The main signs of an electric motor malfunction are increased vibration, uncharacteristic hum, overheating of the housing, the smell of burnt insulation, sparking in the commutator, loss of power and difficulty starting. Any of these symptoms means that the windings, bearings or magnetic system are already deteriorating inside the machine. The earlier the problem is identified, the cheaper the repair will be and the lower the risk of emergency equipment downtime. In this article, Elektromotors engineers in Tashkent analyze 7 key signs, explain their physical nature and suggest when calling a specialist can no longer be postponed.
Why is it important to catch early symptoms
An industrial electric motor rarely fails suddenly. Before final failure, it almost always “signals” - a change in noise, temperature, current consumption. At production facilities in Tashkent and regions of Uzbekistan, we regularly encounter situations where personnel on duty notice a strange hum or vibration 2-4 weeks before an accident, but do not attach any importance to it. As a result, instead of routinely replacing bearings or tightening the terminal box, you have to do a complete rewinding of the electric motor winding and change the rotor.
Regular diagnostics of electric motors is the cheapest way to control the resource. But even without instruments, an experienced mechanic can identify 90% of problems using the seven signs below.
7 signs that it’s time to repair the engine
1. Increased body vibration
The vibration standard for an asynchronous motor of medium power is 1.8–4.5 mm/s according to ISO 10816 standards. If the housing begins to noticeably “shudder” and the vibration level increases by 1.5–2 times, this indicates an imbalance of the rotor, wear of the bearings, or a weakening of the attachment to the frame. Long-term operation in this mode breaks the bearing seats and destroys the stator winding from friction. The solution is balancing the rotor and checking the foundation.
2. Hum, howl or periodic knocking
A healthy engine operates with a smooth, monotonous fan sound. The appearance of a howling hum at the mains frequency (100 Hz) almost always indicates a turn short circuit or a broken rotor rod. Dry metallic knocking is a sign of destruction of the bearing cage. A grinding sound when cold means that the lubricant has lost its properties and the rings are running dry.
3. Overheating of the housing and bearing units
For most industrial motors of insulation class F, the normal temperature of the housing is up to 80–90 °C, bearings - up to 70 °C. If it is impossible to hold your palm on the body with your hand for more than a second (this is about 60 °C for sensations and 90+ °C in reality), and the engine is running under rated load, the problem is in the winding, cooling or overload. Overheating 10 °C above normal reduces the insulation life by half.
4. Smell of burnt insulation or varnish
The characteristic sweetish-acrid odor is the most alarming sign. It means that the enamel of the wire is already burning, and there are from several hours to several days left before the interturn short circuit. In this case, the engine must be stopped immediately and sent to stator rewinding. Continuing work leads to burnout of the grooves and the need to change the magnetic circuit.
5. Sparking and blackening of the commutator (for DC and commutator machines)
In collector and crane machines, sparking under the brushes is higher than degree 1.5 according to GOST - a reason for urgent intervention. Reasons: brush wear, commutator runout, inter-lamella short circuit, incorrect installation of the brush traverse. Ignoring it will lead to a hole in the manifold or its complete replacement. For crane installations, we recommend looking separately at the service repair of crane electric motors.
6. Power drop and current consumption increase
If a machine or pump begins to “not pull” the previous load, and the ammeter shows a 10–20% excess of the nominal value, there is a hidden process going on inside the engine. Most often, this is an interturn short circuit (some of the turns have fallen out of operation, the efficiency has dropped) or a break in one phase (the motor operates as a single-phase motor, heats up and loses torque). Long-term operation in this mode is guaranteed to lead to complete burnout of the winding.
7. Difficulty starting
The engine takes a long time to accelerate, hums at the start, drops in speed or does not start at all. This is a sign of a broken rotor (for asynchronous machines with a squirrel-cage rotor), sticking starting capacitors, a faulty contactor, or burning of the starting resistance. asynchronous electric motors with a wound rotor have the added problem of wear on slip rings and brushes.
Urgency table: when to stop equipment
| Symptom | Danger level | Acceptable time before repair |
|---|---|---|
| Slight vibration within normal limits +20% | Low | Before scheduled maintenance (1–3 months) |
| Bearing noise, dry knock | Average | 2–4 weeks |
| Case overheating above 90 °C | High | 3–7 days |
| Current increase by 10–20% of the nominal | High | 1–5 days |
| Sparking throughout the collector | High | 1–3 days |
| Smell of burning insulation | Critical | Immediate stop |
| Smoke, crackling, machine knocking out | Emergency | Stop, turn off power, call an engineer |
When to call a repair shop urgently
There are three situations when you can’t wait an hour:
- The smell of burnt insulation combined with darkening of the varnish on the end parts of the winding.
- Protection activation (heater, RCD, differential protection) when trying to start.
- Visible smoke or sparksfrom ventilation grilles or terminal box.
In these cases, the engine must be immediately de-energized and contact urgent repair of electric motors. Attempts to “stick it out until the end of the shift” usually end in burnout of the magnetic circuit and an increase in the cost of repairs by 2–3 times.
Prevention: how to avoid major repairs
- Once a quarter, measure the vibration and temperature of the bearing shields.
- Check the insulation resistance with a megger every six months (the norm is not less than 1 MOhm per 1 kV).
- Change the grease in the bearings according to the manufacturer's instructions - usually every 4000–8000 operating hours.
- Control the symmetry of the phases: voltage imbalance over 2% sharply reduces the service life.
- Clean ventilation grilles from dust - in the conditions of Tashkent and dusty industries, this is critical.
Competent maintenance extends the life of an industrial engine by 1.5–2 times. According to our statistics, regularly serviced cars live up to 15–20 years without major repairs.
Conclusion
Seven signs - vibration, noise, overheating, odor, sparking, loss of power and starting problems - are the language in which the engine communicates impending failure. Train the staff on duty to notice these signals, and you will save tens of hours of downtime and hundreds of thousands of soums on repairs.
Need help? Elektromotors engineers in Tashkent will conduct on-site diagnostics, measure vibration and insulation resistance, and give an opinion on the condition of the equipment. Contact us via the contacts page - we will respond within 15 minutes.