Question 1

The sudden stopping of a motor by mechanical brakes can often harm the motor or load.

Accepted Answer

When a motor is suddenly stopped by mechanical brakes, it can cause an abrupt change in energy and torque, leading to damage to the motor or load. It is recommended to use methods such as gradually reducing the speed or coasting to a stop to avoid harm to the motor or load. When a motor is suddenly stopped by mechanical brakes, the kinetic energy of the rotating load is converted into heat energy, which can damage the motor, load, or both. Therefore, it is recommended to gradually slow down the motor using a deceleration ramp or coasting to a stop, rather than abruptly applying the brakes.

Question 2

Dynamic braking can easily be demonstrated by applying direct current to an AC induction motor and turning the ____.&#10;A)motor shaft by hand&#10;B)operator knob, not pushing it&#10;C)switch to the off position&#10;D)transistor on and off several times

Accepted Answer

By turning the motor shaft by hand, you are causing the rotor to turn faster than the stator's rotating magnetic field. This causes the rotor to generate a voltage that opposes the applied voltage, resulting in a braking effect known as dynamic braking. When direct current is applied to an AC induction motor and the motor shaft is turned by hand, the motor will act as a generator and produce an electrical current that opposes the applied current, resulting in dynamic braking. This can easily be demonstrated in a laboratory setting.

Question 3

It is recommended that the motor starter be included as an integral unit with the brake.&#10;A)never&#10;B)sometimes&#10;C)always&#10;D)in most cases

Accepted Answer

It is always recommended that the motor starter be included as an integral unit with the brake to ensure the proper functioning and safety of the system. It is important that the motor starter be included as an integral unit with the brake to ensure proper coordination and safe operation. This allows the brake to be activated in case of emergency or power failure, preventing the motor from continuing to run and potentially causing damage or injury. Therefore, it is recommended that the motor starter always be included as an integral unit with the brake.

Question 4

Taps on current-limiting resistors provide a means of adjusting the torque over a wide range.&#10;A)down&#10;B)limit&#10;C)polyphase&#10;D)braking

Accepted Answer

Taps on current-limiting resistors provide a means of adjusting the braking torque over a wide range, allowing for more precise control of the motor's stopping ability. Taps on current-limiting resistors provide a means of adjusting the braking torque over a wide range.

Question 5

A self-contained transformer and rectifier provide the direct current required for braking.

Accepted Answer

A self-contained transformer and rectifier can indeed provide the direct current required for braking.

Question 6

Electronic brakes require extensive maintenance, adjustment, and periodic replacement of worn parts.

Accepted Answer

Electronic brakes do not require extensive maintenance, adjustment or periodic replacement of worn parts, unlike traditional mechanical brakes. The electronic components are designed to last longer and often have self-adjusting capabilities. However, like any other electronic component, they may require occasional diagnostic checks and software updates to ensure proper functioning. This statement is false. Electronic brakes typically require less maintenance, adjustment, and replacement of worn parts than traditional mechanical brakes.

Question 7

DC and AC supplies must be connected to a motor at the same time.

Accepted Answer

DC and AC supplies cannot be connected to a motor at the same time as it can cause damage to the motor and potentially be dangerous. A motor should be designed to operate with either a DC or AC supply but not both simultaneously. DC and AC supplies cannot be connected to a motor at the same time as it can damage the motor due to conflicting electrical signals. Only one type of supply should be used to power a motor.

Question 8

Three-phase electric braking reduces the heat buildup in the motor as compared to single-phase braking.

Accepted Answer

Three-phase electric braking distributes the braking energy equally among the three phases, reducing the heat buildup in the motor. Single-phase braking applies the braking energy through only one phase, resulting in higher heat buildup and potential damage to the motor. Three-phase electric braking distributes the braking effect and reduces the heat buildup in the motor, making it more efficient than single-phase braking.

Question 9

With dynamic braking for a wound rotor motor, the circuit may provide three braking options, coast stop, medium stop, and stop.&#10;A)step&#10;B)rapid&#10;C)successive&#10;D)steep

Accepted Answer

Rapid stop is the correct option as dynamic braking provides rapid deceleration of a motor by quickly transferring the energy stored in the motor's rotating mass to a resistor network. The options provided in the question are coast stop, medium stop, and a third option which is not specified. Based on the options given, the best choice would be rapid stop as it provides a clear and specific option for braking. The other options given are vague and do not provide a clear indication of the level of braking that will be provided.

Question 10

It is sometimes difficult to install conventional electromechanical brakes on existing equipment without .&#10;A)the use of magnetic switches&#10;B)overheating the motor&#10;C)extensive rebuilding&#10;D)establishing an arc

Accepted Answer

Conventional electromechanical brakes may require extensive rebuilding of the equipment in order to be installed, making it difficult to add them to existing equipment without significant modifications. Conventional electromechanical brakes require significant modifications to existing equipment, often requiring extensive rebuilding to accommodate the installation. Options A and D are not related to the difficulty of installation, while option B may be a concern but is not the primary reason for difficulty in installation.

Deck 51: Electric and Electronic Braking