Requirement of Transfer Trip
Requirement of Transfer Trip
(OP)
I shall appreciate if someone can highlight the conditions which govern, the requirement of transfer trip in interconnection of embedded generators in transmission or distribution utility network.






RE: Requirement of Transfer Trip
RE: Requirement of Transfer Trip
If you complain or question the need, they will say it is safety-related, and that will pretty much be the end of the discussion.
In some cases, I have been given a choice between transfer trip and installing distance relay that will be set to overreach the utility substation. In theory, the distance relays will cause more unnecessary trips than the transfer trip, but if the line is short and exposure low, the cost savings might be worth it.
There are situations where TT is truly a necessity to make sure the generators get off-line before reclosing or to avoid an islanding situation.
RE: Requirement of Transfer Trip
However my concerns is for smaller generators to the tune of < 500 kW. Is there any protection available which operates fast enough to ensure that the generator is out of the circuit before the re-closer operates.
Next, what is the minimum operating time of 80-R relay (rate of change of frequency).I understand that these relays are normally not supplied with small capacity generators but I am not sure whether there shall be enough rate of change of frequency to initiate these relays when the network load approximately matches the generator capacity.
I shall appreciate if someone can provide, information regarding sites/reading material etc.
RE: Requirement of Transfer Trip
RE: Requirement of Transfer Trip
But as David said, high speed reclosing is normally NOT used on circuits with generation. Normally a delay of at least a second or two is used to give the generator a chance to trip off.
RE: Requirement of Transfer Trip
Davidbeach: I have mentioned earlier that the load imposed on generator will be more or less equal to its name plate rating. I am looking for the relationship between: rate of decay of voltage and frequency with the size of generator at different loads. I am not searching a conceptual relationship and I will appreciate if someone can suggest sites or reading materials in this regard.
Is there any means to trip a 500 KW generator with in re-closing time of 0.5 to 0.8 sec.
dpc: Re-closer can not be removed or re-located for the sake of power quality commited by utility to existing customer. Is the additional intentional delay at the re-closer justifed?, because it will be serving more to profit making embedded generation than to existing customers.
RE: Requirement of Transfer Trip
One thing that you might research and discuss with utility is vector jump sensing. I'm not sure I would accept it, nor am I convinced that it is thoroughly developed, but there is at least one relay, made in Germany, with a vector jump algorithm that is supposed to detect loss of utility with any mismatch between generation and load.
RE: Requirement of Transfer Trip
Some utilities never use high speed reclosing. It's isn't like God handed down the rules for reclosing.
As David said, this needs to be worked out with the local utility. They are all different, but the issues are generally the same.
RE: Requirement of Transfer Trip
I know that some manufactures have some articles on the distributed gnerator protection. Try http://www.selinc.com and http://www.geindustrial.com/multilin/
RE: Requirement of Transfer Trip
RE: Requirement of Transfer Trip
http://doc
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Sometimes I only open my mouth to swap feet...
RE: Requirement of Transfer Trip
RE: Requirement of Transfer Trip
I think that is a loaded question: yeah, they can be a pig to set up! Usually the settings are a compromise between reliably detecting the loss of grid connection and ensuring the relay doesn't operate under recoverable conditions. They work well when the generator is 'small' compared to the utility source. When the generator is comparable in size to, or larger than, the utility source then they become problematic. The newer relays use a combination of both ROCOF and vector shift which supposedly improves security.
If the switchgear configuration is amenable, tripping the utility tie breaker while leaving the generator connected to the load at least avoids dropping the load. This can be a demanding requirement for the generator governor, especially if the export to the utility is large relative to the local load. The load will almost certainly see a frequency excursion. The same applies to use of the intertrip.
Merry Christmas!
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Sometimes I only open my mouth to swap feet...
RE: Requirement of Transfer Trip
In Denmark they use positive sequence under-voltage U1< to detect loss of grid, sometimes together with ROCOF. But there are problems. Generators have been disconnected, when they should have been supporting the voltage during remote faults.
See page 33 "2-phase fault in the 150 kV network".
http://www.energia.fi/attachment.asp?Section=4522&Item=10796
47 CHP plants greater than 2 MW were disconnected at distance of up to 150 km from the fault. The number of disconnected small wind turbines is unknown.
RE: Requirement of Transfer Trip
That is a really interesting article on how distributed generation and wind power has affected Denmark. I sure hadn't realized anywhere had 55% DG.
RE: Requirement of Transfer Trip