General Aspects – POLYPHASE INDUCTION MOTORS

Defining induction motor

An induction motor can be stated as a simple electric transformer which has 2 relatively movable portions. The magneticcircuit of this motor is divided by air gap. Between the 2 sections, one is carried to the secondary winding while the other is carried by the primary winding. When alternating current is supplied from a power system to that motor’s primary windings, which again induces a resisting current in the motor’s secondary winding. This happens when the secondary winding is either closed because of external resistivity or it being short circuited.

There is a key feature that helps in differentiating between other electrical motor types and induction machine. That feature relates the creation of secondary currents by induction itself instead of being dispensed by other power sources or D. C exciter.

In an induction motor, production of relative motion between secondary and primary structures is because of electromagnetic forces which are proportional to the power. Hence, this motion is transferred from the induction motor (across air gaps).

Industrial application

With torque characteristics are these induction motors are available for anindustrial application that suits for every load variety. There are 4 cases which can explain this machinery’s application.

• Apt for major applications, utilization of such motors are highly beneficial. In these cases, the starting torque range of a standard motor is between 120% of full load torque and 150% full load torque.
• In case of drivingmachine industries, they mainly utilize huge flywheels for carrying peak loads. These loads may be either shear or punch presses with a high torque motor. In these types of carrier loads, the available slip at full load up can be nearly 10%. This higher slip is the reason which enables proper flywheel functioning by allowing enough change in its speed.
• Regarding average loads like that of a plunger pumpor a refrigerating machine (smaller size), whose operation is against belt conveyors or full pressure conveyors, specific torque is used. In this case, the utilized motors have a starting torque whichis 2 times the normal full load torque.
• For the machinery with external resistances and satisfactory controllers which are linked with motor winding in a series, they use wound rotors. With this combination, it is easy to acquire starting torque at any value,and it can reach to highest breakdown torque. We can find these motors to be highly adaptive. This is because of its constant speed drives regarding huge friction loads by controlling at the initial level.

Benefits

There are mainly 8 benefits which make 3 phase induction motor highly sought motor in industrial areas. For an effective application, those benefits are:

1. Easy operation
2. Simple speed control and gear control
3. Simple design
4. Reliable operation
5. Higher efficiency
6. Simple maintenance
7. Rugged construction
8. Low initial cost

Links of Previous Main Topic:-

• Current Electricity Basic Concepts
• Introduction to Alternating Current
• Introduction Three Phase A C Circuits
• Magnetic Field
• General Aspects
• Elementary Theory of Ideal Transformer

Links of Next Electrical Engineering Topics:-

• Classification of A C Motors
• Constructional Details
• Production of Rotating Magnetic Field
• Theory of Operation of an Induction Motor
• Slip
• Frequency of Rotor Current
• Rotor E M F and Rotor Current
• Torque and Power
• Effect of Change in Supply Voltage on Starting Torque
• Effect of Change in Supply Voltage on Torque and Slip
• Torque Slip and Torque Speed Curves
• Operating Characteristics 3 Phase Squirrel Cage Induction Motor
• Shows a Wound Rotor Induction Motor with Controller Rheostat
• Power Stages in an Induction Motor
• Induction Motor as Transformer
• Equivalent Circuit of an Induction Motor
• Starting of Induction Motors
• Factors Governing Performance of Induction Motors
• Effects of Operating Conditions
• Ratings of 3 Phase Induction Motors
• Squirrel Cage Motors Advantages Disadvantages and Applications
• Wound Rotor or Slip Ring Induction Motors Advantages Disadvantages and Applications
• Comparison of a Squirrel Cage and a Slip Ring or Phase Wound
• Comparison Induction Synchronous Motors
• Highlights in Polyphase Induction Motors