Solution Manual for Electric Motor Control, 10th Edition

Motor control is an easy task when several machines are connected to a common line shaft driven by a motor which requires starting and stopping a few times a day. But in the case of the individual drive motor controller has to be designed to fit the machine needs to which the motor is connected as the motor is the integral part of the machine. The device or group of devices which controls the operation of the electric motor is called a motor controller. The controller can be a simple toggle switch or a complex system with components such as relays, timers, and switches.  Motor controller can be manual or remote controlled.

Operation accomplished by mechanical means by a human operator is called manual control. Devices such as toggle switch, safety switch, drum controller and faceplate controller are used to control the motor manually. Common practice to start and stop the machine is by manual control but in some industrial processes and machines automatic starting and stopping is used thereby saving time and materials. In automatic control a push button remote control may be used to control the motor. In such a case magnetic or electric switches should be included. The operation of the magnetic switch is by electromagnet actuated by electrical energy. The devices used to control the motor automatically are float switch, limit switch, pressure switch, thermostat and time clock.

The following are the functions of the motor controller.

1. The controller controls the starting action of the motor by connecting it directly across the voltage source. And to protect the machine from sudden inrush of current at starting, slow and gradual starting is provided by the controller.

2. The controller controls the stopping action of the motor by allowing motors to coast to a standstill or by imposing braking action for quick stopping.

3. The controller controls the reverse action of the motor by changing the direction of rotation of machines automatically or as per operator’s command at a control station.

4. The controller controls the running action of the motor by maintaining the desired operational speeds and characteristics. While running the controller protects motors, operators, machines, and materials.

5. The controller controls the speed of the motor as per the requirement.

6. From unsafe conditions the controller protects the operator.

7. Controller also protects the apparatus from faulty conditions.