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Type and characteristics of inverter load
Date of issue：2015-01-05 16:03:08  see：
Mechanical load includes all kinds, but its speed torque characteristics can be divided into three categories: constant torque load, square reduced torque load and constant power load. The following describes the various types of load.


According to the mechanical characteristics of the load classification: 1. Constant torque load: for the friction load such as conveyor belt, mixer, extrusion machine, crane or elevator, the torque required by the load is basically a constant value, which is the torque load. For example, no matter the lifting speed of a crane, the gravity generated by its weight under the action of the earth's gravity will never change, that is, a constant torque load. The power P of the motor can be expressed as P = TN / 975, where t is the torque, n is the speed, and the product of speed and torque is power, then the energy consumed by the load with constant torque characteristics is directly proportional to the rotational speed.


Square drop torque load: fan, fan, pump and other fluid machinery (wind water hydraulic machinery), at low speed, due to the low flow rate of the fluid, the load only needs a small torque. With the increase of motor speed, the flow speed is accelerated, and the required torque is larger and larger, and the torque increases or decreases in proportion to the square of the speed. Such load characteristics are called square reduced torque load In this case, because the energy consumed by the load is directly proportional to the third power of the rotational speed, a significant energy-saving effect can be obtained by controlling the speed of fluid machinery by frequency converter.


Constant power load: the main shaft drive of machine tool, paper machine, central transmission part of plastic film production machinery, winch, etc., the output power is constant, independent of speed, such load characteristics are called constant power load. For example, a winder requires a certain speed with the same tension. At the beginning of coiling, because the diameter of the paper coil is small, in order to keep the constant speed, the paper coil must rotate at a higher speed, and the torque can be small; but with the gradual increase of the diameter of the paper coil, the speed of the paper roll will decrease, and the torque must be increased accordingly.


According to the load operation process classification: due to the diversification of production process, mechanical equipment also has a variety of different working states and control modes, mainly including the following: 1) Continuous constant load: refers to the load in a long enough time continuous operation, and during the operation, the torque is constant. "Long enough" here means that during this time the temperature rise of the motor will be sufficient to reach a steady value. A typical example is a constant operating fan.


2) Continuous variable load: refers to the load in a long enough period of continuous operation, but during the operation, the torque is often changed,. The typical cases of this kind of load are the working condition of lathe when turning workpiece and the main drive of plastic extruder.


3) Intermittent load: refers to the load running and stopping from time to time. During operation, the temperature rise is not enough to reach a stable value; during shutdown, the temperature rise is not enough to drop to zero. Lifting machinery, such as cranes, elevators, etc., belong to this kind of load.


4) Short term load: the time of load operation is very short. During the operation, the temperature rise can not reach the stable value, and the interval between the two operations is long enough to make the temperature rise of the motor drop to the ambient temperature. The drag system of sluice gate belongs to this kind of load. For this kind of load, as long as the motor has enough overload capacity.


5) Impact load: the load with impact is called impact load. For example, the impact load produced at the moment when the steel ingot of the rolling mill is pressed in, and the impact load produced at the moment of stamping by the stamping machine is the most representative. For these machines, the generation of impact load can be predicted in advance and easy to handle.


Of course, there are also some unexpected phenomena of impact load, such as the treatment of fans containing dust, powder, when the long-term accumulation of powder hard block falling into the blade, is also a kind of impact load.


Impact load can cause two problems, namely, over-current trip and excessive speed change.


For impact load, YH series high slip three-phase asynchronous motor is often used in China. It is a derivative series of Y series motor. It has the characteristics of large locked rotor torque, small locked rotor current, high slip and mechanical characteristics. It is especially suitable for uneven impact load and working occasions with many positive and reverse rotation times, such as hammering machine, scissor machine, impact machine and forging and smelting machine Mechanical equipment.


6) Pulsating torque load: in reciprocating compressor, the rotary motion of motor is converted into reciprocating motion by crankshaft, and the torque changes with the angle of crankshaft. In this case, the current of the motor will produce large pulsation with the change of load. This kind of load is a kind of periodic crankshaft load, which must consider the flywheel inertia, because once the method of increasing the flywheel to smooth the pulsating torque, the acceleration and deceleration schedule will be increased, otherwise the feedback energy will be increased.


7) Load: when the load requires that the torque produced by the motor is opposite to the rotation direction of the motor, such load is called a load,. There are usually two types of loads.


① Due to the need of speed control, the face is in the four quadrant operation of mechanical equipment. For example, when the crane lowers the heavy object, the motor rotates in the direction of being pulled by the load. At this time, the torque generated by the motor hinders the weight from being lowered, that is, it is opposite to the rotation direction. This kind of load includes traveling crane, crane, elevator and so on.


② Mechanical equipment operating in four quadrants for torque control. In the process of coiling sheet material, the running speed of the take-up machine and prime mover is set to exert tension on the workpiece, while the motor is only required to produce braking torque. This kind of load includes unwinding and rewinding equipment for paper making, pinch roll for iron and steel, jigger and dyeing machine for textile.


8) Large starting torque load: similar to blenders, extruders, metalworking machines, etc., it can only be started after overcoming great friction at the initial stage of starting, so it belongs to large starting torque load.


9) Large and chronic load: centrifugal separator is a kind of large and chronic load, which is not only hard to start but also time-consuming to stop.

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