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Sunday, September 23, 2012

PowerPoint Presentation On Electric Motors

PPT On Electric Motors

Electric Motors Presentation Transcript:
1. Training Agenda: Electric Motors
Introduction Types of electric motors
Assessment of electric motors
Energy efficiency opportunities

2. Introduction
An electric motor is an electromechanical device that converts electrical energy to mechanical energy. The mechanical energy can be used to perform work such as rotating a pump impeller, fan, blower, driving a compressor, lifting materials etc.
It is estimated that about 70% of the total electrical load is accounted by motors only. That is why electric motors are termed as “Work Horse” in an industry.

3. How Does an Electric Motor Work?
The general working mechanism is the same for all motors and shown in the figure
An electric current in a magnetic field will experience a force.
If the current carrying wire is bent into a loop, then the two sides of the loop, which are at right angle to the magnetic field, will experience forces in opposite directions.
The pair of forces creates a turning torque to rotate the coil. (note: a “torque” is the force that causes the rotation)
Practical motors have several loops on an armature to provide a more uniform torque and the magnetic field is produced by electromagnet arrangement called the field coils

4. Three types of Motor Load
In understanding a motor it is important to understand what a motor load means. Load refers to the torque output and corresponding speed required. Loads can generally be categorized into three groups:
Constant torque loads are those for which the output power requirement may vary with the speed of operation but the torque does not vary. Conveyors, rotary kilns, and constant-displacement pumps are typical examples of constant torque loads.
Variable torque loads are those for which the torque required varies with the speed of operation. Centrifugal pumps and fans are typical examples of variable torque loads (torque varies as the square of the speed). Constant power loads are those for which the torque requirements typically change inversely with speed. Machine tools are a typical example of a constant power load

 5. Type of Electric Motors
Motors are categorized in a number of types based on the input supply, construction and principle of operation. We will start at looking at various forms of the DC motor such as shunt and series, followed by the AC motors including synchronous and induction motors.

6. DC Motors – Components
Direct-Current motors, as the name implies, use a direct-unidirectional current. A DC motor is shown in the figure and has three main components:
Field pole. Simply put, the interaction of two magnetic fields causes the rotation in a DC motor. The DC motor has field poles that are stationary and an armature that turns on bearings in the space between the field poles. A simple DC motor has two field poles: a north pole and a south pole. The magnetic lines of force extend across the opening between the poles from north to south. For larger or more complex motors there are one or more electromagnets. These electromagnets receive electricity from an outside power source and serve as the field structure.
Armature. When current goes through the armature, it becomes an electromagnet. The armature, cylindrical in shape, is linked to a drive shaft in order to drive the load. For the case of a small DC motor, the armature rotates in the magnetic field established by the poles, until the north and south poles of the magnets change location with respect to the armature. Once this happens, the current is reversed to switch the south and north poles of the armature.
Commutator. This component is found mainly in DC motors. Its purpose is to overturn the direction of the electric current in the armature. The commutator also aids in the transmission of current between the armature and the power source.

7. DC motors
The main advantage of DC motors is speed control, which does not affect the quality of power supply. It can be controlled by adjusting: the armature voltage – increasing the armature voltage will increase the speed the field current – reducing the field current will increase the speed.
DC motors are available in a wide range of sizes, but their use is generally restricted to a few low speed, low-to-medium power applications like machine tools and rolling mills because of problems with mechanical commutation at large sizes. Also, they are restricted for use only in clean, non-hazardous areas because of the risk of sparking at the brushes.
 DC motors are also expensive relative to AC motors.

8. For more please refer our PPT. Thank You.

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