Question 1

The speed of the rotating magnetic field is known as the ____.&#10;A) synchronous speed&#10;B) asynchronous speed&#10;C) synchronous velocity&#10;D) asynchronous velocity

Accepted Answer

The speed of the rotating magnetic field in an AC motor is referred to as the synchronous speed. This speed is determined by the frequency of the electrical supply and the number of poles in the motor, and it is the speed at which the magnetic field rotates.

Question 2

Variable frequency drives intended to control motors under 500 Hp generally use SCRs or GTOs.

Accepted Answer

Variable frequency drives intended to control motors under 500 Hp generally use Insulated Gate Bipolar Transistors (IGBTs) for their switching components, not SCRs (Silicon Controlled Rectifiers) or GTOs (Gate Turn-Off Thyristors). IGBTs are preferred for their efficiency and performance in lower power applications.

Question 3

In a variable frequency control, the ____ control sets the maximum amount of current the drive is permitted to deliver to the motor.&#10;A) volts per hertz&#10;B) maximum Hz&#10;C) current limit&#10;D) minimum Hz

Accepted Answer

The current limit control in a variable frequency drive (VFD) sets the maximum amount of current the drive is allowed to deliver to the motor, protecting the motor and drive from overcurrent conditions.

Question 4

____ are devices used to change direct current into alternating current.&#10;A) Inverters&#10;B) Oscillators&#10;C) Rectifiers&#10;D) Transformers

Accepted Answer

The answer of ____ are devices used to change direct...

Question 5

In a variable frequency control, the ____ sets the ratio by which the voltage increases as frequency increases or decreases as frequency decreases.&#10;A) volts per hertz&#10;B) maximum Hz&#10;C) current limit&#10;D) minimum Hz

Accepted Answer

The volts per hertz control in a variable frequency drive sets the ratio by which the voltage increases as frequency increases or decreases as frequency decreases, ensuring the motor receives the appropriate voltage for its speed.

Question 6

A great advantage of drives using IGBTs is the fact that SCRs are generally used in the power supply.

Accepted Answer

IGBTs (Insulated Gate Bipolar Transistors) and SCRs (Silicon Controlled Rectifiers) are both used in power electronics, but the advantage of drives using IGBTs does not stem from the use of SCRs in the power supply. Instead, IGBTs are favored for their high efficiency, fast switching, and ability to be controlled easily, which are intrinsic qualities unrelated to the use of SCRs.

Question 7

____ is used to accelerate or decelerate a motor over some period of time.&#10;A) Coasting&#10;B) Damping&#10;C) Driving&#10;D) Ramping

Accepted Answer

Ramping is the process used to gradually increase or decrease the speed of a motor over a specified period of time, which helps in reducing mechanical stress and electrical current surge.

Question 8

The power ratings for oscillators range from a few milliwatts to megawatts and their frequency from a few cycles to several billion cycles per second.

Accepted Answer

Oscillators can vary widely in power and frequency, from low-power applications like radio transmitters to high-power applications like industrial RF heating, covering a broad frequency spectrum.

Question 9

Saturating the transistor causes the collector-emitter voltage to drop to between .04 and .03 volts.

Accepted Answer

When a transistor is in saturation, the collector-emitter voltage drops to a very low value, typically between 0.03 and 0.2 volts, indicating a strong connection or "on" state, which aligns with the given range.

Question 10

Due to the problem of excessive voltage spikes caused by IGBT drives, some manufacturers produce a motor that is &#34;inverter rated.&#34;

Accepted Answer

"Inverter rated" motors are specifically designed to handle the voltage spikes and other stresses caused by the rapid switching of power electronics, such as those found in IGBT (Insulated Gate Bipolar Transistor) drives, thus mitigating potential damage and extending the motor's lifespan.

Deck 28: The Oscillator