Power quality, in a general sense, refers to high-quality power supply, including voltage quality, current quality, power supply quality and electricity quality.
It can be defined as: the deviation of voltage, current or frequency that causes the failure or failure of electrical equipment to work normally, including frequency deviation, voltage deviation, voltage fluctuation and flicker, three-phase unbalance, temporary or transient overvoltage, waveform distortion (harmonic), voltage sag, interruption, swelling and power supply continuity.
The quality of power can be measured from voltage deviation, frequency deviation, voltage three-phase unbalance, harmonics and interharmonics, voltage fluctuations and voltage flicker.
1. Voltage deviation: Voltage deviation refers to the instability of the power supply voltage, and the existence of voltage rise or ** situation.
2. Frequency deviation: All power grids have the same requirements for grid frequency, which will not change due to different power users, and each country has corresponding regulations on frequency deviation.
3. Three-phase unbalanced voltage: the value of three-phase voltage exceeds the specified standard.
4. Harmonics and interharmonics: the current or voltage whose frequency is an integer multiple of the fundamental wave and is manifested as a sinusoidal is called harmonics. Non-integer multiples are collectively referred to as interharmonics.
5. Voltage fluctuation and flicker: The regular change of voltage in the power grid is called voltage fluctuation, or the multiple of the change range is 09-1.Random variation between 1. Flicker refers to the visual effect of voltage instability on the lighting of the bulb.
The common treatment methods for these problems mainly include: capacitance compensation, tuning compensation, single-phase separate compensation, dynamic switching compensation, passive filtering, active filtering, etc. Each approach is mainly aimed at one aspect of problem governance, but at the same time it will affect other aspects, or it will have an adverse effect, or it will have a helping effect in passing.
Therefore, in order to avoid the impact of subsequent treatment methods on electrical equipment and production, it is better to monitor the power quality in the early stage.
The use of a power quality monitoring device can detect voltage, current, harmonics and other parameters in real time, can timely find power quality problems, improve the efficiency of the power system, prevent the occurrence of power accidents, and ensure the safe and stable operation of electrical equipment.
Next, we will introduce the power quality monitoring device of CET CLP technology, including imeter D7 power quality monitoring device, imeter 6 high-end smart meter, imeter7A-power quality monitoring device and other products, whose role and main advantages are reflected in the following aspects:
1) Location of the source of sagging
More than 80% of the power quality problems are caused by voltage sag, and accurately judging whether the disturbance causing voltage sag occurs on the user side or the system side, and determining the location of the voltage sag source can provide strong data support for the selection of reasonable governance measures, and can be used as an important basis for coordinating disputes between power departments and users in the power market environment.
2) Diagnosis and localization of harmonic sources
Measure and visually display the voltage, current amplitude and phase of 2 63rd harmonic, and calculate harmonic energy; The installation of the imeter series at some public connection points or some key bus bars within the user can help users quickly diagnose harmonic sources, understand the degree of harmonic distortion, evaluate the possible impact on electrical equipment, help users diagnose the main harmonic sources in the comprehensive load, and determine the main harmonic sources on the system side and the user side.
(3) Asymmetric analysis
Measure the amplitude and phase of the positive, negative and zero sequence of three-phase voltage and current, calculate and analyze the voltage and current unbalance, including the negative sequence unbalance and the zero sequence unbalance, monitor the three-phase asymmetry in real time, assist the user to understand the asymmetry source of the system, avoid the damage to the electrical equipment caused by the asymmetry, and provide data basis for the user to adjust the load structure.
4) Voltage tolerance analysis
At the same time, it can also capture the sub-cycle transients of 20 s, record the transient process characteristic data in detail, and cooperate with the analysis of the voltage tolerance curve of ITI-CBEMA and SEMI-F47 to evaluate the tolerance of sensitive electrical equipment such as mainframe computers and semiconductor industries to external voltage interference, and provide data support for the comprehensive evaluation of the impact of voltage disturbance events.
5) Distributed recording and diagnosis function
The disadvantages of the traditional centralized fault recording device: once a fault occurs, the entire substation cannot record waves; A large number of cables need to be laid, and the cost remains high; The distribution interval between the high and low voltage sides is far away, which makes it impossible to accurately sample and analyze synchronously.
The CET power quality monitoring system can solve the shortcomings of the traditional centralized fault recorder. The typical hardware products in the solution, iMeter 7A and iMeter D7, have a distributed recording function, which can be used as a decentralized fault recorder, and can be interconnected through the GOOSE function to realize the synchronous recording of different monitoring node terminals in the system.
(6) Ultra-high harmonic detection
New electrical equipment such as converters, rectifiers, and inverters are connected to the power grid, and more and more 2K-150KHz ultra-high harmonics are injected into the power grid, resulting in serious electromagnetic interference and affecting the normal operation of the equipment, such as: incorrect meter display or communication interruption, non-control interruption of the electronically controlled system, abnormal heating of the equipment or even burning, etc., which seriously threatens the continuity and reliability of production. CET power quality monitoring device has 2K-150kHz ultra-high harmonic monitoring and analysis functions.
Through real-time monitoring and alarm of the whole station, the CET power quality monitoring device and its Diagasys system can quickly confirm the location of the accident and generate a diagnostic analysis report for the accident that has occurred, so as to assist the user to quickly complete the accident handling and restore the power supply, ensure the safe, reliable and continuous operation of production, and reduce the economic loss of the user.