I have seen many electric motors burn out accidents in my work. When an electric motor burnout, it affect production and safety.
As an electrical engineer, I know very well that, one of the most important tasks of electric engineers is to keep all assets working safely and properly. What causes an electric motor to burn out? This is question I will answer it in details.
Motor burned out meaning
Motor burned out means the windings of the motor get short circuited and get damaged, this may cause the winding to smoke and go black in color like a real burn out with fire. In fact, if the motor is large enough and the protection devices failed to stop it, the windings can catch fire.
In my work, we face this fire catching situation with electrical generators, the windings catch fire and we need fire extinguisher to put it out. I will show you a photo of one burnt out generator below in this article.
What causes Electric Motor to Burnout?
One of the vital issues that leap to mind is electric motor burnout after exploring electric motor problems and solutions. The reasons behind electric motor failure are not only because of electrical issues but mechanical too. In this article, we will discuss both types to help you identify electric motor problems in the future.
Common causes of electric motor failure
Excessive current running through the motor winding to maintain torque due to high mechanical load leads to motor overload. Excessive load on the motor is the main reason for overcurrent.
When the motor draw current higher than motor full load current causes motor overheating, resulting in motor winding insulation failure and then burnout. 30% of electric motor failures occur due to overloading.
Locked shaft and single phasing are examples that can cause motor overcurrent.
You can install overload relays to protect motor against overcurrent. Take in to account that on starting motor current usually rises to six times the full load current rating.Its important to override this instant rise when choosing the motor protection device.
When the motor achieves its operating speed, the current becomes stable. The electric motors are designed to withstand the overcurrent condition for a short time at the starting. If the motor remains in this overcurrent condition for any reason, it will burn out if the protection device failed.
Overcurrent protection avoids motor overload by interrupting the voltage supply. The circuit breakers and fuses can protect the motor from overload, ground faults, or short circuits.
However, as the motors draws more current while starting, that’s why fuses need to be rated accordingly (This is why fuses and circuit breakers has an operating curve and delay time). Therefore, fuses would fail to protect the motor at normal operating conditions.
Advanced overload relays are used to protect motors during temporary overloads for a specific period during startup. If the overload continues and exceeds the set time, the relay will break the circuit and protect the motor. After that, you can easily reset the relay, making sure the overload condition is cleared.
Multiple factors such as poor low voltage, voltage imbalance, or a high environmental temperature lead to overheating. 50% of insulation life reduces on every 10°C of motor temperature rise. This temperature rise causes winding insulation breakdown, the insulation breakdown causes a short circuit that burns the electric motor if the protection device fail to operate.
Its important to keep the motor cool during its normal operation. Here under some tips to keep any motor cool
How to keep the motor cool?
- Keeping the motor operating in cool condition and minimize the overheating problem, you should select a perfect installation location where the motor gets enough space to exhaust heat.
- Keep the ventilation openings of the motor clear.
- Consistently monitor the performance and temperature of the motor.
- Check the cooling fan operation and make sure its blades are not broken.
- If your motor gets hot upon considering all potential issues, then it must have any internal problem.
I use thermal imaging camera to detect motor temperature rise. In many cases, I find plastic bags closing the fan cooling openings, and of course the motor temperature becomes higher. Once I clear the cooling fan openings and remove any plastic bags, the motor gets cool again.
A 3% voltage imbalance results in an 18% temperature increase leading to overheating. Although, phase voltage imbalance should not be greater than 1%. In addition, the voltage unbalance that compels a three-phase motor to operate on two phases can cause the motor to burn out.
Variable frequency drive (VFD) fixes the voltage imbalance, overload, and short cycling faults.
Moreover, the relay is structured to monitor the voltage and current of three phases separately. The relay utilizes the input values to detect current unbalance, voltage unbalance, low voltage, high voltage, overcurrent, and undercurrent.
It is challenging to control, and one of the most common causes of motor burnout is low resistance. This is caused by damage to insulation due to corrosion, physical damage, aging or overheating.
In addition, low resistance because of insufficient isolation among conductors leads to short circuits and leakages, resulting in motor failure. To avoid low resistance, regular inspection of insulation is required.
I have written a detailed article about How To Megger A Motor, I Recommend To Have A Look At It.
Physical and environmental conditions
It is essential for motors to withstand physical and environmental effects for proper operation.
Chemicals and dust contamination causes motor failure. The dirt particles which get into the motor can originate vibrations, belt tension, or misalignment by denting bearing balls and raceways.
Moreover, these particles can jam the cooling fan, which disturbs the temperature regulation and causes overheating.
An environment containing high temperatures or moisture produces serious issues that should be avoided.
For example, while installing and maintaining an electric motor, you should consider the following causes of motor burnout.
- Improper lubrication not only can result in bearing issues but also can affect winding with grease.
- Condensation because of moisture can produce rust in the motor, causing rotor jam.
- A completely covered enclosure of the motor can overheat.
Misalignment occurs when the motor drive shaft or the component that couples the electric motor with load is not correctly aligned. Many professionals believe that flexible coupling reduces misalignment.
