For industrial squirrel cage induction motors are used mostly for the motor and drive systems applications. Synchronous motors are very rarely used below 40kW output because of the higher cost compared to induction motors.
In addition to the higher initial cost synchronous motors needs dc excitation source and starting and control devices are usually more expensive. However for particular output range and speed high initial cost of synchronous motor varnishes are economical compared to induction motor. Where applications involve high kW output and low speed synchronous motors are economical compared to induction motors.
The various classes of service for which synchronous motors are employed may be classified as:
Power factor correction
Constant speed constant load drives
Synchronous motors are used in generating stations and in substations connected to the busbars to improve the power factor. For this purpose they are run without mechanical load on them and in over-excited condition. These machines when over excited delivers the reactive power to grid and helps to improve the power factor of the system. The reactive power delivered by the synchronous motors can be adjusted by varying the field excitation of the motor. These motors used for power factor correction applications can also be termed as “synchronous condensers”. Advantage of synchronous condensers compared to shunt capacitors is that shunt capacitors generate constant reactive power whereas on the other hand synchronous condensers can able to deliver different reactive power levels by varying the excitation of machine.
Because of the higher efficiency compared to induction motors they can be employed for loads which require constant speeds. Some of the typical applications of high speed synchronous motors are such drives as fans, blowers, dc generators, line shafts, centrifugal pumps, compressors, reciprocating pumps, rubber and paper mills.
Synchronous motors are used to regulate the voltage at the end of transmission lines.
In textile and paper industries synchronous motors are employed to attain wide range of speeds with variable frequency drive system.
Applications in the Industrial Field
Apart from the many different functions facilitated by carefully designed motors, the tasks performed in the industry are perhaps the most complicated. Some electric motors are used in coal mining, while some motors provide the energy for crushing and shredding in the cement industry. For steel mills, on the other hand, a stable input is required to ensure the continuity of their production process in an extremely warm atmosphere. For this reason, they often use special motors for conveyor belts. The sugar industry relies on customized high-voltage motors or the IE4 super premium motors, as these can provide a higher voltage without requiring much electrical energy.
Applications in Production Machines
Electric motors are used not only to supply fields and equipment but also to drive a whole range of production machines. The motors underneath are the ones that drive a propeller, turn up a turbine or suck in smoke and debris in a crowded public or private environment. In waterworks, it is the electric motors that help to pump up the water. In addition, there are advanced three-phase electric motors that are used in compressors because they can cool themselves sufficiently and thus withstand higher temperatures. These advantages also make them a perfect choice for industrial boilers.
In electrical systems such as those we use either in industry, power stations, or in private households, motors and generators have become an everyday device. With the demand for systems with high energy efficiency and lower power consumption, the invention of new models of these electrical devices can be observed. The basic calculation factor for the reliable operation of motors and generators is the power factor. It is the ratio of the power applied to the power required. Usually, the total power consumed in industries and factories is calculated on the basis of the power factor. The power factor should therefore always be kept at a uniform value. However, due to the increase in reactive power in these devices, the power factor decreases. Many methods are introduced to keep the power factor at a uniform value. The concept of the synchronous motor is one of them.
The Synchronous Motor: What is it?
This is how a synchronous motor is defined: An alternating current motor in which, in the stationary state, the rotation of the shaft is synchronous with the frequency of the applied current. A synchronous motor does not work with an induction current. Unlike induction motors, these motors have multi-phase AC magnets on the stator that generate a rotating magnetic field. In this case, the rotor has a permanent magnet that is synchronous with the rotating magnetic field and rotates synchronously with the frequency of the current supplied.
The functionality of a Synchronous Motor
The function of synchronous motors is based on the interaction of the magnetic field of the stator in combination with the magnetic field of the rotor. 3-phase windings are included in the stator and are operated with a 3-phase current. The stator winding thus generates a three-phase rotating magnetic field. The rotor is supplied with a direct current.
If the load is greater than the breakdown load, the motor is desynchronized. The 3-phase stator winding offers the advantage that it determines the direction of rotation. With single-phase winding it is not necessary to determine the direction of rotation and the motor is able to start in both directions. Starting devices are necessary for controlling the direction of rotation in these synchronous motors.
Usage Areas of Synchronous Motors
Synchronous motors are normally used in applications in which a constant and precise speed is required. Typical applications of these low power motors are positioning machines. They are also used in robot actuators. Synchronous motors are also used in ball mills, watches, record players, and turntables. They are also used as servo motors and timing machines.
Such motors are available in a range from horseshoe size to industrial high performance size. Although they are used in industrial high performance sizes, these motors are able to perform two essential functions. One is as an efficient means of converting alternating current energy into mechanical energy and the other is as a power factor correction.