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Power Cable Test Methods 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 Power Cable Test Methods flashcards as text

  1. What does a Dielectric Absorption Ratio (DAR) value greater than 1.25 typically indicate for cable insulation?

    Answer: Good insulation condition

    A DAR above 1.25 indicates the insulation resistance is still rising after 60 seconds, suggesting acceptably dry and clean insulation.

  2. When using the step voltage test on a cable, what does a sharp increase in leakage current at a specific voltage step indicate?

    Answer: Incipient or existing insulation weakness at that stress level

    A disproportionate current rise at a particular voltage step indicates the insulation has a defect that becomes active at that stress level.

  3. Which test is considered non-destructive and is recommended by IEEE 400 as a preferred diagnostic for medium-voltage XLPE cables?

    Answer: VLF tan delta (dissipation factor)

    VLF tan delta (loss angle) measurement is non-destructive and detects water treeing and insulation aging in XLPE cables without risk of damage.

  4. Before performing any hi-pot test on a cable, what must always be done first?

    Answer: Perform an insulation resistance test and verify cable is de-energized and isolated

    Verifying the cable is de-energized, isolated, and performing a preliminary IR test establishes baseline condition and ensures safety before applying high voltage.

  5. A shielded 15 kV XLPE cable fails a VLF withstand test. What is the most likely root cause indicated by this result?

    Answer: Insulation has degraded below minimum withstand strength

    Failure of a VLF withstand test means the insulation cannot sustain the required dielectric stress, indicating degradation such as water trees or thermal damage.

  6. What effect does increasing cable length have on the charging current required during a 60 Hz AC hipot test?

    Answer: Charging current increases proportionally

    Cable capacitance increases proportionally with length, so longer cables require higher charging current from the 60 Hz test set.

  7. When testing an unshielded medium-voltage cable with a megohmmeter, which measurement correction factor is most important to apply?

    Answer: Temperature correction to 20°C

    Temperature significantly affects insulation resistance readings and must be corrected to the standard 20°C baseline for meaningful comparison.