2006 Muttrah Incident Report - authority for electricity regulation, oman

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8 SITE SAFETY 8.1 Use of Limitation of Access As indicated in Section 6 above the work at Muttrah substation was being carried out under a Limitation of Access issued by a duly authorised engineer of MEDC. According to the Safety Rules of the MHEW (the Rules currently in force in MEDC) a Limitation of Access is a form issued and cancelled by a Senior Authorised Person or Authorised Person specifically authorised to do so, defining the limits and nature of work which may be carried out in the vicinity of Live apparatus. Under normal circumstances the use of a Limitation of Access (rather than a Permit to Work or Sanction for Test) for the work being carried out at Muttrah was perfectly acceptable. The racking in/out of OCB/trucks with the busbar and feeder alive is common practice and does not normally require even a Limitation of Access. However in the particular circumstances of the incident the VCB/trucks were actually being adjusted to fit and tested in a Brush cubicle for the first time. The use of a Permit to Work (with the busbar and feeder spouts dead) would have been more appropriate. It should be noted that the incident could still have occurred once the busbar and feeders were made alive following cancellation of the Permit to Work because of the design defects noted in this report. In their report on the incident MEDC state that verbal instructions were given to the ABB Arab technicians that they were to carry out all adjustments of the trucks in the rackedout position and that they should inform MEDC when they were ready to rack-in the breakers. ABB Arab has disputed that these instructions were ever given. Any additional instructions to be given in respect of a Limitation of Access, for example, should be written on the Limitation. Having said that, the inquiry believes that the presence or not of MEDC engineers is irrelevant; the design defects would have manifested themselves whenever the breaker was racked into the service position. 8.2 Conclusions – Site Safety In respect of site safety precautions the inquiry concludes: • That the use of a Limitation of Access was not appropriate given that the VCB/trucks had never been tested in a Brush cubicle; and 32
• That the design defects identified in this report would have manifested themselves in any case irrespective of the site safety precautions. 33
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 and 16: contracts were subsequently awarded
Page 17 and 18: 5 SEQUENCE OF EVENTS The sequence i
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: Subsequent to the incident it emerg
Page 35: 10 RECOMMENDATIONS The inquiry make

2006 Muttrah Incident Report - authority for electricity regulation, oman

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