setting 67 relay
setting 67 relay
(OP)
Want to install a 67 relay in the bushing transformer, looking in direction system->transformer, as a remote backup protecion of equipment. Should be submitted to the following currents:
1 - Current direction transformer->system:
Load = 8000 A
remote fault = 12000 A
2 - Current direction system->transformer:
Load = 100 A
remote fault = 800 A
Question:
1- Assume that relay must operate in direction system->transformer , which would be the pickup current of the relay:
Ipick > 100 A or Ipick> 8000 A?
2- The results of a program of short circuit will be reliable when the fault current is much greater than the load current,
which is not our case (load = 8000A, 800A = fault)?
1 - Current direction transformer->system:
Load = 8000 A
remote fault = 12000 A
2 - Current direction system->transformer:
Load = 100 A
remote fault = 800 A
Question:
1- Assume that relay must operate in direction system->transformer , which would be the pickup current of the relay:
Ipick > 100 A or Ipick> 8000 A?
2- The results of a program of short circuit will be reliable when the fault current is much greater than the load current,
which is not our case (load = 8000A, 800A = fault)?






RE: setting 67 relay
RE: setting 67 relay
But, let's say relay must see from system -> transformer, assume 100A is the full load and 800A is the end-of-line fault, you may chose the pickup setting > 200% of the full load, and < 50% of the end-of-line fault.
If your system has a fault-to-load ratio less than 4:1, you may use 21 element. Or use load encroachment feature on your 50/51 element.
RE: setting 67 relay
That was the setting selected(> 100A). But there were objections:
1- Relay is a multfunction numeric type, and we are using 67 function.The logic diagram of the function used (Figure 2-15 of the manual) shows that if it is adjusted under load (8000A) it will be in the starting state (Pickup) and become permanent depending only on the direction to take command of the trip.
The ideal is that the relay will start when overcurrent and right direction at the same time, not only due to overcurrent. Already referenced by the logic diagram that would only be possible through the internal logic(CFC).
2- The results of a program of short circuit are reliable only when the fault current is much greater than the load current, which is not our case (load = 8000A, short = 800A). In fact the actual current is obtained through the theorem of superposition where the final current is the sum of the load current plus the current produced by the short. In our case the current would continue in the same direction as the load would be the sum of 8000-800 = 7200A in the direction of the load. The relay would not operate.
pwrtran
I am eliminating the details of the project. The relay is already bought and function 67 was the only one available. I do not know about "load encroachment feature on your 50/51 element."
RE: setting 67 relay
RE: setting 67 relay
RE: setting 67 relay
If I understand this correctly, your transformer has a sufficiently large enough source on it's secondary terminals that it can supply 12,000A of remote fault current to a system type fault...but the HV system is weak enough to only supply 800A? Is that 800A a fault on the primary of the transformer or the secondary? My assumption is the secondary.
I'm confused why bullet point #1 is an objection, that's how every 67 element I've set operates and I've never had a problem with them mis-operating.
RE: setting 67 relay
If we assume bullet point #1, so relay operate only by direcional unit.
2- My concern is whether the calculations (800A) are feasible because of theorem of superposition.Are they ?
We have to find another solution.
RE: setting 67 relay
Could you say write down a reference about this application.
RE: setting 67 relay
Transformer has a high side and a low side.
What is the winding on the high side?
What is the winding on the low side?
Where is the relay, high side or low side?
Where is the positive sequence source, high side or low side?
RE: setting 67 relay
67 is connected at bushing CT installed at secondary(delta) of ST transformer. Normal load current BG1->system is 8000A.
A short circuit at 440V far point "fault" current at bushing CT will be 800A.
RE: setting 67 relay
RE: setting 67 relay
We do not permit relay of Auxiliary System trip Transformer units (4gen + ST). There are different maintenance crews to service and assist the transformer unit.
Transformet Unit relay should provide back up protection for auxiliary system.
RE: setting 67 relay
RE: setting 67 relay
Why don't you put a relay on the breaker on the HV side of the small transformer with the 440V secondary?
RE: setting 67 relay
RE: setting 67 relay
RE: setting 67 relay
RE: setting 67 relay
RE: setting 67 relay
RE: setting 67 relay