parramanuel
Electrical
- Jan 21, 2012
- 6
Hello.
I work in an electrical utility as a protection engineer, and we are planning to put in service a 48 MVAR capacitor bank in a 230 kV Bus.
230 kV Capacitor Bank specs:
- 48 MVAR
- Connection: ungrounded wye
- Each phase of the cap bank have 10 series group each one with 8 capacitor unit in parallel.
- Each capacitor unit is 200 kVAR ; 13,28kV ; external fuse protected (20T)
The protection scheme consists of two numerical relays (Main: ABB REF 543 and Backup: ABB DPU2000R). Each relay sense the line currents to the cap bank, the residual current and the 230 kV line to ground bus voltages.
The IEEE standard establish that for an ungrounded wye banks is recommended to use a PT connected to the neutral of the cap bank with an residual overvoltage protection (59N) but we dont have that equipment, i only have the ABB relays to protect the cap bank.
I have read that is also possible to protect the capacitor bank for an unbalance condition using a numerical relay with a neutral overvoltage protection (59N) using the calculated 3U0 from the 3 line to ground voltages measured in the relay, so i can do that with the ABB REF 543 or DPU relay.
In other hand with only 1 unit out of service we have a overvoltage of 1.10 p.u in the remaining units of the group, this is because we only have 8 capacitor units in parallel, so the unbalance protection it has to be adjusted with a sensitive setting.
I really apreciate any comment or suggestion about this topic.
230 kV Capacitor Bank specs:
- 48 MVAR
- Connection: ungrounded wye
- Each phase of the cap bank have 10 series group each one with 8 capacitor unit in parallel.
- Each capacitor unit is 200 kVAR ; 13,28kV ; external fuse protected (20T)
The protection scheme consists of two numerical relays (Main: ABB REF 543 and Backup: ABB DPU2000R). Each relay sense the line currents to the cap bank, the residual current and the 230 kV line to ground bus voltages.
The IEEE standard establish that for an ungrounded wye banks is recommended to use a PT connected to the neutral of the cap bank with an residual overvoltage protection (59N) but we dont have that equipment, i only have the ABB relays to protect the cap bank.
I have read that is also possible to protect the capacitor bank for an unbalance condition using a numerical relay with a neutral overvoltage protection (59N) using the calculated 3U0 from the 3 line to ground voltages measured in the relay, so i can do that with the ABB REF 543 or DPU relay.
In other hand with only 1 unit out of service we have a overvoltage of 1.10 p.u in the remaining units of the group, this is because we only have 8 capacitor units in parallel, so the unbalance protection it has to be adjusted with a sensitive setting.
I really apreciate any comment or suggestion about this topic.