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Under the Magnifying Glass

Sep 1, 2000 12:00 PM, By Marleen Canniff

Taking a close look at a motor's stator during condition-based maintenance keeps power running at capacity at this busy power plant.

When the condition-based maintenance (CBM) department at Alabama Power Company's Miller Steam Plant suggested altering the way the plant conducted preventive maintenance on its critical motors five years ago, their ideas were met with some apprehension. After all, Miller Steam Plant is a major producer of electricity for the utility, which provides service to nearly 1.3 million homes, businesses, and industries in the southern two-thirds of Alabama.

As a base-load, coal-fired plant, Miller runs its four energy-producing units at or near capacity almost 100% of the time. So, as Miller CBM Specialist Jeffery Brasher recalls, there was some concern about introducing new technology when preventive maintenance scheduling had worked for years.

According to Brasher, when it came to critical motors, the old method was to select 10 to 12 motors a year and send them out to be reconditioned, whether they showed signs of deterioration or not. Large motors (up to 7000 hp supplied by 13.8kV) were reconditioned every seven to eight years. These motors would be removed and sent to motor vendors - a very labor-intensive and costly process.

What Miller's CBM department wanted was a way to trend motor condition. "We work on percentages in condition-based maintenance," says Brasher. "We don't have time to do everything, so we have to look for innovative technologies."

The staff used vibration tests, oil analysis, laser alignment, and infrared devices to evaluate the motors, but these tools could not assure them of the electrical integrity of the motors.

"When motors run within the environment of a coal-fired plant, they operate 24-hours-a-day in coal dust and fly ash, the by-product of burned coal," says Brasher. "When the motor turns, the cooling fan (which is connected to the rotor) pulls the fly ash and coal dust right into the motor housing. We were rolling the dice on our critical motors."

To address this problem, Miller purchased a Motor Circuit Evaluator (MCE) system from PdMA Corp., of Tampa, Fla. Since he began using this 10-min test in 1995, Brasher has been extremely pleased with its performance.

The staff uses this test to check the ground wall insulation and graph leakage current in their critical motors. When the inside of a motor has buildup of contaminants, the buildup can cause current to arc, leading to degradation and eventual destruction of the motor.

"With this test, you can immediately recognize a stator's insulation condition and tell if coal dust or fly ash has contaminated the stator," says Brasher.

The most dramatic change resulting from the MCE investment is the cost savings the utility's enjoyed in reduced scheduled maintenance.

In fact, these results are so impressive that the Miller Steam Plant's CBM department has been recognized as one of the top CBM teams in the Southern Company (the utility's holding company), and the department has been visited by companies from across the United States.

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