rogerj1
Electrical
- Jan 5, 2007
- 23
Folks,
Got a situation that I believe is a first for our utility. On a segment of our 115kV system, we have a few long radial feeds serving distribution (115-13.2 kV) loads. Planning Dept wants 15MVAR banks installed on the far end of these radial for system voltage support. In these cases, the 15MVAR bank will be installed on the 115kV side of the local distribution sub, which is a 115-13.2 kV TX, 25MVA, serving residential/commercial loads. The 13.2kV bus at the distribution sub also has a cap bank as well, 3600KVAR. Since these are radials on the 115kV system, they'll lose 115kV source voltage for any line faults, in which we normally have 5, 15 second recloses. My concern here is the discharge of these 115kV 15MVAR banks. For now, we don't have PT's available on the 115kV bus, so the relaying there would not have a local indication of bus voltage,,else, I'd go with a loss of potential timer to trip the bank offline. So, a couple of questions to consider:
1. Considering the 115kV 15MVAR banks would be in service with multiple parallel loads (ie, the local distribution load, and other nearby 115-13.2 stations serving load), would the bank discharge "fast" enough to be safe for reclosing back from the remote 115kV terminal? Our practice as always been upon de-energizing the bank, to block re-energizing after a 5min delay. This allows for a designed internal discharge of the bank.
2. If remote transfer trip is not an option, and considering we do not have a local PT available for 115kV bus voltage indication, what other protection scheme could be implemented under these conditions?
Thanks for your help!
Got a situation that I believe is a first for our utility. On a segment of our 115kV system, we have a few long radial feeds serving distribution (115-13.2 kV) loads. Planning Dept wants 15MVAR banks installed on the far end of these radial for system voltage support. In these cases, the 15MVAR bank will be installed on the 115kV side of the local distribution sub, which is a 115-13.2 kV TX, 25MVA, serving residential/commercial loads. The 13.2kV bus at the distribution sub also has a cap bank as well, 3600KVAR. Since these are radials on the 115kV system, they'll lose 115kV source voltage for any line faults, in which we normally have 5, 15 second recloses. My concern here is the discharge of these 115kV 15MVAR banks. For now, we don't have PT's available on the 115kV bus, so the relaying there would not have a local indication of bus voltage,,else, I'd go with a loss of potential timer to trip the bank offline. So, a couple of questions to consider:
1. Considering the 115kV 15MVAR banks would be in service with multiple parallel loads (ie, the local distribution load, and other nearby 115-13.2 stations serving load), would the bank discharge "fast" enough to be safe for reclosing back from the remote 115kV terminal? Our practice as always been upon de-energizing the bank, to block re-energizing after a 5min delay. This allows for a designed internal discharge of the bank.
2. If remote transfer trip is not an option, and considering we do not have a local PT available for 115kV bus voltage indication, what other protection scheme could be implemented under these conditions?
Thanks for your help!
