Maloperation of auto-reclosing feeder CB
Maloperation of auto-reclosing feeder CB
(OP)
I am having problems with a particular model of auto-recloser failing to operate under fault conditions, and instead the upstream protection operating. The picture is this: Single transformer 33/11kV substation, 5MVA, Dyn. Single incoming 33kV line, 33kV CB with overcurrent protection (IDMT, BS142 std inverse). Transformer has harmonic restrained biassed differential protection. Two 11kV feeders, each with the same type of recloser CB and contoller. The CB is KFME, controller is Form 4C. The reclosers are mounted on spun concrete poles in the substation yard. Earthing appears to be in accordance with the book. Auxiliary volts come from an aux transformer in the substation, connected at 11kV.
The problem: Occasionally (NOT every time) a fault on a feeder(no pattern to the type) will not be tripped by the recloser, but is seen and cleared by the transformer HV overcurrent. The recloser has been found open on at least one occasion after the 33kV protection cleared the fault. There is no transfer tripping or inter-tripping scheme. The recloser behaves perfectly in the lab. There is plenty of grading margin. Records from the Form 4C and the waveforms recorded by the 33kV protection indicate that the F4C should have cleared the fault with a margin of around 600msec.
Anybody got any ideas? Leprechauns sound good at the moment ... :-)
Bung
The problem: Occasionally (NOT every time) a fault on a feeder(no pattern to the type) will not be tripped by the recloser, but is seen and cleared by the transformer HV overcurrent. The recloser has been found open on at least one occasion after the 33kV protection cleared the fault. There is no transfer tripping or inter-tripping scheme. The recloser behaves perfectly in the lab. There is plenty of grading margin. Records from the Form 4C and the waveforms recorded by the 33kV protection indicate that the F4C should have cleared the fault with a margin of around 600msec.
Anybody got any ideas? Leprechauns sound good at the moment ... :-)
Bung






RE: Maloperation of auto-reclosing feeder CB
Is this happening on one particular recloser, or on both?
Is it possible there are external control signals (ground block) that might be blocking operation?
RE: Maloperation of auto-reclosing feeder CB
One thought, with Dy transformer, during a L-L fault the primary protection can see 115% more current than the secondary protection, so the secondary has to grade with 115% of the primary setting.
RE: Maloperation of auto-reclosing feeder CB
RE: Maloperation of auto-reclosing feeder CB
RE: Maloperation of auto-reclosing feeder CB
Grading isn't a problem - nor is disk integration on 'pecking' faults - we replaced the old CO rleay on the high side because that was one theory we had. We now have an instantaneous reset electronic relay (Alstom's Micom P123)from which we can get fault waveforms.
Fault types experienced have been both phase and esarth - no pattern discernible. It happens at two different substations, on four different feeders, and it is random. A colleague in a different area 400 miles away has had a similar problem with the same recloser and controller. We do not have any similar problems with other recloser / controller types (so far!).
I suspect some kind of induction or interference in the umbilical between the controller and CB, but can't / don't know how to approach tracking it down.
regards, and thanks for the interest so far...
RE: Maloperation of auto-reclosing feeder CB
If your control power is coming directly from the station service transformer, is is possible that your recloser is losing control voltage during the fault?
Are you using current transformers internal to the breaker/recloser? Did you test operation of controller using primary current injection?
I would talk with the Form 4C supplier (Cooper?) and see if they have had reports of similar problems. Maybe you can talk them into replacing or upgrading to the new version.
RE: Maloperation of auto-reclosing feeder CB
- Power supply - what backup power option do you have, internal battery or external DC? If battery, is the battery OK?
- Are the tripping capacitors in satisfactory condition? Have you tried a trip test with a simultaneous external power supply failure?
- Do the waveform records indicate that the Form 4C controller issued a trip command to the recloser? If so, then I think you must suspect the trip capacitor arrangement.
RE: Maloperation of auto-reclosing feeder CB
We have the same F4 controls
I´m agree with DPC and we had problems with downstream faults but the force between conductors make a fault upstream; this new fault is only view by the upstream protection.
If you don´t understand me I will try to explain better
Thanks
RE: Maloperation of auto-reclosing feeder CB
Bung
RE: Maloperation of auto-reclosing feeder CB
RE: Maloperation of auto-reclosing feeder CB
If this is the case, then your conductor spacing is inadequate, or the conductor sag is too great. There are mid-span spacers available that could correct this situation, or you could consider insulated conductor for the problem span(s) - depending on the circuit voltage.