Re: Protection,s

Spir Georges GHALI

ikram shehzad said:

Hello dear,s

              please tell me that what is “Residual protection, magnetic protection, instantaneous protection.

              Is Any body can explain?

Dear Mr. Ikram ;


Residual Protection :

We use this kind of protection against any Indirect Earth Faulf, that means any short circuit betwwen any phase and the protection line, where normally the current fault value is small or too small from ” 0.01 mA ” up to ” 30 A “. We can obtain this protection by many kind of protection equipments like : RCCB, RCD, MCCB equiped by Residual Protection, and even ACB equiped by Residual Protection. Also, in some equipments we have ” Timming Delay ” for this protection.

Magnetic Protection :

We use this kind of protection against any short circuit that can happen between : 2 phases, or 3 phases with or without neutral, or 1 phase with neutral. There's adjustabe magnetic protection that means we can adjust it accordingly to the results of study of short circuit currents, and others have a fixed values. we find this protcetion in all circuit breaker : MCB, MCCB, & ACB. Some of this protection have ” Timming Delay ” to realize the Discriminitaion or Selectivity. In some kind of Earthing Systems we use this protection also against Direct Contact ( short circuit between phase and the protcetion line where the value of earth fault current is big ).

Instantaneous Protection :

This main role of this protection likes the role of magnetic protection, but there's some differences that are :

– We find this protection in all ACB and in w few type of MCCB.

– In some cases, the value of this protection is ” Fixe “, and in other cases are ” Adjustable ” and also we can switch-off.

– No timming delay for this protection.

Normally, we try to do adjustment value of this protection more than the Magnetic protection in circuit breakers that have also ” Timming Delay ” for the magnetic protection to realize the discrimination, so, once the value of short circuit current ” Isc3 ” is equal that of the magnetic protection, the circuir breaker will trip after the timming delay adjustment, but when the ” Isc3 ” is bigger and we don't want to delay the tripping the instantaneous protection trip the circuit breaker without delaying. This protcetion is very important in the networks specialy in the 1st level.