When Servicing Motors, More Is Certainly Better
Motor service today is “more critical in terms of the cost of electricity being higher and therefore efficiency being more important,” stated Chuck Yung, technical support specialist with the Electrical Apparatus Service Association (EASA) in St. Louis, MO. But reliability is more important as well, he pointed out.
The end-user now “is being required to do more with fewer personnel,” Yung said. “So the relationship between the end-user and the service shop is a lot more important than it has been in years past.” Maintenance is being outsourced more and more.
The larger companies are doing more predictive maintenance, he said. “These end-users are doing a better job certainly than they were 20 years ago.” On the other hand, we have other companies with budget constraints. With those firms, maintenance is the first thing to get cut when things get tight.
In the short term, cutting maintenance is a problem. But in the long term, he remarked, “It’s an opportunity for the repair industry.”
Yung noted, “We’re starting to see more of the smaller companies rely on their service shop to come in and do vibration analysis, do thermography, and identify potential motor problems and head them off before they become a catastrophic failure.” To maintain motor efficiency, “attention to detail in terms of the basics is very important.”
CONSIDER SYSTEM EFFICIENCYRegarding the phasing out of older motors and installing new high-efficiency motors, Yung says there is a broad misconception right now.
“The Department of Energy is anxious to see energy efficiency overall improved. When you look at an older electric motor that may have 85% to 90% efficiency and then compare that to the pump it’s operating, which may be 70% or 75% efficient, or a boiler at 40% efficiency, or a compressor at 60% to 70% efficiency, it’s obvious that the electric motor is a lot more efficient than the equipment it’s driving.”
And older motors are not less efficient than newer models across the board, he stated. For smaller motors, “let’s say 50 or 100 horsepower on down, the newer EPAct motors are more efficient than most of the older motors. But in the larger motors, the designs have been very efficient for a long time.
“There are even U-frame motors that meet the EPAct levels — motors that are 40 years old. So particularly when you get over a few hundred horsepower, I would caution people not to just blindly replace an old motor with a new one under the assumption that it will be more efficient. Because, many times, that’s not the case.”
How long a motor runs is a consideration as well. Yung was in Panama recently for a seminar and he pointed out that the motors operating the locks in the Panama Canal are a couple hundred horsepower but they only run for about one minute, six to eight times per day. “Why on earth would you replace that motor with an energy-efficient motor?” he asked.
The longer a motor runs per year, the more the user should be concerned about efficiency. In many cases motors “don’t run enough hours to give a reasonable payback period,” he said.
RELIABILITY IS NO. 1Although there’s a lot of talk about efficiency, Yung believes that the single most important concern of end users is reliability. For example, in the paper industry, downtime can cost a company over $10,000 an hour. In the petrochemical industry, downtime can drain a business of as much as six figures an hour. “So potential energy savings pales by comparison when they start looking at reliability issues,” he related.
Something that may be overlooked is aftermarket modifications to a motor to customize it and improve its suitability for an application. This can be such things as special seals or replacing the shaft with one made of stainless steel to prevent corrosion.
Some studies have also shown that by increasing the slot fill, service shops can improve efficiency by 1/2% to 2%. This is because the manufacturers wind motors by machine, while service people rewind by hand. Manual rewinding enables the slot fill to be maximized. “Basically, you pack more copper into the motor,” said Yung. Increasing the copper also provides the added benefit of making the motor more reliable.
Publication date: 03/19/2001