You don’t often hear about an electrical utility being told it can only use a generator on an emergency basis, and that if it is used, it has to be operated from a long distance away, because of the impact of the possible failure.
But that’s exactly what Newfoundland Hydro was told about its Hardwoods turbine before the turbine underwent maintenance this past fall. The repair was because of stress cracks in metal retaining rings in the turbine’s alternator.
Newfoundland Hydro had found cracks in retaining rings in a turbine of the same age and design in Stephenville — they knew they had a problem in the similar Hardwoods equipment.
“There is a high probability that the retaining rings are near failure, which has resulted in the restriction that the unit can be run only in an emergency situation,” Hydro told the province’s Public Utilities Board in a report.
How dangerous a mess could that be?
Well, the report cautions that no Hydro employees should be onsite when the turbine was running. Power consultant Brush GMS had told the utility in an April 23, 2013 letter: “Consistent with our previous discussions with respect to ongoing operations of the Hardwoods unit, in the event the NL Hydro is required to run the Hardwoods unit, it is our recommendation that the Hardwoods Gas Turbine should only operate on an emergency basis and that the operation should be remote and unmanned given the safety risks associated with respect to potential retaining ring failures.”
Problems with the rings weren’t new; they were known in the late 1980s, when the manufacture of retaining rings of the same metal composition as those at Hardwoods was discontinued as a result of stress cracking, particularly in maritime climates like our own.
So the cracks, while a surprise when they were found in Stephenville, should not have been that surprising. As Brush put it in its analysis, “There is supporting industry experience that retaining rings fabricated with 18-5 stainless steel are prone to failure. This problem is well documented.”
The $8.1 million in work clearly had to be done.
So why was the Hardwoods repaired during the fall, a repair that ended up not being completed by the time the utility needed power from Hardwoods and rolling blackouts started across the province?
Well, that’s an interesting story, too.
It’s the time Newfoundland Hydro picked.
“It is now recommended by Newfoundland and Labrador Hydro (Hydro) that the strategy to return the alternator to a safe and reliable working condition involves replacing the stator and rotor along with a protection upgrade in October 2013. This strategy would minimize the amount of time the unit would be unavailable, allowing it to be available for operation in emergency situations during the 2013 summer season. During the summer of 2013 no Holyrood units are planned to be operated for power production. Therefore, it is essential that the Hardwoods unit be available in the event of a contingency situation,” the utility said when it asked the PUB for permission to do the work.
Why no Holyrood?
Keeping a unit ready to operate at Holyrood to allow the maintenance program would have cost too much. Running Holyrood would have displaced hydroelectric power, spilling water and costing the utility an extra $10.5 million in “energy spilled.”
It will be interesting if the rolling blackout costs wind up matching that $10.5 million.
It is a fascinating story of the balance between costs and rolling the dice on system reliability. It’s also far from reassuring.