We should all know about DC motors and AC motors. These two motors have existed for a long time; and the emergence of this motor has greatly improved the process of industrialization. As a type of AC motor, the three-phase asynchronous motor has been greatly developed because of its advantages in many aspects. Compared with other types of motors, it has many advantages. At present, the three-phase asynchronous motor has been widely used.
The three-phase asynchronous motor has the characteristics of simple structure, reliable operation, durability, low price, and convenient maintenance. It is a power equipment that converts electrical energy into mechanical energy to supply production machinery to achieve various movements. Most production machinery uses three-phase asynchronous motors as prime movers for towing, such as machine tools, lifting equipment, material transport devices, electric shovels, fans and textile machinery. With the development of agricultural mechanization, the application of three-phase asynchronous motors in the agricultural field is becoming more and more extensive. Some agricultural machinery such as rice milling, oil pressing, and crushing are mostly towed by three-phase asynchronous motors.
The three-phase asynchronous motors of the YS series are suitable for small lathes and are widely used in the transmission of small power equipment because of their low power.
Now let's take a brief look at the torque and speed issues related to three-phase asynchronous motors:
About torque
1. The important reason why the torque of three-phase asynchronous motors is not large is because of the low power factor at startup rather than the low voltage at startup.
2. If the rotor resistance of the three-phase asynchronous motor is increased, the starting torque will increase and the starting current will decrease. (The maximum torque remains unchanged)
3. Overload capacity means that the larger the overload factor, the stronger the overload capacity. Overload factor = maximum torque/rated torque, ranging from 1.8-2.5.
About speed
1. If the resistance of the rotor of the three-phase asynchronous motor is increased when the mechanical load remains unchanged, the speed will decrease.
2. When the power supply is reduced when the mechanical load remains unchanged, the speed of the rotor will also decrease.
3. When the mechanical load of the three-phase asynchronous motor increases during operation, the current of the stator will increase and the speed of the rotor will decrease.
Expansion
1. When selecting a three-phase asynchronous motor, the rated power is an important indicator. The so-called rated power refers to the output mechanical power rather than the electrical power.
2. The rated power is the power supply frequency during operation.
3. Rated voltage refers to the line voltage applied to the stator winding of the three-phase asynchronous motor during operation.
4. Rated current refers to the line current of the stator winding.
In order to ensure the normal operation of the motor, in addition to normal use according to the specifications, regular inspections should be carried out during operation, and maintenance of the three-phase asynchronous motor should be done well, so as to prevent faults and ensure the safe operation of the motor.
If the motor is used in a dusty environment, it is best to clean the dust and sludge on the outside of the base every day. Regularly check the motor terminals, terminal boxes, and terminal screws for looseness and burns.
1. Check the fixed part screws to see if the three-phase asynchronous motor is installed securely; if there is any looseness, tighten it;
2. Check the transmission device for damage and whether it is securely installed;
3. Check whether there are burn marks on the wiring parts of the motor starting equipment and whether the grounding wire is in good condition;
4. After the bearings have been used for a period of time, they should be cleaned and replaced with grease or lubricating oil. The cleaning time should be reasonably arranged according to the working environment and usage of the motor. If the environment is poor and there is a lot of dust, they should be cleaned and replaced frequently;
5. The insulation strength of the insulating material varies with the degree of dryness. It is very important to check the dryness of the motor shaft. The most common is the grounding fault of the winding winding, which is the insulation damage; we should check the insulation resistance during use, and also pay attention to whether the grounding of the motor housing is reliable;
6. After one year of operation, the three-phase asynchronous motor should be overhauled. The purpose is to conduct a thorough and comprehensive inspection of the motor and replace the worn accessories in time.
Doing routine maintenance can help reduce the occurrence of failures and extend the service life of the motor.
