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…
Volvo FL Electric E-mobility is since a while not just a domain of electric cars. Manufacturers of buses and trucks also develop the electric variants of their vehicles and bring them to the market. Volvo Trucks [1, 2], the world Read more…
E-mobility Our blog is generally focusing on medium voltage drive systems. However, we can’t ignore the trend and the huge potential of electromobility (e-mobility). Since the technology is based on electric motors, variable frequency drives and other power electronics we 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 Read more…
Motor start with VFD Our experience shows that the VFD motor start is sometimes not fully understood. This post shall explain how motor start with VFD works, what are the main benefits and how does it compare to a direct Read more…