What is the characteristic of the variable pole speed method?

Answer:

Third, cascade speed control method Cascade speed regulation refers to the winding motor in the rotor loop into the adjustable additional potential to change the motor slip, to speed control purposes. Most of the slip power is absorbed by the additional potential in series, and the additional device is used to return the absorbed slip power to the grid or to convert the energy. According to the slip power absorption and utilization, cascade speed can be divided into motor cascade speed, mechanical cascade speed control and thyristor cascade speed form, the use of thyristor cascade speed, which features: The process of the slip loss back to the grid or production machinery, the higher efficiency; device capacity and speed range is proportional to the investment province, for speed range in the rated speed of 70% -90% of the production machinery; Device failure can be switched to full speed operation, to avoid shutdown; thyristor cascade speed power factor is low, the greater the impact of harmonics. This method is suitable for use in wind turbines, water pumps and rolling mills, mine hoists, extruders. Fourth, winding motor rotor series resistance speed control method Winding asynchronous motor rotor series into the additional resistance, so that the motor slip increase, the motor running at a lower speed. The greater the resistance of the series, the lower the motor speed. This method is simple and easy to control, but the slip power is consumed in the form of heat. Is a level of speed, mechanical characteristics of soft.

Edit this paragraph speed method First, variable pole alignment speed method This kind of speed control method is to change the stator winding winding way to change the cage motor stator pole pairs to achieve speed control purposes, features are as follows: with hard mechanical properties, good stability; no slip loss, high efficiency; wiring Simple, easy to control, low price; stepless speed regulation, large level difference, can not get smooth speed control; can be used with voltage regulator, electromagnetic slip clutch with the use of high efficiency and smooth speed control characteristics. This method is suitable for production machinery that does not need stepless speed regulation, such as metal cutting machine tools, lifts, lifting equipment, fans, pumps and so on. Second, the frequency control method Frequency conversion is to change the frequency of the motor stator power supply, thereby changing the speed of its synchronous speed control method. Frequency converter system can be divided into AC - DC - AC inverter and AC - AC inverter two categories, most of the current domestic use - cross - frequency converter. Features: high efficiency, no additional loss during the speed control process; wide range of applications, can be used for cage type asynchronous motor; speed range, hard and high precision; technical complexity, high cost, maintenance and repair difficult. This method is suitable for applications requiring high precision and better speed performance. Frequency conversion speed is divided into the following basic frequency and frequency above the speed, the fundamental frequency is constant torque speed control mode, the frequency above the speed is constant power speed mode.

Three-phase asynchronous motor speed formula: n = 60f / p (1-s) From the above equation can be seen, change the power supply frequency f, the motor pole p and slip rate s can achieve the purpose of changing the speed. From the nature of the speed point of view, different speed control mode is nothing more than to change the AC motor synchronous speed or do not change the synchronous turn two. In the production machinery is widely used does not change the synchronous speed of the speed control method There are winding motor rotor resistance, chopping speed, cascade speed and the application of electromagnetic slip clutch, hydraulic coupling, oil film clutch, etc. Speed ??control. Change the synchronous speed of the stator to change the number of pole pairs of multi-speed motor, change the stator voltage, the frequency of the frequency control can not change the motor speed and so on. From the energy point of view of the speed control point of view, there are two methods of efficient speed control and inefficient speed control: high speed control when the slip rate is constant, so no slip loss, such as multi-speed motor, frequency control As well as the speed loss can be recovered speed control methods (such as cascade speed, etc.). There are slip loss of the speed control method is a low efficiency, such as the rotor string resistance control method, the energy loss in the rotor circuit; electromagnetic clutch speed control method, the energy loss in the clutch coil; hydraulic coupling speed , Energy loss in the oil of the hydraulic coupling. In general, the slip loss increases with the speed range, if the speed range is not large, the energy loss is very small.

Seven, hydraulic coupler speed control method The hydraulic coupler is a hydraulic drive, generally composed of a pump wheel and a turbine, which collectively referred to as a working wheel and placed in a sealed housing. The shell is filled with a certain amount of working fluid, when the pump wheel in the prime mover driven under the rotation, in which the liquid by the blade to promote the rotation, under the action of centrifugal force along the outer ring into the turbine wheel, in the same direction to the Turbine blades are thrusted to drive the production machinery. The power transfer capacity of the hydraulic coupler is consistent with the size of the relative filling fluid in the shell. In the course of work, change the liquid filling rate can change the coupler's turbine speed, made stepless speed regulation, which is characterized by: power to adapt to a large range, from several tens of kilowatts to thousands of kilowatts to meet the different power needs; Simple, reliable, easy to use and maintenance, and low cost; small size, can accommodate large; easy to control and easy to achieve automatic control. This method is suitable for fan, pump speed.