Fault current considerations for integrated transformer of CHB drive Introduction Cascaded H-bridge (CHB) variable frequency drives (VFD) have the input transformer as an integral part of the VFD. This transformer has high number of secondary windings (equal to the number of VFD power cells). Such multi-winding transformer represents a challenge Read more…
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…
What do the protection function numbers mean? In single line diagrams and other documents depicting protection details you can see various numbers. These numbers are also called ‘ANSI codes’ as they are defined in the ANSI/IEEE standard. What do the protection function numbers mean? You have surely seen them: the Read more…
Arc resistant design solutions In our introduction last time we have explained the danger of an electric arc flash for the personnel and the equipment. The arc reaches extremely high temperatures and releases pressure and sound waves into the surrouding. Besides personal protective equipment (PPE) the risk of an arc Read more…
VFD as soft starter Welcome to the next article in our motor starting series. This time we will talk about VFD as a soft starter. Our first post focused on direct on-line motor start as the cheapest and simplest method. The second article provided a brief overview of common motor Read more…
Protection of VFD transformers In the introduction to this series we have explained the differences between a distribution/power transformer and a VFD transformer [1]. Due to different design, construction and operation of VFD transformers the protection requirements shall be adapted as well. While many end users, system integrators, EPCs and Read more…
How to choose a medium voltage VFD:Protection concept A variable speed drive system with gaps in protection philosophy is a ticking bomb. It might have a huge impact on plant availability and potentially also on personal safety. Therefore, no compromises shall be accepted. Other topics in this series are definitely Read more…