Lock-out relays

Hi everyone,

I am doing an arc flash study for a generating station that protects the main generator buses through lockout relays (i.e. 50/51/87 etc. element actuates the 86 element which in turn initiates the circuit breaker trip coil). It turns out there is a wide variance of activation times on these lockout relays (from reading on-line specs) and it is not particularly easy to get this data from the client. How does everyone incorporate the 86 element time into their model? I have heard times ranging from 130ms all the way down to 8ms... makes a pretty big difference in HRC.

Thanks in advance for the input.

Tim Ricard

Electroswitch says .5 cycle.