2006 Muttrah Incident Report - authority for electricity regulation, oman

FIGURE 10 Contact Damage
The damage found on the isolating
contacts (‘tulips’) is probably due to
improper assembling and design and
thus could not withstand the short circuit
current from the feeder and busbar.
6.4 Technical Conclusions
In an investigation of this type it is not possible to be definitive about the exact cause of
failure. However both the KEMA and ABB Italy Reports identify the most probable cause
as a flashover between the conductor arms on the truck and the rear feeder shutter on
the cubicle.
Both reports are coincident in attributing this failure to shortcomings in the design by
ABB Arab of the interface between the truck and the cubicle. Furthermore as indicated in
the report by MEDC engineers, the truck assembly was never tested in a Brush cubicle
which could have identified the design shortcomings prior to installation.
Additional shortcomings in the design and manufacturing of the truck assembly were
also identified in both reports. These shortcomings include:
• Contact support pillars and their machining on-site;
• Low transversal stiffness of the truck which could have affected operation of the
shutter mechanism;
• Inadequate design of the truck position interlocking mechanism.
On the basis of the above findings the inquiry concludes that the prime cause of the
failure at Muttrah was poor design by ABB Arab of the interface between the truck and
cubicle. Furthermore there were a number of other design and manufacturing
28