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wnt . 0 N Kcx 1 ' FF RIVERSIDE PUBLIC U'T'ILITIES _ J Boaxd Memorandxn PUBLIC UTILITIES BOARD OF PUBLIC UTILITIES DATE: April 15, 2011 ITEM NO: 4 SUBJECT: HUNTER SWITCHGEAR NO. 3 AND NO. 4 BUS TIE REPAIR —WORK ORDER NO. 1112682 ISSUE: Board of Public Utilities approval is requested for Work Order No. 1112682 and for the purchase of bus, bus supports, and bus duct for the Hunter Switchgear No. 3 and No. 4 Bus Tie Repair, RECOMMENDATIONS: That the Board of Public Utilities: 1. Approve Work Order No. 1112682 in the amount of$105,450 forthe Hunter Switchgear No. 3 and No. 4 Bus Tie Repair; and 2. Approve the purchase of bus, bus supports, and bus duct from Myers Power Products in Ontario, California, for the amount of$53,229 including sales tax. BACKGROUND: Hunter Substation is one of the City of Riverside's (City) 14 substations which distribute power to Riverside Public Utility(RPU)customers(see attached vicinity map). Hunter Substation has six main transformers that reduce the electrical voltage levels from 69 kilovolts (kV) to 12 kV or 4 W. Each of the six transformers feeds a corresponding lineup of switchgear including medium voltage bus work and circuit breakers. Each lineup of switchgear generally has a main bus tie, comprised of bus and bus duct, which allows a lineup of switchgear to be connected to another lineup of switchgear. This main bus tie is important because it allows RPU to maintain power to a lineup of switchgear when its corresponding transformer is taken out of service which provides operational flexibility in the event of equipment failure. In late December 2010,the main bus tie between Switchgear No. 3 and No. 4 at Hunter Substation failed on two occasions and resulted in customer outages. The first main bus tie failure occurred on December 23, 2010 when a section of the bus inside Switchgear No. 3 short circuited to ground. This caused Switchgear No. 4 to lose power for a number of hours, but customer power was quickly restored by circuit switching outside of the substation. Switchgear No.4 was put back into service after removing the section of damaged bus. On December 24, 2010, the second main bus tie failure occurred when a section of the bus duct short circuited to ground. This caused Switchgear No.4 to lose power again until the damaged section of bus duct was physically and electrically isolated from Switchgear No. 4. An investigation by staff revealed that the bus insulation failed for a number of reasons. First of all, moisture was a contributing factor as the humidity levels hovered at or below 100%during the time of the failure. Also, dust and particle infiltration was also a contributing factor to the failure. Furthermore, insulation abrasion due to the original bus support design was also suspect. Finally, natural degradation of the insulation was suspect because the bus and bus duct are more than 40 years old and have reached the end of their useful life.