2006 Muttrah Incident Report - authority for electricity regulation, oman

6 TECHNICAL INVESTIGATION
Following the incident a series of investigations have taken place in order to determine
the probable cause of the incident. These investigations, led by the Authority have
involved personnel from MEDC, Al-Wadi and ABB. The Power Systems Engineering
Department of Sultan Qaboos University also assisted the inquiry. The Authority
engaged the services of KEMA to act as an independent expert and received a copy of
the internal Design Evaluation Report from ABB Italy.
The main basis of the technical findings was site inspections carried out by KEMA and
ABB on the failed equipment at Muttrah substation, on the ‘prototype’ equipment at Al-
Falaj substation and on the Brush OCB equipment remaining in service. In addition the
‘prototype’ VCB truck, a sample of the final delivered VCB truck and a Brush OCB truck
were taken to ABB Italy for the ABB Design Evaluation.
6.1 The KEMA Report
The KEMA report is reproduced in full at Appendix A.
The Report identifies the following damage to the failed VCB truck and Al Harthy cubicle
by arcing:
• 4 out of 6 isolating contacts
• three bushings on the feeder side
• three insulated copper conductors on the feeder side
• one shutter on the feeder side
• copper conductors near three top terminals of vacuum circuit breaker
• copper conductors near two lower terminals of vacuum circuit breaker
• cast resin housing of the vacuum interrupters
• marks of welding on the earth contact on the truck caused by earth fault current
Photographs 3 and 4 show the simulated configuration of the VCB, cable side bushings
and one shutter on cable side.
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