Question 1

IGBTs have an insulated gate different from all types of field effect transistors (FETs).

Accepted Answer

IGBTs (Insulated Gate Bipolar Transistors) and FETs (Field Effect Transistors) both have insulated gates, which is a characteristic feature of these types of transistors, allowing control of the device without direct contact between the gate and the semiconductor material.

Question 2

Many variable-frequency drives can provide the characteristic that is so desirable in DC motors.&#10;A)low-speed torque&#10;B)low power factor&#10;C)high-speed torque&#10;D)high power factor

Accepted Answer

Many variable-frequency drives can provide the low-speed torque characteristic that is so desirable in DC motors. This is achieved through the ability of the drive to vary the frequency and voltage supplied to the motor, allowing it to maintain torque at lower speeds.

Question 3

The values of current limit, speed, ramping time, and so on for variable-frequency drives are .&#10;A)more difficult to adjust&#10;B)less accurate than adjusting trim resistors&#10;C)hard to read&#10;D)programmed into the unit

Accepted Answer

The values of current limit, speed, ramping time, and so on for variable-frequency drives are programmed into the unit, which makes it easier to adjust and more accurate than adjusting trim resistors. The values of current limit, speed, ramping time, and other parameters for variable-frequency drives are programmable and stored in the unit's memory. Therefore, they can be easily adjusted and set according to the specific application requirements.

Question 4

The primary purpose of a variable-frequency drive is to provide speed control for an AC motor.

Accepted Answer

A variable-frequency drive (VFD) is an electronic device that controls the speed and torque of an AC motor by varying the frequency and voltage of the power supplied to it. Thus, the primary purpose of a VFD is to provide speed control for an AC motor. The primary purpose of a variable-frequency drive is to provide speed control for an AC motor. A VFD can also improve energy efficiency and reduce wear and tear on the motor by controlling the frequency and voltage of the power supplied to the motor.

Question 5

Variable-frequency drives control motor speed by controlling the frequency of the power supplied to the motor.

Accepted Answer

Variable-frequency drives (VFDs) are electronic devices that control motor speed by varying the frequency of the alternating current (AC) power supplied to the motor. By changing the frequency, VFDs can adjust the speed of the motor and match it to the specific application requirements. Variable-frequency drives (VFDs) use electronic devices called inverters to convert the incoming AC power to DC power, and then back to variable-frequency AC power at the desired frequency to control the speed of the motor. The higher the frequency, the faster the motor spins, and the lower the frequency, the slower the motor spins. Therefore, VFDs can precisely control the motor speed by adjusting the output frequency of the drive.

Question 6

The magnet wire used in the construction of inverter rated motor windings has a lower rated insulation than other motors.

Accepted Answer

Magnet wire used in inverter rated motor windings typically has a higher rated insulation to withstand the electrical stresses caused by high frequency switching and potential for voltage spikes from the inverter output.

Question 7

Inverter-rated motors generally have phase paper .&#10;A)to provide a larger surface area&#10;B)to provide continuous cooling for the motor&#10;C)to help draw air through the motor&#10;D)added to the terminal leads

Accepted Answer

Inverter-rated motors often have phase paper added to the terminal leads to provide additional insulation against the high-frequency electrical noise generated by inverters. This helps in protecting the motor from potential damage caused by the inverter's output.

Question 8

Drives using IGBTs generally use to rectify the AC voltage into DC.&#10;A)SCRs&#10;B)GTOs&#10;C)diodes&#10;D)thyristors

Accepted Answer

IGBTs are typically used in conjunction with diodes to rectify AC voltage into DC. The IGBTs control the flow of current, while the diodes ensure that the current flows in a single direction. This combination allows for efficient and precise control of the motor in the drive system. IGBTs (Insulated Gate Bipolar Transistors) are typically used in AC motor drives to control the speed and direction of the motor. To convert the AC voltage into DC, diodes are used in a process called rectification. IGBTs are then used to control the DC voltage going to the motor. Therefore, the best choice is C, diodes.

Question 9

Speed regulation is accomplished by sensing the speed of the motor and .&#10;A)connecting current transformers to the input of the drive&#10;B)feeding this information back to the drive&#10;C)sensing the increase in current as load is added&#10;D)adjusting this speed

Accepted Answer

Speed regulation requires feedback of the actual motor speed back to the drive to enable adjustments to the speed as needed. Option A is incorrect as current transformers are used for monitoring current, not speed. Option C is incorrect as an increase in current may not always indicate a decrease in speed. Option D is incorrect as speed regulation requires adjustments to be made to maintain a constant speed, not just adjusting the speed. Speed regulation involves feeding back the speed information to the drive in order to adjust the speed accordingly. Option A does not explain how the current transformers would regulate the speed, option C is describing how motor load is sensed, and option D repeats the question without providing an explanation.

Question 10

DC motors are still used in many industries.

Accepted Answer

DC motors are still widely used in industries such as automotive, robotics, and manufacturing for their efficiency and precise control. DC motors are still commonly used in industries such as manufacturing, automotive, aerospace, and robotics. They are known for their reliability and precise speed control.

Deck 55: Ac Adjustable Frequency Drives