Why do you need a partial discharge free test chamber?

Electrical components that operate in environment that requires safety as a critical matrix have a specification of very low partial discharge (e.g. <5pC). After the process of manufacture there is a needs to measure very low partial discharge in such electrical components. Ambient electrical noise in the measuring system and other external interference can very well exceed the minimum partial discharge threshold. For example, if the ambient electrical noise in a test setup is about 30pC, it is impossible to measure 5pC in such a test setup. Test equipment used for measuring the partial discharge such as transformers, capacitors should also have very low partial discharge (lower than the required measuring threshold). Using source filters can eliminate some ambient noise but this is not enough. Therefore eliminating external interference is essential - which calls for a need to have a partial discharge free chamber where the test equipment and the device under test needs to be setup.