If you had multiple substations single ended with a single ended sparing substation and the substations had ground fault mains with the neutral/ground bond at the xfmr withtin the sub how would you prevent a main on one substation from tripping under a ground fault? For example if a fault occurs on substation #2 what is to prevent it from taking out the GFI on the main circuit breaker in substation #1 because all the grounds are connected to the new building ground mat therefore the substations are on the same ground? Could you do this throught some kind of protective relaying?? Just curious?
Multiple Substations and ground fault protection??
- Thread starter mike0w
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poweringtech
Member
One solution is to convert your system grounding to High Resistance Grounding. IEEE Green Book
wirenut1980
Senior Member
- Location
- Plainfield, IN
Perhaps you could use a time delay on the "protected" GFP, so that you get the two coordinated in a sense.
rcwilson
Senior Member
- Location
- Redmond, WA
GF sensors can be cross connected to cancel out fault currents from other sources. What type of system is it? If you have a 3-phase 3-wire with no neutral except at the transformers, the breakers should only trip for faults in their system. If it is 3-phase 4-wire with a neutral, proper selection of ground fault sensing CT location will assure that only the affected breaker trips.
If the GF devices use a CT on the grounding/bonding conductor and the transformer neutrals are tied together, there will be some false trips.
The fact that all transformers are tied to the same ground grid should have no effect. Fault current should only return to the transfomrmer feeding the fault.
If the GF devices use a CT on the grounding/bonding conductor and the transformer neutrals are tied together, there will be some false trips.
The fact that all transformers are tied to the same ground grid should have no effect. Fault current should only return to the transfomrmer feeding the fault.
brian john
Senior Member
- Location
- Leesburg, VA
These are single ended subs fed from a single transformer? The neutral to ground bond is at the transformers? If this is the case a Zero Sequence GFP scheme will operate adequatly if installed at the main encompassing all phase conductors and neutral grounded conductor with no downstream grounds on the neutral.
If not read Bob Wilson's post, interconnected ground fault CT's on the neutral ground bond (ground return GFP), with proper controls will work.
If not read Bob Wilson's post, interconnected ground fault CT's on the neutral ground bond (ground return GFP), with proper controls will work.
The Layout is as follows:
Two lines to the facility from the local utility 13.2Kv:
New 15Kv line-up Main-Tie-Main Configuration:
A Basic Primary Selective - Radial Secondary System
There are to single ended substations with one-sparing substation, the problem occurs when the tie is closed and there happens to be a ground fault, thanks for all you responses.
Two lines to the facility from the local utility 13.2Kv:
New 15Kv line-up Main-Tie-Main Configuration:
A Basic Primary Selective - Radial Secondary System
There are to single ended substations with one-sparing substation, the problem occurs when the tie is closed and there happens to be a ground fault, thanks for all you responses.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I'm rather fuzzy on this one, but you should do a google search on 'directional ground relay'.
A normal ground fault relay will detect unbalanced current at its sensor, but can't tell you which side of the sensor has the fault. With multiple power sources in parallel, groundfault current can go 'upstream', from _all_ of the sources to a single failure. A directional ground fault relay can determine the direction of power flow to the ground fault, providing correct information to your protective relaying scheme so that you can isolate the section with the fault.
See http://www.schneider-electric.com/cahier_technique/en/abstracts/directional_protection.htm
-Jon
A normal ground fault relay will detect unbalanced current at its sensor, but can't tell you which side of the sensor has the fault. With multiple power sources in parallel, groundfault current can go 'upstream', from _all_ of the sources to a single failure. A directional ground fault relay can determine the direction of power flow to the ground fault, providing correct information to your protective relaying scheme so that you can isolate the section with the fault.
See http://www.schneider-electric.com/cahier_technique/en/abstracts/directional_protection.htm
-Jon
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Use relays and protective devices with zone selective interlocking.
brian john
Senior Member
- Location
- Leesburg, VA
While this is an a GFP scheme an engineer should design and sign off on. I still fell Bob's post answers the question best. Zone Selective is (in my understanding) utilized where there are multiple levels of GFP, such as a Main and and then downstrean GFP on sub feeders. With Zone Selective GFP, the OCP with GFP closes to the fault sends a restraint to the upstream GFP's as it opens the OCP device to clear the ground fault.
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