Cable components such as the conductor wires, insulation, shielding, and jacket material can all be tested to reveal signs of degradation. By applying the right testing method or combination of methods effectively faults that typically occur at cable connections can be confirmed; these include termi­nations, penetrations, and/or splices that have been exposed to mechani­cal stress, oxidation, or corrosion. Other faults include end-device failure such as motor windings, sensors, transmitters, and detectors that may also be detected using appropriate testing methods (AMS Corp., 2010).

Cable analysis and assessment methods require observing, measuring, and trending indicators of cable condition that correlate to the physical condition of the cable or its functional performance (U. S. NRC, 2010b). According to the NRC, an ‘ideal’ condition monitoring technique should have the following desired attributes: ‘nondestructive and nonintrusive, capable of measuring property changes or indicators that are trendable and can be consistently correlated to functional performance during normal service, applicable to cable types and materials commonly used in nuclear power plants, provides reproducible results that are not affected by the test environment or, if they are so affected, the results can be corrected for those effects, able to identify the location of any defects in the cable, allows the establishment of a well-defined end condition, and provides suf­ficient time before incipient failure to allow corrective actions’ (U. S. NRC, 2010b). However, because the nuclear industry relies primarily on manufac­turer qualification data, it does insufficient testing to confirm that cables can operate dependably in the long term (IAEA, 2011).

Cable testing methods can be characterized in multiple ways (see Table 6.1). In the broadest terms, two cable ageing methods are avail­able: laboratory tests (involving microsampling, e. g. conducted in non­operational conditions in a lab) and in-situ tests (conducted on cables as installed in a plant) (U. S. NRC, 2010a; IAEA, 2011). However, another way of categorizing cable ageing methods is life testing versus electrical testing. Life-testing techniques involve testing — visually, physically, or chemically — the physical properties (e. g. hardness) of spare cable samples of the same cables actually installed and in operation at the plant. When such ‘real-time’ testing is not possible or desirable, accelerated life testing can compress the time required to test the ageing processes by ‘pre-ageing’ cable samples and monitoring their performance when installed in the same environment as actual in-service cables.

Electrical testing of cables involves the testing of electrical properties such as insulation resistance/polarization index, voltage withstand, dielec­tric loss/dissipation factor, time and/or frequency domain reflectometry, and partial discharge. These electrical testing methods can be further catego­rized according to whether the inspection or test is performed in-situ on electric cables in the plant or whether it is a laboratory-type test performed on representative material specimens in a controlled laboratory setting.

Which of these testing techniques is used will depend on the type of insu­lation material in the cable and type of environmental stressors to which the cable is subjected (Hashemian, 2010). For example, historically, visual and tactile inspection techniques have been the most commonly used meth­ods for cables that are accessible. Some, such as the gel content and other

Cable testing technique

Visual/tactile (visual screening test)

Ні-Pot test (high voltage test may damage insulation)

AgeAlert™ (wireless sensors attached to cables)

TDR (time domain reflectometry)

RTDR (reverseTDR for coaxial shielded cables)

Impedance measurements (inductance, capacitance, and AC resistance)

Partial discharge

Insulation resistance (dielectric absorption ratio, polarization index) (sustained higher DC voltage resistance)

Dissipation factor (Tan Delta)

AC voltage withstand (low frequency, high voltage)

DC step voltage

chemical and mechanical tests like the cable indenter, were developed spe­cifically for evaluating the condition of the protective jacket or insulation on a cable (AMS Corp., 2010).