Original scientific paper
Medium and Low Voltage Cable Measurements - TD, PD, LIRA
Josip Čeović
; Elmont d.o.o Krško Cesta Krških Žrtev 135e, 8270 Krško, Slovenia
Matko Širola
; Elmont d.o.o Krško Cesta Krških Žrtev 135e, 8270 Krško, Slovenia
Abstract
Elmont d.o.o. Krško – We have spread our main scope of the services from electrical
maintenance, modifications implementations and quality control to cable testing area. The main
reason for expanding our scope was to support Nuclear Power Plant Krško Cable Aging Management
program and the world trend of LTE (Life Time Extension) in power plants.
Scope of work – We are identifying potential downgraded conditions for safety and operational
important cables in special areas (heat, water, radiation). Our main scope is visual control, and testing
with analysis.
For low voltage cables the main testing method is Line Resonance Analysis (LIRA). LIRA
technology is based on the transmission line theory, through the estimation and analysis of the
complex line impedance as a function of the applied signal frequency. We can monitor the global,
progressive degradation of the cable insulation due to harsh environment conditions (high
temperature, humidity, radiation) and detect local degradation of the insulation material due to
mechanical impacts or local abnormal environmental conditions.
For medium voltage cables we are using new methods with a power generator that uses Very
Low Frequency – 0,1Hz (VLF). The main reason for this is that the measurement unit needs 500
times less energy than the unit which uses 50Hz frequency (50/0,1=500). With this power source we
are performing dielectric loss measurements – Tan delta (TD) and Partial discharge measurements
(PD).
TD measurements show the severity of Water treeing in the measured cable. Water trees mainly
come from moisture and are therefore present in cables that lie in manholes filled with water or they
submerged in any other way.
PD measurements show the severity of voids or other types of defects in cable insulation. These
defects can arise during the manufacturing of the cable or they can arise during the installation of the
cable or from an accident with the cable during the operational time.
Keywords
Line Resonance Analysis; Tan Delta; Partial Discharge; Water Treeing
Hrčak ID:
199623
URI
Publication date:
15.10.2017.
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