2006 Muttrah Incident Report - authority for electricity regulation, oman

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Amp isolating contacts. The contracts called for the delivery of 24 VCB/truck assemblies with 400 Amp contacts, 3 with 800 Amp contacts and 6 with 1200 Amp contacts (see above). MEDC decided that the retrofitting should commence at Muttrah Old Stores Primary Substation. The following section describes events leading up to the incident. It should be noted that employees of ABB Arab (ABB) in accordance with the contract between Al-Wadi and ABB carried out the actual installation work. 16
5 SEQUENCE OF EVENTS The sequence is based on the correlated evidence of the investigation reports issued by the Muscat Electricity Distribution Company (MEDC) and interviews with personnel involved. • ABB commenced work on site on 26 March 2006. On 26 & 27 March no work was carried out on the switchboard itself. The contractor was involved in unpacking and inspecting the switchgear trucks (including the new vacuum circuit breakers). • At 0840 hrs on 28 March 2006 Limitation of Access (LOA) No 32152 was issued by a Senior Authorised Person of MEDC to the supervisor of ABB. The LOA clearly specifies that the 11KV Cables and Busbars were live. At the time of issue of the LOA both Sections of the 11 KV Busbar were alive fed from their respective 33/11 KV Transformers. The following feeder circuit breakers were open but the 11 KV cables were alive because of back feeding: Darsait, Oman House (on Section 1) and Gharifa, Al Harthy (on Section 2) • The work to be carried out as specified on the LOA was: To replace oil CBs to vacuum CBs for the following CBs Oman House, Ghanifa Fdr and Darsait Fdr. Al Harhty Fdr • MEDC state that the LOA was issued to the contractor only for working on the Circuit Breaker in the withdrawn position for doing the necessary testing and alignments. MEDC also state that verbal instructions were given to the contractor to inform the MEDC engineer, after completing his testing and alignments, that he was ready to rack in the circuit breakers. • During the testing and alignment of the new circuit breaker trucks in the withdrawn position ABB determined that the contacts (tulips) on the truck isolating contacts (i.e. the contacts that engage in the busbar and feeder spouts when the breaker is racked 17
Page 1 and 2: REPORT INTO THE INCIDENT AT MUTTRAH
Page 3 and 4: GLOSSARY OF TERMS The terms defined
Page 5 and 6: 1 INTRODUCTION AND SUMMARY OF FINDI
Page 7 and 8: 2 SCOPE OF INVESTIGATION AND METHOD
Page 9 and 10: 2.3 Methodology In preparing its re
Page 11 and 12: outages on the distribution system
Page 13 and 14: FIGURE 2 Brush OCB Truck removed Mu
Page 15: contracts were subsequently awarded
Page 19 and 20: The protection relay indications fo
Page 21 and 22: BUSHING SHUTTER FIGURE 4 Reconstruc
Page 23 and 24: FIGURE 7 Truck - Cubicle Interface
Page 25 and 26: the shutter mechanism is mounted is
Page 27 and 28: 6.3 Cause of the Incident Based on
Page 29 and 30: shortcomings in the trucks supplied
Page 31 and 32: Subsequent to the incident it emerg
Page 33 and 34: • That the design defects identif
Page 35: 10 RECOMMENDATIONS The inquiry make

2006 Muttrah Incident Report - authority for electricity regulation, oman

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