City electric workers have identified the part that failed on the steam turbine generator hydraulic safety system that put Pratt in the dark for almost four hours early Tuesday morning.
Now they are waiting on that part to come in so they can get the steam turbine back on line, said Kelly Hemphill, Pratt City electric utility director.
In the meantime, a pair of dual fuel generators is working smoothly and keeping the lights on in Pratt.
Normally, Pratt buys its power from Sunflower Electric because it is cheaper than making electricity at the power plant. However, the city had to disconnect from Sunflower Electric Monday so Sunflower could work on a substation.
The city was getting power from the steam turbine generator when the hydraulic safety system developed a leak and the system shut down. The hydraulic safety system prevents the generator from running too fast if something should go wrong.
That’s when the city called on its dual fuel generators to get Pratt back up and running. It took a while to get the dual fuels on-line and when they brought up some circuits in the city, it overloaded the system and some areas had a second power failure.
It took from about 1:10 a.m. to 5 a.m. to get the entire city up and running on the dual fuel generators.
The dual fuel generators can run on either natural gas or diesel. Right now they are running on 100 percent diesel because the generators operate more efficiently on diesel than natural gas. They get a little better torque on diesel and handle instantaneous load swings better, too.
Each of the dual fuel generators is 10,000 horsepower and can generate 7 megawatts each. Usually during this time of year Pratt will draw 5 megawatts at night and just over 10 megawatts during the day, Hemphill said.
The weather forecast for the next three weeks indicates the city should draw about 10 megawatts a day so the dual fuel generators should handle the load easily.
The dual fuel generators run about 400 hours a year. The controls are set to very tight parameters so they require maintenance every time they run, Hemphill said.
The electric department wants to get the steam turbine back on line as soon as possible because it can handle a circuit trip better than the dual fuel generators.
When the dual fuel generators are using diesel, it takes about 30 minutes to get a unit on line. For the steam turbine it takes much longer.
If the steam turbine has been running and is hot, it takes about two hours to get it on line if it isn’t running. If the steam is just warm, it can take up to eight hours to get it on-line.
When the hydraulic system failed, more employees were called in to help solve the problem. The crew stayed up all night to make sure the power got on so Pratt could go to work Tuesday.
The electric department has 12 employees at the plant and 11 on the line gang.
While the dual fuel generators are operating efficiently on diesel now, they work better on natural gas when Southern Pioneer calls on the city to produce electricity for the Southern Power Pool.
Southern Pioneer is part of the Southern Power Pool that serves a wide area with electricity. As a part of their agreement with the power pool, Southern Pioneer is required to maintain a certain electrical capacity so the power pool has enough energy to draw from for the entire power pool.
Occasionally, Southern Pioneer will call on Pratt to hook into their system and produce electricity to meet that need. When Pratt does that Southern Pioneer compensates them so they see a cost savings on their bill from Southern Pioneer.