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Seven Speed Regulation Methods of Three-phase Asynchronous Motor
Update time:2019-04-08 19:41:00Clicks:1252
Today, we introduce seven speed regulation methods and their characteristics of three-phase asynchronous motors, and point out their applicable occasions and conditions.
The speed formula of three-phase asynchronous motor is: n=60f/p(1-s)
Today, we introduce seven speed regulation methods and their characteristics of three-phase asynchronous motors, and point out their applicable occasions and conditions.
The speed formula of three-phase asynchronous motor is: n=60f/p(1-s)
From the above formula, it can be seen that changing the power supply frequency f, the pole logarithm P and slip s of the motor can be too much to the intention of changing the speed.
Classification:
1. In terms of the essence of speed regulation, different methods of speed regulation are nothing more than changing the synchronous speed of the communication motor or not changing the synchronous speed.
The speed regulation methods without changing synchronous speed are as follows.
1) Speed Regulation of Rotor String Resistance of Winding Motor
2) Chopper speed regulation
3) Cascade Speed Regulation and Application of Electromagnetic Slip Clutch
4) Hydraulic Coupling
5) Oil film clutch and other speed regulation
The speed regulation method without changing synchronous speed is widely used in production machinery.
2. Multi-speed motor with changing stator pole logarithm and synchronous speed, variable frequency speed regulation with or without commutation motor speed regulation by changing stator voltage and frequency, etc.
3. From the viewpoint of energy consumption in speed regulation, there are two ways: high-efficiency speed regulation and low-efficiency speed regulation: high-efficiency speed regulation means that the slip rate is constant at the time, so there is no slip loss, such as multi-speed motor, frequency conversion speed regulation and speed regulation methods that can recover slip loss (such as cascade speed regulation). The speed regulation method with slip loss belongs to low-efficiency speed regulation, such as rotor series resistance speed regulation method, energy loss in the rotor circuit; electromagnetic clutch speed regulation method, energy loss in the clutch coil; hydraulic coupling speed regulation, energy loss in the oil of hydraulic coupling. Generally speaking, slip loss increases with the expansion of speed regulation scale. If the speed regulation scale is small, the energy loss is very small.
Seven Speed Regulation Methods of Three-phase Asynchronous Motor
I. Variable Pole Logarithmic Speed Regulation Method
This kind of speed regulation method is to change the stator pole number of the cage motor by changing the connection mode of the stator winding to achieve the purpose of speed regulation, which is characterized by its rigid mechanical characteristics, good stability, no slip loss, high efficiency, simple wiring, convenient control and low price, stepped speed regulation, large gradient difference, and no smooth speed regulation; it can be used with voltage regulation speed regulation and electromagnetic slip clutch. The smooth speed regulation characteristic with high efficiency can be obtained by using it together.
This method is suitable for production machinery without stepless speed regulation, such as metal cutting machine tools, lifts, lifting equipment, fans, pumps, etc.
2. Frequency Conversion Speed Regulation Method
Frequency conversion speed regulation is a method of changing the frequency of the stator power supply of the motor, thereby changing its synchronous speed. The main equipment of the variable frequency speed control system is the converter which provides the variable frequency power supply. The converter can be divided into AC-DC-AC converter and AC-AC converter. At present, most of the domestic converters are AC-DC-AC converter. Its characteristics are high efficiency, no additional loss in the process of speed regulation; wide application range, can be used for cage asynchronous motor; wide speed regulation range, hard characteristics, high accuracy; complex technology, high cost, difficult maintenance and inspection.
This method is suitable for high precision and good speed regulation performance occasions.
