In recent years, with the rapid development of information technology, the proportion of sensitive loads such as computer and microprocessor based electrical equipment and various power electronic devices in the power system load has significantly increased. Their requirements for power quality are more stringent than general electrical equipment. Therefore, voltage sags have become an important factor affecting the stable operation of electrical equipmentPower quality monitoringOne of the problems. Voltage Sag refers to a sudden decrease in the effective value of the power supply voltage to 0.1~0.9 pu in a short period of time, typically lasting between half a cycle and a few seconds. Its main characteristic is a significant decrease in the effective value of the voltage. Short circuit faults, large sensitive motor starting, and lightning strikes are the three main causes of voltage sags. Fast and accurate detection of voltage sags is one of the focuses of compensation research. The existing methods for sag detection include defect voltage method, effective value calculation method [3], instantaneous voltage dq transformation method, etc. These methods have poor real-time performance in calculating the effective value, peak value, and fundamental wave, and cannot obtain the voltage phase. Although the method based on dq transformation can detect the characteristic quantity of single-phase voltage, it still requires a 60 ° delay.

Modern power networks are often disturbed by voltage spikes and sags. More than 90% of power quality monitoring events can be traced back to voltage events with a short duration (less than 1 second). Although this droop is often undetected, it can lead to direct production losses in critical process operations. The key process operations affected by voltage dips include:
Semiconductor manufacturing
PLC controlled automated robots
• Chemical and petroleum process production
• Dairy, food and beverage production
The fundamental cause of voltage drop is the operation of surge protection devices during lightning surges on high voltage power lines in public utilities. During the SPD discharge function, an instantaneous line to ground short circuit occurs, which leads to a sudden decrease in line voltage. The duration of the event is brief, but it poses challenges to many key process operations that rely on stable voltage.