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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. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
X1 - X2...
magnetic field
Vs Ns = Vp Np
short circuit
2. Function of the dielectric oil
directly proportional
Insulates - cools transformer by convection - dissipates heat
Eh/Ex=Th/Tx
Hysteresis - Eddy - Current
3. 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
variable transformers
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
closed-ended core
Eddy
4. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
hysteresis losses (lagging losses)
transformers efficiency law
X1 - X2...
Simple Transformer
5. Both the primary and secondary coils in a transformer are arranged around this
central magnetic core
the number of turns of wire in the primary and secondary coils
continuous path
Distribution transformer
6. 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
by using silicon iron core
Class 200 transformers
directly proportional
class 400 transformers
7. How coils serve as the primary and secondary windings for an autotransformer
Low
flux leakage
CORE: Core losses are caused by eddy currents set up by the magnetic field.
one coils serves as the primary and secondary windings
8. A transformer which when supplied from a constant potential source automatically maintans a constant current in its secondary circuit under varying conditions of load impedance. Used on series street light circuits.
constant current transfomers
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
closed-ended core
9. Core losses are _____ loss and _____ - _____ loss.
eddy currents
Hysteresis - Eddy - Current
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
current related to voltage law
10. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
closed-ended core
shell core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Electromagnetic Induction.
11. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
one coils serves as the primary and secondary windings
primary winding
transformers efficiency
secondary coil
12. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
Voltage - Current
closed-ended core (square/doughnut shaped)
grounded system
13. Used to increase the magnetic flux in a transformer
central magnetic core
Copper Losses - Core Losses
leakage flux
electromagnetic mutual induction without loosing too much energy
14. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Transformer
Step-up
Voltage - Current
flux
15. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Secondary
magnetic flux
polarity
coercivity
16. The transformer winding to which voltage is supplied is called the _____ winding.
the number of turns in the coil
Primary
Electromagnet
Simple Transformer
17. _____ currents are reduced by laminating the core.
phase
Eddy
primary coil - secondary coil - central magnetic core
18. The loss of power required to reverse the core magnatism each time the current reverses. This loss is caused by friction between the molecules of iron as these particles are aligned first in one direction and the in the opposite direct as current dir
Copper Losses - Core Losses
Voltage - Current
Hysteresis
die to leakage flux
19. How coercivity is minimized
the number of turns in the coil
low rententivity
by using silicon iron core
Insulates - cools transformer by convection - dissipates heat
20. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
fuse
Secondary
low rententivity
21. A single electrical circuit.
high frequency transformer
Voltage
phase
ratio of a transformer
22. The number of turns can be adjusted in these types of transformers
central magnetic core
Insulates - cools transformer by convection - dissipates heat
variable transformers
Electromagnetic Induction.
23. Anything above 600 volts is _____?
closed-ended core
directly proportional
High voltage
a magnetic field that varies quickly in direction and stregnth
24. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
ammeter
step-up (high voltage) transformers - step down transformer - autotransformer
Current
ratio of a transformer
25. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
Electromagnetic Induction.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
class 400 transformers
closed-ended core (square/doughnut shaped)
26. Refers to the transformer's ability to avoid power loss (heat)
transformers efficiency
Electromagnetic Induction.
flux leakage
Class 200 transformers
27. A large amount of power wasted with the open-ended core
Eh - lH = Ex - lX
die to leakage flux
primary winding
Vs Ip = Vp Is
28. 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
a magnetic field that varies quickly in direction and stregnth
Ip Ns = Is Np
saturable reactor
the number of turns in the coil
29. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
central magnetic core
Voltage - Current
coercivity
hysteresis losses (lagging losses)
30. Waste of power known as transformer loss - often produced by closed-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Secondary
eddy currents
primary coil
31. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
magnetic flux
X1 - X2...
change the input voltage
air core
32. The terminals of the low voltage winding are marked _____.
rating
directly proportional
X1 - X2...
ammeter
33. A simple design has a core within each coil
air core
leakage flux
variable transformers
open-ended core
34. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
current related to turns ratio law
Electromagnet
high frequency transformer
grounded system
35. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Same
Choke coil
Hysteresis - Eddy - Current
flux leakage
36. A choke coil uses this to induce current
an iron core and coil
Voltage - Current
Kilovolt -- Amperes (kVA)
Step-down
37. 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.
low rententivity
polarity
How a transformer works
Electromagnet
38. Transformer losses are classified as _____ and _____.
ammeter
Exciting
Copper Losses - Core Losses
39. The capacity of a transformer is rated in ____ _____.
leakage flux
Kilovolt -- Amperes (kVA)
Vs Ip = Vp Is
primary winding
40. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
the number of turns in the coil
Measuring
dielectric oil
Copper Losses - Core Losses
41. Kind of wire is the secondary coil in a transformer
How a transformer works
thin copper wire coated with insulated material (shellac or enamel)
the number of turns of wire in the primary and secondary coils
shell core
42. What is a rotation meter?
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
dielectric oil
shell core
fuse
43. has a laminated iron core (layers of metal plates)
X1 - X2...
closed-ended core
Step-up
transformers efficiency
44. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
wigginton
step-up (high voltage) transformers - step down transformer - autotransformer
a magnetic field that varies quickly in direction and stregnth
flux
45. A transformer loses less than _% in energy
fuse
one coils serves as the primary and secondary windings
5
electromagnetic mutual induction without loosing too much energy
46. How a variable degree of core saturation is accomplished in a saturable reactor?
low rententivity
Measuring Equipment
by varying the size of the applied DC
open-ended core
47. A partial or total local failure in the insulation or continuity of a conductor.
primary coil
current related to voltage law
fault
48. An electromagnetic device that operates on the principle of self induction. It uses AC.
step-up (high voltage) transformers - step down transformer - autotransformer
Choke coil
Electromagnet
constant current transfomers
49. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
closed-ended core
closed-ended core
magnetic field
50. Reference to a jumper or conductor - to or from a piece of electrical equipment.
Kilovolt -- Amperes (kVA)
electromagnetic mutual induction without loosing too much energy
The ratio of useful power output to its total power input.
leg(s)