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Zero sequence current protection principle

        Zero sequence current protection:Neutral point direct grounding system grounding short circuit,will produce a large zero sequence current,the use of zero sequence current component protection,can be used as a major grounding short circuit protection.Zero sequence overcurrent protection does not reflect three-phase and two-phase short circuits,and there is no zero sequence component in normal operation and system oscillation,so it has better sensitivity.But the zero sequence overcurrent protection by the power system operation mode transformation of a greater impact on the sensitivity is reduced,especially in short-distance lines and complex ring network,the speed of the protection range is too small,or even no protection range,resulting in zero sequence current protection of the performance of each section seriously deteriorated,so that the protection action time is very long,the sensitivity is very low.

       Zero sequence current protection is the biggest characteristic:only to respond to single-phase.Because the other non-ground short-circuit faults in the system do not produce zero sequence.
       
       Zero-sequence current protection with directional and non-directional is a simple and effective grounding protection. Its advantages are:
 
       (1) the structure and working principle are simple, and the correct action rate is higher than other complex protection;
 
       (2) the whole set of protection intermediate links is small, especially for the near faults, which can achieve quick action, which is conducive to reducing the development failure;
 
       (3) under the condition that the zero order network of the power network is basically stable, the protection scope is relatively stable.
 
       (4) the protection reaction is the absolute value of zero sequence current, which is less affected by the fault transition resistance;
 
       (5) the protection of the fixed value is not affected by the load current, and it is basically not affected by the short circuit fault of other neutral points, so the sensitivity of the protection delay segment is protected.
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