However, a misaligned shaft with a flexible coupling transmits damaging forces to the motor and increases the mechanical load, leading to overload.
Its worth to mention that motor alignment is the responsibility of mechanical crew, but it affects the electric motor. So its important to cooperate with mechanical crew in this part.
Wrong connection and operation
Its important to double check motor nameplate data before connecting it to the power supply.
I have written a detailed article about motor name plate data and specs, you can check it here:motor nameplate data
The following items on the name plate are important:
- Motor nominal voltage. Over and under voltage can cause the motor to bur out.
- Motor connection type (Star or delta).
- Motor full load current, to connect the motor to a proper protection devices.
- Motor duty cycle, make sure that the motor is suitable to the operating periods.
Water inside motors
My workplace is a desert, we have induction motors outside in heavy rain, dust and moisture. Some days, the weather gets heavy foggy.
If the motor is not enclosed properly, the fog enters into it and decreases the winding insulation resistance and can cause the motor to burn out. So, large motors have space heaters to protect the motor from moisture while it is not working.
Space heaters are small heaters installed inside the motor and works when the motor is off. Space heaters don’t work while the motor is working, In fact there is no need for the space heater in this case because the motor winding produces heat in normal condition.
Read my other detailed article about motors in wet locations for more information.
How to Check Electric Motor?
How to check electric motor is an important tech. skill. Whenever a motor stops working, it is difficult to know the reason of its failure by just looking. Many times a physically new looking motor stops working.
Electric Motor Common Failures
I have seen many electric motors failures. Many of them are listed below:
- Bearing failure, causing damage in the motor body.
- Burning winding due to moisture and fog.
- Burning winding due to protection circuit failure.
- Damaged cooling fan.
- Over loaded motors. Causing circuit breaker tripping.
- Wrong connection of the motor, For example connecting a star motor on delta voltage.
- Winding burning due to internal insulation failure.
- Misalignment. The motor drive end shaft is not properly alignment with the load.
When you are about to check a motor, Based on the fault you start the check sequence.
Motor Quick Checklist Guide
- Check motor data on the name plate, Check voltage, current, insulation class, service factor, power factor and motor power.
- Record all the data above.
- Visual check the motor body for any abnormal corrosion, rust or breaks.
- Check the earthing connection of the motor.
- Check the protection circuit elements and make sure all are well designed for the motor.
- Listen carefully to the motor while it is running, It should rotate quietly. If the bearing has an issue there will be abnormal sound.
- Check the motor temperature using laser temperature detector. Compare it with the insulation class of the motor. I will discuss it below.
- Make sure the voltage on the motor matches the nameplate voltage.
- Use clamp meter to check the motor current.
I highly recommend using My free android application Fast Electrical Calculator for current, power conversion and many electrical calculations. Install the app and make the calculations very easy.
Now let’s discuss some points of how to check electric motor in details.
Check Motor Name Plate Data
Check the nameplate data, and make sure its match the source.
- Make sure the operating voltage of the motor is matched to that of the source.
- The current of the motor should be less than or equal to the nameplate current. Any over current situation should be deeply inspected to find the cause of it.
- Also the frequency should match the source.
If the Motor Can’t Start
The first thing to check is the circuit breaker of the motor. If it is tripped then, you should try to connect it but keep every one away of the motor body, if the breaker tripped again instantly then the motor or its cable has a short circuit.
If the circuit breaker is not tripped then use your AVO meter and check the voltage on the motor. If there is no voltage, then check the voltage of the source.
If the circuit breaker and the voltage on the circuit breaker side are good, Then the next step is to check the cable from the circuit breaker to the motor.
Check the cable for any short circuit or any cuts. You can do so using the continuity test of the AVO meter. But make sure to disconnect the power.
Other reason is the bearing, if it is damaged the motor can stuck.
The Circuit Breaker Trips
If the breaker trips instantly, then there is a short circuit in the motor winding or in the cable.
If the breaker trips after running for a short period, then the breaker can be damaged or the motor is over loaded. Check the current of the motor.
Read also my articles:
- bad circuit breaker, Signs, Causes and Repair.
- 5 Reasons to make breaker tripping. What should you do?
Fog And Moisture
High foggy weather is destructive to the motor if it is not designed to operate in this weather.
I have seen many damaged motors that the foggy weather destroyed. In fact not only motors but also generators. see the below damaged generator image.
Make sure the motor IP is designed for the outdoor work.
Read my article : IP Rating
Check Motor Temperature Rise
Motors operation produces heat generation. The temperature rise has allowable limits. Temperature class is the main information that give you an indication about if the motor is overheated.
Check the motor temperature using a laser detector or thermal imaging camera.Many reasons can make the motor get overheated. some are listed below:
- Under voltage.
- Bad bearing.
- Continuous operation for non continuous duty motors.
How to Check Electric Motor Outside?
There are some conditions on the outside of the motor which can decrease its life. If any of the following issues appears on the outside of a motor, it may be the main reason of the motor failure.
