Principle and Application of Zero Sequence Protection

Under normal circumstances, the three-phase current in the power system is symmetrical, and the zero-sequence current is zero. However, when a grounding fault occurs, the fault current will flow into the earth through the grounding point, resulting in the generation of zero sequence current. Zero-sequence protection judges whether a ground fault occurs by detecting the magnitude and direction of zero-sequence current, and takes corresponding protection measures. 

Zero sequence protection is widely used, mainly including the following aspects: 

1. Neutral point ungrounded system: In neutral point ungrounded system, zero sequence protection can be used to detect single-phase ground faults and send out alarm signals or jump commands in time to avoid fault expansion. 

2. Neutral point grounding system through arc suppression coil: In the neutral point grounding system through arc suppression coil, zero sequence protection can be used to detect ground faults and used in conjunction with arc suppression coils to improve the detection sensitivity of ground faults and reliability.

3. Neutral point direct grounding system: In neutral point direct grounding system, zero sequence protection can be used to detect ground faults and be used in conjunction with other protection devices to achieve rapid jumping and fault isolation. 

 
Advantages of zero sequence protection include: 

1. High sensitivity: Zero sequence protection can detect very small ground fault currents and has high sensitivity. 

2. High reliability: Zero-sequence protection is not affected by system operation mode and load changes, and has high reliability. 

3. Good selectivity: Zero-sequence protection can achieve selective jumping by setting different action currents and action times to avoid malfunctions. 

In short, zero sequence protection is a very important power system protection technology, which is important for ensuring the safe and stable operation of the power system Line is of great significance.