Practice Test Geeks(EETC) Electrical Technician Certification Practice Test
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Transformers Flashcards

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

Read the first 7 Transformers flashcards as text

  1. Transformer inrush current occurs when a transformer is first energized and can be as high as:

    Answer: 8 to 12 times the rated full-load current

    Inrush current can peak at 8–12 times rated current due to residual flux in the core and the point on the voltage wave at which the transformer is energized.

  2. What is the purpose of a Buchholz relay installed on an oil-filled transformer?

    Answer: To detect internal faults by sensing gas accumulation and oil surge

    A Buchholz relay detects gases produced by incipient internal faults (arcing, overheating) and activates an alarm or trip signal.

  3. In a transformer, leakage flux refers to flux that:

    Answer: Links only one winding and does not contribute to energy transfer between windings

    Leakage flux follows a path through air rather than the core, linking only its own winding and producing leakage reactance rather than mutual coupling.

  4. Which standard test is used to verify that transformer windings can withstand overvoltages from lightning or switching surges?

    Answer: Applied voltage (hi-pot) and impulse (BIL) tests

    The impulse test applies a high-voltage wave simulating lightning or switching surges to verify the Basic Insulation Level (BIL), while the hi-pot test checks turn-to-turn and winding-to-ground insulation.

  5. A distribution transformer is rated 25 kVA, 7200V/240V. What is the full-load secondary current?

    Answer: 104.2 A

    I_secondary = kVA × 1000 / V_secondary = 25,000 / 240 = 104.2 A.

  6. The dielectric strength of transformer insulating oil is tested primarily to determine:

    Answer: Its ability to withstand electric stress without breaking down

    Dielectric strength testing applies increasing voltage between electrodes submerged in the oil to find the breakdown voltage, indicating insulation quality and moisture contamination.

  7. When a transformer is subjected to a sudden short circuit on the secondary, the mechanical forces on the windings are proportional to:

    Answer: The square of the fault current

    Magnetic forces between conductors follow F ∝ I², so short-circuit forces can be hundreds of times greater than normal operating forces.