What is Circle Diagram of Induction Motor – Definition, Construction & Its Parts

Hi guys welcome to the new post. Here we will discuss What is Circle Diagram of Induction Motor – Definition, Construction and its Parts. In the electrical engineering world circle diagram of the induction motor is a very beneficial parameter that is used to study and analyze the operation of this device. In this post, we will discuss different parameters for a circle diagram. So let’s get started with What is Circle Diagram of Induction Motor

Understanding Induction Motors

Before discussing the circle diagram first have an understanding of the induction motor. These mtoro is mostly used in different applications from small houses applications to heavy industries as they are reliable and efficient. They operate on the principle of electromagnetic induction where a rotating magnetic field induces a current in the rotor and the rotor rotates.

What is a Circle Diagram of an Induction Motor?

A circle diagram of an induction motor is a graphical representation of motor operation. It is the best parameter to get the feature of the motor working in different load conditions. The current phasor is drawn like a radius from the origin point and the voltage phasor is shown as the diameter of the circle. The angle between the 2 phasors is the power factor angle of the motor.

The circle diagram is used to find different parameters such as

• The output power of the motor
• The losses in the motor
• The efficiency of the motor
• The maximum torque that the motor can produce
• The slip of the motor

 Parts of the circle diagram of an induction motor

• Stator voltage phasor: It is phasor denotation of voltage provided to the stator winding of the motor
• Stator current phasor: This phasor denotes current passing in the stator winding of the motor.
• Power factor angle: It is the angle between the stator voltage phasor and the stator current phasor. it is a measurement of how effectively a motor is transforming power into mechanical power..
• Output power: It is mechanical power that the motor produces. it is dentoed by an area covered by stator current phasor and voltage phasor.
• Losses: These are the losses that occur in the motor, such as copper losses and iron losses. They are represented by the shaded area in the circle diagram.
• Efficiency: It is the ratio of output power to input power. It is denied by the percentage of shaded area that is covered by the stator current phasor and voltage phasor.
• Slip: It is the difference between the synchronous speed of the motor and the actual motor speed. it is denoted by the distance between the stator current phasor and origin point

Read also: DC Motor Starters and Circuit Diagram

Construction of Circle Diagram of Induction Motor

A circle diagram was drawn by plotting stator current with stator voltage, with the angle between two phasors as parameters. The circle diagram can be used to find these parameters of induction motors.

• No-load current
• Blocked rotor current
• Slip
• Power factor
• Torque
• Efficiency

Follow these steps to construct the circle diagram of an induction motor:

1. Make a vertical line denoting rated stator voltage V1.
2. Choose the best scale for the current.
3. Make a line OB lagging V1 by an angle Φsc equal to the blocked rotor current for normal voltage.
4. Link AB which denotes the output line of the motor.
5. Make a perpendicular bisector to line AB, it joins the horizontal line AX at point C.
6. Make a line from point O to point C. This line denotes the air gap power Pg.
7. Draw a line from point B to point F, such that BF is parallel to V1. This line denotes the rotor copper losses Prc.
8. Make a line from point F to point G, like FG is parallel to V1. This line represents the stator copper losses Psc.
9. The area covered by the curve OABFCG is the output power of the motor.

The circle diagram can be used to check the performance of the induction motor under different operating conditions. For instance, the no-load current and slip can be found by measuring the lengths of the lines OA and OB, respectively. The power factor can be measured by calculating the angle between the lines OA and V1. The torque can be found by measuring the distance of any point on the curve from the line V1. The efficiency can be found by measuring the ratio of the area covered by the curve OABFCG to the area of the triangle OAB.

Here are some more points to be noted when constructing the circle diagram of an induction motor:

• The scale for the current must be selected so that the blocked rotor current is clearly visible.
• The angle between the lines OA and V1 must be calculated carefully, as it is a measurement of the slip.
• The area under the curve OABFCG should be calculated correctly as it is a measure of the output power of the motor.

