sykimk
Electrical
- Dec 28, 2003
- 55
Hello,
I have a situation to install 4.16kV, 600kVAR capacitor on the three (3) existing 2500HP motors and all three (3) 2500HP motors on the same bus for power factor improvement. For self-excitation, 600kVAR is selected below 90% of motor no load current (106A) due to self-excitation issue.
Anyway, each 600kVAR capacitor will be connected to the motor starter and will be switched with motor together. I am wondering what if the 3rd capacitor with motor will be switched on when the other two (2) capacitors are already online.
Should I consider capacitor back-to-back switching inrush current when the 3rd capacitor switched together with 2500HP motor? That is, 1200kVAR capacitors are already connected to the bus and now 600kVAR with motor will be switching together onto the bus. Based on simple calculation per IEEE C37.012, I expect approximately 5.5~6.5kA of capacitor back-to-back switching inrush current from 1200kVAR to 600kVAR without considering motor equivalent circuit.
Does motor starting (i.e. switching with capacitor together) help to mitigate capacitor back-to-back switching inrush current? If not, I don’t think the contactor’s rated making current can be higher than 5kA. In this case, I should have to install inrush reactor with this capacitor.
Do you think I really have to install inrush reactor for my application? Do you have any recommendations or corrections for my application?
Thanks.
I have a situation to install 4.16kV, 600kVAR capacitor on the three (3) existing 2500HP motors and all three (3) 2500HP motors on the same bus for power factor improvement. For self-excitation, 600kVAR is selected below 90% of motor no load current (106A) due to self-excitation issue.
Anyway, each 600kVAR capacitor will be connected to the motor starter and will be switched with motor together. I am wondering what if the 3rd capacitor with motor will be switched on when the other two (2) capacitors are already online.
Should I consider capacitor back-to-back switching inrush current when the 3rd capacitor switched together with 2500HP motor? That is, 1200kVAR capacitors are already connected to the bus and now 600kVAR with motor will be switching together onto the bus. Based on simple calculation per IEEE C37.012, I expect approximately 5.5~6.5kA of capacitor back-to-back switching inrush current from 1200kVAR to 600kVAR without considering motor equivalent circuit.
Does motor starting (i.e. switching with capacitor together) help to mitigate capacitor back-to-back switching inrush current? If not, I don’t think the contactor’s rated making current can be higher than 5kA. In this case, I should have to install inrush reactor with this capacitor.
Do you think I really have to install inrush reactor for my application? Do you have any recommendations or corrections for my application?
Thanks.
