The IAEA has stated that electrical properties — voltage withstand, insula­tion resistance, capacitance, attenuation, and/or signal propagation — are the ‘most important functional properties’ of cables (IAEA, 2011). Such prop­erties provide a direct measure of the loss of cable resistance or dielectric parameters and therefore its loss of functionality (IAEA, 2011). Electrical measurements are primarily suitable for cable conductors, connectors, splices and penetrations. Most electrical measurement techniques are less sensitive to problems with cable insulation material though they can reveal them (IAEA, 2011).

Two types of electrical tests are available: destructive methods, which iden­tify cable failure locations before the cable is installed, and non-destructive methods, which are better suited to identifying cable degradation (U. S. NRC, 2001). Non-destructive tests can be categorized by direct current (DC) and alternating current (AC) methods. DC tests generally require the least expen­sive test equipment, but may be less appropriate for some power cables and cables used in AC applications (U. S. NRC, 2001). The primary advantage of electrical techniques is that they can be used in-situ on installed and less accessible cables, providing information on the entire length of a cable, not just those points which are tested (IAEA, 2011). Because some methods also enable trending based on baseline measurements, electrical techniques can be used to note changes over time for ageing management purposes (IAEA, 2011). The most important electrical parameters in cables are insu­lation resistance, leakage current, loss factor, permittivity, and breakdown voltage. Provided that one or both ends of the cable are accessible to mea­surement and the cable can be de-energized, these electrical parameters can usually be measured on any cable (Hashemian, 2010).

296 Materials’ ageing and degradation in light water reactors There are two general types of in-situ electrical cable tests:

1. Insulation quality tests, which include insulation resistance (IR), high-potential (Hi-Pot), partial discharge, quality factor, dissipation fac­tor, and AgeAlertTM.

2. Impedance tests, which include LCR (inductance, capacitance, and resis­tance), time domain reflectometry (TDR), and frequency domain reflec — tometry (FDR).

Many of these electrical tests are simple and have been in use for decades. In recent years, LCR measurements have been added to the TDR test to improve cable diagnostics, help identify the nature of a fault, and pinpoint its location along a cable. Used together, electrical methods like the TDR and LCR tests provide an overall picture of cable health as well as informa­tion for expediting any repairs that may be needed (Hashemian, 2010).

Many conventional electrical test methods such as IR and LCR are only used to give a snapshot of the current condition of a cable. Others, such as TDR, FDR and RTDR, can identify the fault location within the length of cable, but may not differentiate whether the problems are in the connection or the end device. Additional tests are normally required to help distinguish whether the fault is in the cable or to diagnose the cause of the end device problem (AMS Corp., 2011). In recent years, the TDR and FDR techniques have been either combined or packaged and introduced under such names as LIRA (line impedance resonance analysis) a method which seems to be essen­tially the same as the FDR technique and JTFDR (joint time and frequency domain reflectometry) which combines TDR and FDR in a single test.