The motor is a device that converts electrical energy into mechanical energy. In production and manufacturing, AC motors are mainly used, especially three-phase asynchronous motors. It is widely used in various industries because it has the characteristics of simple structure, durability, reliable operation, and easy maintenance. Here we share the inspection work before starting the three-phase asynchronous motor:
1. The insulation resistance of the newly installed or motor equipment that has been out of use for more than three months should be checked before starting. The measured insulation resistance value is not less than 1MΩ.
2. It is necessary to check whether the fastening screws of the motor are tightened, whether the bearings are short of oil, and whether the wiring of the motor meets the requirements.
3. Check whether the coupling screws and pins are in a tight state, whether the belt connection is intact, whether the tightness is appropriate, whether the unit rotates flexibly, whether there is any jamming, movement and abnormal sound, etc.
4. Check whether the rated current of the fuse meets the requirements and whether the installation is secure.
5. Check whether the wiring of the starting equipment is correct, the flexibility of the starting device, whether the contact point is good, and whether the metal casing of the starting equipment is reliably grounded or zeroed.
6. Check whether the three-phase power supply voltage is normal, whether the voltage is too high or too low, or whether the three-phase voltage is asymmetric.
If there is a problem in any of the above points, it must be solved thoroughly, and the machine can be started only after confirming that the above inspection work is correct.
The starting process of a three-phase asynchronous motor generally takes a few tenths to a few seconds. After power is turned on, the motor speed gradually increases to the rated speed. So what should we pay attention to when starting? Here, we will explain to you the precautions when starting a three-phase asynchronous motor:
1. YS series three-phase asynchronous motors are all full-voltage started, but it should be noted that the full-voltage start is about 5-7 times the rated current, but it should not be done frequently.
2. When the power phase sequence A, B, and C correspond to the terminal block wire posts Ul, V1, and W1 respectively, the direction of the motor is clockwise from the main shaft end.
3. The motor should generally have a thermal protection device. According to the rated current of the motor, adjust the setting value of the protection device.
4. After closing the switch, if the motor does not rotate, the switch should be pulled quickly and decisively to avoid burning the motor.
5. After the motor starts, pay attention to the transmission device, production machinery and line voltage and current. If there is any abnormal phenomenon, it should be stopped immediately to find out the fault and eliminate it before re-closing and starting.
6. According to the technical requirements of the motor, the number of continuous starts of the motor is limited. Generally, the number of continuous starts without load shall not exceed 3 times. The motor shall not be started more than 2 times after long-term operation until it is hot and stopped.
7. When several motors are powered by the same transformer, they cannot be started at the same time. They should be started one by one from large to small.
8. When the frequency of the power supply deviates from the value on the nameplate by more than ±1% or the voltage deviation exceeds -10%, the motor cannot guarantee continuous output power. The motor that works continuously is not allowed to be overloaded by more than 1.05 times.
The above are the matters that need to be paid attention to when starting a three-phase asynchronous motor.
Three-phase asynchronous motors can be divided into cage type and winding type. Cage type rotors are relatively simple in structure, reliable in operation, light in weight and cheap in price. They are widely used in production operations. Their main disadvantage is that they are difficult to adjust in speed. Next, let's learn about the characteristics of three-phase asynchronous motors:
Three-phase asynchronous motors can be divided into inherent mechanical characteristics and assumed mechanical characteristics:
1. Ideal no-load point, the motor is idling without any load, at which time the speed is the largest;
2. Rated operating point, the normal operation of the motor under load;
3. Starting operating point, the moment when the motor is just started, that is, it has not started, and the torque when overcoming the rotor's deadweight;
4. Critical operating point, when the three-phase asynchronous motor is dragging the maximum torque of the load, the speed is also moderate.
Artificial mechanical characteristics
1. Voltage reduction. When the motor is running, if the voltage is reduced too much, its overload capacity and starting torque will be greatly reduced, and the motor may even fail to carry the load or cannot start at all;
2. When the stator circuit is connected to a resistor, the maximum torque is larger than the original one. When the rotor circuit is connected to a resistor or the stator power supply frequency is changed, the starting torque will increase and the maximum torque will remain unchanged.
