This series brings topics answering basic questions around VFDs such as fundamental components of VFDs, drive system components, working principles, dimensioning considerations etc.
Short circuit current contribution of a VFD Electric motors and generators contribute to the total fault level at the connection point. Their short circuit current is typically in the range 4…6-times the nominal current of the machine. How is the situation with a variable frequency drive? The answer is rather Read more…
Fuseless is not useless This post addresses the VFD protection concept and particularly the concept eliminating medium voltage fuses – so called fuseless design. We explain the advantages of such approach and why it is definitely not a useless feature. Concept of fuseless design Solid protection concept is key point Read more…
Reactors in drive systems: Where do we find them? Reactors are widely used in variable speed drive systems. They appear as sub-components inside the VFD or as external components on the grid side or machine side. In this post we look at various types of reactors, their location, function and Read more…
How do water-to-water and water-to-air heat exchangers compare? Medium and high power variable frequency drives (VFD) predominantly use liquid cooling. For such purpose either a water-to-water or water-to-air heat exchanger is used as part of the cooling system. There is sometimes a bit of confusion about how the heat exchanger Read more…
When is transformer pre-magnetization recommended? Some medium voltage drive systems feature a pre-magnetization unit. In certain VFDs the pre-magnetization might be a standard. Other VFDs offer such functionality as an option. And most VFDs probably do not have the pre-magnetization at all. No wonder that some end users may be Read more…
Why do larger drives achieve better efficiency? How does the efficiency of a drive system scale with the power? And why do larger drives achieve better efficiency? That is the subject of this blog post. What is efficiency Efficiency is the ratio between output power and input power, typically expressed Read more…
What types of VFD grid connection exist? How is the VFD connected to the supplying grid? There are several ways. In this post we look at the conventional ones as well as more specific solutions regarding variants of VFD grid connection. 1. Connection through at input isolation transformer Most common Read more…
VFDs and conventional wisdom Welcome to our blog about variable frequency drives and drive systems. This time on the topic: VFDs and conventional wisdom. The message we try to convey is that what many people usually believe and what seems logical at first point is not necessarily right. Does it Read more…
What makes protection firing so brilliant? Protection firing, sometimes also called “firing through”, is a VFD protectionconcept used in some medium voltage drives. The principle is well described in its name:In case of a severe fault the VFD will turn on all the active switches (such as power semiconductors in Read more…
What is behind the recooling of electric rooms? VFDs generate certain heat load that is dissipated into the ambient. Despite the high efficiency of the VFD, there is some portion of losses that heats up the electric room where the equipment is installed. Hence, it is important to ensure proper Read more…