An electric motor is a machine that converts electrical energy into mechanical energy. It is used in a wide variety of applications, including fans, pumps, conveyor belts, and elevators. Electric Motors can be either AC (alternating current) or DC (direct current).
What is a high motor temperature?
A high motor temperature is any temperature that is above the motor's rated temperature.
The rated temperature is the maximum temperature that the motor can safely operate at. If the motor's temperature exceeds the rated temperature, it can damage the electric motor's insulation and windings, which can lead to premature failure.
Why is it important to keep motor temperatures low?
It is important to keep motor temperatures low to prevent premature failure. When a motor's temperature exceeds the rated temperature, the insulation and windings can be damaged. This damage can lead to a number of problems, including:
Please check the following tips for the Reasons and solutions for high motor temperature;
1.What temperature can a general motor work normally? What is the maximum temperature that a motor can withstand?”
Answer: If the temperature of the motor cover is measured to be more than 25 degrees above the ambient temperature, it indicates that the temperature rise of the motor has exceeded the normal range.
The temperature rise of a general motor should be below 20 degrees. The coil of a general motor is wound by enameled wire, and when the temperature is higher than about 150 degrees, its enamel film will fall off due to excessive temperature, causing a short circuit of the coil.
When the coil temperature is above 150 degrees, the temperature displayed on the motor casing is about 100 degrees. Therefore, if its casing temperature is used as a basis, the maximum temperature that the motor can withstand is 100 degrees.
The temperature of the motor should be below 20 degrees Celsius.
That is, if the temperature of the end cover of the motor exceeds the ambient temperature by more than 20 degrees Celsius, but what causes the motor to heat up more than 20 degrees Celsius?
Answer: The direct cause of motor heating is due to large current. Generally, it may be caused by coil short circuit or open circuit, demagnetization of magnetic steel or low motor efficiency. In normal cases, it is caused by long-term large current operation of the motor.
What causes motors to heat up? What is this process like?
Answer: When the motor runs under load, there is power loss inside the motor, which will eventually become heat energy. This will cause the motor temperature to rise and exceed the ambient temperature.
The value by which the motor temperature exceeds the ambient temperature is called “temperature rise.”
Once there is a temperature rise, the motor will dissipate heat to its surroundings; The higher the temperature, the faster it dissipates heat.
When the amount of heat emitted by a motor per unit time equals that dissipated, its temperature no longer increases but remains at a stable and constant temperature, which is in a state of balance between heating and cooling.
What is generally considered an allowable temperature rise for motors? Which part of a motor’s temperature rise has the greatest impact? How is it defined?
Answer: When a motor runs under load and carries as much load as possible to maximize its output power (without considering mechanical strength),
its output power should be as large as possible and its loss power should be as large as possible. The higher its output power and loss power are, the higher its temperature will be.
We know that insulation materials are weakest in terms of heat resistance inside motors, such as enameled wire. There is a limit to their heat resistance.
Within this limit, their physical, chemical, mechanical and electrical properties are very stable and their working life is generally about 20 years.
Beyond this limit, their life span will be drastically shortened or even burned out. This limit on temperature resistance is called “allowable temperature” for insulation materials.
The allowable temperature for insulation materials is also called “allowable temperature” for motors; The life span of insulation materials generally corresponds to that of motors.
High temperatures are one of the common types of faults in electric motors. So what causes electric motors to overheat?
Below are common reasons for high electric motor temperatures and their solutions:
When an electric motor’s instantaneous voltage exceeds its rated voltage by more than 10%, or when an electric motor’s instantaneous voltage drops below its rated voltage by more than 5%, it will cause an electric motor to generate heat and increase in temperature under rated load. In such cases, check and adjust voltage.
If the three-phase power supply voltage of the motor is unbalanced, it will also cause the motor to heat up.
This is because when the unbalance degree of the three-phase power supply voltage exceeds 5%, it will cause the unbalance of the three-phase current. The solution is to check and adjust the voltage.
