Motor-driven equipment accounts for 64% of the electricity consumed in the U.S. industrial and commercial sectors. All industrial or commercial operations have some type of motor in their facilities, whether it’s used to drive fans, pumps, compressors, saws, crushers or conveyors.
Regardless of its purpose, though, all motors are prone to failure if not properly sized, installed and maintained. Even the best motors will fail prematurely if they’re installed in applications or conditions they’re not rated for, or if preventative maintenance guidelines are not followed.
Maximize Your Motor Life and Improve Your Operations By Taking Preventative Measures Against These Common Causes of Electric Motor Failure:
1 – Motor Overloads
The first is a motor overload, which causes the motor to draw more current. This, in turn, produces more heat than the motor was designed for, which reduces the life of the motor. Motor overloads usually result from improperly sizing the motor or a change in the driven load, including plugging of the system, a broken gear or frozen bearings.
However, according to Jon Prince, IBT’s Electrical Group Director, if the motor-overload protective device trips and takes the motor off-line repeatedly, it is not nuisance tripping and the cause should be located, rather than simply installing larger protective devices.
2 – Short Cycling
Short cycling is the process of repeatedly stopping a motor that is already heated to operating temperature, and then starting it again before it has a chance to cool. The result of underestimating the starting frequency of an application may lead to more starts per hour than the motor is rated for. Most electric motor manufacturers specify the maximum number, or frequency, of starts for a given motor type.
3 – Electrical Supply
“Low or high voltage is actually not the cause of electric motor failure as frequently as one would suspect,” says Prince, “unless the voltage change is greater than 10%.” Motors do not give satisfactory service if the voltage consistently varies by more than +/- 10% from the nameplate rating.
Phase voltage unbalance in a three-phase supply can cause electric motor failure due to an excess temperature rise. A 3% voltage unbalance causes an 18% temperature rise in the motor and a current increase of six to ten times the voltage unbalance. Phase voltage imbalance should be less than 1% for proper motor operation. If a motor must be operated with a phase unbalance greater than 1%, the motor should be derated. A motor should not be operated if the phase unbalance is greater than 5%.
Single phasing refers to conditions where one phase of a three-phase electrical system is de-energized. Single phasing creates a problematic situation for a three-phase motor that can continue to operate by drawing more current (thus more heat) on the remaining two phases. Many standard motor starters contain overload relays which will not respond to this situation, however, three-phase “phase protection relays” are available to protect motors.
4- Physical and Environmental Conditions
Motors must be rated and installed to withstand the physical and environmental conditions their operation subjects them to.
Restricted ventilation, or covering the motor’s enclosure with materials, will cause a motor to operate higher than the desired temperature. “A typical compressor room or pump house will heat up quickly if the room is not properly ventilated,” according to Senior Member of Siemens’ Large Motors & Pumps, William R. Finley.
Improper lubrication will not only damage bearings, but can also throw grease into the windings.
Moisture in the form of condensation can cause rust within a totally enclosed motor.
Vibration, belt tension and misalignment are among the major causes of motor failures that started as bearing failures. Where vibration is a problem, electrical connections, if not tight and secure, will be an endless cause of trouble.
“Causes of vibration may be in the motor, such as: unbalance of the rotating element, rubbing parts, loose parts, oil film instabilities, anti-friction bearing problems, electrical design and resonant parts,” says Finley. “Causes of vibration may also be external to the motor, such as: foundation, installation, misalignment, adjacent parts in resonance, and changing conditions after installation and start-up.”
High ambient temperatures (over 104° F for a 40° C rated motor) must be taken into account by derating to a lower horsepower or installing a motor designed with proper insulation for operation at higher ambient temperatures.
According to Finley, successful motor operation depends on many things, but most importantly, the application and environment must be known and its effect on motor performance, understood.
The first step to solving the question “why has my motor failed” is to inspect everything.
A simple inspection of the bearing and motor windings can often point you in the right direction: Do the bearings show obvious wear or lack of lubrication? Now look at the windings of the motor; If overloaded, all the windings will appear to be evenly burned. Is there lubricant in the windings? What does your motor tell you?
IBT & Siemens, Working Together For You
IBT has a dedicated team of electrical product specialists who have been consulting customers on every aspect of electric motors, and helping them solve their toughest electrical problems, since the 1970’s. Together, with industry leaders like Siemens, there’s no challenge we aren’t willing to take on. So when it comes to solving electric motor failure, minimizing downtime or getting more life out of your current machinery, IBT has the product knowledge and expertise you need to make it happen.