current setting and time setting of relay

~ the relay pick-up current must must be adjustable.

~ this is called current setting.

~ the percentage of  setting the plug to be brought to the bridge by removing various tap from the relay coil can be adjust from the figures shown on the bridge.

~ this setting range from 50% to 200% in 25% step for over current relay and 10% to 70% in 10% step for earth fault relay. 

~ this is indications by the percentage of the total load setting of the CT for the tapping relay. 

~ if the current rises above this value the disk start operating, and the contact is blocked.

~ plugs are placed in the bridge to determine the setting for ex. the over current relay setting is kept at 150%.

~ the ratio of current transformer is 500/5.

~ now the rated secondary current of CT is 5A and 150% tapping.

~ so 150 pick up current 7.5 when A or more occurs the relay disc will start rotating 100 and the contact will close.

~ that is the relay will operate when the fault current is 500*150/100*5=750a,