Ch.14 Adjustable Speed Drives

AC motors should not be driven at a speed higher than ___% above the motor's rated nameplate speed unless a licensed engineer is consulted.

10

___ placed in the DC bus section of an adjustable-speed drive are used to prevent capacitors from drawing too much current.

Current-limiting resistors

___ control is a method of controlling the voltage applied to a shunt field.

DC field-current

___ is a method of controlling the voltage sent to a motor by controlling the amount of time a transistor is ON and conducting current.

Pulse-width modulation (PWM)

___ is the ratio of voltage to frequency in a motor.

Volts-per-hertz ratio (V/Hz)

Inverter drives include ___ inverters.

all of the above

The main section of adjustable-speed drives is the ___ section.

all of the above

___ control is a type of variable-speed DC motor control.

all of the above

An AC adjustable-speed drive changes the frequency of the voltage applied to a motor by taking the incoming DC voltage, converting it to an AC voltage, and inverting it back to variable-frequency DC?

false

Carrier frequency is the frequency of the voltage a motor uses, but the fundamental frequency actually delivers the carrier frequency voltage to the motor?

false

The converter section of an adjustable-speed drive controls the voltage level, voltage frequency, and amount of current that a motor receives?

false

The inverter section of an adjustable-speed drive filters the voltage and maintains the proper DC voltage level?

false

The ___ frequency is the frequency of the voltage used to control motor speed.

fundamental

The primary function of an adjustable-speed drive is to convert the ___________ to an altered voltage level and frequency that can safely control the motor connected to the drive and the load connected to the motor.

incoming supply power

A(n) ___ stores energy in the form of a magnetic field.

inductor

A(n) ___ drive, or scalar drive, is a standard adjustable-speed drive that uses pulse-width modulation to control speed and torque.

inverter

A(n) ___ motor is an electric motor specifically designed to work with AC adjustable-speed drives.

inverter-duty

A(n) ___ vector drive, or sensorless vector drive, is a vector drive that has no feedback from the motor.

open-loop

A voltage difference greater than 3% between the output voltage at no-load and full-load conditions indicates that the adjustable-speed drive is underpowered and/or overloaded?

true

All adjustable-speed drives are designed to remove power when there is a problem, and some drives allow conditions and faults to be monitored and displayed?

true

By varying the voltage applied to the motor, the torque that the motor can deliver to the load is varied?

true

Derating an adjustable-speed drive decreases the demand put on a drive, and increasing heat sink size adds additional cost to a drive?

true

Drives with analog or digital feedback signals can be used where extremely precise speed regulation is required?

true

Most adjustable-speed drives are supplied with 3-phase power?

true

The DC bus section, or DC link, includes DC voltage supplied by the converter section and the DC filter components?

true

The simplest way to adjust the drive output is to set an internal reference voltage?

true

When voltage spikes caused by an adjustable-speed drive become a problem, the lead length should be reduced and/or filters that suppress voltage spikes should be added?

true

AC adjustable-speed drives are used to change the speed of AC motors by changing the frequency of the voltage applied to the motor?

true?

AC adjustable-speed drives create problems for standard motors because the drives produce voltage spikes?

true?

Because of capacitive filtering, ___ drives can tolerate voltage dips on the power lines.

variable-voltage-inverter