Tag: induction motor

How to control the speed of three phase induction motor? The speed control method includes: changing the number of poles, stator voltage control, stator frequency conversion, cascade speed control, double-feed speed regulation, hydraulic coupler, electromagnetic slip clutch, etc.
The actual speed of three phase asynchronous motor is given by n=n_s (1 - s) =120f /p (1-s). It can be seen from the formula that the speed of 3 phase induction motor can be changed by the means of changing the number of induction motor’s poles "p", the slip "s" and the frequency of power supply"f".

How does an 3-phase induction motor work? In short, it works based on the principle of electromagnetic induction. When the stator windings are supplied with three-phase alternating current, a rotating magnetic field is generated between the stator and the rotor. The rotating magnetic field cuts the rotor windings to generate induced electromotive force and current in the rotor circuit. The current in the rotor conductor forces the rotor to rotate under the effect of the rotating magnetic field. Below, let’s specifically analyze the generation of rotating magnetic field, its direction and speed as well as slip.

The starting methods of three phase induction motor generally are direct-on-line starting, reduced-voltage starting and soft starter.
Direct-on-line starting is the most basic and simplest in the motor starting. The method is characterized by less investment, simple equipment and small quantity. Although the starting time is short, the torque is smaller at starting and the current is large, which is suitable for starting small capacity motors.

Induction motor, also known as asynchronous motor, is a kind of AC electric motor. According to the different power phase, it can be divided into single-phase and three-phase. The main construction of induction motor is composed of two parts - stator and rotor. In addition, there are end bells, bearings, motor frame and other components. The following will give more details about the structure of three-phase induction motor or asynchronous motor.

AC motors are divided into two types, synchronous motors and asynchronous motors which are also called induction motors. The biggest difference between synchronous motors and asynchronous motors (induction motors) is whether the speed of rotor is consistent with the speed of the rotating magnetic field in the stator. If the rotor’s rotation speed and the stator’s field speed are the same, it is called synchronous motor; if not, it is asynchronous motor. Furthermore, there are big differences specific to the performance parameters and applications between the two.

The traditional industrial agitator usually conducts no regulation or regulates the speed in mechanical method. The speed regulation in mechanical method will increase the loss of the industrial agitator. Meanwhile, the industrial agitator will work in fluctuating status. Furthermore, it will also work in the status of "big rated power with small load power", which is quite not economic. The motor power of the industrial agitator in operating under the frequency conversion speed control is similar to its characteristics of the revolving speed and pump load. Using VFD for speed regulation will obtain a substantial power saving rate.

The wire-cut EDM is to utilize the metal linear tool electrode (or named as wire electrode) to process workpieces with the principle of impulsive discharge to erode the metals. High speed wire-cut EDM is applied in the processing of the metal pieces with high precision, complicated shape, especially the mould and so on.

Because the induction motor has incomparable advantages: Simple and solid structure, cheap price, and easy maintenance. So using the means of VFD dragging three-phase induction motor replaces the means of traditional speed regulating, can solve the problem of high failure rate of the tower crane fundamentally. Moreover, it has advanced technology and significant energy saving effect. It is the ideal transmission controlling device of the tower crane.

The overhead crane is a kind of hoisting machinery with quite extensive application in the industrial and mining enterprise. Its operating organism is constituted by three basically independent dragging systems, which are respectively the cart dragging system, dolly dragging system and hook dragging system. This article ATO will take the practical application of VFD for overhead crane improvement in thermal power plant as the example, illustrating the application and improvement scheme of VFD for the overhead crane comprehensively.

The VFD speed control system regards the network pressure as the control object. The pressure transmitter changes the pressure in the air storage tank into the electrical signal to send into the PID regulator inside the VFD, so as to compare with the pressure setting value. Then calculation will be made according to the set PID control mode based on the difference value. The control signal will be generated to control the output signal and inverter frequency of the VFD, thus adjusting the revolving speed of the induction motor, so as to maintain the practical pressure to be always as the setting pressure.

The working principle of the automatic industrial washing machine is: under the unified deployment and management of the time schedule controller. The VFD controls the induction motor to carry out positive and negative revolving uninterruptedly, thus achieving the non-synchronous movement of the water and the clothes, so as to enable the water and the clothes to rub and knead, thus being cleaned.

Using VFD for speed regulating has many advantages. Many small power motors adopt single phase power supply. How to use VFD to regulate speed for single phase motors? ATO will provide the following methods.

The wire drawing machine is one of the main equipment of the metal wire processing as well as the cable and wire industry. It is mainly used to process the metal wires into the fine lines of various specifications. It usually constitutes the paying off, water cooling, winding up, winding displacement and other components. Its electric drive part is mainly realized by paying-off motor, winding-up motor and winding displacement motor. The wire drawing machine belongs to the constant-torque load. Its characteristics require that the VFD has a big start-up torque and can satisfy the full-load output in low speed. Meanwhile, it requires realizing the coordinated control of several motors in high precision percentage.

When the roots blower has went through improvement by VFD, the system can realize soft starting and soft stopping, so as to reduce the shock of the system to the power grid in start-up, thus reducing the system start-up times and ensuring a stable operation. What's more, because of the deceleration of the revolving speed in roots blower operation, it can reduce the mechanical wear and prolong the operating life of both the motor and the roots blower. If the system employs pressure closed-loop control improvement, the fully automatic control and unattended operation can be realized.

The variable frequency drive has the following ten protections on the motor:
Over-voltage protection: The variable frequency drive output has automatic voltage regulator function to control the external overtop power input to be not exceed the motor rated voltage.