There are many reasons why an electric motor can fail, with the most common being motor overload. Whether electrical or mechanical, a motor overload occurs when the motor’s output torque is no longer enough to move a given load.
Below, we go into further detail about this issue and tips to get your motor back online.
Telltale signs that your electric motor is overloaded
Electric motors are often set to run under an overloaded state for days or even weeks. Most motors today have a Service Factor rating that allows for regular short bursts of overloads, not prolonged ones. As such, overloading a motor for an extended amount of time will accelerate wear and eventually cause failure. The main symptoms of motor overload include overheating, insufficient torque, and excessive current draw. The most telling signs of overload in an electric motor include:
- A burning smell after or during operation
- Increased noise and vibration levels caused by the shaft working harder to turn the load
- Increased temperature that exceeds the usual baseline
- Motors equipped with overload measures will fail to start due to a blown fuse or tripped circuit breaker
- Capacitor failure
Several tests can check for motor overload before it causes failure. For starters, you can use a multimeter with a clamp attachment to test for overcurrent, undercurrent, or fluctuating current instances that result in overload. Next, you can perform a vibration analysis to check for worn bearings and detect shaft misalignment. Lastly, you should monitor the motor’s temperature during regular operations and look for unusual fluctuations and increases.
Causes of Motor Overload
As mentioned, there are two types of motor overload: mechanical and electrical. Mechanical overloads are non-electric problems that cause a motor to work harder than it should, thus drawing more power to compensate. Using more current for a prolonged period will damage the windings and eventually lead to failure. Some of the most common issues that cause a mechanical motor overload include:
- Higher torque output than what the motor is rated for to turn heavier loads. An example is in crushing machines, where there is generally a lot of variation in the objects it has to crush and the required load for each.
- Worn or damaged bearings caused by vibration, contaminants, broken-down lubrication, and overheating will place excessive strain on the spinning shaft and require more current to operate the motor.
- Misalignment of the motor shaft or bearings on the shaft will cause a motor to run in an overloaded state.
In some cases, mechanical overloads can be resolved with simple fixes like getting electric motor spare parts in Singapore to replace worn-out components, while in others, full servicing may be necessary.
On the other hand, electrical overloads occur when a motor fails because of an overvoltage, undervoltage, or fluctuating voltage situation at the motor controller or power source. For running in over-voltage situations, it is generally advised to go no more than 110% of the rated voltage on the motor’s nameplate. Similarly, avoid anything less than 90% when undervolting. Electrical overloads are typically caused by:
- Power delivery issues from the main power grid
- Power imbalances in the operating environment or building
- In certain situations where a generator is powering the motor
Since electrical overloads are often beyond one’s control, using an overload device to protect your motors is highly recommended.
Tips on preventing chronic motor overloading
Electric motors get overloaded for a reason, and it is vital to get to the bottom of it as soon as possible. In general, the three keys to preventing future overload incidents are:
1. Checking the motor’s voltage and current for electrical overloads
Ruling out an electrical overload generally involves two steps. The first is testing the motor’s power source input to ensure there are problems with the motor controller or power cable and verifying that its voltage and current match what is stated in the motor’s nameplate ratings or at least within 10% of it. Should the voltage be too high, too low, constantly fluctuating, or the motor is being supplied with too much current, the issue typically lies in either the controller or power source. Alternatively, if the motor is observed to be drawing more current, it may be working with a heavier load, or the power source is insufficient.
2. Evaluating recent changes to operational processes for mechanical overloads
Any change in operational processes may inadvertently cause your motors to work harder without anyone realising it. For instance, a food production company that works with dough may add a new recipe that causes the motors in their mixer machines to work harder, eventually causing a mechanical overload. This means no matter how simple the change, it is best to re-evaluate the entire system to ensure that your motors can handle the new workload.
3. Using an overload protection device
Last, installing an overload protection device is a small but incredibly beneficial investment that safeguards your motors from unexpected overload situations. There are now many options in this regard, such as an overload relay, starter, or variable frequency drive. Choose the ones that best suit your needs and ensure to size them correctly for your equipment.
Understanding the causes of motor breakdowns or overload is vital to prevent it from happening again. Beyond that, learning to recognise the common symptoms and making sure the motor matches the intended application guarantees you will not damage your costly assets. When a motor failure does occur, working with the experts to conduct the necessary servicing, whether it be electrical motor overhauling or rewinding, is the best way to get your equipment back online as soon as possible.