Practice Test Geeks(NETA) InterNational Electrical Testing Association Certified Technicians Practice Test
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Motor and Generator Testing 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 Motor and Generator Testing flashcards as text

  1. When performing a surge comparison test on a motor winding, what condition is indicated when the two surge waveforms do NOT match?

    Answer: Turn-to-turn insulation fault within the winding

    Mismatched surge waveforms indicate a turn-to-turn insulation fault because the fault alters the inductance of that coil group, causing a different impedance response.

  2. According to NETA MTS standards, what is the minimum recommended polarization index (PI) value for a motor winding rated above 1 kV to be considered acceptable for service?

    Answer: 2.0

    NETA MTS specifies a minimum PI of 2.0 for windings rated above 1 kV; values below this indicate moisture or contamination that poses a dielectric risk.

  3. A motor's no-load current is measured at 45% of full-load current. What does this elevated no-load current most likely indicate?

    Answer: Shorted turns in the stator winding

    No-load current exceeding approximately 30–35% of full-load current for standard induction motors often signals shorted stator turns, which increase magnetizing current demand.

  4. During vibration analysis of a generator, a prominent frequency component at exactly 2× line frequency (2× 60 Hz = 120 Hz) is detected. What is the most probable cause?

    Answer: Loose stator core laminations or electromagnetic excitation

    Electromagnetic forces in AC machines produce twice-line-frequency (120 Hz) vibration, commonly caused by loose or uneven stator core laminations responding to alternating flux.

  5. What does a high AC resistance (compared to DC resistance) ratio in a motor winding suggest?

    Answer: Significant skin effect or proximity effect losses in the conductors

    A high AC-to-DC resistance ratio indicates elevated skin and proximity effects, which increase effective conductor resistance at power frequencies and contribute to winding losses.

  6. When testing a DC motor, a high resistance reading between adjacent commutator bars using a milliohmmeter most likely indicates:

    Answer: An open armature coil or broken riser connection

    High resistance between adjacent commutator bars points to an open armature coil or a broken riser where the coil connects to the commutator segment.

  7. A generator's dielectric absorption ratio (DAR) is calculated as the ratio of insulation resistance at:

    Answer: 60 seconds to 30 seconds

    The DAR is the ratio of the 60-second insulation resistance reading to the 30-second reading, providing a quick indicator of insulation condition.