3. Cascade Speed Regulation Method
Cascade speed regulation refers to the winding motor rotor circuit in series with adjustable additional potential to change the motor's slip, to achieve the purpose of speed regulation. Most of the slip power is absorbed by the additional potential in series, and then used to generate additional devices to return the absorbed slip power to the power grid or to convert energy for use. According to the mode of slip power absorption and utilization, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation. Most of them adopt thyristor cascade speed regulation. Its characteristics are that slip loss in the process of speed regulation can be fed back to the power grid or production machinery with high efficiency; the capacity of the device is proportional to the speed regulation range, and the investment is low, so it is suitable for the speed regulation range at rated speed. On the production machinery with speed of 70%-90%; when the speed regulating device fails, it can be switched to full speed operation to avoid shutdown; the power factor of cascade speed regulating of thyristor is low, and the harmonic effect is great.
The method is suitable for use in fan, water pump, rolling mill, mine hoist and extruder.
4. Speed Regulation Method of Rotor Series Resistance of Winding Motor
The winding asynchronous motor rotors are connected with additional resistance in series, which increases the slip rate of the motor and makes the motor run at a lower speed. The greater the resistance in series, the lower the speed of the motor. This method is simple in equipment and convenient in control, but slip power is consumed on resistance in the form of heating. It belongs to stepped speed regulation with soft mechanical characteristics.
V. Method of Stator Voltage Regulation and Speed Regulation
When the stator voltage of the motor is changed, a set of different mechanical characteristic curves can be obtained, thus different rotational speeds can be obtained. Because the motor's torque is proportional to the square of voltage, the maximum torque decreases a lot, and its speed range is small, which makes it difficult for general cage motors to apply.
In order to expand the range of speed regulation, cage motors with large rotor resistance should be adopted, such as moment motors for speed regulation or frequency sensitive resistors in series on winding motors. In order to expand the stable operation range, feedback control should be adopted when the speed is above 2:1 to achieve the purpose of automatic speed regulation. The main device of voltage regulation and speed regulation is a power supply which can provide voltage variation. The commonly used voltage regulation modes are series saturated reactor, autotransformer and thyristor voltage regulation. Thyristor voltage regulation mode is the best.
The characteristics of voltage regulation and speed regulation are that the voltage regulation and speed regulation circuit is simple and easy to realize automatic control; slip power is consumed in the form of heating in the rotor resistance during the voltage regulation process, and the efficiency is low. Voltage regulation and speed regulation are generally applicable to production machinery below 100KW.
6. Electromagnetic Speed Regulation Electricity
The speed formula of three-phase asynchronous motor is: n=60f/p(1-s)
From the above formula, it can be seen that changing the power supply frequency f, the pole logarithm P and slip s of the motor can be too much to the intention of changing the speed.
Classification:
1. In terms of the essence of speed regulation, different methods of speed regulation are nothing more than changing the synchronous speed of the communication motor or not changing the synchronous speed.
The speed regulation methods without changing synchronous speed are as follows.
1) Speed Regulation of Rotor String Resistance of Winding Motor
2) Chopper speed regulation
3) Cascade Speed Regulation and Application of Electromagnetic Slip Clutch
4) Hydraulic Coupling
5) Oil film clutch and other speed regulation
The speed regulation method without changing synchronous speed is widely used in production machinery.
2. Multi-speed motor with changing stator pole logarithm and synchronous speed, variable frequency speed regulation with or without commutation motor speed regulation by changing stator voltage and frequency, etc.
3. From the viewpoint of energy consumption in speed regulation, there are two ways: high-efficiency speed regulation and low-efficiency speed regulation: high-efficiency speed regulation means that the slip rate is constant at the time, so there is no slip loss, such as multi-speed motor, frequency conversion speed regulation and speed regulation methods that can recover slip loss (such as cascade speed regulation). The speed regulation method with slip loss belongs to low-efficiency speed regulation, such as rotor series resistance speed regulation method, energy loss in the rotor circuit; electromagnetic clutch speed regulation method, energy loss in the clutch coil; hydraulic coupling speed regulation, energy loss in the oil of hydraulic coupling. Generally speaking, slip loss increases with the expansion of speed regulation scale. If the speed regulation scale is small, the energy loss is very small.
