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ECET 211 Electric Machines & Controls

Lecture 8 Motor Control Circuits

(2 of 2)

Text Book: Electric Motors and Control Systems, by Frank D. Petruzella, published by McGraw Hill, 2015.

Paul I-Hai Lin, Professor of Electrical and Computer Engineering Technology

P.E. States of Indiana & California

Dept. of Computer, Electrical and Information Technology

Purdue University Fort Wayne Campus

Prof. Paul Lin

Lecture 8 Motor Control Circuits

Part 1. NEC Motor Installation Requirements

• Sixing Motor Branch Circuit Conductor

• Branch Circuit Motor Protection

• Selecting a Motor Controller

• Disconnecting Means for Motor ad Controller

• Providing a Control Circuit

Part 2. Motor Starting

• Full-Voltage Starting of AC Induction Motors

• Reduced-Voltage Starting of Induction Motors

• DC Motor Starting Prof. Paul Lin 2

Part 3. Motor Reversing and Jogging

• Reversing of AC Induction Motors

• Reversing of DC Motors

• Jogging

Part 4. Motor Stopping

• Plugging and Anti-plugging

• Dynamic Breaking

• DC Injection Breaking

• Electromechanical Friction Brakes

Part 5. Motor Speed

• Multispeed Motors

• Wound-Rotor Motors

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Lecture 8 Motor Control Circuits

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Part 3. Motor Reversing and Jogging

Reversing of AC Induction Motors

• Reversing three-phase Induction Motor Starter

Figure 8-29 Magnetic full-voltage three-phase reversing

Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

• Figure 8-30 Mechanical interlocking of forward and reverse contactors

Figure 8-31 Magnetic reversing starter with electrical interlock in the motor starter

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Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

• Figure 8-32 Reversing starter circuit implemented using IEC symbols

Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

• Figure 8-33 Pushbutton interlocking

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Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

• Figure 8-34 Limit switches incorporated into a reversing starter circuit to limit travel

Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

Figure 8-35 Reversing a single-phase motor

The direction of rotation is changed by interchanging the start winding leads, while those of the run winding remain the same

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Part 3. Motor Reversing and Jogging

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Reversing of AC Induction Motors

Figure 8-36 Reciprocating machine process

a repeated forward and reverse action

Part 3. Motor Reversing and Jogging

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Reversing of DC Motors

The reversal of a DC motor can be accomplished in two ways:

• Reversing the direction of the armature current (IA); leaving the field current the same

• Reversing the direction of the field current (IF) and leaving the armature current the same

Figure 8-37 DC motor reversing power circuits

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Part 3. Motor Reversing and Jogging

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Jogging

Jogging (sometimes called Inching) is momentary operation of a motor for the purpose of accomplishing small movements of the driven machine.

Figure 8-38 Push button job circuit

Part 3. Motor Reversing and Jogging

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Jogging

Figure 8-39 Jog circuit with control relay

Figure 8-40 Start/stop/selector jog control circuit

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Part 4. Motor Stopping

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Motor Stopping

Remove the power supply plus electric braking

Plugging and Antiplugging

Plugging – stops a polyphasemotor quickly by momentarily connecting the motor for revere rotation while the motor is still running in the forward direction.

Figure 8-41 Plugging switch

Figure 8-42 Plugging a motor to stop it

Part 4. Motor Stopping

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Plugging and Antiplugging

Figure 8-43 Antiplugging protection circuit

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Part 4. Motor Stopping

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Dynamic Braking

Figure 8-44 Dynamic braking applied to a DC motor

Part 4. Motor Stopping

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DC Injection Braking

Figure 8-45 DC injection braking applied to an DC

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Part 4. Motor Stopping

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Electromechanical Friction Brake

Figure 8-46 Electromechanical drum and shoe-type friction brake used on DC series motor drives

Part 4. Motor Stopping

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Electromechanical Friction Brake

Figure 8-47 AC electromagnetic brake

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Lecture 8 Motor Control Circuits

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Part 5. Motor Speed

• Multispeed Motors

Figure 8-48 Two-speed separate winding across-the-line motor starter

Lecture 8 Motor Control Circuits

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Part 5. Motor Speed

• Wound-Rotor Motors

Figure 8-49 Wound-rotor magnetic motor controller

Low speed (full resistance) – both S & H are open

Medium speed – S closed

Maximum speed – H closed

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Summary & Conclusion

Questions?

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