In looking at a coordination study there is a note adjacent to one of the TCC’s that indicates the breakers are multiplied by a factor of “x.xxx” to account for parallel generation, however there is no explanation of why or how the multiplier was calculated. Just curious if anyone on the forum can point me in the direction of where I might find documentation on this when you have parallel sources?
Time Current Curve "Current Mutliplier"
- Thread starter Mike01
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When there are multiple generators contributing to ta fault each generator relay only sees a fraction of the fault current that the downstream device sees. For instance lets say you have two generators connected to a bus and then a feeder breaker off that bus. For a fault on the load side of the feeder breaker the feeder breaker will see 100% of the fault current however each of the two generator relays will only see 50% of the fault current since they equally contribute (assuming same impedances) to the total fault current.
So in order to coordinate properly you need to multiply the generator relays by a factor of "X" with "X" being the total number of generators. The multiplying factors allows you to accurately coordinate the generator relay with the downstream relay comparing "apples to apples" in terms of fault current.
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Philly, thanks the report I am looking at has 4-parallel gens with two different sizes it uses mutlipliers of 3.2 and 5.3 just curious how they arrived at these and where I can find some information on this topic I would assume IEEE has some documentation somewhere hoping someone could point me in the right direction…
multiplier
Philly, thanks the report I am looking at has 4-parallel gens with two different sizes it uses mutlipliers of 3.2 and 5.3 just curious how they arrived at these and where I can find some information on this topic I would assume IEEE has some documentation somewhere hoping someone could point me in the right direction…
Just want to make sure we're singing the same tune.
Did you mean to say "breaker TCCs" and "multipliers" as inst pickup multipliers?
If yes, then those multiplier settings will be set according to the possible current on a fault downstream of the breaker location. The idea is to prevent other breakers on the same bus from tripping when their circuit is healthy.
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