Impulse (BIL) Testing Reactors & Transformers: A Short Explanation

Docta Reacta: Power Magnetics was in the news again recently, this time for BIL testing. In case you missed it, this is just a quick update on some news you may be able to use, intended to help you be smarter buyers of magnetics. If you want to read the article, check out the links below – including the one on the Institute Blog. Don’t miss the links to the photos[…]

Step Down Auto Transformers: Closely Coupled’ versus ‘Loosely Coupled’ Winding Configurations

Dr. Transformer: Picking up from the previous post on Step Down Auto Transformers: Eliminating Output Distortion, I promised to cover ‘closely vs loosely coupled’ windings. Magnetics designers commonly use the terms ‘closely coupled’ and ‘loosely coupled’ to describe winding configurations, and though they may know what the terms mean, they may not be understood by other engineers, including those who are responsible for applications using step down auto transformers. In[…]

Step Down Auto Transformers: Eliminating Output Distortion

Dr. Transformer: Today’s lecture on step down auto transformers is short and sweet: what most transformer designers do not know can hurt you, the specifier or buyer and have a negative effect on your application. There is an issue with step down auto-transformers that is neither readily obvious nor generally known to most transformer designers.  Stated succinctly it is that unless the ‘series’ winding is in a ‘closely coupled’ (low[…]

Plate Transformers and VPI (Vacuum Pressure Impregnation) In Detail

Dr. Transformer:  Welcome back to the Power Magnetics Institute, my friends!  Our customers have been asking for a clarification of the VPI and plate transformers post we discussed earlier. Vacuum Pressure Impregnation (VPI) is the process of treating the finished coils with varnish by placing it a vacuum chamber.  First, the transformer is placed in an oven and heated to approximately 275 ˚F. This heat treatment drives out moisture from the[…]

Percentage Impedance of Transformers

Dr. Transformer: Back from the holidays transformed!  Got on the scale this morning and.. oh, my! Certainly transformed!  Enough!  The questions about impedance continue to come in unimpeded! So let’s get to it! It is very common to see transformers specified with ‘Percent Impedance’. Because stating impedance in percentage terms is as a result of the ‘per unit’ system favored by power engineers, it isn’t surprising that it causes confusion[…]

Scott ‘T’ Connections for Furnace Transformers, Auto Transformers and Distribution Transformers

Dr. Transformer:  Welcome back to PMI Institute for today’s discussion of Scott ‘T’ Connections!  Say what?  Social networking?  Not here!  And no Scotty beam me up, either! (Get it?)  No, this is about transformers!  Furnace Transformers, Auto Transformers and Distribution Transformers in particular and their connection options.  This is one part of the story. The ‘Scott’ connection is the most popular way to connect three phase, 3Ø, to two phase,[…]

Vacuum Pressure Impregnation, VPI, and Atmosphere Dip – The Trade-offs

Docta Reacta:  Today’s topic at PMI Institute addresses when Vacuum Pressure Impregnation, VPI, makes sense for your transformers, like a high voltage plate transformer or medium voltage trap reactor and when it does not and Atmosphere Dip is more appropriate. Thank you for the applause.  Thank you! Thank you!  Wow, what a warm reception!  I realize that this is my first appearance on the new stage here at Power Magnetics Institute, and I[…]

Advantages of AutoTransformers vs Isolation Transformers

Dr. Transformer: Let’s get basic: in an Auto Transformers (versus an Isolation Transformers), the input and output windings are one continuous electrical circuit (see diagram); which is to say that the primary and secondary circuits are not isolated. Docta Reacta: You jumped right into it, huh? Let me a least welcome the Power Magnetics Institute readers!  Welcome! Dr. Transformer: Let me get on with the show!  So, compared to an[…]

Temperature Rise and Insulation System Ratings

Dr. Transformer:   Welcome back to Power Magnetics Inc. Institute!  Temperature rise and insulation for transformers, reactors and inductors is today’s hot topic.  Your burning questions as a design engineer and these answers can hopefully increase the reliability of your products in the field.  And some of those are deployed in pretty extreme environments, like our Trap Reactors and Current Limiting Reactors and Furnace Transformers.  You can find them in steel mills, deserts of the Middle[…]