect the stability of power supply quality
- Aggravate harmonic pollution
IV. The Role of Power Quality Detector
Power quality detectors are mainly used to detect and analyze power quality problems, and ensure the stable supply of electricity by detecting and analyzing the quality of power grid operation. This type of instrument can monitor and display all power quality parameters specified by national standards, such as system frequency, 2-63 harmonic voltages and harmonic currents of the power grid, three-phase voltage imbalance, voltage fluctuation and flicker, voltage deviation, voltage fundamental RMS value and true RMS value, current fundamental RMS value and true RMS value, fundamental active power, true power factor, etc. Therefore, power quality detectors are crucial to ensure the stable and safe operation of power systems, and can promptly detect and solve potential power quality problems to ensure power supply safety and normal use.
V. Summarize
The practicality of the power quality detector is reflected in its improvement of the stability and reliability of the power system. It is suitable for use by power workers and professionals in many fields such as industrial production, commercial buildings, power systems and transportation.
