This series brings topics answering basic questions around VFDs such as fundamental components of VFDs, drive system components, working principles, dimensioning considerations etc.
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
Scalar control – What does it actually mean? Many times we see that the term ‘scalar control’ is used in incorrect way or being misinterpreted. In this article we will briefly discuss scalar control – what does it actually mean? How does it differ from a field oriented control? What Read more
What VFD properties matter the most to you? Medium voltage VFD is often a long term investment. The expected lifetime is typically at least 20 years. Thus, it is important to make the right choice when purchasing it. That is easily said, right? But there are several products on the Read more
Why do VFDs sometimes trip during grid faults? Grid disturbances and faults appear now and then. And it is desirable that the VFD does not trip every time such event occurs. Thus certain immunity against grid disturbances is desired. In fact, many products claim to have a capability to withstand Read more