The circle diagram is useful for understanding the performance of an induction motor. It can be used to troubleshoot issues with the motor and to optimize its performance

 

Significance of lines on the Circle Diagram

 The different lines on the circle diagram have this significance:

• Input line (ON): This line denotes the input power to the motor. The vertical distance between any point on the circle and the line ON denotes the input power to the motor at that operating point.
• Output line (O’F): This line shows the output power of the motor. The vertical distance between any point on the circle and the line O’F denotes the output power of the motor at that operating point.
• Air gap power line (O’L): This line is the air gap power of the motor. The air gap power is the power that is available to drive the rotor of the motor.
• Torque line (EL): This line shows the torque produced by the motor. The torque is the force that the motor gives to the load.
• Slip line (AB): It denotes the slip of the motor. Slip is the difference between the rotor speed and the synchronous speed.
• Power factor line (MN): This line defines the power factor of the motor. The power factor is the ratio of the real power to the apparent power.

The circle diagram can be used to determine the following points:

• The maximum output power of the motor
• The maximum torque of the motor
• The operating point at which the motor has maximum efficiency
• The operating point at which the motor has minimum losses
• The effect of varies in the supply voltage or frequency on the motor’s performance

Here are some more points about the significance of the lines on the circle diagram:

• The input line and the output line intersect at the point of maximum efficiency.
• The torque line and the slip line intersect at the point of maximum torque.
• The power factor line is parallel to the output line at the point of maximum efficiency.
• The circle diagram can be used to determine the losses in the motor. These losses are represented by the area covered by the torque line, the slip line, and the circle.

FAQs

What is a circle diagram in induction motors?

A circle diagram is a graphical representation of the performance of an induction motor. It is best to understand the relationship between the motor’s input voltage, current, and torque. The circle diagram can be used to measure the motor’s efficiency, losses, and power output.

How to draw circle diagram of single phase induction motor?

The circle diagram of a single phase induction motor is more complicated than the circle diagram of a three-phase induction motor. This is because the single-phase motor has a pulsating magnetic field, which makes it  difficult to analyze. But, there are some methods that can be used to draw the circle diagram of a single-phase induction motor.

One is to use the equivalent circuit of the motor. The equivalent circuit is a simplified representation of the motor that can be used to measure motor operation performance. When the equivalent circuit has been made, the circle diagram can be drawn by plotting the input voltage and current of the motor.

The second method for drawing the circle diagram of a single-phase induction motor is to use a computer simulation. Computer simulations can be used to correctly calculate the performance of the motor under a different of conditions.

What is 3 phase slip ring induction motor?

A three-phase slip ring induction motor is an induction motor that has a rotating shaft. The rotor of the motor has slip rings, which are attached to external resistors. The resistors can be used to control the speed of the motor.

What is an induction motor PDF?

There are different PDFs available online that offers information about induction motors. These PDFs can be a great resource for learning about the principles of induction motors, their construction, and their applications.

Is induction motor AC or DC?

Induction motors are AC motors. They require an alternating current supply to operate.

What is induction motor principle?

The principle of an induction motor is based on electromagnetic induction. When the stator windings of the motor are energized with an alternating current, they produce a rotating magnetic field. This rotating magnetic field induces a current in the rotor windings. The interaction between the stator and rotor currents generates a torque, which rotates the rotor.

Why it is called induction motor?

The induction motor is known as an induction motor because the rotor current is induced by the stator magnetic field. The rotor current is not provided by an external source, like a DC motor.

What is torque of a motor?

Torque is the force that rotates the shaft of a motor. The torque of an induction motor is proportional to the product of the stator current and the rotor current.

What is induction motor types?

There are 2  main types of induction motors: squirrel cage motors and wound rotor motors. Squirrel cage motors are the most commonly used type of induction motor. They have a rotor that is created with a series of copper or aluminum bars that are short-circuited at each end. Wound rotor motors have a rotor that is created with a series of copper windings. The windings of the wound rotor motor can be attached to external resistors to control the speed of the motor.

What is a 3-phase motor?

A three-phase motor is a motor that is powered by a three-phase electrical supply. Three-phase motors are more effective than single-phase motors and they can give more power.

What is the DOL starter?

The DOL starter is a  motor starter that is used to start three-phase induction motors. The DOL starter connects the motor directly to the power supply when the motor is started. The DOL starter is a simple and less costly starter, but it can cause a large inrush current when the motor is started.

What is stator and rotor?

The stator is the static part of an induction motor. It is created with a set of windings that are placed in slots in the stator core. The rotor is the rotating part of an induction motor. It is made up of a series of bars or windings that are mounted on a shaft.