A Brief Discussion on the Accumulation of Motor Maintenance Experience
Accumulate daily maintenance experience
For electric motor products, on the one hand, customers should be made aware of the maintenance and upkeep items during the operation of the motor through appropriate means; On the other hand, we should continuously accumulate experience and common sense.
Usually, product maintenance manuals or user manuals provide detailed explanations for the maintenance and upkeep of motors. Regular on-site inspections and problem resolution are effective ways to continuously accumulate experience and knowledge, and avoid major quality accidents.
When inspecting and checking the operation of the motor, you can touch the motor casing with your hand to determine if the motor is overheating. The temperature of the casing of a normally running electric motor is not too high, usually between 40 ℃ and 50 ℃, so as not to be excessively hot to the touch; If it burns your hands, the temperature rise of the electric motor may be too high.
A more accurate method for measuring motor temperature is to insert a thermometer (the hole can be sealed with cotton yarn or cotton) into the motor lifting ring hole to measure. The temperature measured by the thermometer is generally 10-15 ℃ lower than the hottest point temperature of the winding (empirical value). Based on the measured temperature, the hottest point temperature should be calculated. During normal operation, it should not exceed the maximum allowable temperature specified by the insulation level of the motor.
2 Reasons for High Temperature of Electric Motor
The causes of high temperature in electric motors are multifaceted, including power supply, motor itself, load, working environment, and ventilation and heat dissipation.
Power quality
(1) The power supply voltage is higher than the specified range (+10%), causing excessive magnetic flux density in the iron core, increasing iron loss and overheating; It also increases the excitation current, leading to an increase in winding temperature.
(2) The power supply voltage is too low (1.5%), and under constant load, the three-phase winding current increases and overheats.
(3) The three-phase power supply is out of phase, and the motor runs out of phase and overheats.
(4) The three-phase voltage imbalance exceeds the specified limit (5%), causing an imbalance in the three-phase power supply and additional heating of the motor.
(5) The power frequency is too low, resulting in a decrease in motor speed and insufficient output, but the load remains unchanged, winding current increases, and the motor overheats.
The electric motor itself
(1) Accidentally connecting the △ shape to the Y shape or the Y shape to the △ shape can cause overheating of the motor winding.
(2) Short circuits or grounding between windings can cause an increase in winding current and an imbalance in three-phase current.
(3) Some branches in the parallel winding branch are broken, causing three-phase current imbalance, and the winding of the unconnected branch is overloaded and heats up.
(4) The stator and rotor rub against each other and generate heat.
(5) The conductor of the squirrel cage rotor is broken, or the winding of the wound rotor is disconnected. The motor generates heat due to insufficient output.
(6) The motor bearings are overheated.
load
(1) The electric motor is overloaded for a long time.
(2) The motor starts too frequently and takes too long to start.
(3) Mechanical failure caused by dragging, resulting in an increase in motor output or being stuck and unable to rotate.
Environment and ventilation heat dissipation
(1) The ambient temperature is above 35 ℃, and the inlet air is overheated.
(2) Excessive dust inside the machine is not conducive to heat dissipation.
(3) The windshield or internal wind deflector is not installed, resulting in poor airflow.
(4) The fan is damaged, not installed or installed backwards.
(5) The enclosed motor housing has too many missing heat sinks, and the protective motor air duct is blocked.
