Industrial Gas Company

Motor Rotor Bar Performance Diagnostics

This video case study follows one specific motor’ rotor bar problem over eleven years to show how the problem progresses. Initially, the problem is only minor and does not have any effect on the motor’ performance. Over time, the vibration spectra clearly show the degrading condition which culminates in a dramatic change in the rotor’ balance condition. This research shows that motors with rotor bar issues can operate for years without any harm to the machine or its performance. Being able to identify the severity of the problem using vibration also makes it much easier to know when to resolve the issue without causing residual damage to other parts of the machine.

As a result, this customer was able to operate for eleven years past the initial problem, saving at least a $100,000 investment in a new 10,000 horse power motor. The time value of money would show that that $100,000 investment is worth over $189,000 in today’ dollars with an 11 year investment at a conservative 6% rate. So you get a much better feeling for the savings the predictive maintenance program provided on just this one motor. Now, after getting years of profitable production, the customer could purchase a new motor and have $89,000 in their pocket in addition to all the profit they made without interruption. Conversely, the customer could have purchased a replacement motor eleven years ago and now face the daunting reality that the second motor also needs to be replaced. Sometimes, the ability to confidently do nothing is extremely valuable.

Being able to identify a problem is only part of what the vibration program provided. Its ability to determine the severity of the motor’ problem was also critical in determining the proper time to conduct the replacement. Very few modern predictive or nondestructive technologies could even identify this type of problem accurately and none of them could accurately identify the severity for determining when it was the proper time for replacement.

To a certain extent, it may be better for the customer to not use a technology that could identify a rotor bar problem because, most likely, they would replace a motor way too early in its actual life cycle, wasting considerable money. Alternatively, if the customer were to let the unit run to failure, the costs become ridiculously expensive when the cost of production loss is thrown into the calculation.

It took this customer six weeks to find a replacement motor. If they had let the unit fail, they would not have been able maintain their production schedule. So based on their loss of production conservatively costing approximately $500,000 per week, we are in the ball park of $3,000,000 in production losses. The installation and motor shipping costs would likely have been charged at premium rates and performed on an emergency basis. This, certainly, would have been more expensive than if the installation was pre-arranged around a planned outage.

In the end, while it is much less costly to know the problem is coming, it is even better to be able to determine the severity of the problem and to maximize the useful life of every one of your machines.

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