With the simple and very efficient method, the dielectric condition of cables of medium voltage networks can be evaluated, and treeing in the insulation can be detected.
Whilst tan delta measurement is suitable for detecting water trees, with the measurement of partial discharge, damage to the insulation and electrical trees can be detected and located.
Data collected during the procedure is compared to measurement values of the same cable gathered during the acceptance-test.
This allows simple and quick classification of the dielectric condition (new, strongly aged, faulty) of the cable under test.
The portable PD cable diagnostics systems are compact and designed for mobile use.
Essentially, they consist of the following units:
As with VLF cable testing a sinusoidal 0.1 Hz VLF (very low frequency) voltage is used for measurement of partial discharge.
The PD series systems are available for 4 different voltage ranges - 34 kV peak, 62 kV peak, 90 kV peak and 120 kV peak.
Measurement of partial discharge is applicable for cables and accessories of medium voltage networks with various insulation materials:
Moreover, assessment of the following plant is possible:
The PC based software serves for display and analysis of measurement results.
The intensity of partial discharge is measured in pico Coulomb (pC) and displayed versus time.
By means of a fully automatic analysis of the reflectograms collected during the measurement – via a method referred to as time domain reflectometry TDR – a location of insulation irregularities is possible and they are displayed in a partial discharge mapping format.
A phase related depiction of the partial discharges provides additional information, useful for the evaluation of the device under test.
In a report all relevant measurement values are recorded:
Just like the hipot testers of the HVA series
the diagnostic systems of the PD series are simple and intuitive in their use.
Thus, any operator is capable of performing measurement without extensive training.