Having a “Motor Management Program,” at your facility, is essential to proper maintenance and monitoring of operational assets as well as proper testing and storage of all your spares. In this article we will address some critical aspects of Motor Management, with an emphasis on spare motors. Some of the key components for success of motor management are:
- Develop motor repair and rewind specifications for low voltage and medium / high voltage motors.
- Develop a Motor Acceptance Program,” if properly implemented and effectively managed, it can eliminate encountering defective spares. All new, repaired, and rewound motors must meet your acceptance specifications before they enter the warehouse.
- Hire a professional auditor to evaluate the motor repair shops that you utilize. This can also be used to find the best shop if you choose exclusivity for a repair facility.
- Negotiate with a motor manufacturer to provide all your motors. This can provide better pricing and technical support, while also facilitating a level of standardization.
- Routinely monitor assets with multiple technologies to identify failure mechanisms and provide for considerable data correlation.
- Establish a Reliability Group to include vibration, infrared, ultrasound, motor testing, power quality, lubrication and oil analysis.
- Provide or contract a facility for motor storage. The best type of facility will be temperature and humidity controlled.
You have heard the phrase “NEW doesn’t necessarily mean good.” How about this one from way back in my high school football days, “Your team is only as good as the worst guy on the bench.” Both these phrases can be applied to your spare motor inventory. Let’s add the word motor to the first phrase and motor reliability to the second; new motor doesn’t necessarily mean good motor; your motor reliability is only as good as your worst motor on the bench, or in the warehouse.
Spares are often overlooked. Even facilities that have programs established to monitor and maintain their motors often neglect the spares. This can lead to major downtime. Another area of concern is “size matters,” or does it? By that I mean emphasis seems to be placed on motors of higher horsepower and higher voltages instead of criticality, for condition monitoring and storage maintenance.
Recently, as part of a service availability, we were tasked to test a customer’s on-site spares. Several serious problems were identified. The customer also had motors stored at an environmentally controlled warehouse maintained by a local motor shop. The shop had been contracted to rotate the shafts and test resistance to ground monthly. When we went to check the motors, we found that none of the motors were connected in a wye configuration to facilitate proper testing. Some of the shafts were blocked and some were heavily plastic wrapped, and the shafts could not be turned. We will leave it to you to make an integrity assessment.
Statistically, defective spares usually fail within 24 hours of installation. This is true of both electrical and mechanical failure mechanisms.
How do we preclude the above types of incidents? It will take a dedicated program, but-results will more than pay for the investment.
The first step is to establish “Acceptance Testing.” Develop sets of standards for both new and refurbished motors. “ALL” motors get tested before being placed in inventory. “ALL” motors in inventory get tested annually. You may have a fractional horsepower motor that drives a lube oil pump for a critical sleeve bearing motor, or transformer oil pump or cooling water pump. That fractional horsepower motor is every bit as critical as the motor or transformer it supports. So, ALL motors in the warehouse get tested. Motors stored off site should be tested as well. If this storage is contracted and includes periodic testing, then routine unscheduled spot checks should be accomplished. Remember the phrase, “trust but verify?”
The next step is to establish a program of shaft rotation. Motor rotors are quite heavy and place considerable weight on bearings. Have you ever been in a warehouse and a forklift drives by? Did you feel the slight vibration of the concrete floor? The motor sitting near you on a pallet or shelf felt that same vibration, only it is exposed to those vibrations constantly. This can lead to brinelling. The bearing individual rolling elements will wear in one spot where they contact the bearing race. This will cause excessive friction and lead to rapid failure when the motor gets installed. Another issue is related to the weight of the rotor. Gravity takes its toll on everything including motor rotors that are heavy and only supported by bearings on both ends of the shaft. Motors stored for considerable time periods can enable slight sag of the rotor which may result in rubbing when energized.
At minimum a slight rotor sag will result in an uneven air gap, eccentricity, and result in vibrations that will lead to premature failure. Worst case a rotor rub will occur. That can destroy a rotor and stator!
Spare motor reliability is every bit as important as that of “in service” motors. Remember New motor does not mean good motor and your reliability is only as good as your worst motor in the warehouse.