Contact problems with the power switch of the motor and one-phase fuse breaking will cause phase loss operation, which will cause the temperature of the motor to rise. The solution is to repair or replace damaged parts.
Wiring errors in the winding of the motor will cause overheating of the motor running under rated load. The solution is to correct the wiring errors of the winding.
Inter-turn or inter-phase short circuit or grounding of the stator winding of the motor will increase the current of the motor and cause temperature rise. The solution is to add central insulation or directly replace the winding.
The cage rotor of the motor is broken or the winding rotor coil joint is loosened, which will cause the current of the maintenance network to increase and produce heating, the solution is to weld the patch or replace the rotor.
When the bearing of the motor is worn out seriously, it will produce large rubbing and heat, the solution is to check whether the bearing is loose and whether the stator and rotor are poorly matched.
The overheating problem can be solved by reducing the load or replacing the high power motor.
The motor starts too frequently, the temperature of the environment is too high, the ventilation is not good, etc. will also lead to the high temperature of the motor, reduce the number of starts, reduce the ambient temperature, ensure that the air duct is smooth, eliminate dust and oil, keep the fan running well can help solve similar overheating problems.
If the motor is running, if the current does not exceed the rated current of the motor, it means there is basically nothing wrong with the circuit. If the original load is not changed, test whether the voltage is at the rated voltage, generally 380V is plus or minus 5% normal. See if the ambient temperature is too high. Whether the bearing is short of oil. Whether the heat sink fan is damaged.
(1) The load is too large. Reduce the load or replace the motor with a larger capacity.
(2) Two-phase operation. Check whether the fuse is fused and the contact point of the switch is in good contact, and troubleshoot.
(3) The motor air duct is blocked. The air duct should be cleared of dust or grease.
(4) The ambient temperature rises. Take cooling measures.
(5) Short circuit between turns or phases of stator winding. Use megohmmeter or multimeter to check the insulation resistance between two-phase winding; use current balance method to check the three-phase winding current, the phase with high current is short-circuit phase, also use short-circuit scout to check whether the winding turns are short-circuit.
(6) Stator winding grounding. Available multimeter or indicator check, the resistance is zero for the grounding phase.
(7) The power supply voltage is too low or too high. Check the power supply voltage at the input of the motor with the voltage file of multimeter or voltmeter.
Supplementary motor hot reasons.
1, bearing work is not normal, must cause the electric motor hot Whether the bearings work normally can be judged by hearing and temperature experience. Can be hand or thermometer to detect the bearing end to determine whether the temperature is within the normal range; can also be used to listen to the rod (copper rod) contact bearing box, if you hear the impact sound, said there may be one or several ball rolling broken, if you hear a sibilant sound, that is, the bearing lubricant is insufficient, the motor should be in operation 3,000 hours ~ 5,000 hours or so for a grease.
2, the power supply voltage is high, the excitation current increases, the motor will overheat Excessive voltage will endanger the insulation of the motor, so that it is at risk of breakdown.
When the supply voltage is too low, the electromagnetic torque will be reduced, if the load pitch is not reduced, the rotor speed is too low, then the increase in the rate of rotation will cause the motor to overload and heat up, and a long time overload will affect the life of the motor.
When the three-phase voltage is not symmetrical, that is, when the voltage of one phase is high or low, it will lead to a phase of excessive current, the motor will heat up, and at the same time, the reduction of the rotation distance will issue a "humming" sound, which will damage the windings over time.
In short, no matter the voltage is too high, too low or voltage asymmetry will make the current increase, motor heating and damage to the motor.
Therefore, in accordance with national standards, the motor power supply voltage should not exceed the rated value of ± 5% of the change, the motor output power can maintain the rated value.
Electric motor power supply voltage is not allowed to exceed the rated value of ± 10%, the difference between the three-phase power supply voltage should not exceed the rated value of ± 5%.
