Cap Bank & PTs - Ferroresonance?
Cap Bank & PTs - Ferroresonance?
(OP)
We recently had an operation that caused 2 primary (2.4kV L-N) PT fuses to blow & are thinking it could be caused by Ferroresonace, but wanted to see if anyone has had similar experience.
A relay mis-operation (no fault) caused several CB to trip that left 2 cap banks (1200kVAR each) connected to a bus with no other source or load. Before the operation caps were online & bus was fed by utility & feeding load. I have attached a sketch to help illustrate the setup. Circuit breakers # 1 & #4 tripped.
Upon trying to re-energize the bus it was discovered that 2 primary PT fuses (1E) were blown (PT#2 on sketch). We know the PT were in-service prior to the mis-operation. Another set of PTs on adjacent bus did not blow fuse, but its fuses are 2E. Unfortunately we have no digital relaying for event records.
Anyone had similar occurrences?
Thanks
Andy
A relay mis-operation (no fault) caused several CB to trip that left 2 cap banks (1200kVAR each) connected to a bus with no other source or load. Before the operation caps were online & bus was fed by utility & feeding load. I have attached a sketch to help illustrate the setup. Circuit breakers # 1 & #4 tripped.
Upon trying to re-energize the bus it was discovered that 2 primary PT fuses (1E) were blown (PT#2 on sketch). We know the PT were in-service prior to the mis-operation. Another set of PTs on adjacent bus did not blow fuse, but its fuses are 2E. Unfortunately we have no digital relaying for event records.
Anyone had similar occurrences?
Thanks
Andy






RE: Cap Bank & PTs - Ferroresonance?
RE: Cap Bank & PTs - Ferroresonance?
Thanks
Andy
RE: Cap Bank & PTs - Ferroresonance?
You might want to check or replace the fuses that didn't blow. They could be damaged from partial melting.
RE: Cap Bank & PTs - Ferroresonance?
Do you think that either closing in the utility source or load bus gave it the sufficient path to discharge? Grounded PT not good enough path?
Thanks
Andy
RE: Cap Bank & PTs - Ferroresonance?
The ferroresonance phenomenon could be possible when the PTs are connected WYE grounded on an ungrounded or high resistance grounded systems.
I have read some cases where ferroresonance produced high voltages in three phase power systems had immediately followed the blowing of a fuse, non-simultaneous opening and closing of switch contacts or breaking of the line conductors.
Also be sure to check the condition of the lightning arrestors (if installed).
Did you perform any single phase primary switching at the transformer ??
Regards
Santosh
RE: Cap Bank & PTs - Ferroresonance?
I have heard of this phenomena on PTs connected to long HV lines that were switched off, and the remaining DC component discharged itself via the PT primary winding (low DC ohmic resistance).
The solution was to add a resistance winding in series with the copper winding on the PT primary to limit the DC current to a safe value. This was on SF6 GIS switchgear at the 220KV level. I did not see this first hand but heard about this from another supplier.
Others may have better information.
rasevskii
RE: Cap Bank & PTs - Ferroresonance?
From my poin of view is not good situation, why capacitor bank was not disconnected from bus in the no voltage situation ( see again post of rasevskii ),27 function will be added.
From other hand possible feroresonance situation too.