Answer / mprajaneb

restraining coils are used in the relay for controlling the
sensitivity characteristic of the relay. Differential
relays are highly sensitive relays. restraining coils
prevents the unwanted tripping of the transformer due to
the spill current due to CT saturation effect, or due to
the mismatch current due to CT characteristic.

Answer / arvindmanavazhagan

The concept is simple. In any relay there are two forces namely controlling and deflecting force. Controlling force is responsible for the normal operation of the relay that is during normal current flow (during non faulted conditions). Whenever a fault occurs as we know that the impedance will get reduced and hence the fault current raises above the rated value and flow through the secondary of the CT connected to the relay circuit. Actually both the forces are present during normal operations also. But during fault due to the high fault current the deflecting force raises above the controlling force thus actuating the relay operation. Controlling force is created by the restraining coil and the deflecting force is created by the operating coil. This force production is as simple that it is based on the fact that a current carrying coil experiences a force.  

Answer / m raviteja

the function of the restraining coil is to avoid the mal
fuctioning of the main relay. restraining current is
flowing through the restraining coil is to prevent the
external faults. the increase the current increase the
restraining torque.

Answer / arvind manavazhagan

The concept is very simple. If we consider any relay there are two forces namely controlling and deflecting force.Both the forces are present during normal operation also. Controlling force keeps the contacts of a relay in normal position during normal operating conditions.When a fault occurs we know that due to a reduced impedance high fault current may flow through the circuit and hence through the secondary of the CT that is connected to the relay also.This in turn increases the deflecting force than the controlling force thus operating the relay.Controlling force is produced by the restraining coil and deflecting force is produced by restraining coil.   

Answer / madivalanagaraja@gmail.co

T the bias force produced due to the restraining coil greater than the operating force produced by the operating coil is relay is inoperative. When the internal fault occurs, the operating force becomes more than the bias force. Due to this, Beam moves and the trip contact sir closer to open a circuit breaker

Answer / vikash kumar barnwal

restraining coil is given to avoid mal-functioning of differential relay.
since differential relay works on the principle of balancing the incoming and outgoing currents from alternator coils and due to the inductive effect of alternator coils, there is some phase angle difference between these currents..
so even there is no fault it may cause to operate the relay coil.
hence, restraining coil is given to limit the sensitivity of the differential relay.

Answer / tarun singh

restraining coil is used to avoid the trouble arising due to
difference in ct ratios..

Answer / gunasekaran

restaining coil is used for restaining the 2nd and 5th
hormonics in inrush current

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