Power Transformers

Acoustic Emission Systems can be used to detect and/or locate PD (partial discharge) in transformers.

Acoustic emissions are transient elastic waves in the range of ultrasound, usually between 20 kHz and 1 MHz, generated from the rapid release of energy from a source. PD’s are pulse-like and cause mechanical stress waves (acoustic waves) to propagate within the transformer. If the stress propagates to the transformer tank wall, they may be detected with a transducer that is tuned to the right frequency. PD sources can be located by measuring the relative time of arrival of acoustic waves at multiple transducer locations.

Acoustic emission (AE) can be used when the transformer is on-line and during transformer applied voltage or induced voltage tests. AE is non-invasive. Some commercial systems can differentiate between actual PD and other acoustic noises.


The MISTRAS VPAC™ II, licensed from British Petroleum, is widely used in refineries, offshore platforms, power and process plants for estimating through-valve gas losses to flare, and steam generating losses.

There are more than 1000 systems in routine use. The reported cost savings exceed USD $1million per site.

A measurement taken in seconds is converted to through-valve loss using a formula developed by best-fit to actual physical mass flow tests on >1000 valves over a 10-year period.

The VPAC™ II is a quick, accurate and reliable instrument.