For many years, PD measurements in transformers installed at stations were made only using the AE method. These measurements are made during normal operation of the transformer. Due to the development of measurement technology, for the last several years it has also been possible to use under these conditions the electrical method and UHF. In measurement practice, very often these two methods are used simultaneously. A UHF probe is placed in the middle of the transformer using an oil evacuation valve. On the other hand, in the electrical method it is the measurement terminals of bushings that are usually the source of the measurement signal.

Fig. 1. View of an UHF probe fixed to the transformer tank oil evacuation valve
Fig. 2 View of a bushing’s measurement terminal

Energo-Complex makes PD measurements when transformers are supplied with rated voltage from a so-called rigid network or from an external source. A significantly lower level of interference is obtained when power is supplied from a system consisting of a generator and a transformer that increases voltage. In this case it is also possible to make measurements in a wider voltage range. However, the selection of the power source for measurement purposes is an individual matter and depends on the specific situation of the transformer and network conditions.

Fig. 3. PD measurements using an external power source

In the measurement practice, Energo-Complex uses Montesto 200 measuring and recording system, which enables a simultaneous analysis of electrical signals as well as signals recorded in the ultra-high frequency band by a UHF probe.

Fig. 4. View of Montesto 200 measuring and recording system