Advantages and disadvantages of wound-rotor asynchronous motors. Wiring diagram of wound-rotor asynchronous motors

Advantages and disadvantages of wound rotor asynchronous motors

As a common type of motor, wound-rotor asynchronous motor has the following advantages and disadvantages:

advantage:

Simple structure and low manufacturing cost;

High reliability and low failure rate;

Highly adaptable, can be used in equipment and machines in different fields;

Large torque, smooth starting and running, not easy to damage the driven load;

Simple maintenance and servicing, easy to inspect and repair.

shortcoming:

The starting current is large, which may cause impact on the power grid;

Low efficiency, especially at part load;

The speed regulation performance is poor, and it usually requires the use of devices such as frequency converters to achieve speed regulation;

The noise and vibration are high, which may have a negative impact on the surrounding environment;

The torque stability is poor and it is not suitable for occasions requiring high-precision control. In short, the wound-rotor asynchronous motor has some significant advantages, such as simple structure, high reliability, strong adaptability, etc., but it also has some disadvantages, such as large starting current, low efficiency, poor speed regulation performance, etc. In actual application scenarios, its advantages and disadvantages should be comprehensively evaluated according to the specific situation to select the appropriate motor type.

Wiring diagram of wound rotor asynchronous motor

When the winding asynchronous motor is started with a resistor in series with the rotor, a suitable three-phase symmetrical resistor is connected in series in the rotor circuit of the winding asynchronous motor. If the resistance value of the resistor is correctly selected, the maximum torque of the rotor circuit is generated at the moment of motor starting, thereby shortening the starting time and achieving the purpose of reducing the starting current and increasing the starting torque. As the motor speed increases, the variable resistance decreases step by step.

After starting, the variable resistance is reduced to zero, the rotor winding is directly short-circuited, and the motor runs at rated conditions. The advantage of this starting method is that it can not only reduce the starting current, but also keep the starting torque within a larger range. Therefore, it is widely used in equipment that requires heavy-load starting, such as bridge cranes, winches, gantry cranes, etc. Its disadvantages are that more starting equipment is required, part of the energy is consumed in the starting resistor, and the number of starting stages is small.

Frequency-sensitive rheostat connected in series in the rotor circuit for starting control. A frequency-sensitive rheostat is a static contactless electromagnetic element whose impedance value changes significantly with frequency (sensitive to frequency). It is essentially a three-phase reactor with very large core loss. When the motor starts, the frequency-sensitive rheostat is connected in series in the rotor winding. Since the equivalent impedance of the frequency-sensitive rheostat decreases as the rotor current frequency decreases, the purpose of automatic resistance change is achieved. Therefore, only one level of frequency-sensitive rheostat is needed to start the motor smoothly. The disadvantages of connecting the frequency-sensitive rheostat in series: due to the presence of inductance, the power factor is low and the starting torque is not very large. Therefore, when the wound-rotor asynchronous motor is started under light load, the advantage of using the frequency-sensitive rheostat method is more obvious. For heavy load starting, series resistance starting is generally used.

Here is a wiring diagram of a wound-rotor three-phase asynchronous motor. The rotor winding of the three-phase wound-rotor asynchronous motor is started by short-circuiting three resistors one by one. If no external resistor is connected, the three slip ring output lines can be directly short-circuited.