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Test your basic knowledge |
Transformers
Start Test
Study First
Subject
:
engineering
Instructions:
Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can
study here
.
Match each statement with the correct term.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.
This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.
1. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
constant current transfomers
voltage ralated to turns ratio
Measuring
secondary coil
2. Connected to earth or to some conducting body which serves in place of the earth.
coercivity
Secondary
grounded (Earthed)
Eh/Ex=Th/Tx
3. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Distribution transformer
Secondary
transformers efficiency law
hysteresis losses (lagging losses)
4. A partial or total local failure in the insulation or continuity of a conductor.
transformers efficiency law
saturable reactor
coercivity
fault
5. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
magnetic flux
Primary
Current
Choke coil
6. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Measuring
air core
open-ended core
7. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
central magnetic core
Voltage
Current
High voltage
8. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
air core
coercivity
Volt-Amperes (Eh-lh=ExLx)
the number of turns of wire in the primary and secondary coils
9. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
Voltage
central magnetic core
hysteresis losses (lagging losses)
5
10. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
central magnetic core
Same
current related to turns ratio law
Eh/Ex=Th/Tx
11. Waste of power known as transformer loss - often produced by closed-ended core
high frequency transformer
magnetic flux
leg(s)
eddy currents
12. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
closed-ended core
Electromagnetic Induction.
Distribution transformer
13. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Choke coil
high frequency transformer
ratio of a transformer
open-ended core
14. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Same
variable
flux
5
15. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
polarity
the number of turns in the coil
highly permeable material - iron or stalloy
16. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Primary
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
die to leakage flux
rated KVA of a transformer
17. How coercivity is minimized
ratio of a transformer
by using silicon iron core
closed-ended core (square/doughnut shaped)
short circuit
18. The voltage induced in the coil is directly proportional to this
saturable reactor
Hysteresis - Eddy - Current
closed-ended core
the number of turns in the coil
19. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
highly permeable material - iron or stalloy
Voltage - Current
phase
20. Modern; used to control filament circuit; replaced both the rheostat and choke coil; operated on the electromagnetic principle that if an iron core within or near a coil is saturated with magnetic flux by an independed source of direct current - the
highly permeable material - iron or stalloy
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
saturable reactor
Exciting Current
21. Core losses are _____ loss and _____ - _____ loss.
transformers efficiency
Hysteresis - Eddy - Current
Choke coil
phase
22. The winding to which the load is connected is called the _____ winding.
Secondary
Distribution transformer
How a transformer works
fuse
23. An instrument used to measure electrical current.
constant current transfomers
High voltage
ammeter
Measuring Equipment
24. How a variable degree of core saturation is accomplished in a saturable reactor?
flux leakage
magnetic field
die to leakage flux
by varying the size of the applied DC
25. Central magnetic core made of
current related to turns ratio law
Eh - lH = Ex - lX
highly permeable material - iron or stalloy
rated KVA of a transformer
26. Determines if the transformer is a step up or step down transformer
current related to turns ratio law
the number of turns of wire in the primary and secondary coils
flux leakage
Electromagnetic Induction.
27. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
transformers efficiency law
low rententivity
Secondary
Step-down
28. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
continuous path
Distribution transformer
Step-up
29. Two coils wound on a closed iron core form a ________.
Autotransformer
Simple Transformer
Distribution transformer
Vs Ip = Vp Is
30. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
Step-up
coercivity
change the input voltage
31. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
Choke coil
step-up (high voltage) transformers - step down transformer - autotransformer
Vs Ip = Vp Is
32. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
shell core
wigginton
variable transformers
33. Used to increase the magnetic flux in a transformer
phase
central magnetic core
primary coil - secondary coil - central magnetic core
Measuring Equipment
34. A designated limit of operating characteristics based on definite conditions.
rating
5
Eh - lH = Ex - lX
phase
35. When an alternating current is applied to the high-voltage (H) winding of a transformer with no load on the secondary (X) winding - a small current - called the _____ current - flows in the primary.
grounded (Earthed)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Exciting
eddy currents
36. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
current related to turns ratio law
Transformer
Autotransformer
37. A test instrument used to indicate low voltage potentials in the range of 110 to 600 volts either alternating or direct current. (slang term: wiggy)
saturable reactor
leakage flux
Measuring Equipment
wigginton
38. A magnet made by winding a coil of wire around a soft iron core. Current passed through this winding produces magnetic lines of force in the coil.
leakage flux
variable
Electromagnet
saturable reactor
39. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
an iron core and coil
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Measuring
silicon steel
40. In a transformer the _____ current will always flow in such a direction that its magnetizing action will oppose the magnetizing action of the primary winding.
Secondary
Step-up
The ratio of useful power output to its total power input.
41. The capacity of a transformer is rated in ____ _____.
grounded system
step-up (high voltage) transformers - step down transformer - autotransformer
Vs Ip = Vp Is
Kilovolt -- Amperes (kVA)
42. A large amount of power wasted with the open-ended core
secondary coil
die to leakage flux
ammeter
primary coil
43. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Electromagnet
H1 - h2...
Voltage - Current
open-ended core
44. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
transformers efficiency
flux leakage
Secondary
hysteresis losses (lagging losses)
45. Function of the dielectric oil
open-ended core
H1 - h2...
5
Insulates - cools transformer by convection - dissipates heat
46. How the voltage and the number of turns are related for the voltage related to turn ratio
by using silicon iron core
Voltage
leakage flux
directly proportional
47. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
5
short circuit
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
air core
48. The entire transformer is placed in a metal tank then immersed in ________.
High voltage
Secondary
magnetic flux
dielectric oil
49. Anything above 600 volts is _____?
High voltage
Primary
Exciting
phase
50. Both the primary and secondary coils in a transformer are arranged around this
closed-ended core
5
grounded (Earthed)
central magnetic core
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