Reyrolle Type 'LSR' SF6 Circuit Breakers

Operational Safety Notice OSB 00298 was issued end of 1998 informing customers of failures of integrity of LSR
Circuit Breaker housings leading to a loss of SF6 gas pressure and reduced circuit breaker performance. This Safety
Notice update is to inform customers of the current situation following our investigations.
Two modes of failure have been identified, during our investigations, both of which involve loss of gas from the SF6
enclosure. It is our contention that the first failure mode (which has shown to occur within 3 years of manufacture) is
the result of variable stresses which may have occurred during the forming of the tank.
The second failure mode is the result of a combination of the creep performance of the material and the
environmental conditions within the substation.
We must point out, in our opinion the risk of failure is extremely low, (approximately 1% of the total population to
date), and since the issue of the previous Safety Notice there has been one recorded failure.
To date every failed unit has failed "to safety". ie as the gas pressure has reduced, the electrical safety interlock
tripped the Circuit Breaker.
Finally we feel that it is important to notify our Customers that none of the failures have resulted in any injury or
collateral damage.
As a result of our investigation we would update the recommendations as follows:-
1. All 630A & 1250A LSR Type circuit breakers should be operated 'remotely whenever possible. (Generally LSR
units would have been supplied fully equipped for remote operation, if this facility has not been utilised or no
remote control location exists, then a simple modification can be done to convert the unit for electrical 'lanyard'
operation. -- For more information on this please contact Reyrolle)
2. Low SF6 Gas Pressure alarm switch contacts should be wired out to an indication point that is remote from in
front of the switchgear.
3. If a Circuit breaker has tripped due to Low SF6 gas pressure the circuit should be isolated before removal of the
circuit breaker for further inspection. NOTE :- Under NO circumstances should the electrical interlock be defeated
by attempting to close the circuit breaker manually.
4. If an energised circuit breaker becomes inoperative in the closed position due to low gas pressure 'Lockout'
conditions, that circuit must be isolated before manual tripping and further inspection.
5. Presence in the substation in the vicinity of 630A and 1250A LSR circuit breakers should be kept to a minimum