Download Download

237 TIME FOR A BREAK - LET'S HAVE AN EARTHQUAKE by D. J. Van Brink* SUMMARY The following paper recounts the loss of supply and subsequent restoration of the Bay of Plenty Electric Power Board' s sub transmission and distribution systems following the advent of the Edgecumbe earthquake of 2 March 1987. The paper details the effects on the Board's customers and staff, restoration procedures, and matters relating to the restoration of supply and repair of the distribution system. The emphasis is more on the operational and organisational aspects of the event, rather than being a report of structural damage and remedial repairs. Technical aspects of this sort are dealt with in greater detail by other organisations. Editor's Note: This paper is an edited version of a paper published in the Trnasactions of the 58th Annual Conference of the Electric Supply Authority Engineers' Institute of New Zealand Inc., vol. 57, 1987 and is reprinted with their permission. INTRODUCTION The title chosen for this paper may seem at Electricity suppliers are well accustomed first glance to be somewhat flippant, to coping with emergency situations, however the title has been chosen in order however the earthquake produced a situation to bring to the reader's attention the which is inverted to the normal emergency effect the earthquake of 2 March 1987 had that a supply authority would have to deal on the public. The magnitude of the quake, with. With emergencies such as floods and and its resultant ground movement, ranks storms there is usually an escalation of alongside those quakes which have struck damage, and staff are called out as the overseas locations with disastrous need arises. The earthquake produced damage consequences (in terms of structural damage to plant and equipment in a period of some and loss of life). There was no loss of twenty seconds. life and limited serious injuries sustained as a result of the earthquake. It could The main shock struck the area at 1.42 pm have been a lot more severe, and should and all damage had been sustained at that enable us all to scrutinise the Boa~d•s time. Subsequent to this main shock the response to this event in detail, without ground was moving and shaking continuously fear of appearing judgmental of the Board's for a long period. Table 1 gives an idea of response to the disaster. The title the magnitude, extent, and frequency of indicates that the earthquake could be main shocks. This situation proves regarded as a large scale exercise. It must stressful on the public and on staff, in be stated at the onset that the Board's that there is no indication as to the decay staff were working under considerable of after shocks and thus makes restoration stress, both as a result of the magnitude procedures disruptive. of the work in hand and also as a result of the conditions the relatives and friends of Board's staff were living under in the days LOSS OF SUPPLY immediately following the quake. Incoming supplies to the Electricity Another reason for the choice of the title Corporation substations at Kawerau and emphasises the speed and finality of the Edgecumbe were completely interrupted earthquake. The suddenness of the main (refer to Figure 1). All 220kV and llOkV quakes on the afternoon of 2 March struck incoming lines bringing power into the everybody by surprise. A series of small Board's area had tripped. At Edgecumbe the tremors some days before the main quake T2 transformer bank which supplies the made people aware of the potential danger Opotiki Substation at 5OkV suffered damage, of earthquakes, however the public were requiring replacement of one of the single completely unprepared for the quakes when phase units. The spare transformer, which they struck. is normally out of service and de energised, was displaced from its mountings and all three banks suffered damage. Other transformer banks supplying the Board's * Assistant Engineering Manager, load at Edgecumbe and at Kawerau were also Bay of Plenty Electric Power Board, damaged and shaken off their mountings. Whakatane. BULLETIN OF THE NEW ZEALAND NATIONAL SOCIETY FOR EARTHQUAKE ENGINEERING, Vol. 21, No. 4, December 1988 238 TABLE 1 - EARTHQUAKE SEQUENCE SUMMARY Time Magnitude (a) Main Shocks 1335 5.2 2 March 1341 4.7 1342 6.3 1351 5.6 1402 3.5 1403 4.7 1407 5.3 1412 4. 