Mechanical Failures Plague Arizona’s Power Grid

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Researched by Industrial Info Resources (Sugar Land, Texas). The west has experienced a major decrease in generating capacity over the past month due to unplanned maintenance outages on critical units and the extension of existing unplanned outages. The Navajo Generating Station as well as the Palo Verde Nuclear Generating station, both located in Arizona, have ongoing forced outages, which are affecting the power supply in the west.

The Navajo Generating Station, which supplies power to Arizona, Nevada, and California, has all three units in the process of being repaired. Unit 01, which produces 803 Megawatts (MW), has been running at 50%, because of repairs on an air-heater shaft. The shaft failed during the afternoon of October 9, 2006, after experiencing operational problems over the weekend. Engineers at the plant decided to run the unit at a lower power level to make necessary welding repairs instead of having several units offline concurrently. Unit 03, also 803 MW, was brought down October 10th with a leak found in a boiler tube. Unit 02, the most recent occurrence, tripped offline October 11th, also due to repairs on a boiler tube. Mending to both tube leaks are expected to take approximately 3-4 days.

Another station in flux is the Palo Verde Nuclear Generating Station, the largest nuclear plant in the nation. It serves power to Arizona, New Mexico, Texas, and California. The plant has suffered frequent unplanned shutdowns throughout the summer and the units continue to suffer from persistent technical issues. The latest concern for the facility is the return of Unit 01, which has the capability to produce over 1,300 MW. The unit initially came offline in late September, because of recurring problems with pressurizer heaters. The heaters were replaced, but then a valve on the safety injection system prevented the unit from returning. This malfunctioned valve had to be taken apart and fixed which caused about a week delay on the return of the unit.

During the time of the repairs on Unit 01, Unit 02 was taken offline for a planned maintenance refueling outage that is to last until early November. Unit 01 was expected to return the first weekend in October, but was delayed because of another problem that was discovered. There was a back-leak exposed on one of the turbine valves while the unit was proceeding to Mode 3, 2 levels away from entering the start-up process. After repairs where completed on the leak, progression towards start-up was again halted because of an electrical switch failure. The switch had to be replaced and officials stated that parts were to be delivered on October 10th with repairs expected to take about 3-4 days. The unit is scheduled to ramp up over the weekend, unless more setbacks arise.

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