1 Daily maintenance experience accumulation
For motor products, on the one hand, customers should be made aware of the maintenance and care items during the operation of the motor through appropriate means; on the other hand, experience and common sense should be accumulated continuously. ● Usually, the product maintenance instructions or user manuals have detailed explanations of the maintenance and care items of the motor. Regular on-site inspections and problem resolution are effective ways to continuously accumulate experience and common sense and avoid major quality accidents. ● When patrolling and checking the operation of the motor, you can touch the motor housing with your hand to determine whether the motor is overheated. The housing temperature of a normally operating motor will not be too high, generally between 40℃ and 50℃, and will not be too hot; if it is hot enough to burn your hand, the temperature rise of the motor may be too high. ● A more accurate method of measuring the motor temperature is to insert a thermometer into the motor ring hole (the hole can be sealed with cotton yarn or cotton) to measure. The temperature measured by the thermometer is generally 10-15℃ lower than the hottest point temperature of the winding (experience value). The temperature of the hottest point is calculated based on the measured temperature. During normal operation, it should not exceed the maximum allowable temperature specified by the insulation grade of the motor.
2 Causes of overheating of motors
There are many reasons for overheating of motors. The power supply, the motor itself, the load, the working environment and the ventilation and heat dissipation conditions can all cause the motor to overheat. ●Power supply quality (1) The power supply voltage is higher than the specified range (+10%), which makes the core magnetic flux density too large, the iron loss increases and overheats; it also increases the excitation current, resulting in an increase in winding temperature. (2) The power supply voltage is too low (-5%). Under the condition of unchanged load, the three-phase winding current increases and overheats. (3) The three-phase power supply is missing a phase, and the motor runs in a missing phase and overheats. (4) The three-phase voltage imbalance exceeds the specified range (5%), which causes the three-phase power supply to be unbalanced and the motor to generate additional heat. (5) The power supply frequency is too low, resulting in a decrease in motor speed and insufficient output, but the load remains unchanged, the winding current increases, and the motor overheats.
●The motor itself (1) The △ shape is mistakenly connected to the Y shape or the Y shape is mistakenly connected to the △ shape, and the motor winding is overheated. (2) The winding phases or turns are short-circuited or grounded, resulting in an increase in the winding current and an imbalance in the three-phase current. (3) Some branches in the winding parallel branches are broken, causing an imbalance in the three-phase current, and the windings of the branches that are not broken are overloaded and heated. (4) The stator and rotor are rubbed and heated. (5) The squirrel cage rotor bars are broken, or the winding of the wound rotor is broken. The motor output is insufficient and heats up. (6) The motor bearings are overheated.
● Load (1) The motor is overloaded for a long time. (2) The motor is started too frequently and the starting time is too long. (3) The towed machine fails, causing the motor output to increase, or the motor is stuck and cannot rotate. ● Environment and ventilation and heat dissipation (1) The ambient temperature is higher than 35°C and the air inlet is overheated. (2) There is too much dust inside the machine, which is not conducive to heat dissipation. (3) The wind hood or wind shield inside the machine is not installed, and the air path is blocked. (4) The fan is damaged, not installed or installed upside down. (5) There are too many missing heat sinks on the enclosed motor housing, and the protective motor air duct is blocked.