电流互感器饱和后的二次侧电流有效值分析

Analysis on the Secondary Current Valid Value for Saturation of Current Transformers

当电流互感器在大短路电流故障情况下出现磁路饱和时,一次侧短路电流无法按照电流互感器变比正常转换为相应的二次侧电流值,这对基于电流有效值继电保护的动作可能会带来影响。在不考虑非周期分量情况下,通过分析铁芯的饱和特性、研究电流互感器饱和时二次侧电流的波形,可以得出二次侧电流有效值的计算公式,再通过与电流互感器未饱和时二次侧电流有效值进行比较,可以得出饱和电流有效值总大于不饱和电流有效值。对于过电流类有效值保护,如果铁芯不饱和时能正确动作,则在铁芯饱和后仍能正确动作。

The magnetic road of current transformers will be saturated when faults occur with large short-circuit current.The value of the secondary current will not increase with the primary fault current normally,which may have influence to the operation of relay protections based on the current valid value.By analyzing magnetizing curves of the magnetic road,and saturated shapes of the secondary current,the valid value calculations can be got for saturated state without the non-periodic current.By comparing with not-saturated state calculations,the results show that the valid value for the saturated state is always larger than the valid value for the not-saturated state.So for the over-current relay protection based on the current valid value,it can surely operate when the magnetic road of current transformers is saturated if it operates effectively when the magnetic road is not saturated.