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…
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…
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…
Protection of VFD-fed motors How to properly protect an inverter-duty variable-speed electric motor? What protection is covered by the VFD? What shall be done externally? Which protection elements are most suitable? The article on protection of VFD-fed motors brings the answers. General considerations System and equipment protection is of crucial Read more…
Root cause of VFD transfomer failures Before we dive into the topic let us stress the fact that transformers belong to very reliable electric equipment and their failure rate is very low. This statement is generally valid also for VFD transformers. But no matter how reliable a certain device is, 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…