Ageing of electric cables in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 230

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 fac-
tor, and AgeAlert TM .
2. Impedance tests, which include LCR (inductance, capacitance, and resis-
tance), time domain refl ectometry (TDR), and frequency domain refl ec-
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 informa-
tion 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 essen-
tially the same as the FDR technique and JTFDR (joint time and frequency
domain refl ectometry) which combines TDR and FDR in a single test.

Insulation quality tests

Insulation resistance, ' Hi-Pot, ' partial discharge, AgeAlert TM , and quality/
dissipation factor are electrical measurement tests for the entire cable cir-
cuit (cable, connections, and end device) to identify cable insulation degra-
dation, failed end devices, and moisture intrusion on the cable.
Insulation resistance (IR) - the simplest and most common test for moni-
toring cable ageing - quantifi es the quality of cable insulation by energizing
the cable conductor and measuring for leakage current through degraded
insulation (AMS Corp., 2011; U.S. NRC, 1990). One of two fundamental
wire insulator properties, insulation resistance is the resistance to current
leakage through and over the surface of the cable material. Insulation can
also be impacted by cable length; humidity or moisture in the cable and
insulation as well as dirt, oil, and other surface contaminants (U.S. NRC,
2010a). IR changes in a progressive, ongoing basis as a cable is exposed to
these environmental stressors (IAEA, 2011).

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