Variable Frequency Drives

Question 1

What the 8 things Variable Frequency Drives are used for?

Answer 1

1. Control the speed at which the motor operates at
2. Control the direction of a rotation of a motor
3. Control the rate at which the motor accelerates and decelerates
4. Control a fixed speed motor in such a way that it can operate at multiple speeds
5. Control the amount of torque a motor produces
6. Reduce the amount of break-away start-up shock loading to the driven load
7. Reduce the amount and frequency of maintenance
8. Reduce the amount of electrical energy consumed by the process.

Question 2

What ar other names for Variable Frequency Derives?

Answer 2

1. Variable Voltage Variable Freqency Drive (VVVFD)
2. Adjustable Frequency Drive (AFD)
3. Variable Speed drive (VSD)
4. Adjustable Speed Drive (ASD)
5. Variable Frequency Drive (VFD)

Question 3

What does a VFD Do?

Answer 3

1. They are electronic motor controllers
2. They act like a common motor starter , in that they Start, Stop, and protect three phase motors

Question 4

VFD’s recieve a standar utility three phase, (in some cases single phase), and convert it to a:

1. Quasi-or-pseudo-sinusoidal three phase electrical signal that is truly DC, but the motor does not know that.
2. An AC current 220v or 460v

Answer 4

1. Quasi-or-pseudo-sinusoidal three phase electrical signal that is truly DC, but the motor does not know that.

Question 5

How can people communicate with a VFD?

Answer 5

With a Human Machine Interface which usually involves a touchscreen or a keypad.

Question 6

What are some classifications of VFD’s

Answer 6

Methods used are:

a. Braking capacity how fast the motor can be stopped or interupted without being destroyed or causing an electric arc with unacceptable duration. a kind of a short.
b. Comunication method
c. The converter topology or layout of the componants
d. Cooling methods
e. Power source AC-DC
d. Type of power electronics such as GTO, IGBT, MCT,MOSFET
e. Votage rating, such as low braking volts or less medium 13 KV

Question 7

How can you measure the perforamnce of a VFD?

Answer 7

1. The efficiency, energy in to the energy out ratio
2. harnonics, current and voltage
3. Overload capacity. Ability of theu drive to operate under an overload condition without tripping off line.
4. Regenerative capability. Ability of the VFD to convert the energy contained in an overhauling load to electrical power.
5. Ride through capacity. Tolerance of brief power outages
6. Speed accuracy. Error in speed as a percentage of rated speed.
7. Speed range. ratio of Max to min kspeed, typically 10 to 1
8. Speed regulation. Response time to a step change in the speed command.
9. Starting torque. Amount of break-away and acceleration torque that the VFD can generate.

Question 8

What are the disadvantages of a VFD’s

Answer 8

1. they are best with more costly “inverter grade” motors
2. generates harmonic currents, may require additional filtering equiptment
3. High efficiencey motors tend to run hotter when powered ny a VFD
4. Limited operating voltages are available

Question 9

What are the benefits of using a VFD?

Answer 9

1. Ability to control themotor’s direction of rotation
2. Ability to control the amount of torque produced by the motor
3. Ability to control the motor speed as the process phase changes
4. Ability to control the rate of acceleration and deceleration of the motor
5. The ability to vary the speed of the motor in a linear or step manner
6. Reduce maintenance cost and frequency
7. Reduce the total amount of energy comsumed by the process

Question 10

What technology was used before the VFD’s

Answer 10

DC motors had to be used as it was way more simpler to control by inserting a rheostat into the low-power DC field circuit, which was feasible with available technology. These simple motor controls varied the speed and torque, and were the most economical way to do so for a number of decades.