NEDeR:                                  2013/0722/00

Plant Involved:                        Circuit Breaker – Reyrolle Pacific LMVP 1250A – 11kV

During a routine HV (11kV) Standby Generator run the system was being returned to mains supply. The Standby Generator VCB was opened remotely and the Incomer VCB was closed remotely. The Incomer VCB failed to close. The electrical supply to the facility was reinstated from the Standby Generator supply. The VCB truck was removed from service and the opening and closing operations were investigated. The VCB failed to close.

Apr 2013

NEDeR:                                  2013/0721/00

Plant Involved:                        UK Power Networks

After the failed operation the engineer noticed that the open/close LED indications were no longer illuminated signalling a dc supply failure. Further investigation proved that fuse 2 trip close actuator had blown.  The same problem has occurred on two further CB’s on the same 55 panel switchboard. All three CB’s have been replaced by manufacturer- factory report attached site checks to be carried out. The manufacturer believes the problem is associated with a manufacturing tolerance issue.

SOP:                                        2013/0384/00

Plant Involved:                        Pole Mounted Air Break Switch Disconnector – LEL type – 33kV

Flashover at isolation gap on LEL type interrupter head.

SOP – these type are not to be used as a point of isolation.

NEDeR:                                  2013/0720/00

Plant Involved:                        Circuit Breaker – FKI Eclipse – 11kV

During the site inspection on site at Maidstone Grid South discharge was detected from 11kV switchgear. The switchgear was de-energized and inspected. The L3 phase VT disconnector contacts were covered in carbon. When cleaned the contacts were functional although there were some small marks caused by low current sparking across the joint.

The poor contact continuity was caused by the combination of 2 factors:

1) The unsupported weight of cables caused cable connection plate displacement on L3 phase.

2) When VT disconnector handle is operated slowly but in full extents, contact blades don’t travel quite as far as when operated normally, although this is not an issue without problem of 1) above.

Remedial action – Ensure that the cable weight is supported by cleats in switchgear panel and cable support fixings underneath the panel as it is instructed in the Eclipse IOM

DIN:                                        2013/0006/01

Plant Involved:                        Circuit Breaker – Hawker Siddley Switchgear HG12 – 11kV

Disruptive failure of the busbar cable box with the circuit breaker removed for investigation.

Update – Equipment inspected in Plant Workshops with the busbar cable box found to have been jointed without terminal shrouds. Clearance without shrouds adequate for system voltage (11kV) but marginal for required impulse level (75kV 1.2/50uS).  Significant treeing on surface of SRBP between L3 terminal and earth indicates growing PD prior to L3 to earth flashover, developing into three phase-earth arc.  Commencement of PD over SRBP surface considered to be due to damp conditions in substation.

DIN:                                        2011/0062/05

Plant Involved:                        Voltage Transformer – 33kV – AEG

AEG VT connected to the Red Phase on Alstom WS Switchgear failed. All three VT’s have been replaced. The faulty VT has been returned to Schneider for investigation.

Updated- Following a failure investigation by the VT manufacturer it is proving difficult to establish an exact cause. No further update will be issued.

DIN:                                        2011/0065/01

Plant Involved:                        Circuit Breaker VT – 20kV Areva Visax

Cast resin VT failure.

Updated – Following investigation by the manufacturer the root cause of the failure could not be identified.