- Broken mounting holes
- Darkened paint or darkened body color. It indicates overheating or burning inside.
- Dirt or other matter pulled into the winding due to breaking or any opening in the housing.
How to Check Electric Motor Bearings?
I can say that bearing failure is one of the most common motor faults I face in my work every day as an electrical engineer.
Many times the motor stops working due to fault in the bearings. The bearings allow the shaft to rotate freely inside the motor casing. They are located at both ends of the motor or sometimes hiding inside casing from one end in case of DC motors. They are also called as the “end bells” or “bell housings”.
The failure of the bearing happens gradually, So its important to check the motor sound while it is running. Any abnormal hard sound may indicate a bearing failure.
Rotational Movement of Bearings
To check the bearings place the motor on a solid surface and then spin the shaft. Listen carefully if there is any indication voice of rubbing or feel if it is difficult to rotate the shaft or the shaft is not rotating freely.
Also listen if there are other sounds coming on rotating the shaft with hand. If the rotor is good, it should spin quietly and freely.
Slight linear movement
Push the bearings in and out, feel carefully if there is a slight movement. It will be better for the motor to rotate freely otherwise if there is no movement during pushing and pulling it makes the rotation of the shaft difficult and heat them. It may also cause the failure of motor.
How to Check Electric Motor Windings?
Mostly the electric motors fail due to the problems in their winding. There are many issues which can occur with the motor winding. Let’s discuss in steps to clearly answer the question how to check electric motor.
Check the winding for short circuits
Sometimes the winding inside the motor may be disturbed and short circuited due to some reasons. In order to know how to check the electric motor if the winding is short circuited, the main signs are opened fuse, tripping of the circuit breaker instantly after turning on the switch. When the short circuit occurs in winding the motor will fail and stop working.
Checking resistance value
To do this task set the ohmmeter to the resistance. Choose the highest scale and touch both probes with each other to zero the meter. Then locate the ground screw of the motor and connect the test probe with it.
After this connect the other test probe to each of the motor leads one by one. In ideal situation, the meter should move off the higher resistance. Make sure your hands are not touching to any metal during this process otherwise the reading will not be accurate.
The value of the resistance will depend on the type of motor you are testing but in most cases the motors have low resistances. If the resistance is accurate the resistance will be several hundred thousand ohms (500,000). It is acceptable resistance but higher numbers are more desirable.
Read also my article : How to megger a motor?
Checking for open windings
While checking the resistance with ohm meter consult the wiring diagram of the motor to make sure that meter is measuring across each winding. Check the resistance of each part by zeroing the meter again and again and by connecting to each lead.
Make sure the meter will show the low resistance. For a normal working motor low resistance are accepted.
If the resistance is high then the normal cases it means that there will be a potential problem inside the wiring of the motor winding. Make sure that your hands are not touching the probes of the ohm meter.
Look at the wires deeply, if the wires are blown due to some reason their color will be darkened than normal wires. It may also be happened that the insulation inside the motor is removed during the work and windings are attached to the frame. In all these conditions the motor winding will stop working and cause motor failure.
Check Motor Cooling Fan
Some electric motors are totally closed and cooled with the help of fan (TEFC). This fan is attached to the one end bell of the motor. The fan blades are inside the metal casing.
Make sure the fan is fastened, and is not clogged with dirt. The fan may also broken when too much debris or dirt come in the metal casing and try to stop the fan. If fan stops the motor will be heated and it will cause the motor failure.
What is Short Circuit Fault in Motor?
A short circuit in a motor is a fault condition that happens when an energized conductor of the motor winding touches each other or the motor body.
The voltage in the system will most likely drop short circuit in a motor form, and a stable voltage source will cease to exist. By functioning as a power source, the magnetic field revolving inside the rotor attempts to maintain the lower voltage scenario.
The motor is now supplying additional current to the damaged electrical system due to a short circuit fault in the motor.
Read also my other article Motor temperature rise.
Also you can check out this article Electric motors, 5 Answers.
How You Can Tell if Motor is Short Circuited?
To determine whether there are short or open wounds in motor, you should check the T1-T2 connection as well as the T2 and T3, then the T1-T3 connection. I
t is important to note that certain motors feature different markings, such as the U to V, V to W, and W to U. You will find the configuration of your motor in the user’s manual.
Generally, the goal is to get an ohm reading between .3 to 2 Ohms. If you get zero, you must rerun the test and check if you’ve gotten zero again. A reading of 0 indicates you’ve got a short in your phases.
A shortfall means that the wires are cut off in length to the ground. This typically causes the breaking of the wire. If the reading you’re getting is higher than 2, you could have an open wound. An open winding is simply a sign that there’s a damaged wire.
It is not surprising that the windings of electric motors are essential for their mechanical functions. It is recommended to regularly check your windings to see if they are worn out, but you also should evaluate their resistance. In the first place, you’re going to require an instrument to test the windings.
In the beginning, set the multimeter’s reading to the ohms. You can then examine the motor’s wires and terminal. The windings should be tested to determine if there is a “short to ground” in the circuit.
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