Ageing of electric cables in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 233

denser and loses volume. This change results in a change in resistance of the
AgeAlert TM microsensor. The resistance data can be transmitted wirelessly
using radio frequency identifi cation (RFID) technology for short distances
and can be acquired by a handheld RFID reader or a personal digital assis-
tant (PDA) type device. If needed for long distance transmission, active
wireless transmission technology could also be used. The AgeAlert TM has no
internal power source, receiving power from the radio frequency (RF) sig-
nal that is used to interrogate it and read the resistivity data from the sensor
(AMS Corp., 2010). The AgeAlert TM sensors can be installed by wire/cable
manufacturers during manufacture of the cable or bonded to the cable after
installation (IAEA, 2011).
Dissipation factor (DF) and quality factor (QF) represent a fi nal insu-
lation quality test. The ratio of the energy loss in a dielectric to the total
energy transmitted through the dielectric, DF represents the departure of
a cable from an 'ideal' capacitor. If the cable is free of defects or contami-
nants, its dielectric properties are similar to a perfect capacitor. If the cable
dielectric contains impurities, the resistance of the insulation decreases, and
it no longer acts as a perfect capacitor (Hashemian, 2010). Similarly, QF
represents the departure of a cable from an 'ideal' inductor. Quality factor
applies to electrical circuits that contain resistance, inductance, and capaci-
tance and is the ratio of energy stored to energy dissipated in a system at a
specifi c frequency.

Impedance tests

LCR, TDR, and FDR are cable testing techniques that measure imped-
ance in cables in order to detect anomalies. There are two basic types of
impedance tests - lumped data and distributed measurement - based on
the ability of the test to localize its measurement. Lumped data tests like
LCR typically identify anomalies in cables with greater accuracy than dis-
tributed measurement methods. But once the fault is detected, the distrib-
uted measurement methods (TDR and FDR) can determine the distance
to the fault.
The LCR test uses an LCR instrument or meter at specifi c frequencies to
make impedance measurements along the cable at specifi c frequencies to
verify the characteristics of the cable conductor, insulating material, and the
end device. The results are evaluated to determine if they are as expected
for the type of circuit being tested. Imbalances, mismatches, or unexpectedly
high or low impedances between the cable leads indicate problems caused
by cable degradation and ageing, faulty connections and splices, or physi-
cal damage. For example, abnormal capacitance measurements indicate a
change in cable dielectric or insulation. In addition to providing information
about cables, connectors, and end devices, LCR measurements can identify

￿ ￿ ￿ ￿ ￿ ￿