Converter duty transformers / rectifier duty transformers / VFD transformers – these are all synonyms for transformer supplying power electronic based converters. What is so special about these animals? How do they differ from a normal distribution or power transformer? How to protect these transformers and maximize their reliability?
What is the definition of short-circuit impedance? Short-circuit impedance, also called impedance voltage, is an important design parameter of a transformer [1]. Thus, it is crucial to understand this parameter. In this brief post we introduce three ways of definition of short-circuit impedance. Definition 1 Short-circuit impedance (reactance and resistance) Read more…
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…
Can 50 Hz rated equipment operate on 60 Hz grid and vice versa? Globalization affects various areas of our lives. Variable speed drive systems are no exception. It happens that components manufactured in a “50 Hz country” will be used in a “60 Hz country” or the other way round. Read more…
What is a Phase-Shifting Transformer? VFD multi-winding transformers typically use phase-shifting feature in order to eliminate (cancel) certain harmonic orders in the spectrum of the current drawn from the grid. There are, however, other transformers that also use phase-shifting, but it a completely different power range and application. This blog Read more…
What is transformer K-factor? Transformers supplying power electronic equipment are exposed to non-sinusoidal load current. The harmonics cause additional losses in the transformer. One way to express the transformer design with respect to immunity against harmonic distortion is so called K-factor. Since transformer K-factor is a potential source of confusion, Read more…
What are the transformer guaranteed values? Like other electric equipment also transformers are generally designed in accordance with international standards. There are multiple parameters stated in the technical specification or a data sheet. However, which of them are the transformer guaranteed values? And what does the guarantee actually mean? Does Read more…
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 is whether a tap changer is needed or not. The 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, losses, sound level, reliability or equipment price. Welcome to ONAN/ONAF 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 at all. No wonder that some end users may be Read more…
309 days on site! 309 days…that is exactly how long our rental transformer was on site. This example illustrates the importance of a backup solution when you experience fault of a VFD transformer. It was the beginning of December 2021 when we received an inquiry to rent a drive transformer. Read more…