3, the abnormal vibration or noise of the motor is likely to cause the motor to heat up This situation belongs to the vibration caused by the motor itself, most of them are due to bad dynamic balance of the rotor, as well as poor bearing, bending of the rotor, end cap, seat, rotor different axis, loose fasteners or motor installation foundation is not level, installation is not in place, may also be the mechanical end passed over, should be excluded for the specific situation.
4, the air gap between the motor stator and rotor is very small, easily lead to stator and rotor touch each other In the small and medium-sized motor, the air gap is generally 0.2mm ~ 1.5mm.
When the air gap is large, the excitation current is required to be large, thus affecting the power factor of the motor; air gap is too small, the rotor may occur friction or collision.
Generally due to bearing serious over poor and end cover bore wear deformation, so that the seat, end cover, rotor three different axis caused by sweeping, it is easy to make the motor hot or even burned.
If you find the bearing wear should be replaced in a timely manner, the end cover for replacement or brush plating treatment, a relatively simple method of treatment is to the end cover set.
5, almost more than half of the motor burned are caused by the motor is out of phase operation Lack of phase often causes the motor can not run or start after the slow speed, or rotating powerless current increase "buzz" phenomenon.
If the load on the shaft does not change, the motor is in a serious overload state, the stator current will reach 2 times the rated value or even higher. Within a short time, the motor will be hot or even burned.
The main causes of out-of-phase operation are as follows:
Power line due to other equipment failure caused by a phase power failure, connected to the line of other three-phase equipment will be out of phase operation.
Circuit breaker or contactor a phase due to partial voltage burn or poor contact caused by the lack of phase. Electric motor connected into the line due to aging, wear and other reasons caused by the lack of phase. Motor a phase winding break, or junction box in a phase connector loose.
6, material leakage into the motor inside, so that the motor insulation is reduced, so that the allowable temperature rise of the motor is reduced Solid materials or dust from the junction box into the motor inside, it will reach the motor stator, rotor air gap between, resulting in motor sweeping, until the wear motor winding insulation.
So that the motor damage or scrap. If the liquid and gas medium leak into the motor, will directly cause the motor insulation drop and trip.
General liquid and gas leaks have the following forms of expression:
Various containers and transport piping leakage, pump body seal leakage, flushing equipment and ground . Mechanical oil leaks into the motor from the front bearing box gap.
With the motor connected to the reducer and other oil seal wear, mechanical lubricating oil along the motor shaft into the motor, after accumulating inside the motor, dissolve the motor insulation paint, so that the motor insulation performance gradually reduced.
7, winding short circuit, turn-to-turn short circuit, phase to phase short circuit and winding disconnection.
After the insulation between two adjacent wires in the winding is damaged, so that the two conductors touch each other, known as winding short circuit.
A winding short circuit occurring in the same winding is called an inter-turn short circuit.
A short circuit in the winding occurring between two phases of the winding is called a phase-to-phase short circuit.
No matter which one it is, it will increase the current in one or both phases, cause local heating and damage the motor by aging the insulation.
A winding break is a fault caused by the stator or rotor winding of the motor touching off or burning off.
Whether it is a short circuit or broken winding may cause the motor to heat up or even burn. Therefore, the occurrence of this situation must immediately stop processing.
8, other non-mechanical electrical failure causes Other non-mechanical electrical failure causes the motor temperature rise, when serious may also lead to motor failure. Such as high ambient temperature, the motor lack of fan, fan incomplete or lack of fan cover.
This situation must be forced cooling to ensure ventilation or replace the fan blades, etc., otherwise the normal operation of the motor can not be guaranteed.
In order to be able to use the correct method of motor troubleshooting, it is necessary to be familiar with the characteristics and causes of common motor failures, seize the key factors, regular inspection and maintenance, so as to take fewer detours, save time, troubleshoot as soon as possible, so that the motor is in normal operating condition. Thus to ensure normal production in the workshop.
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