bejoyengineer
Member
I am sorry if this is a long one but as i read through this topic i had some doubts to be cleared.... This is a topic related to Current Transformers
""""If the current which is interrupted is high, or if it contains a large
dc component and is interrupted when total flux is high, remanence will be substantial, perhaps being above the flux equivalent of the knee point.
When the current transformer is next energized, the flux changes required will start from the remanent value, and if the required change is in the direction to add to the remanent flux, a large part of the cycle may find the current transformer saturated. When this occurs, much of the primary current is required for excitation, and secondary output is significantly reduced and distorted on alternate half cycles. This condition can be corrected by demagnetizing the current transformer. It is accomplished by applying a suitable variable alternating voltage to the secondary, with initial magnitude sufficient to force the flux density above thesaturation point, and then decreasing the applied voltage slowly and continuously to zero."""""""
Question: as i read this i thought of an example... now say a certain situation occurs like this for the first time a fault occurs and the breaker trips(say CB of outgoing feeders) and after 5 minutes again a fault occurs and again another occurs.. so by now the above said instance has already occured i.e (""""When this occurs, much of the primary current is required for excitation, and secondary output is significantly reduced and distorted on alternate half cycles."") so does this mean that the personal must go to the substation to apply a suitable variable alternating voltage to the secondary, with initial magnitude sufficient to force the flux density above the saturation point, and then decreasing the applied voltage slowly and continuously to zero so the the CT is demagnetized???
****************relay***********************
""""If the current which is interrupted is high, or if it contains a large
dc component and is interrupted when total flux is high, remanence will be substantial, perhaps being above the flux equivalent of the knee point.
When the current transformer is next energized, the flux changes required will start from the remanent value, and if the required change is in the direction to add to the remanent flux, a large part of the cycle may find the current transformer saturated. When this occurs, much of the primary current is required for excitation, and secondary output is significantly reduced and distorted on alternate half cycles. This condition can be corrected by demagnetizing the current transformer. It is accomplished by applying a suitable variable alternating voltage to the secondary, with initial magnitude sufficient to force the flux density above thesaturation point, and then decreasing the applied voltage slowly and continuously to zero."""""""
Question: as i read this i thought of an example... now say a certain situation occurs like this for the first time a fault occurs and the breaker trips(say CB of outgoing feeders) and after 5 minutes again a fault occurs and again another occurs.. so by now the above said instance has already occured i.e (""""When this occurs, much of the primary current is required for excitation, and secondary output is significantly reduced and distorted on alternate half cycles."") so does this mean that the personal must go to the substation to apply a suitable variable alternating voltage to the secondary, with initial magnitude sufficient to force the flux density above the saturation point, and then decreasing the applied voltage slowly and continuously to zero so the the CT is demagnetized???
****************relay***********************