Sustainable drive systems throughout the entire life cycle Sustainability is a popular word in today’s dictionary. In our opinion this is very good as long as the efforts are sincere and it is not just marketing. Variable frequency drives (VFD) Read more
Harmonic filters The continuation of our “Network harmonics” series [1] presents an article about AC harmonic filters. We explain the purpose of harmonic filter. Different types of harmonic filters are shown. Several design considerations are discussed. Main items are illustrated Read more
Trolleybus Skoda 9 Tr Lot of cities nowadays invest in more environmental friendly public transportation. Due to that trolleybuses experienced a renaissance in the last couple of years. Many cities that used to have trolleybus lines and discontinued their operation Read more
Network harmonics: Mitigation methods Today’s post focuses on harmonic mitigation methods. Let us review the most common, well proven methods of minimization of harmonic distortion on the grid side. Previous articles presented a general view on harmonics, their origin and Read more
VFD harmonic spectrum Introduction After the theoretical introduction [1] we jump to variable frequency drives as sources of harmonics. This post is about VFD harmonic spectrum. As already mentioned, VFDs belong to non-linear devices with non-sinusoidal currents and/or voltages that Read more
Transformer winding connection, clock number and vector group This article explains the winding connections, clock number and vector group of phase-shifting transformers used to supply variable frequency drives (VFD). Motivation Some of the most common keywords that bring the readers Read more
Energy saving assessment for a drive system Variable frequency drives (VFD) often allow considerable energy savings for the end user. We have previously shared case studies on variable speed fans [1] and variable speed pumps [2]. Resulting payback time can Read more
VFD transformers: Your questions The articles from VFD transformers [1] series belong to the most frequently read posts in our blog. It seems that many visitors find us through internet search using keywords such as “converter duty transformer”, “24 pulse Read more
Overvoltage protection of transformers This is the continuation of [1] that made an introduction into protection of VFD transformers. The focus of this article is on overvoltage protection. Particular attention is paid to very fast transient overvoltages caused by switching Read more
High altitude Majority of variable frequency drive (VFD) systems is installed at altitudes below 1’000 meters above sea level (masl). In such cases no additional considerations due to installation height apply. However, there are sites located at high altitudes. How Read more