Seven Speed Regulation Methods of Three-phase Asynchronous Motor
I. Variable Pole Logarithmic Speed Regulation Method
This kind of speed regulation method is to change the stator pole number of the cage motor by changing the connection mode of the stator winding to achieve the purpose of speed regulation, which is characterized by its rigid mechanical characteristics, good stability, no slip loss, high efficiency, simple wiring, convenient control and low price, stepped speed regulation, large gradient difference, and no smooth speed regulation; it can be used with voltage regulation speed regulation and electromagnetic slip clutch. The smooth speed regulation characteristic with high efficiency can be obtained by using it together.
This method is suitable for production machinery without stepless speed regulation, such as metal cutting machine tools, lifts, lifting equipment, fans, pumps, etc.
2. Frequency Conversion Speed Regulation Method
Frequency conversion speed regulation is a method of changing the frequency of the stator power supply of the motor, thereby changing its synchronous speed. The main equipment of the variable frequency speed control system is the converter which provides the variable frequency power supply. The converter can be divided into AC-DC-AC converter and AC-AC converter. At present, most of the domestic converters are AC-DC-AC converter. Its characteristics are high efficiency, no additional loss in the process of speed regulation; wide application range, can be used for cage asynchronous motor; wide speed regulation range, hard characteristics, high accuracy; complex technology, high cost, difficult maintenance and inspection.
This method is suitable for high precision and good speed regulation performance occasions.
3. Cascade Speed Regulation Method
Cascade speed regulation refers to the winding motor rotor circuit in series with adjustable additional potential to change the motor's slip, to achieve the purpose of speed regulation. Most of the slip power is absorbed by the additional potential in series, and then used to generate additional devices to return the absorbed slip power to the power grid or to convert energy for use. According to the mode of slip power absorption and utilization, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation. Most of them adopt thyristor cascade speed regulation. Its characteristics are that slip loss in the process of speed regulation can be fed back to the power grid or production machinery with high efficiency; the capacity of the device is proportional to the speed regulation range, and the investment is low, so it is suitable for the speed regulation range at rated speed. On the production machinery with speed of 70%-90%; when the speed regulating device fails, it can be switched to full speed operation to avoid shutdown; the power factor of cascade speed regulating of thyristor is low, and the harmonic effect is great.
The method is suitable for use in fan, water pump, rolling mill, mine hoist and extruder.
4. Speed Regulation Method of Rotor Series Resistance of Winding Motor
The winding asynchronous motor rotors are connected with additional resistance in series, which increases the slip rate of the motor and makes the motor run at a lower speed. The greater the resistance in series, the lower the speed of the motor. This method is simple in equipment and convenient in control, but slip power is consumed on resistance in the form of heating. It belongs to stepped speed regulation with soft mechanical characteristics.
V. Method of Stator Voltage Regulation and Speed Regulation
When the stator voltage of the motor is changed, a set of different mechanical characteristic curves can be obtained, thus different rotational speeds can be obtained. Because the motor's torque is proportional to the square of voltage, the maximum torque decreases a lot, and its speed range is small, which makes it difficult for general cage motors to apply.
In order to expand the range of speed regulation, cage motors with large rotor resistance should be adopted, such as moment motors for speed regulation or frequency sensitive resistors in series on winding motors. In order to expand the stable operation range, feedback control should be adopted when the speed is above 2:1 to achieve the purpose of automatic speed regulation. The main device of voltage regulation and speed regulation is a power supply which can provide voltage variation. The commonly used voltage regulation modes are series saturated reactor, autotransformer and thyristor voltage regulation. Thyristor voltage regulation mode is the best.
The characteristics of voltage regulation and speed regulation are that the voltage regulation and speed regulation circuit is simple and easy to realize automatic control; slip power is consumed in the form of heating in the rotor resistance during the voltage regulation process, and the efficiency is low. Voltage regulation and speed regulation are generally applicable to production machinery below 100KW.
6. Electromagnetic Speed Regulation Electricity
