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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. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
High voltage
silicon steel
coercivity
Measuring
2. has a laminated iron core (layers of metal plates)
Current
hysteresis losses (lagging losses)
class 400 transformers
closed-ended core
3. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
flux leakage
closed-ended core (square/doughnut shaped)
Primary
current related to turns ratio law
4. The capacity of a transformer is rated in ____ _____.
by varying the size of the applied DC
Kilovolt -- Amperes (kVA)
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
variable
5. How coils serve as the primary and secondary windings for an autotransformer
Vs Ip = Vp Is
5
one coils serves as the primary and secondary windings
air core
6. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
rated KVA of a transformer
voltage ralated to turns ratio
Autotransformer
flux
7. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
step-up (high voltage) transformers - step down transformer - autotransformer
Secondary
flux leakage
8. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
rating
variable
flux
primary coil - secondary coil - central magnetic core
9. The 3 types of transformer power loss
grounded system
Class 200 transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
10. Reference to a jumper or conductor - to or from a piece of electrical equipment.
current related to turns ratio law
leakage flux
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
leg(s)
11. Central magnetic core made of
grounded (Earthed)
closed-ended core
Autotransformer
highly permeable material - iron or stalloy
12. 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
Vs Ip = Vp Is
saturable reactor
step-up (high voltage) transformers - step down transformer - autotransformer
fuse
13. Determines if the transformer is a step up or step down transformer
Eh - lH = Ex - lX
the number of turns of wire in the primary and secondary coils
continuous path
Vs Ip = Vp Is
14. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
high frequency transformer
Voltage
Eh/Ex=Th/Tx
central magnetic core
15. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Class 200 transformers
Current
grounded (Earthed)
current related to voltage law
16. A ___________ transformer is a continuously adjustable Autotransformer.
The ratio of useful power output to its total power input.
variable
die to leakage flux
variable transformers
17. An instrument used to measure electrical current.
Primary
ammeter
Low
Eddy
18. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
electromagnetic mutual induction without loosing too much energy
High voltage
19. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
transformers efficiency
ratio of a transformer
voltage ralated to turns ratio
Primary
20. Refers to the transformer's ability to avoid power loss (heat)
5
low rententivity
eddy currents
transformers efficiency
21. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
die to leakage flux
change the input voltage
the number of turns of wire in the primary and secondary coils
central magnetic core
22. This core is more efficient than the air core because the iron core in each coil intensifies the magnetic flux in both primary and secondary coils when they become magnetized as current flows through each set of coils
Step-up
Class 200 transformers
fuse
open-ended core
23. Anything above 600 volts is _____?
Primary
Voltage - Current
High voltage
open-ended core
24. Function of the dielectric oil
by varying the size of the applied DC
air core
Insulates - cools transformer by convection - dissipates heat
secondary coil
25. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
Eh - lH = Ex - lX
class 400 transformers
dielectric oil
26. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
eddy currents
Class 200 transformers
Voltage - Current
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
27. Transformers with 4800 volt primaries and 120/240 volt secondaries - either pole or subway type - with two secondary windings terminating at internal links which provide for parallel operation of the secondary windings at 120 volts or series operatio
leakage flux
Class 200 transformers
Voltage
leg(s)
28. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
rated KVA of a transformer
Primary
closed-ended core
wigginton
29. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
shell core
Measuring
Voltage
the number of turns in the coil
30. The formula for the current related to voltage law
step-up (high voltage) transformers - step down transformer - autotransformer
Step-up
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Vs Ip = Vp Is
31. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
air core
class 400 transformers
constant current transfomers
Volt-Amperes (Eh-lh=ExLx)
32. A partial or total local failure in the insulation or continuity of a conductor.
Eh - lH = Ex - lX
variable transformers
fault
H1 - h2...
33. The transformer winding to which voltage is supplied is called the _____ winding.
Simple Transformer
die to leakage flux
Primary
flux
34. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
variable
Voltage
Primary
35. The number of turns can be adjusted in these types of transformers
variable transformers
short circuit
air core
36. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
saturable reactor
Measuring Equipment
CORE: Core losses are caused by eddy currents set up by the magnetic field.
thin copper wire coated with insulated material (shellac or enamel)
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)
the number of turns of wire in the primary and secondary coils
grounded system
Measuring
wigginton
38. This type of core is moderately efficient due to closing the core and layering design which reduces power loss from less leakage flux which provides a continuous path for magnetic flux and an increase in field strength
an iron core and coil
closed-ended core
Voltage
Distribution transformer
39. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
Hysteresis
change the input voltage
wigginton
40. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Ip Ns = Is Np
low rententivity
Eh - lH = Ex - lX
flux
41. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
silicon steel
closed-ended core (square/doughnut shaped)
air core
Current
42. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
transformers efficiency law
Exciting Current
Low
eddy currents
43. A choke coil uses this to induce current
highly permeable material - iron or stalloy
Current
an iron core and coil
grounded (Earthed)
44. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
hysteresis losses (lagging losses)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Copper Losses - Core Losses
coercivity
45. The winding of a transformer to which electrical energy is supplied.
high frequency transformer
primary winding
the number of turns in the coil
Eddy
46. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
an iron core and coil
silicon steel
Same
Transformer
47. The voltage induced in the coil is directly proportional to this
a magnetic field that varies quickly in direction and stregnth
the number of turns in the coil
polarity
transformers efficiency law
48. Waste of power known as transformer loss - often produced by closed-ended core
closed-ended core (square/doughnut shaped)
polarity
eddy currents
high frequency transformer
49. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
class 400 transformers
magnetic field
Eh/Ex=Th/Tx
ammeter
50. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
primary coil
rated KVA of a transformer
closed-ended core
flux