In any industrial setting, you can only work as hard and reliably as your technology does. Uptime is indispensable to successful operations and profitability, and that means all your systems and machinery need to be operating properly, full-time.
Industrial electric motors, in particular, are essential to many industrial oil and gas operations, as well as in naval and civilian vessels, mining, and manufacturing. These motors (along with associated machinery like generators and pumps) are as sophisticated as they are powerful, so keeping yours running at peak performance with as few mishaps and as little downtime as possible is vital. Any problems need to be identified and remedied quickly and effectively. You need to be aware of common problems that can lead to motor failure and also be proactive about industrial motor service and maintenance like rotor balancing and motor rewinding to avoid failures to your most important devices. And having a response team on call 24/7/365 to deliver the quickest, highest-quality motor and pump repair services in the event that you experience a breakdown is an absolute must.
The electric motors driving today’s industry are sophisticated and complex machinery that are integrated with multiple additional pieces of technology. Accordingly, they are subject to a wide range of stresses and irregularities that can impair their effectiveness, require industrial motor service, and become contributing causes to failure.
Some of these problems trace back to the installation of the motors or associated machinery. Others are related to the irregularities in the motor’s power supply or to improper functioning in the VFD (Variable Frequency Drive) that manages it, while some contributing causes of failure are simply the result of normal operational wear and tear. Knowing the roots and symptoms of these causes of motor failure can help you troubleshoot issues and initiate service, repair, or replacement before more extensive and costly damage occurs. Let’s take a quick look at some of the most common of these issues.
Unevenness in the mounting feet or the surface on which they sit creates a condition known as soft foot. This may go unnoticed during initial installation, and it leads to torsional stresses being induced into the motor frame causing increased strain in the rotational assembly and malfunctions if not remedied. Ensuring your motor has been installed as per OEM requirements will alleviate this costly issue.
Even a properly situated pump and motor installation can become a problem over time due to changes in surrounding and attached elements: shifts in foundation, incidents of physical impact, or damage to braces, pipe hangers, and other stabilizing devices. This can lead to pipe strain, which can cause misalignment of the motor/pump shaft. If caught early through routine inspection during maintenance, pipe strain is a minor problem. However, the misalignment inevitably leads to greater and more widespread malfunction over time, requiring pump repair services or even total replacement of multiple pieces of equipment.
Problems with Power Quality
Unbalanced voltages are unequal voltage values on a 3-phase circuit that can exist anywhere in a power distribution system. This is an important part of any motor assessment that is done. Being able to measure the variance of voltage reaching a motor ascertaining whether it is a distribution problem or a motor issue is one of the most basic checks that can be done but is also one of the most overlooked areas. Voltage imbalances of just 1% can in turn cause a current imbalance of up to 10%. When this type imbalance is allowed to persist in a motor it can cause unequal heating of the wound phases internal to a motor and cause premature failure of the motor.
QUICK NOTE: NEMA states that polyphase motors shall operate successfully under running conditions at rated load when the voltage unbalance at the motor terminals does not exceed 1%. Operation of a motor with above a 5% unbalance condition is not recommended, and will probably result in damage to the motor.
When there is excess AC current in a motor winding, harmonic distortion occurs. A limited amount of this phenomenon is actually a normal part of motor operation, and the extra energy circulates through the winding components, canceling excess current without affecting the rotation of the motor shaft. But sustained harmonic distortion compromises efficient operation and leads to thermal buildup that will damage insulation. As with voltage imbalance, a three-phase power quality analyzer is used to monitor harmonic distortion and to detect when it has reached problematic levels.
VFD Failure Factors
PMW Signal Reflection
A VFD (Variable Frequency Drive) governs the power sent into a motor to optimize performance. PMW (Pulse Width Modulation) or PDM (Pulse-Duration Modulation) breaks the electrical signal into discrete parts for maximum control and minimum loss of power. These chopped-up signals can sometimes reflect due to impedance imbalance. Any number of factors can disrupt proper PMW activity and lead to increased heat/insulation breakdown, including worn, mismatched, or improperly installed components. Routine maintenance can usually detect this problem before it leads to significant downtime or causes additional damage, but such failures can be quite costly if PMW reflection goes undiagnosed.
Improper frequency signals, voltage levels, and capacitance and inductance of conductors can lead to disruption/inequality of the three-phase distribution and create stray sigma currents in the motor cabling. This can cause unintended tripping and excess heat. Sigma currents are usually easy to detect with an oscilloscope as part of routine service.
Sometimes an electric motor is simply overloaded. Excessive current draw, high heat, and/or slow torque can be signs that a motor has become overloaded, and it can cause premature wear and failure of all the motor’s components, even if none seem to be functioning improperly. Power monitoring can alert technicians to operational overload before it causes motor failure.
Over the course of operation or as the result of some event, the coupling or the drive shaft of a motor can come to be in various types of misalignment. Periodic checks of the shaft alignment are crucial for the longevity of rotational equipment. Ensuring that the couplings are properly selected and that they are aligned as per manufactures tolerances is crucial to the longevity of equipment life.
An irregularity known as imbalance occurs when the rotational center fails to meet the axis. There can be many reasons why this has happened in rotational equipment. Worn components, missing fasteners, missing weights from the factory balance, and improperly installed equipment on rotational assemblies. This displacement of mass away from its proper place on the axis and onto the rotor causes excessive vibration and wear, which can quickly compromise the motor. Shaft imbalance can be detected and corrected during rotor balancing or by use of a vibration tester if you suspect imbalance exists.
Staying Ahead of Motor Failure
The best time to deal with motor failure is before it occurs, and the problems above are only a partial list of the issues that can cause failure and costly downtime. Your operation should have a maintenance, and repair partner who specializes in industrial motor service and who knows your industry and your machinery inside and out. From initial installation to routine visits and on-call emergency interventions be sure they are ready to analyze, calibrate, and repair your motors and all the equipment you count on, from rotor balancing and laser alignment to motor rewinding and complete unit replacement. To preserve your uptime and ensure successful operations, trust the people, technology, and solutions of Ward Leonard. Contact us today.