Thanks. And relays can shut down below 80%? The IEEE C37.90 working group claims their 80% value is in line with IEC. One explanation offered for the difference from relay to breaker is the voltage drop from the relay near the battery in the control building to the breaker in the yard. But sometimes relays are in the breaker cabinet..? Anyone have some more insight on this?
The present day numerical relays accept very wide range for DC voltage supply.
With regard to a low figure of 70% for breaker trip coil, it occurs only at the time of picking up of the breaker trip coil and is understandable considering huge magnitude of current that the trip solenoid would draw.
Typically a breaker trip coil burden would be 200W as against a couple of watts (at the most) of a protection relay.
It may also be noted that the high speed, high impedance trip relays like type MVAJH of Areva are designed to pick up and close the trip contacts positively even at 50% of rated DC voltage.
Of course the time of tripping is right when you don't want your relay crapping out. Even if the trip itself is successful, relay may still weld its contacts trying to interrupt the trip current before the aux switch does.
Unless a separate circuit is pulled for the relay, a relay installed at the breaker will see the full voltage drop. When retrofitting a microprocessor relay into a breaker cabinet that had electromechanical relays for example.
ANSI breakers are required to trip down to about 56% nominal. Sounds to me like the last gasp of a dying battery. But the relay is out at 80%.
Areva's 50% sounds a lot more reasonable. Shouldn't be that big a deal anymore with the wide ranging power supplies available.
Any input from the manufacturers? Is Davidbeach listening?
