What should I do if the motor gets wet? How to quickly deal with damp motors
What are the maintenance methods for the motor when the motor enters water and damp? In the production site, due to motor selection reasons, storage, improper maintenance, environmental factors, etc., moisture enters the motor to form condensation or the motor directly enters water, which causes the motor insulation resistance to drop and affects the motor's performance Normal use and safe operation. Mainly analyze and introduce the drying methods of squirrel-cage motors that are damp on site under different conditions, focusing on the principle of current drying method and iron loss drying method and on-site application methods.
Small capacity asynchronous motor is damp
Drying method: It is more convenient to disassemble and disassemble the small-capacity asynchronous motor. It can be dried on the spot or disassembled to the maintenance room according to the site environment. Generally, the following two methods can be used to dry the motor.
Generally, small low-voltage asynchronous motors are suitable for external heating and drying of motors. The operation is relatively simple. The principle is to use the radiation, convection and conduction of external heat sources to dry the motors during drying. Generally, there are two methods:
1. Use light bulb (or infrared light bulb), oven for drying, and hot air blower for drying
2. When using a bulb or iodine tungsten lamp to dry, do not get too close to the coil to prevent the coil from being damaged. Safety protection lamps must be used, and the temperature cannot exceed 100°C when using the oven.
Large and medium asynchronous motors are damp
There are several drying methods:
1. Current drying method
The basic principle of the current drying method is to pass low-voltage current into the stator windings of the motor, the rotor is blocked, and the temperature generated by the loss of the motor is used to dry the motor. When drying, the stator and rotor of the motor generate heat at the same time, and the drying speed is faster. Large high and low voltage motors
Note: Calculate the maximum current allocated to each phase of the locked-rotor current, and it should not exceed 50% to 60% of the original rated current, and then you can select the voltage level for drying.
U→Voltage after falling
Iq→Starting current, generally 5～8 times of rated current
Method 1: Directly feed low-voltage three-phase AC power to the stator windings of the motor without pulling out the motor rotor. The stator and rotor of the motor are dried at the same time, which is convenient for on-site implementation. Large motors require a large power supply capacity, which may be restricted by site conditions. 6 kV motor site Generally, 380 V power supply is used for drying. If the motor insulation is low, the rotor can be blocked for drying. If the motor insulation is greater than 0.5 Ω, three-phase AC power can be used for drying.
Method 2: The three-phase windings of the motor are connected in series end to end (or the opposite string can be used to reduce the current). The motor used for 6 outlet ends uses an AC/DC welding machine or a voltage regulator to adjust the current through the motor stator winding to dry the motor. It is suitable for the drying of high and low voltage motors when the on-site power supply capacity is insufficient. When turning on or cutting off the current of the welding machine, the current should first be adjusted to zero to prevent high voltage from damaging the motor insulation. The on-site treatment does not need to extract the motor rotor, which is convenient.
Method 3: Three-phase windings of the motor are connected in parallel (for motors with 6 outlets) or two phases are connected in series and then connected in parallel with another phase (for motors with 3 outlets). Use an AC/DC welding machine or a voltage regulator to adjust the current input The motor stator windings are used to dry the motor.
Example of drying motor by current drying method
Take a model YKK710-10, a motor with a capacity of 2 800 kW, a current of 335 A, and a voltage of 6 kV as an example: the motor is an outdoor motor. During the infrastructure construction period, the motor is ready to be put into trial operation. The insulation resistance is measured on site and the weather is 2 MΩ. Moderate rain, high humidity. After 36 hours of putting in the heater of the motor, the insulation resistance measured about 3 MΩ did not change much. It is prepared to increase the motor current drying method for drying when the original motor is continuously heated.
Implementation method: set up a temporary rain shed around the motor, connect to the site 380 V power supply for drying, take the starting current Iq 7 times the rated current 2 345 A, and use 3+1 core 35 mm2 copper core cable for calculation and measuring equipment: 2 500 One V megohmmeter, one clamp-on ammeter, one infrared thermometer, the junction box of the motor, and the inspection holes on both sides to open a gap, which is conducive to moisture emission. After 12 hours, the insulation resistance stabilized at about 36 MΩ, achieving the purpose of drying. The measured current on site is 146 A, and the temperature is monitored through on-site measurement and DCS screen. The maximum coil temperature is 85℃.
