Auxiliary Relays and it's Testing

         All relays are not for tripping of circuit breaker but also used for signalling or interlocking. Auxiliary relays which is voltage operated attracted armature type relay is used for this purpose. It has DC coil, NO and NC contacts. It's contact are silver/copper alloy. They are shaped and positioned to ensure a reliable and low resistance contacts. When DC coil get supply it's contact changeover (NO become close, NC become open). When DC gone it's contact return into their original position So it is Self Reset type relay.

            

            DC coil with various voltage rating like 24-30V, 48-50V, 110-125V or 220-250V are avaliable in market. Generally This relays operate between 75% to 120% of rated voltage. It;s Operating time at rated voltage is 15-20 msec.

ALSTOM, EE, AREVA, GEC ALSTHOM MAKE VAA SERIES ARE AUXILIARY RELAYS.

            We can make logic using this relays for example:- In motor feeder, you need to stop motor (Open the motor circuit breaker )from remote via simple push button (place where motor mouneted). So we can make wiring using this relays like this.

              As shown in image, When you press stop button from motor it will energize Auxiliary relay, when it energize it's NO Contact close which result into energization of master trip which trip the Motor circuit breaker.

Single coil Auxiliary relay

              As shown in image, this auxiliary relay can be used for 110V as well as for 250V DC. If we want to use it as 110V dc then you need to bypass resistor which is mount in series with the coil. NO. NC Contacts easily shown over the coil.

Double coil Auxiliary relay

            As shown in image, it has two different coil which has it's own NO NC Contact. Both coil has rated voltage of 110V DC. This 30 number tag is for reference in drawing. from that you can easily found out it's place in drawing. Auxiliary relay cannot trip the circuit breaker directly.

Testing of Auxiliary relay:-
                 In testing of this type of relays Various parameters measured is as follow.

• Coil Resistance:- DC coil is one type of R-L load, so we check resistance of coil. Above VAA11 relay coil has resistance of 5.50k.

• Pickup Voltage:- Voltage at which relay contact changeover from normal position.

• Drop off Voltage:- Voltage at which relay contact return into it's normal position.

• Contact Pressure:- When relay pickup, we need to measure pressure of contact if pressure is below limit it means it need calibration.

• Contact cleaning:- Relay contact has some dust particle over it so it should remove to get low contact resistance hence we need to clean it by spray.

Abnormality can be found in Auxiliary relays:-

1. Coil found open, so relay not pickup at rated volt
2. Relay pickup but it's contact pressure not sufficient.
3. Physical damage.