Are surge arresters suitable for protection of VFD fed motors? Surge arresters are commonly used to protect electric equipment against excessive overvoltages. At the same time, many voltage source inverters produce non-sinusoidal voltages that stress the machine insulation. Thus, one Read more
How do ONAN and ONAN/ONAF transformers compare? Oil natural – air natural (ONAN) and oil natural – air forced (ONAF) variants belong to the most common oil-filled transformer cooling designs. This post compares both of them with regards to dimensions, Read more
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 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 Read more
Insulation materials in electric machines Insulation material plays key role in the construction of electric machines. It is essential for the functionality of the machine by providing dielectric insulation of live parts. Moreover, the long term stability of the insulation Read more
What factors shall be considered when designing a harmonic filter? Most modern variable frequency drives (VFD) have so high power quality that they comply with the corresponding standards without the need for additional harmonic filtering. Nevertheless, there are cases where Read more
How does a grid harmonic filter work? Recently we got a question in our chat group: How does a grid harmonic filter work? It sounds like a very basic question. However, since many people struggle to imagine the flow of Read more
More than 200 blog posts: Get an overview Since our start in November 2018 more than 200 blog posts in almost 40 different categories have been published. We are thankful for all our readers – regular and random – for 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 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 Read more