Transformers

50 Questions | Total Attempts: 945

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Transformers

Questions and Answers
  • 1. 
    Which of the following will cause oil-filled bushing to overheat?
    • A. 

      Cracked on the skirt of the bushing

    • B. 

      Dirty and corroded terminals

    • C. 

      Dusty exterior bushing

    • D. 

      Moisture inside the bushing

  • 2. 
    One winding of the transformer is short circuited, and a voltmeter, ammeter and wattmeter are connected in the circuit of the other  winding. A small voltage is applies to and regulated  to that values of current from 50% to 125% of rated current  of the winding are obtained. The above is part of the description  for a test  of a transformer's:
    • A. 

      Exciting current

    • B. 

      Hysteris

    • C. 

      Iron Loss

    • D. 

      Impedance

  • 3. 
    In a transformer with a turns  ratio of 10:1 the percentage of reactance is 5% on the  high side.  How much is it on the low side?
    • A. 

      .5%

    • B. 

      5%

    • C. 

      8%

    • D. 

      10%

  • 4. 
    On a transformer, the low side is shorted and a little voltage is applied to the  highside in order  to get rated current  to flow in the windings.  Which test are you performing? 
    • A. 

      Testing for Eddy Currents

    • B. 

      Testing for Hystersis Losses

    • C. 

      Testing for Impedance.

  • 5. 
    Two transformers 250 KVA each  are connected in open delta. The power that  can be transferred through  these transformers to pure resistive load is:
    • A. 

      250kva

    • B. 

      365kva

    • C. 

      430kva

    • D. 

      500kva

  • 6. 
    A transformer is considered a total loss if it fails which of the following tests?
    • A. 

      Impedance,load loss

    • B. 

      Resistance measurements

    • C. 

      No-load loss, exciting current

    • D. 

      Dielectric

  • 7. 
    If a transformer failed one of the following tests, which test  will indicate a complete transformer failure?
    • A. 

      Load test

    • B. 

      Non-load test

    • C. 

      Power factor

    • D. 

      Dielectric

  • 8. 
    Two transformers are connected in parallel,one has twice the internal impedance of the other,
    • A. 

      The higher impedance transformer will carry Jess than half the load of the lower impedance transformer.

    • B. 

      The lower impedance transformer will carry more than twice as much load as the higher impedance transformer.

    • C. 

      The lower impedance transformer will overload.

    • D. 

      The higher impedance transformer will short circuit.

  • 9. 
    Low energy spark discharges under oil in a transformer cause gasses to be formed. The most common gasses formed are
    • A. 

      Oxygen and nitrogen

    • B. 

      Acetylene and helium

    • C. 

      Ethylene and chlorine

    • D. 

      Hydrogen and methane

  • 10. 
    The the following Connection a Delta Connection?
    • A. 

      True

    • B. 

      False

  • 11. 
    The following is a Delta connection?
    • A. 

      True

    • B. 

      False

  • 12. 
    A disadvantage of three single phase self cooled  power transformers over a three phase self cooled power transformer is:
    • A. 

      Radiators are more expensive on the single phase units.

    • B. 

      20% more core loss on the single phase unit. (The word "loss" was left out of the) question.)

    • C. 

      Repair costs are lower on the 3-phase unit.

  • 13. 
    Two transformers A & B are paralleled  on the primary and secondary side. an electrical worker pull out the fuses on the primary lines of Transformer B. Which part is considered dead?
    • A. 

      Primary A

    • B. 

      Secondary B

    • C. 

      Lead lines between fuses and primary B

    • D. 

      None of the above Identify

  • 14. 
    The industrial use transformer that normally has 240v or 480v primary and a 120 v secondary is called a(n) ____ transformer.
    • A. 

      Auto

    • B. 

      Distribution

    • C. 

      Isolation

    • D. 

      Control

  • 15. 
    An open delta connection is made using ____ single-phase transformers.
    • A. 

      One

    • B. 

      Two

    • C. 

      Three

    • D. 

      Four

  • 16. 
    When connecting three transformers for three phase use with the delta secondary, a voltage test should be done before closing the secondary.  The correct voltage reading is
    • A. 

      The rated secondary voltage value

    • B. 

      Twice the rated secondary voltage value

    • C. 

      Zero volts

    • D. 

      The sum of the the three transformer primaries

  • 17. 
    When using an open delta with a center tapped transformer, on wire is the "high leg."  The high leg is the one that
    • A. 

      Has the highest voltage measured to ground

    • B. 

      Has the lowest voltage measured to ground

    • C. 

      Has the most amperage

    • D. 

      Is mounted highest on the panel

  • 18. 
    In an open delta with single phase loads, the high leg must be identified by
    • A. 

      Using an orange wire

    • B. 

      Tagging

    • C. 

      Using an orange wire and tagging

    • D. 

      Using an orange wire or tagging

  • 19. 
    In an isolation transformer, all windings will have the same number of volts per turn.
    • A. 

      True

    • B. 

      False

  • 20. 
    When single phase loads are tied to a three phase transformer, the phase currents of the transformer will be automatically balanced.
    • A. 

      True

    • B. 

      False

  • 21. 
    A transformer in which the primary and secondary are phsically separated and not connected by a conductor is called a(n) ____ transformer.
    • A. 

      Isolation

    • B. 

      Auto

    • C. 

      Control

    • D. 

      Distribution

  • 22. 
    A transformer that does not isolate the output from the input is called a(n) ____ transformer.
    • A. 

      Distribution

    • B. 

      Auto

    • C. 

      Control

    • D. 

      Isolation

  • 23. 
    In a transformer test,the reading of the impedance across the leg are as followed: A - B  = 0.08  ohms;B- C = 0.08 ohms, and A- C= 0.153 ohms.  What could happen?
    • A. 

      The cable in Cis twice larger than the cable in A.

    • B. 

      This is a tertiary transformer.

    • C. 

      The transformer is open Delta with A-C is open.

    • D. 

      The primary side of the transformer is shorted.

  • 24. 
    Two transformer with  same KVA rating connecting parallel,the transformer with less impedance will
    • A. 

      Draw higher fault current during fault

    • B. 

      Has higher insulation between primary and secondary Winding

    • C. 

      Has higher winding ratio than the other transformer

  • 25. 
    Losses in a transformer on the primary from voltage that is induced in the core by the primary winding.
    • A. 

      Eddy current losses

    • B. 

      Copper losses

    • C. 

      Hysteresis losses

    • D. 

      Lamination losses

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