Power quality analyzer11-10, 2025

Power Quality, in a general sense, refers to high-quality power supply, including voltage quality, current quality, power supply quality and power quality.
It can be defined as: the deviation of voltage, current or frequency that causes electrical equipment to fail or not work normally, including frequency deviation, voltage deviation, voltage fluctuation and flicker, three-phase unbalance, temporary or transient overvoltage, waveform distortion (harmonics), voltage dip, interruption, temporary rise and supply continuity. In modern power systems, voltage sag and interruption have become the most important power quality problems.
1.Harmonic
The problem of harmonics in power systems was noticed as early as the 1920s and 1930s. At that time in Germany, the voltage and current waveforms were distorted due to the use of stationary mercury arc converters. J.c. Read's 1945 paper on converters harmonics is a classic early paper on harmonics.
2.Function and composition
Power quality analyzer is a special portable product for the detection and analysis of power grid operation quality. It can provide harmonic analysis and power quality analysis in power operation, and can conduct long-term data acquisition and monitoring of power grid operation. At the same time, it is equipped with power quality data analysis software to carry out various analysis of the measurement data uploaded to the computer.
The power quality analyzer is mainly composed of five parts, which are measurement conversion module, analog-to-digital conversion module, data processing module, data management module and peripheral module. The measurement conversion module is composed of voltage transformer, current transformer and signal conditioning circuit. The data processing module includes DSP and external memory SDRAM and FLASH. The peripheral module consists of display, storage and communication sub-modules.
3.Operating principle
The power grid signal is transformed into a small value voltage signal that meets the input requirements of ADC through the voltage/current transformer and signal conditioning circuit; Analog-to-digital conversion module is used to convert small voltage signals into digital signals and transmit them to data processing module; The data processing module uses DSP as the computing core to process the sampled signal of ADC, so as to calculate the power quality parameters such as voltage deviation, frequency deviation, harmonics, three-phase unbalance degree and voltage flicker. The data management module is used to manage the power quality parameters calculated by the data processing module, and complete the man-machine interaction functions such as display, storage and communication.
4.Source of error
（1）Measurement conversion circuit introduced error: When the power quality analyzer works, the voltage and Current signals in the power grid need to be sent to the power quality analyzer through Potential Transformer (PT) and Current Transformer (CT) respectively. Therefore, the proportion error and phase Angle error of PT and CT directly affect the accuracy of measurement results. When the power quality analyzer works under harmonic conditions, the phase Angle error of PT and CT changes, and the conversion ratio of each harmonic voltage and current is inconsistent, the measured signal of the input ADC is deformed, and the measurement error increases.
（2）ADC quantization error: ADC quantization error refers to the error caused by the finite digital signal to represent the infinite precision analog signal when the input signal is converted to digital. Power quality analyzers often use 12-bit or 16-bit ADC, and the larger the ADC number, the higher the conversion accuracy and the smaller the quantization error.
（3）Other errors: including environmental temperature, relative humidity and other factors caused by the hardware circuit error, electronic devices and line aging factors caused by the measurement results error.
5. Self-calibration technique
Automatic calibration of power quality analyzer mainly involves three aspects: virtual instrument technology, bus technology and programmable instrument standard command.
（1）Virtual Instrument technology: Virtual instrument technology utilizes high-performance modular hardware combined with efficient and flexible software to complete a variety of test, measurement and automation applications. The United States NI company first proposed the concept of virtual instrument, since the 1990s, NI company has developed virtual instruments that support a variety of bus systems, especially the company launched LabVIEW, through the graphical software program flow chart programming to realize the measurement and testing functions of virtual instruments.
（2）Bus technology is the key to the communication of automatic calibration system, and the commonly used buses for instrument measurement mainly include: GPIB(General Purpose Interface Bus), LAN(LocalArea Network), serial bus (RS-232, RS-422, RS-485), etc.
（3）Standard Commands for Programmable Instruments (SCPI) : SCPI is a standard command set specification, hardware independent, whether GPIB, LAN or serial port based instrument can use SCPI-compliant command set. SCPI statements exist as ASC II text and can be added to any computer test programming language, such as BASIC, C, or C++. It can also be used in specialized test program development environments such as LabVIEW, LabWindows/CVI.
6. Harmonic and reactive power problems
Harmonics and reactive power are important indicators of power quality in power grid, which are of great significance to both power grid and users. Although harmonic and reactive power are two relatively independent problems, there is a very close relationship between them. This is because:
(1)Harmonics, in addition to their own problems, also affect the load and reactive power of the grid;
(2)The devices that generate harmonics are also mostly devices that consume fundamental reactive power;
(3)The harmonic control device is usually also a device that compensates the fundamental reactive power.