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 in the article (or see them in the blog post), in particular the one at the testing lab.  (Frankenstein could have used that setup!)

A good portion of our transformers and particularly our medium voltage harmonic filter reactors are required to meet a specific level of BIL (Basic Impulse Level) to protect against transients.

BIL is essentially an indicator of the dielectric strength of the design and construction of the transformer or reactor. There are two tests, lightning and switching impulse tests which test for each of those respectively. The lightning impulse test uses a full wave shape to reach a maximum in 1.2 microseconds and then decays 50% in 50 microseconds. The switching impulse test uses a chopped wave to simulate switching transients in the circuit.

Full Wave BIL Test Graph

Full Wave BIL Test Graph

While many manufacturers design to various impulse levels, few have 3rd party independent testing labs who have certified their designs. Power Magnetics recently completed another impulse test and we have results for 95kV, 125kV, and 170kV.

What does that mean for you? You can specify a BIL level for your magnetics and have complete confidence that your design will meet that requirement.

As always, if there is anything we can help you with, please give us a call.


Representative Media Coverage

Yahoo Finance


EE Times

Power Magnetics Institute (blog post)

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  • Tru Tech

    Very useful article. Very interesting to read this article. I would like to thank you for the efforts you had made for writing this awesome article. Transformer

  • Thanks for your ideas towards BIL. Power magnetics in recent days are becoming more powerful and are easy to use compared to other such kinds. These devices should become more popular and easily available in markets. Great Post!!

    Power transformers in India | Wire harness manufacturer in India

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