Motors Book - Chapter 6

A slip ring is a metallic ring mounted on a motor shaft and electrically insulated from the shaft. Slip rings are used in electrical machines to transmit power and electrical signals from a stationary part to a rotating part. They allow for continuous electrical connection between the stationary and rotating parts, even when the rotation causes the wires to twist. Slip rings are commonly used in applications such as generators, motors, and wind turbines.

Resistors designed for starting motors are able to dissipate the heat generated during the short time required for starting the motor. When a motor starts, there is an initial surge of current flowing through the resistors, which causes them to heat up. These resistors are specifically designed to handle this temporary increase in heat and prevent any damage to the motor or other components. By dissipating the heat efficiently, these resistors ensure a smooth and safe start for the motor.

When the maximum resistance is connected to the rotor and the induced frequency is at its highest, it means that there is a greater opposition to the flow of current in the rotor. This increased resistance results in a stronger magnetic field and greater torque production. Torque is the rotational force that causes an object to rotate, so when there is a higher torque, there is a greater tendency for the object to rotate. Therefore, the maximum torque is produced in this scenario.

A pigtial is an extended, flexible connection or a braided copper conductor. It is commonly used in electrical and electronic applications to provide a secure and reliable connection between components. The braided copper conductor allows for flexibility and durability, making it ideal for applications where movement or vibration is present. Pigtails are often used in wiring harnesses, grounding systems, and as connectors for various devices.

A wound-rotor motor is an induction motor with the squirrel-cage conductor bars replaced with coils of wire, and with added slip rings, brushes, and a resistor circuit. This type of motor allows for variable speed control and improved starting torque, making it suitable for applications that require adjustable speed and high starting torque. The slip rings and brushes provide electrical connections to the rotor windings, allowing external resistors to be added to the circuit, which helps control the motor's speed and torque characteristics.

A wound-rotor motor regulator is a device that contains high-wattage resistors, allowing it to control the speed of a wound-rotor motor. This regulator operates in variable-speed mode, meaning it can adjust the motor's speed as needed. It is designed to be used for as long as necessary, providing a reliable and adjustable power source for the motor.

A wound-rotor motor can be distinguished from a squirrel-cage induction motor by the presence of coils of wire in the winding slots instead of the solid conductor bars. Additionally, a wound-rotor motor has three slip rings on the shaft, which are used to connect external resistance to the rotor circuit. Therefore, the correct answer is "all of the above" as all three options differentiate a wound-rotor motor from a squirrel-cage induction motor.

The external resistor circuit is responsible for carrying the entire rotor current. In an electric motor, the rotor current is the current flowing through the rotor windings, which is necessary for the motor to operate. The external resistor circuit is connected to the rotor windings and helps control the speed and torque of the motor. By adjusting the resistance in the circuit, the amount of current flowing through the rotor can be regulated, allowing for precise control of the motor's performance.

The correct answer is "all of the above" because all three options mentioned - drum switch, three-pole rheostat, and silicon-controlled rectifier - are types of regulators.

Increasing the resistance of the rotor while it is running reduces the current in the rotor windings and reduces the speed of the motor. This is because increasing the resistance in the rotor circuit limits the flow of current, which in turn reduces the torque produced by the motor. As a result, the motor slows down and its speed decreases.

A three-pole rheostat is a switch with tapped resistors used to switch a set of resistors in or out of a wound-rotor circuit. It allows for variable resistance and control over the speed and torque of a wound-rotor motor. This type of switch is commonly used in industrial applications where precise control over motor performance is required.

A rheostat is a type of variable resistor that is used to control the flow of electric current in a circuit. In the context of starting a wound-rotor motor, a wire control circuit would be used with a rheostat. This circuit would allow for the adjustment of the resistance in the circuit, which in turn would control the starting current and speed of the motor. By using a wire control circuit with a rheostat, the motor can be started smoothly and gradually, preventing any sudden surges in current that could damage the motor.