Fault current limitation without reactors
Fault current limitation without reactors
(OP)
Hello Gentleman,
Thanks for taking the time to read my question.
I work in utility Industry. We are building a 66/4 kV sub station with dual winding banks. Banks are 15 MVA 66/12/4 kV. Planning report indicated to build station to 12 kV but cost conversion were high at the feeder level so it was decided to build station to 4 kV.
Station has three banks and two banks are paralleled at all times. Horizon fault levels show fault level of 40kA at feeder head when two banks are tied. High fault level number was missed by the engineer before he agreed to build the station at 4 kV instead of 12 kV ( At 12 kV fault level is low).
Station is 80 % build and there is no space for reactors. G&W CLIPS were option but it changes the whole station protection.My standards group tells me that distribution equipment (fuse, fuse cutouts ) outside the station at 4 kV can not handle fault more than 12.5 kA. Station egress is all 1000 MCM cable before it becomes over head. Most of the egress outside the station is cable up to few hundred meters.
I have asked my protection group to tell me the exact location at each feeder when the fault level becomes less than 12.5 kA. An example would be feeder 1 fault level drops below 12.5 kA after 400 meters from the station. I have reommended like to upgrade all the equipment to a level between the station eqress and the point when fault level drops below 12.5 to handle fault current of 12.5 kA. I have agreed to use operation constraints with operating no banks in parallel.
I would appreciate if somebody can comment on this possible scenario. I think cable would be subjected to high fault current but that is the risk I have to take.
Does the solution to upgrade all equipment to limit fault current to horizon 20 kA (when no bank is parallel).
Thanks a lot for your input.
Thanks for taking the time to read my question.
I work in utility Industry. We are building a 66/4 kV sub station with dual winding banks. Banks are 15 MVA 66/12/4 kV. Planning report indicated to build station to 12 kV but cost conversion were high at the feeder level so it was decided to build station to 4 kV.
Station has three banks and two banks are paralleled at all times. Horizon fault levels show fault level of 40kA at feeder head when two banks are tied. High fault level number was missed by the engineer before he agreed to build the station at 4 kV instead of 12 kV ( At 12 kV fault level is low).
Station is 80 % build and there is no space for reactors. G&W CLIPS were option but it changes the whole station protection.My standards group tells me that distribution equipment (fuse, fuse cutouts ) outside the station at 4 kV can not handle fault more than 12.5 kA. Station egress is all 1000 MCM cable before it becomes over head. Most of the egress outside the station is cable up to few hundred meters.
I have asked my protection group to tell me the exact location at each feeder when the fault level becomes less than 12.5 kA. An example would be feeder 1 fault level drops below 12.5 kA after 400 meters from the station. I have reommended like to upgrade all the equipment to a level between the station eqress and the point when fault level drops below 12.5 to handle fault current of 12.5 kA. I have agreed to use operation constraints with operating no banks in parallel.
I would appreciate if somebody can comment on this possible scenario. I think cable would be subjected to high fault current but that is the risk I have to take.
Does the solution to upgrade all equipment to limit fault current to horizon 20 kA (when no bank is parallel).
Thanks a lot for your input.






RE: Fault current limitation without reactors
RE: Fault current limitation without reactors
RE: Fault current limitation without reactors
RE: Fault current limitation without reactors
Pwrtran's suggestion of converting parts of the feeders to 12 kV would also work, but you would have to buy the step-down transformers.
RE: Fault current limitation without reactors
12 kV is not possible because of cost prohibitive reasons.
I am thinking of a possible solution. No parallel operation of banks and upgrade all devices to handle 20 ka fault current, even install 24 kV device on a 4kV system as long as it can handle 20 kA fault current.
Could you please also comment on any current limiting fuse that can handle 20 kA.
Thanks
Harry.
RE: Fault current limitation without reactors