Test your knowledge about medium voltage drive systems
How well do you know medium voltage variable frequency drives? Test your knowledge in our short quiz. Submit your answers and get a chance to win a small prize.
1. What is the meaning of the abbreviation ‘VSD’ in our context?
a) Very Special Device
b) Virtual Shared Disk
c) Variable Speed Drive
d) Very Secret Diaries
For more information read our article Abbreviations and definitions.
2. What is the relationship between VFD and VSD?
a) Every VFD is a VSD but not every VSD is a VFD.
b) Every VSD is a VFD but not every VFD is a VSD.
c) The meaning is the same.
For more information refer to our article What is the difference between VFD and VSD.
3. What is the heart of a power electronic drive?
a) Copper busbar
b) Power semiconductor
c) Capacitor bank
A little hint in case of doubts.
4. What driven loads may benefit from variable speed with regard to energy savings?
a) Centrifugal pumps
b) Fans and blowers
c) Centrifugal compressors
d) All above
You can get some inspiration in this article on energy efficiency.
5. How does the grid voltage distortion of AFE drive changes with inverter load (active power delivered to the motor)?
a) grid voltage distortion increases with inverter load
b) grid voltage distortion decreases with inverter load
c) grid voltage distortion is independent on inverter load
6. Which statement is true about grid side power factor?
a) Asynchronous motor drive has higher grid power factor than synchronous motor drive
b) Synchronous motor drive has higher grid power factor than asynchronous motor drive
c) Grid power factor has no relation to motor type
In case of doubt, this article on asynchronous versus synchronous motor drives may help.
7. What is the definition of a field weakening point?
a) Speed point above which the flux in the machine starts reducing
b) Speed point where motor reaches its rated stator voltage
c) Temperature point above which the motor starts to demagnetize
Try to mark the right answer on your own. Afterwards, you can get a confirmation here: Adjusting the field weakening point.
8. What are the most common braking methods in inverter-fed motors?
a) braking chopper, counter-current braking, regenerative braking
b) braking chopper, regenerative braking, passive braking (coasting)
c) eddy-current braking, braking chopper, regenerative braking
I am sure you know the answer. Just in case you want to read more about braking options, here is one of our resources.
9. What is a common mode voltage?
a) fundamental voltage (without harmonics) used for control and protection
b) zero sequence voltage generated by inverter modulation
c) standardized inverter output voltage (e.g. 4.16 kV, 6.6 kV, 11 kV)
Your turn. No hint here 🙂
10. What defines the acceleration of VFD-fed motor drives?
a) Parameterization of speed ramp in control system, torque capability of the system and total inertia
b) Inverter current capability, settings of speed controller and motor inertia
c) Threshold of overspeed protection, torque limiters and process control system
Your turn. No hint here 🙂
11. What means “phase-shifting” in converter transformers?
a) Transformer cooling medium is changing the phase from liquid to gaseous (heat pipes principle)
b) Transformer is dedicated to supply thyristor based VFDs with phase angle control
c) Transformer secondary windings have a relative phase displacement to cancel certain harmonics
More on phase shifting here: VFD transformers – Multi-winding design.
12. Where is a VFD typically installed?
a) In the machine room
b) In the electric room
c) In the control room
No hint. That would be too easy 🙂
13. What is the most frequently used medium voltage VFD topology (number of installed units)?
a) Cascaded H-bridge
b) Load-commutated inverter
c) Flying capacitor inverter
Get the direction from this article: Most common MV VFD topologies.
14. What applications can benefit from variable frequency drives (VFDs)?
a) Pumps and fans
b) Compressors
c) Mixers and extruders
d) Conveyors
e) All above
15. What is a typical efficiency of a VFD at nominal load?
a) 85% to 88%
b) 93% to 95%
c) 97% to 99%
No doubt that you know the answer. For a bit deeper dive, check this article on expected efficiency.
16. What are the strategies to minimize grid harmonic distortion?
a) Utilize VFDs with multi-pulse diode rectifier, use synchronous motors with power factor 1.0
b) Utilize VFDs with active front end or with multi-pulse diode rectifier
c) Utilize VFDs with active front end or install a transformer premagnetization system
Common harmonic mitigation methods are briefly described here: Harmonic mitigation methods.
17. What motor length is supported by medium voltage VFDs?
a) Tens of meters in case of VSI without any output filter
b) Several hundred meters in case of VSI with a dv/dt filter
c) Up to several kilometres in case of CSI or VSI with an output sine filter
d) All above
Facing the challenge with long motor cables? Check out this article.
18. Differential protection of multi-winding transformers
a) is a complex solution with high cost
b) requires lot of components
c) is typically not recommended for transformers with more than 3 windings
d) All above
For more details on the subject can be found in this blog post.
19. Advantages of multi-drive solution include:
a) Reduced footprint and reduced rating of certain hardware (transformer, switchgear)
b) Reduced investment cost (CapEx)
c) Better efficiency thanks to regeneration through DC link
d) All of them
Hey, we have an entire series of articles on the subject: VFD multidrives.
20. Which statement is correct with respect to lifetime of a VFD?
a) Typical design lifetime is at least 20 years
b) Regular maintenance boosts the lifetime
c) Lifetime can be extended through control upgrades
d) All above statements are correct
If you want to know more on this subject, here is one resource from an industry expert.
Got the answers? Send them to us (format example 1b, 2a, 3c,…) or use the comment section below. A small award is waiting for you…
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