Tag: induction motor

When a single phase induction motor is working, it will involve the problems of start capacitor and run capacitor. Because single phase is different from three phase, a single phase motor cannot form a rotating magnetic field when it is started, and uses the characteristic of the current in the capacitor to generate a rotating magnetic field to start the motor. Therefore, the start capacitor in a single phase motor is essential. But the run capacitor is not necessary.

Single phase motors generally refer to low-power single phase asynchronous motors powered by a single phase AC power supply. It is also called a single phase induction motor. This kind of motor usually has two phase windings on the stator, and the rotor is of ordinary squirrel cage type. The distribution of the two phase windings on the stator and the different power supply conditions can produce different starting characteristics and operating characteristics.
Single phase motors have a large production volume and are closely related to people's daily lives. Especially with the improvement of people's living standards, the consumption of single phase motors for household appliances is also increasing.

Slip-ring induction motors, also known as three-phase wound-rotor AC asynchronous motors, must be connected in series with a resistor or resistors in the motor rotor in order to reduce the starting current and increase the starting torque and power factor, effectively improving the motor starting performance. This article describes the principle and structure of slip-ring motors.

Squirrel cage induction motor is a three-phase asynchronous motor with rotor windings made of copper or aluminum strips instead of copper strips, welded with short-circuit rings. Squirrel cage induction motor failure is mainly divided into two parts: mechanical and electromagnetic.

Squirrel cage induction motor is the simplest and most widely used type of asynchronous motor. Its rotor coil is cast aluminum and shaped like a squirrel cage, so it is called a "squirrel cage motor". These motors are a specific kind of induction motor, which uses the electromagnetic induction effect to transform electrical current into rotational energy. This article will explain the principles of squirrel cage motors, their specifications, and what kinds of applications they are used for. This way, we can make informed choices when choosing the right motor.

Through the relative motion of the rotating magnetic field generated by the stator (its speed is synchronous speed n1) and the rotor winding, the rotor winding cuts the magnetic induction line to generate induction electromotive force, thus induced current is generated in rotor winding. The induction current in the rotor winding acts on the magnetic field to produce electromagnetic torque, thus making the rotor rotate. As the rotor speed approaches the synchronous speed, the induced current decreases and the electromagnetic torque decreases accordingly. When the asynchronous motor works in the motor state, the rotor speed is smaller than the synchronous speed. In order to describe the difference between rotor speed n and synchronous speed n1, slip ratio is introduced.

Compared with other motors, the ATO induction motor has the advantages such as simple structure, convenience in manufacture, use and maintenance, high operational reliability, light weight, low cost. Taken the ATO three-phase induction motor as an example, compared with the DC motor with the same power and speed, the former weight is only half of the latter at one-third cost. It also has the load characteristics of constant speed that can satisfy machinery driving requirement of a majority of industrial and agricultural production. Its limitation is that due to the poor speed controlling performance caused by the fixed slip between its rotate speed and the synchronous speed of its rotating magnetic field, so it is not so economic or convenient as direct current motor under the usage occasion that requires a wider range of smooth speed control such as rolling mill, winding engine, large size machine tool etc. In addition, induction motors draw reactive power from the power system during the operation, resulting in the deterioration of power factor of power system. Therefore, on the occasion of high power and low speed such as driving ball grinding mill and compressor, using synchronous motors is more reasonable.

Different motors of the same rated horsepower may have different starting currents, torque curves, speeds and other variables. NEMA (National Electrical Manufacturers Association) has A, B, C, D four different designs for electric motors.
NEMA Design B: Is the most common design of electrical motors and ATO single phase AC induction motors are of NEMA design B. Its starting torque is similar to that of design A, but sometimes still lower, providing a relatively low starting current. However, in industrial application, it locks locked rotor and still allows starting load. The rotating-speed difference is lower than or equivalent to 5%. The electric efficiency and full-load power factor are relatively high. The typical applications include pump, fan and machine tool.

Variable Frequency Drive (VFD), aka variable speed drive (VSD), generally it's using for controlling 3-phase AC motor in variable speeds. It's important to know, control 1-phase motor speed by a VFD may cause overheat of the motor, as well as the service life. It's recommended to upgrade the motor to three phase AC motor, which you can also connect the 3-phase motor to single phase power supply by using a single phase to three phase VFD, then control the speeds. Anyway, in technical it's possible to use a VFD for single phase motor speed controls, here ATO will show you details about running a single phase motor on a VFD.

Troubles with the induction motors are generally divided into two categories. One is the electrical faults, such as the various faults of switches, buttons, fuses, electric brushes, stator winding, rotor, starting equipment and so on. The other is the mechanical problems, such as the problems of the bearing, fan blade, motor frame, coupling, end bell, bearing cover, spindle and so on.
Once the induction motor has any problem, there might be some abnormal phenomena, for instance, the rising temperature, over current, vibration and abnormal noise and so on. Therefore, learn about these phenomena, find out the cause, and then troubleshoot it. The following is some common faults and troubleshooting method of three-phase induction motors for your reference.

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.