Electrical Measurements as Diagnostic Tool for HV-Insulation

The electric condition is related to the capability of the insulation to withstand high
voltages and electric fields. The methods for condition determination of component and HV-
equipment are manifold. A plenty of physical measured values and parameters are consulted,
which gives direct or indirect information about the equipment condition. With equivalent
mathematical combination and analyse functions, an early diagnosis of an initiated system
fault can be made.
Diagnostic techniques are in use to observe relevant parameters and are supposed to provide
an early warning. Different diagnostic methods (thermal, mechanical and electrical) and
systems (Online - Offline) of power equipment will increase the reliability in service.
The electrical methods of this diagnostics are dielectric, breakdown and partial discharge
behaviour. The observation and evaluation of the interaction between electromagnetic field
and insulation material is named as dielectric diagnostic. Thereby the different polarization
mechanisms and the reaction of the dielectric material at a suitable voltage stress are
registered.
With breakdown analysis volume, weak spots and surface properties can be evaluated on
insulation models or separated equipment. The appearance and the intensity of partial
discharge is a quality criterion for a rating of electrical equipment and an estimation of the
condition of the insulation system can be done. The purpose is the detection of structural
changes, humidity and contamination during the service life