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Test your basic knowledge |
Transformers
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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. A ___________ transformer is a continuously adjustable Autotransformer.
variable
voltage ralated to turns ratio
closed-ended core
Hysteresis - Eddy - Current
2. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Primary
Same
thin copper wire coated with insulated material (shellac or enamel)
current related to voltage law
3. The winding to which the load is connected is called the _____ winding.
X1 - X2...
Secondary
H1 - h2...
flux leakage
4. A large amount of power wasted with the open-ended core
Exciting
Secondary
die to leakage flux
Eh/Ex=Th/Tx
5. How a variable degree of core saturation is accomplished in a saturable reactor?
leakage flux
by varying the size of the applied DC
Step-down
primary coil
6. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
hysteresis losses (lagging losses)
variable
Low
central magnetic core
7. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
by using silicon iron core
saturable reactor
air core
short circuit
8. It refers to the direction of current flow in a closed circuit.
primary coil
coercivity
closed-ended core
polarity
9. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Simple Transformer
closed-ended core
voltage ralated to turns ratio
grounded system
10. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Insulates - cools transformer by convection - dissipates heat
H1 - h2...
ratio of a transformer
rated KVA of a transformer
11. 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.
short circuit
constant current transfomers
Current
a magnetic field that varies quickly in direction and stregnth
12. Central magnetic core made of
highly permeable material - iron or stalloy
air core
current related to voltage law
magnetic flux
13. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
class 400 transformers
Vs Ip = Vp Is
central magnetic core
polarity
14. 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
Measuring Equipment
open-ended core
variable
Primary
15. Core losses are _____ loss and _____ - _____ loss.
ammeter
Hysteresis - Eddy - Current
variable
Step-up
16. 3 types of transformers
saturable reactor
shell core
step-up (high voltage) transformers - step down transformer - autotransformer
closed-ended core
17. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
continuous path
Distribution transformer
die to leakage flux
Current
18. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
Volt-Amperes (Eh-lh=ExLx)
magnetic flux
wigginton
19. Anything above 600 volts is _____?
wigginton
closed-ended core
primary coil - secondary coil - central magnetic core
High voltage
20. A part of a circuit made of a low melting point material so that it will melt and break the circuit when a specified current exceeded. Always the weakest point in the circuit.
fuse
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
How a transformer works
Copper Losses - Core Losses
21. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
open-ended core
step-up (high voltage) transformers - step down transformer - autotransformer
coercivity
eddy currents
22. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
Hysteresis
transformers efficiency law
primary winding
23. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Secondary
primary coil
central magnetic core
Autotransformer
24. both coils in this core are heavily insulated
closed-ended core
How a transformer works
Step-down
die to leakage flux
25. has a laminated iron core (layers of metal plates)
Eh/Ex=Th/Tx
by using silicon iron core
closed-ended core
Eh - lH = Ex - lX
26. The simplest type of transformer core
Copper Losses - Core Losses
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Current
air core
27. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
by varying the size of the applied DC
Voltage
electromagnetic mutual induction without loosing too much energy
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
28. The capacity of a transformer is rated in ____ _____.
open-ended core
Simple Transformer
rating
Kilovolt -- Amperes (kVA)
29. Reference to a jumper or conductor - to or from a piece of electrical equipment.
highly permeable material - iron or stalloy
leg(s)
directly proportional
Autotransformer
30. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
Hysteresis
CORE: Core losses are caused by eddy currents set up by the magnetic field.
by using silicon iron core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
31. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Current
Simple Transformer
the number of turns in the coil
grounded system
32. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
coercivity
hysteresis losses (lagging losses)
Current
the number of turns of wire in the primary and secondary coils
33. Is concentrated in the metal core
by varying the size of the applied DC
magnetic field
Primary
34. _____ currents are reduced by laminating the core.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Eddy
primary winding
Electromagnet
35. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
Electromagnetic Induction.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
short circuit
36. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
primary coil
Electromagnet
flux
air core
37. 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.
Choke coil
eddy currents
transformers efficiency law
Secondary
38. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
air core
flux leakage
current related to turns ratio law
Insulates - cools transformer by convection - dissipates heat
39. The current related to turns ratio law
Ip Ns = Is Np
eddy currents
wigginton
die to leakage flux
40. A transformer loses less than _% in energy
eddy currents
continuous path
fuse
5
41. The 3 principle components of a transformer
Ip Ns = Is Np
primary coil - secondary coil - central magnetic core
one coils serves as the primary and secondary windings
X1 - X2...
42. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
High voltage
flux leakage
Current
5
43. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Step-down
transformers efficiency law
ratio of a transformer
phase
44. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
rated KVA of a transformer
flux
Primary
45. Copper loss is known as _____ loss.
Hysteresis - Eddy - Current
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
High voltage
46. 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
Low
one coils serves as the primary and secondary windings
variable transformers
closed-ended core
47. The terminals of the low voltage winding are marked _____.
Simple Transformer
silicon steel
X1 - X2...
ammeter
48. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Exciting
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
central magnetic core
49. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Eh - lH = Ex - lX
change the input voltage
saturable reactor
Volt-Amperes (Eh-lh=ExLx)
50. 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.
ratio of a transformer
variable transformers
Electromagnet
wigginton
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