Coordination time intetval

[sasalu]

Hi,

I had a requirement from end user to have a coordination time interval between two relays to be 100 ms because of numerical relays and fast tripping breakers.As per IEEE guidelines minimum coordination interval of 0.12 seconds to be considered between numerical relays excluding breaker opening time.just want to know from you all 100 ms CTI is safe and or any other guidelines.

Thankyou

 

[dpc]

I would not consider 0.1 seconds to be adequate. We generally try to maintain at least 0.2 sec between digital relays, assuming 3 or 5 cycle breakers. How fast is "fast tripping"? What IEEE guidelines are you referencing (just curious). Blackburn suggests 0.2 to 0.5 seconds. For elector-mechanical relays and 5 cycle breakers, 0.3 to 0.4 sec was typical.

 

[sasalu]

IEEE 242

 

[dpc]

Ah - the Buff Book. I no longer have access to a copy. Thanks.

 

[cranky108]

The coloring books are guidelines, but I would use 0.2 seconds myself, for 3 to 5 cycle breakers.

 

[RRaghunath]

Coordination Time Interval of 120ms mentioned is exclusive of breaker opening time. Considering a 5-cycle breaker, the Coordination time interval to be maintained will be 220ms (50Hz power system).
This is in line with what dpc and other posters have indicated.
I am also used to maintain 200ms margin as a minimum with numerical relays.

 

[sasalu]

Thank you all for your valuable feedback.