Power Quality Analyzer

The ideal power system to provide users with a sine wave voltage should be a constant frequency, and with the development of power electronic technology, DC power transmission, high power single-phase rectifier technology in the industrial sector and the electric equipment widely used, such as high-power silicon controlled devices, switching power supply, inverter and so on, these typical nonlinear load harmonic current from the power grid will be injected into the suction or, causing the distortion of grid voltage, the grid wave pollution, power quality deterioration, the additional losses increase, transmission capacity decreased, as can affect the power quality of the important factors.

In power grid, the three-phase load imbalance, power system resonance grounding will produce negative sequence, high-power rectifier and nonlinear equipment will produce harmonics. Negative sequence and harmonic wave seriously affect the quality of power supply, they first affect the safe operation of power equipment. Harmonics may cause resonance, resonance and high voltage across the capacitor, because the harmonic impedance of the capacitor is very small, so easy to overload and capacitor breakdown; harmonic current flowing into the transformer, the core loss increases; the harmonic current flowing into the motor, not only the core loss increases, and the rotor vibration, seriously affects the processing quality; the higher harmonics malfunction of protection devices, the system loss is increased; the power system harmonic voltage resonance overvoltage caused by the line, will breakdown equipment insulation. Negative sequence and harmonic wave not only have thermal effect, generate local heating, but also cause vibration of generator set, accompanied by noise, which seriously threaten the safe and stable operation of the unit.

Frequency measurement

Measurement range: 45 ~ 55Hz, center frequency 50Hz, measurement conditions: signal basic component is not less than 80%F.S.

Measurement error ≤ 0.01Hz;

Input voltage range: 10V ~ 450V (special range can be customized)

Input current range: 10A (other range according to user requirements)

Fundamental voltage and current amplitude: the fundamental voltage allowed error less than 0.2%; Fundamental current allowed error less than 0.2%

Error of measuring phase difference between fundamental voltage and current: less than or equal to 0.5 degrees

Three-phase voltage unbalance: less than 0.2%

Three phase current unbalance: 0.5%;

Voltage deviation error is less than 0.2%

Power, power factor is less than 0.5%

flicker: 5%;

Voltage fluctuation: 5%.

Device interface (extended function): GPS hard timing, IRIG-B code time or second pulse timing signal.

Working hours: the internal battery 10 hours continuously

Concept editing broadcast

Power Quality (PowerQuality), strictly speaking, the main indicators for measuring power quality are voltage, frequency and waveform. In a general sense, it refers to high-quality power supply, including voltage quality, current quality, power supply quality, and electricity quality. Power quality problems can be defined as: voltage, current, or frequency deviations that cause electrical equipment to malfunction or fail to work properly, including frequency deviations, voltage deviations, voltage fluctuations and flicker, three-phase imbalance, instantaneous or transient transients Voltage, waveform distortion (harmonics), voltage sags, interruptions, swells, and power supply continuity, etc.

An ideal power system should supply power to users at a constant frequency (50 Hz) and a sine waveform, and at a prescribed voltage level (nominal voltage). In a three-phase AC power system, the voltage and current of each phase should be equal in amplitude, with a phase difference of 120. The symmetry state. Because the parameters of the system components (generators, transformers, circuits, etc.) are not ideally linear or symmetrical, the nature of the load varies and varies randomly, coupled with imperfect control methods, operation, external interference, and various faults. This ideal state does not exist in reality, and various problems in the operation of the power grid, electrical equipment and electricity consumption have arisen from this, and the concept of power quality (PowerQuality) has also been produced.

In a general sense, power quality refers to high-quality power supply. But so far, there are still different understandings of the technical meaning of power quality. This is because people look at problems from different perspectives. For example, power companies may simply regard power quality as voltage (deviation) and frequency (deviation). And use statistics to show that 9% of the power system power meets the quality requirements; power users may generally regard power quality as whether the load is normally supplied with power; while equipment manufacturers believe that qualified power quality refers to The power supply characteristics fully meet the needs of the normal design working conditions of electrical equipment, but in fact, the requirements for power supply characteristics of different manufacturers and different equipment may be very different. On the other hand, the understanding of power quality is also restricted by the development level of the power system, especially the performance and structure of the power load. [1]

Power quality index editing broadcast

Power quality indicators are specific descriptions of all aspects of power quality, and different indicators have different definitions. With reference to International Electrotechnical Commission standards, the basic phenomena that cause interference are classified as follows from the perspective of electromagnetic phenomena and interactions and influences.

a. Voltage interruption (interruption, outage): within a certain period of time, one or more phases completely lose voltage (less than 0.8 "standard unit value" is called power failure. According to the duration of time, it is divided into instantaneous power failure (0.5 cycle~3S) temporary power failure (3S~60S) and continuous power failure (greater than 60S).

b. Frequency deviation (frequency deviation): All countries have made clear regulations on this.

c. Voltage drop (sag) (voltage drop, dip): the duration is 0.5 cycles to 1 min, the amplitude is 0.1 to 0.9 (standard unit value), and the system frequency is still the nominal value.

d. Voltage rise (voltage swell, swell): The voltage (or current) duration is 0.5 cycles to 1 min, and the amplitude is 1.1 to 1.8 (standard unit value), and the system frequency is still the nominal value.

e. Instantaneous pulse (impulse): A voltage (or current) change that occurs in a very short time between two consecutive steady states. The instantaneous pulse can be a unidirectional pulse of any polarity, or the first peak of a damped oscillatory wave of any polarity.

f. Voltage fluctuation (fluctuation) and flicker (flicker): Voltage fluctuation is a regular change in the voltage within the envelope, or a series of random changes in voltage whose amplitude usually does not exceed the voltage range of 0.9 to 1.1. Flicker refers to the visual impact of voltage fluctuations on the lighting.

Comparison chart before and after power quality monitoring improvement

Comparison chart before and after power quality monitoring improvement

g. Voltage notch (notch): A voltage notch is a periodic voltage disturbance with a duration of less than 0.5 cycles. The voltage notch is mainly caused by the current switching from one phase to the other when the power electronic device undergoes an instantaneous short circuit between the related two phases. The frequency of voltage notch is very high, and it is difficult to detect it with conventional harmonic analysis equipment. This is the reason why this voltage disturbance has never been officially listed until recently.

h. Harmonics (harmonics): sinusoidal voltages or currents containing integer multiples of the fundamental frequency are called harmonics. Harmonics are caused by the non-linear characteristics of the power system and power load equipment.

i. Inter-harmonics: sinusoidal voltages or currents containing non-integer multiples of the fundamental frequency are called inter-harmonics. Fractional harmonics smaller than the fundamental frequency also belong to this category. Interharmonics can cause visual flicker in the lighting device.

j. Overvoltage (overvoltage): The voltage (or current) duration is greater than 1 min, the amplitude is 1.1 ~ 1.2 (standard unit value), and the system frequency is still the nominal value.

k. Undervoltage (undervoltage): The voltage (or current) duration is greater than 1min, the amplitude is 0.8～0.9 (standard unit value), and the system frequency is still the nominal value.

The power quality problems can be summarized as follows: ①Voltage fluctuation (fluctuation) and flicker (flicker); ②Harmonics (harmonics); ③Voltage three-phase unbalance (unbalance); ④Voltage drop (dip) and power supply Outage.