Due to the increasing of impact and non linearity load, traditional power quality problems such as harmonics, voltage fluctuation, flicker, three-phase unbalanced have worsened ,triggering a lot of anomalies and accidents of production equipment and power grid, including the increased loss of electrical equipment, shortened life expectancy, abnormal working status. At the same time the appearance of large numbers of sensitive load such as control equipment and electronic devices based on computer system make people start paying attention to temporary over-voltage ,transient over-voltage, voltage sag, and power short interruption. The economic loss caused by power quality problems is increasing.
1WB power quality inspection service: we are able to help you locate, predict, prevent the electrical system problems. The power system monitoring is no longer judge subjectively as the traditional practices.
1. Voltage current and frequency
The main analytical parameters: voltage and current effective value, frequency
Application: Through analyzing the waveform of voltage and current , we can determine the existence of harmonics; through inspecting and analyzing the effective value of voltage and current, we can initially determine the presence of voltage bias or current imbalances.
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2. Harmonic
The main analytical parameters: total harmonic distortion, harmonic frequency, harmonic causes
Harmonic generation source
(a)Electronic switch Type: they are mainly variety of AC-DC converter devices (rectifiers, inverters), widely used in chemical industry, metallurgy, electric railways and other large industrial and mining enterprises, as well as home appliances and bi-directional thyristor controlled switching.
(b)Arc-type: during the melting period of steel-smelting electric arc furnace and the welding period of AC arc welders, arc ignition and drastic change engender highly nonlinear current irregular fluctuations.
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Hazards of harmonic
Hazards of harmonic: transformer
Harmonic current, voltage will increase the copper loss, magnetic flux, iron loss of transformer. Power harmonic also increase the noise of transformers, increase the additional temperature rise of transformers, in particular, the higher the frequency of the harmonic, the more significant of the noise and temperature characteristics.
Hazards of harmonic: power cable
The harmonic current is anomaly current. The excessive harmonic currents would make power cable overload and overheating, even burn the conductor insulation down. Conductors have skin effect for high-frequency harmonic currents which makes rated capacity reduced.
Hazards of harmonic: capacitor
There are time limit about overvoltage of high and low voltage capacitor.
The normal reason of capacitance harmonics accidents is parallel resonance of power system expand the harmonic pollution, cause too much harmonic voltage.
3:Power and watt-hour
The main analytical parameters: active power, reactive power, apparent power, power factor, watt-hour
4.Voltage swell ,sag and transient
The main analytical parameters: voltage swell, voltage sag, transient
Harm of the voltage swell and sag
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Equipment |
Impacts and hazards |
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Refrigeration Controller |
When the Voltage is less than 80%, the controller will remove the motor cooling, cause enormous losses. |
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Chip manufacturing |
When the voltage is below 85%, the chips are destroyed, testing is stopped, the internal electronic circuit board is failed. |
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PLC |
When the voltage is lower than 90% and continuing numbers of cycle, the I / O device removed, less than 81%,the PLC will stop working. |
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Precision Manufacturing |
When the voltage is lower than 90% and continuing 2-3 cycle, the precision machining process controlled by computer or robot will be interrupted. |
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DC Motor |
When the voltage is below 80%, the motor protection tripping. |
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VSD |
When the voltage is lower than 70% and continuing more than 6 cycle, VSD is removed; when the voltage is lower than 90% and continuing more than 3 cycle, some motor of sophisticated processing industry tripping. |
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DC contactor |
When the Voltage is lower than 50% and continuing more than 1 cycle, the contactor will trip, sometimes the voltage is lower than 70%, the contactor will trip. |
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Computer |
When the voltage is lower than 50% and continuing more than 10 cycle, the computer will be affected and data might be lost. |
5.Three phase unbalance
The main analytical parameters: voltage and current value of three-phase unbalance, three-phase unbalanced phase angle
Three-phase unbalance causes: three-phase load asymmetry, single-phase high-capacity load (e.g. electrified railways, electric arc furnaces, welding machines), irrational location of capacity and electrical in the system.
Hazard of Three-phase unbalance: cause relay misoperation, additional vibration motor torque and heat.
6.Surge voltage and current monitoring
7.Flicker
1. Definition: People's subjective feelings about brightness caused by the changes of supply voltage virtual value. If the changes of voltage come to 0.5%, 6 to 8 times per second, it will cause significant flicker.
2. Causes: Voltage fluctuations caused by electric arc furnace, rolling mill.
3. Hazard of flicker: The lights flicker caused by supply voltage flicker may stimulate people's optic nerve.
