Everything manufactured has its lifespan, which can be quickly reduced should its proper care and maintenance be neglected. Industrial electric motors are no exception to this. There are many ways to observe your motor’s energy efficiency and lifespan. The average motor typically has five major parts, namely the stator core, rotor, bearings, terminal box, and winding which all need to be overhauled from time to time to ensure efficient and safe operation. Otherwise, what usually happens first is the gradual decrease in its insulation resistance, resulting in short-circuiting and failure of an electric motor.
The first defence against this deterioration is maintaining dryness by adding proper ventilation and anti-condensation heaters. Still, the continued deposits of dust, grease, oil, moisture and ageing of the insulation mean that it is more important to overhaul the entire system periodically. Knowing the main causes of the majority of motor problems is key to determining when to do an overhaul and how to identify them before they develop into more severe issues. With that said, below are the six most common causes of motor malfunctions and how each can lead to faults in the system.
1. Extreme working conditions
Every machine, including motors, is designed and tested to perform optimally under a range of operating conditions. One of the critical factors that play a significant role in determining the life of a motor or the regularity of its maintenance is the temperature of the working environment and the motor itself. Motors are generally designed to work efficiently at temperature ranges between -25℃ to 45℃, which is why prolonged operation below or above this range results in deterioration of its insulation resistance and reduced life of the bearings. Likewise, poor hygiene from choked ventilation ports or overall poor motor ventilation will naturally cause overheating and burnout of the windings.
2. Dust and moisture
Dust, moisture, tiny metal pieces, and other foreign particles may get lodged in the ventilation ducts and reduce the fresh air intake into the system. These dust deposits can also affect the windings and impede proper heat dissipation, which often causes overheating. Similarly, tiny metal scraps and other contaminants may get between the rotor assembly and the stator, restricting shaft movement.
On the other hand, moisture causes various parts of the motor to corrode and wears down its insulation. It can latch onto the rotor, shaft, and bearings, corroding them and restricting their functionality. Other issues that can stem from moisture corrosion include current leakage, efficiency loss, and overall damage to vulnerable parts that will eventually result in motor failure.
3. Vibrations
Vibration in electric motors can be caused by several reasons, such as improper alignment, poor attachment to the platform, corrosion, and damaged bearings. These vibrations can also be external or internal. For instance, external vibration will loosen the electrical connections, fasteners, and lock nuts, while internal vibration causes rubbing of surfaces and eventual damage. Apart from causing normal wear and tear, vibrations also affect a motor’s power output and efficiency, hence the need to keep an eye on their presence at all times via regular maintenance and monitoring of vibration levels.
4. Overcurrent
An electric motor draws in current to its windings to generate torque, and overcurrent occurs when more current passes through than is necessary. This poses an issue as the windings are designed to only safely carry a specific rated current for an indefinite time. An overcurrent situation may be caused by a short circuit, low voltage, or high voltage that forces the windings to draw heavy current, leading to overheating and burnout of the windings. In addition, this issue also negatively affects the resistance of the motor’s insulation and its electrical contact points.
5. Lower insulation resistance
As one of the leading causes of motor failure, reduced insulation resistance makes up nearly 70% of total motor failure cases. This problem occurs when the insulation resistance deteriorates over time, generating scope for current to leak and short circuit the windings. Although the effects are easy to know, the reduced insulation resistance is more difficult to detect on time. At first, a motor’s insulation resistance value can be as high as 1 MΩ (megaohm), but this gradually reduces with heat, wear and tear, moisture, and time. In such conditions, it can no longer prevent electrical contact between the windings and the conductor, leading to the windings getting short-circuited.
6. Overheating
If reduced insulation resistance ranks first among the main causes of all motor troubles, overheating is second to the list. A motor generally overheats under very low or very high voltage conditions when it draws in more current to the windings than it is rated for in the first place and generates lots of heat. Other reasons for this overheating issue are poor air ventilation in the motor, a high-temperature working environment, and overloading, which causes loss of efficiency, performance, and insulation in the short-term and bearing damage, stator damage, and windings burnout in the long term.
Conclusion
Whether electric motor rewinds or overhauls, motors require frequent checks and maintenance to ensure they remain in top working condition and avoid unexpected downtimes or motor breakdowns. By engaging with services providing mechanical and electrical engineering in Singapore, organisations can better maintain their motors and stay on top of the above-mentioned issues.