2. Motor iron loss drying method
The basic principle of the iron loss drying method is to wind the excitation coil on the stator winding iron core of the motor, and pass the alternating current to make the stator iron core generate magnetic flux, and use the temperature rise generated by the eddy current loss of the iron core to dry the motor.
Method 1: Wrap the excitation coil on the stator core of the motor (passing through the stator bore), connect it to 380 V (220 V) AC power, and dry the motor insulation. Scope of application: large and medium-sized motors, with extraction of the motor rotor core.
Method 2: Wrap the excitation coil on the motor stator shell, connect to the power supply through an electric welding machine and a voltage regulator, and dry the motor insulation. Scope of application: large and medium-sized motors, which have been installed on site.
Examples of drying treatment methods for motor iron loss
Take a motor of model Y2-355-4 as an example, with a capacity of 250 kW, a voltage of 6 kV, and a current of 30.4 A.
The measurement of the iron core data is: L=56.5 cm, n and Lf take 0, Da=59 cm, De=36 cm, h=tooth height 6.7 cm.
Average diameter of stator core yoke: Dav=(Da-Hc)=(59-4.8)=54.2cm.
If the motor is dried by iron loss drying method, when 220 V, 50 Hz power supply, magnetic density B=1 T, the number of turns of the excitation coil to be wound is 38 turns, and the excitation current is about 9.9 A.
1. The heating and drying of the motor drawn out of the rotor should be carried out in clean air. Clean all parts of the motor before drying.
2. When the motor is dry, the winding temperature of the motor must be lower than the temperature required by its specified insulation class (to ensure safety, it is better to be lower than its specified temperature by 10°C). Generally, the winding temperature is controlled at 70°C to 80°C during drying. Is the best.
3. For motors with excessively humid windings, the direct current drying method cannot be used. Direct current has electrolysis.
4. When using current and iron loss method to dry, the motor shell must have a good grounding wire to prevent electric shock. When using light bulbs or iodine tungsten lamps for baking, you should also take care to prevent electric shock.
5. For enclosed motors, when the rotor is not drawn out to dry, the junction box or inspection hole of the motor should be opened to a certain gap. Small low-voltage motors can also open the motor end cover to a gap to facilitate the moisture distribution in the motor.
6. During the drying process, regularly measure the temperature and insulation resistance of each part of the winding, and make a record. In the initial stage of drying, it is recorded every 15-30 minutes, and the temperature of the motor must be recorded regularly in the following 1-2 hours to prevent damage to the motor due to overheating at a certain point.
7. During drying, the heating temperature should be gradually increased, and the humid motor should be slowly heated to 50～60℃, kept for 3～4 hours, and then gradually increase the temperature.
8. In the initial stage of motor drying, due to the increase of temperature and the emission of moisture, the insulation resistance will decrease, then gradually increase, the rising speed will slow down, and finally reach stability. At a constant temperature, the insulation resistance value will remain above 3～4 h When it does not change, the drying work can end.
9. During the drying process of the motor where the rotor is not drawn out, if the conditions are met, rotate the motor rotor at 180°C regularly to prevent the rotor from being deformed due to uneven heating, and it is also conducive to moisture emission.
In fact, there are many specific methods to dry the motor after it is damp. In the production site, a suitable drying method should be selected according to the specific situation to dry the motor. However, no matter which method is used to dry the motor, it must be noted that the motor temperature cannot exceed its allowable value. New damage to the motor insulation. Pay attention to the safety of equipment and personal protection during the drying period. In the production site, the motor is often required to be put into operation in time and run safely. The southern environment is rainy and humid. To ensure that the motor is not affected by moisture or water. For transportation or safe operation, specific moisture-proof measures should be developed for the motor and attention should be paid to the selection of the motor in a humid environment.