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Cable Testing and Diagnostics Flashcards

7 cards from real NETA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Cable Testing and Diagnostics flashcards as text

  1. During a cable dielectric absorption (DA) test, a DA ratio less than 1.0 most likely indicates:

    Answer: Insulation that is wet, contaminated, or severely degraded

    A dielectric absorption ratio below 1.0 means current increased over time rather than decreased, strongly indicating wet, conductive, or severely degraded insulation.

  2. Which cable diagnostic test method uses a sinusoidal voltage at 0.1 Hz and simultaneously measures the tan delta to assess insulation condition?

    Answer: VLF withstand test with tan delta monitoring

    VLF tan delta testing applies 0.1 Hz sinusoidal voltage while continuously measuring the dissipation factor to detect insulation aging and water treeing.

  3. When a cable section has been flooded with water, how does this primarily affect megohmmeter insulation resistance readings?

    Answer: IR decreases dramatically, often below 1 MΩ

    Water creates conductive paths through or along insulation, drastically lowering insulation resistance and often producing readings well below 1 MΩ.

  4. According to NETA MTS, the temperature correction factor for insulation resistance tests is applied to normalize readings to which reference temperature?

    Answer: 20°C

    NETA MTS specifies correcting insulation resistance measurements to a reference temperature of 20°C to allow valid comparisons between tests taken at different ambient conditions.

  5. What is the significance of a 'kink' or sudden step in the TDR trace at a location other than the far end of the cable?

    Answer: A fault, splice, or impedance discontinuity at that distance

    A step or kink in the TDR waveform at a mid-cable location indicates a fault, splice, connector, or impedance change at the corresponding distance from the test point.

  6. A cable's polarization index (PI) is calculated as the ratio of insulation resistance at 10 minutes to insulation resistance at which other time interval?

    Answer: 1 minute

    The polarization index is the ratio of the 10-minute IR reading divided by the 1-minute IR reading, with a ratio above 2.0 generally indicating acceptable insulation.

  7. When performing a DC hi-pot test on a cable, why does NETA and IEEE 400 now discourage routine DC hi-pot testing on aged XLPE cables?

    Answer: DC voltage can cause space charge accumulation in XLPE insulation, worsening pre-existing water trees

    DC voltage applied to aged XLPE cables with water trees causes space charge buildup that can accelerate insulation damage and may cause failure shortly after test voltage is removed.