MV Capacitors Bank Failures and Neutral Unbalance Current
Capacitors Bank Applications
Capacitor Banks installed in factories and substation for many reasons like
- Power Factor correction and compensating Load Inductive Reactive Power and this will help to utilize the rated power of the substation power equipment like, transformers, cables, switch gears, … etc to carry more active power instead of inductive reactive power.
- Enhance the system voltage.
- Filter harmonics generated by the nonlinear loads.
MV Capacitors Bank Connections Diagram
In Medium Voltage Networks, Most Common Capacitors Bank Configuration will be Y-Y Double Floating Neutral Stars with Neutral Unbalance Current transformer NCT
- Floating Neutral will prevent Capacitors from participating in External L-G Faults.
- CT between both Neutral points to help 60N Protection function to detect the neutral unbalance current due to any capacitor unit failure.
Real Fault Disturbance Record for Capacitor Unit Fuse Failure 
Simulating Capacitors Bank in healthy condition
This is 132/13.8KV Substation, and we have 7MVAR Capacitors Bank in Y-Y configuration
Each Y have 2 capacitor units, so the phase will have 4 capacitor units.
We can see the Capacitors bank #1 loading current 290A with almost Zero Neutral Unbalance Current and Zero Neutral Voltage.
Simulating Capacitor Unit Fuse Failure
We will disconnect one capacitor unit to simulate one unit fuse failure
- R phase current dropped to 234.8A
- Neutral Unbalance current increased to 39A
- Neutral Voltage increased to 1232V
Simulating Capacitor Branch Fuse Failure
We will disconnect two capacitor unit to simulate branch failure
- R phase current dropped to 169A
- Neutral Unbalance current increased to 84.6A
- Neutral Voltage increased to 2678V
Simulating Capacitor Phase Lost
We will disconnect complete phase to simulate broken phase or Circuit Breaker pole failed to close
- R phase current dropped to Zero A
- Neutral Unbalance current Not Available as both Star neutral points will have the same voltage as both star have the same failure condition
- Neutral Voltage increased to 6573 V
