When is transformer tap changer needed? The input isolation transformer in a drive system may be equipped with a tap changer. Such device provides some flexibility but adds cost and potentially also complexity to the transformer design. Thus, the question Read more
High-speed drives: VFD perspective In the introduction to high-speed drives [1] we have briefly described the design variants of semi high-speed and high-speed motors. The impact on construction of the motor is significant. High-speed motors can be quite different compared Read more
Get our Blog Book in pdf format Do you enjoy reading our blog online? Then you might be interested to get your own copy of all our blog posts in form of a digital blog book. History of our blog Read more
High-speed drives:Introduction Since a long time we wanted to write more about high-speed drives, their theory, design, application etc. Finally we manage to publish this short post providing an introduction into high-speed drives. In line with our blog, the focus Read more
Reactors in drive systems: Where do we find them? Reactors are widely used in variable speed drive systems. They appear as sub-components inside the VFD or as external components on the grid side or machine side. In this post we Read more
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