This guide defines test methodologies and technologies for mechanical acoustic imaging. Acoustic fault recognition mechanisms using acoustic imaging technology are described, enabling, for high voltage reactors, the identification and diagnosis of abnormal radiated noise in a reactor structure caused by mechanical structural abnormalities such as loose structural parts, metal foreign bodies and loose leads. Additional use cases and test considerations are described, to support fault acoustic signal testing of power transformers, switchers and gas insulated substation (GIS).