3 (b) Number of shakes with magnitude greater than 3. POVERTY BAY 2 March 119 E.P.B. 3 March 46 4 March 16 5 March 5 6 March 3 7 March 3 8 March 3 ~(? LAKE WAIKAREMOANA As a result supply was lost to the Board's entire distribution area with the exception of Galatea and Murupara. FIGURE 1 LOCATION DIAGRAM SHOWING THE EXTENT OF THE BAY OF PLENTY At the time of the earthquake the Board's ELECTRIC POWER BOARD'S AREA No.l Generator at Aniwhenua was synchronised to the grid. No. 2 Generator had been out of service for its annual the lOMVA supply transformers toppled overhaul and was in the process of being backwards and impacted with the overhead reinstated. Immediately after the llkV bus bars. The units suffered broken earthquakes No. 1 Generator became llkV insulator bushings and damage to oil disconnected from the grid as a result of coolers. The llkV overhead bus bars, the protection operating on the llOkV line isolators, and supports in the outdoor to Matahina. The Generator remained in substation had been extensively damaged. service however, and continued supplying Substation equipment is supported on the Murupara area of the Board as an reinforced concrete poles and a large isolated system. Maintenance staff at the number of these have cracked, a couple were Station was diverted to immediate broken at ground level. inspection of all plant, and to surveillance of the civil structures and Distribution System embankments. Continuous readings were taken of all standpipes and drain outfalls for There is little doubt that the overhead some hours after the main shock. Flows from reticulation system suffered to a greater drains increased as a result of the quakes, extent then the underground system, but but had reduced to normal by late evening. this could be attributed to the bulk of the No. 2 machine was reinstated at an system in the damage zone being constructed accelerated rate, was commissioned shortly overhead. Underground cables located near after midnight, following test runs, and the areas of ground stress were damaged, was available for service to supply load at and other latent cable faults undoubtedly Whakatane. The Aniwhenua scheme continued exist. Damage to the Board's distribution to supply load as an isolated system until and sub transmission system was sustained approximately 0600 hours on 3 March when to an area spread either side of the grid supply was restored. Many llkV and evident fault line passing through 415V wires were severed by the swaying Edgecumbe, Te Teko and Kawerau. Damage was motion of the poles. On all the lines there also sustained by secondary causes, such as were instances of binder and cross arm slipping and slumping of the unstable ash breakage resulting in falling or displaced soil in areas surrounding Kawerau and conductors. In several cases poles sunk towards the West. Aerial structures were into the peaty soil in the rural areas dislodged and required straining or surrounding Edgecumbe, and the extreme reblocking. At least one reticulation movement of poles during the earthquakes transformer pole collapsed. caused a number of the pre-stressed concrete poles used by the Board to break The number of broken poles (where the at ground level. concrete cracked at ground level) totalled approximately 10-20. A couple of these poles were broken as a result of a slip. DAMAGE TO THE BOARD'S SYSTEM The Board's wooden poles in general survived without breakage, although a few Plains Zone Substation, Edgecumbe of them did actually twist, resulting in localised splitting of the hardwood poles. At the Board's Edgecumbe 33/llkV zone One pine service pole snapped at a knot. substation the four single phase units of 239 FIGURE 2 REPAIRING DAMAGED llKV OVERHEAD BUS AT THE PLAINS ZONE SUBSTATION, EDGECUMBE FIGURE 3 DAMAGE TO 415 VOLT SERVICES IN FIGURE 4 MOVEMENT OF llKV TWO POLE EDGECUMBE SUBSTRUCTURE 240 Two llkV underground spur lines were restoration of supply commenced. A large damaged to the extent that temporary aerial number of the Board's line staff were at connections were required. the Whakatane depot, and staff were sent home about half an hour after the main shock to check up on family. RESTORATION OF SUPPLY Those staff in the field and at Aniwhenua Restoration of supply took several days, who could not contact their family nad the procedure was shaped by two objectives: messages relayed on their behalf. Staff who did go home reported back for duties within 1. To provide secure supply as quickly as quarter of an hour to half an hour to possible to the emergency services commence restoration work. The restoration (including hospitals, civil defence, work and the damage assessment commenced service stations etc). approximately one hour after the advent of the quake. The speed with which staff 2. Provide supply as quickly as possible responded to the emergency was to be to customers in orde~ to provide a commended. Having predetermined roles in sense of security and comfort in the response to a major disaster builds up "clean up" period (including dairy morale and a dssire to part of the "team" sheds for milking, streetlighting, involved in restoration.

Load more