Power quality monitoringIn Chinese, voltage sag refers to a decrease in user duration from 0.5 cycles to 1 minute to 10% to 90% of rated voltage or current due to system malfunction or interference. When the amplitude is between 0.1p.u. and 0.9p.u. (per unit value), the system frequency remains at the nominal value and then returns to normal levels. Internationally, it is generally believed that power supply interruptions with voltage amplitudes below 0.1p.u. (per unit value) or greater than 0.5 cycles are considered power outage faults for both sensitive and strict users. Voltage sag may cause production interruptions or an increase in defect rates for certain users, and the power supply recovery time depends on the action time of automatic reclosing or automatic function conversion devices. Therefore, traditional mechanical circuit breakers can no longer meet the requirements for sensitive and strict electrical loads. Currently, customized power technology is mainly used to solve these problems.
Voltage rise refers to the increase in the effective value of the voltage to more than 110% of the rated value. A typical value of 110% to 180% of the rated value is called voltage rise, which temporarily exceeds the nominal value by more than 10%. The system frequency remains at the nominal value, with a duration of 0.5 cycles to 1 minute, and an amplitude of 1.1 p.u. to 1.8 p.u. (per unit value).
The harm of voltage sag to some equipment
| Equipment | Result of the impact caused by voltage sag |
| Cooling controller | When the voltage is below 80%, the controller acts to cut off the refrigeration motor, resulting in huge production losses |
| Chip tester | When the voltage drops below 85%, the tester stops working and the chip and motherboard are damaged |
| Programmable controller | When the voltage is below 81%, the PLC stops working; Some I/O devices are cut off when the voltage is below 90% and the duration is only a few tens of milliseconds |
| robot | Mechanical tools controlled by robots for precision machining of metal components such as drilling and cutting. To ensure product quality, the working voltage threshold is generally set at 90%. When the voltage drops below this value and lasts for more than 40-60ms, it is tripped |
| DC motor | When the voltage is below 80%, the DC motor is tripped |
| Variable frequency governor | When the voltage is below 70% and the duration exceeds 120ms, the ASD is cut off. For some motors in the precision processing industry, when the voltage is below 90% and the duration exceeds 60ms, the motor will trip and exit operation |
| Motor contactor | When the voltage is below 50% and the duration exceeds 20ms, the contactor will trip; Some studies have shown that when the voltage is below 70% or even higher, the contactor will trip |
| computer | When the voltage is below 60% and the duration exceeds 240ms, the calculation work will be affected, such as data loss
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