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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. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
The ratio of useful power output to its total power input.
Primary
secondary coil
Distribution transformer
2. How a variable degree of core saturation is accomplished in a saturable reactor?
continuous path
Electromagnet
by varying the size of the applied DC
Copper Losses - Core Losses
3. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Insulates - cools transformer by convection - dissipates heat
Ip Ns = Is Np
Primary
flux leakage
4. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
Voltage
Electromagnet
Secondary
5. The winding to which the load is connected is called the _____ winding.
Secondary
5
voltage ralated to turns ratio
grounded (Earthed)
6. Connected to earth or to some conducting body which serves in place of the earth.
H1 - h2...
grounded (Earthed)
fuse
central magnetic core
7. 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
Volt-Amperes (Eh-lh=ExLx)
high frequency transformer
variable transformers
8. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
Transformer
Voltage - Current
central magnetic core
class 400 transformers
9. A transformer loses less than _% in energy
primary coil - secondary coil - central magnetic core
Eh/Ex=Th/Tx
Primary
5
10. A transformer is a device that either increases or decreases alternating current and voltage using this principle
coercivity
secondary coil
ratio of a transformer
electromagnetic mutual induction without loosing too much energy
11. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
magnetic flux
Ip Ns = Is Np
transformers efficiency law
Measuring
12. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
eddy currents
Current
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
central magnetic core
13. Is concentrated in the metal core
5
Same
dielectric oil
magnetic field
14. The capacity of a transformer is rated in ____ _____.
High voltage
leg(s)
Kilovolt -- Amperes (kVA)
15. The 3 types of transformer power loss
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
current related to voltage law
Step-up
16. Kind of wire is the secondary coil in a transformer
Hysteresis - Eddy - Current
grounded (Earthed)
central magnetic core
thin copper wire coated with insulated material (shellac or enamel)
17. With no load on the secondary winding - a small current flows in the primary called _____ _____.
air core
continuous path
Exciting Current
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
18. Refers to the transformer's ability to avoid power loss (heat)
Current
variable
Autotransformer
transformers efficiency
19. What does transformer efficiency mean?
closed-ended core
The ratio of useful power output to its total power input.
phase
thin copper wire coated with insulated material (shellac or enamel)
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.
variable
Vs Ip = Vp Is
fuse
Class 200 transformers
21. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
ammeter
primary coil
primary coil - secondary coil - central magnetic core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
22. 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.
change the input voltage
Electromagnetic Induction.
Secondary
5
23. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
Measuring Equipment
Same
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
24. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
closed-ended core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
voltage ralated to turns ratio
air core
25. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Vs Ns = Vp Np
leakage flux
26. What is a rotation meter?
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
fuse
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Hysteresis
27. How coils serve as the primary and secondary windings for an autotransformer
Vs Ns = Vp Np
one coils serves as the primary and secondary windings
Kilovolt -- Amperes (kVA)
Eh/Ex=Th/Tx
28. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Distribution transformer
phase
How a transformer works
Same
29. A ___________ transformer is a continuously adjustable Autotransformer.
variable
Vs Ip = Vp Is
continuous path
30. The winding to which voltage is supplied is called the _____ winding.
step-up (high voltage) transformers - step down transformer - autotransformer
5
shell core
Primary
31. Transformer losses are classified as _____ and _____.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
fault
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Copper Losses - Core Losses
32. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Electromagnet
transformers efficiency law
flux
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
33. The formula for the current related to voltage law
Hysteresis - Eddy - Current
Vs Ip = Vp Is
leg(s)
wigginton
34. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
Secondary
a magnetic field that varies quickly in direction and stregnth
Distribution transformer
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
35. The terminals of the high voltage winding are marked _____.
hysteresis losses (lagging losses)
H1 - h2...
Kilovolt -- Amperes (kVA)
Low
36. 3 types of transformers
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
step-up (high voltage) transformers - step down transformer - autotransformer
Insulates - cools transformer by convection - dissipates heat
Exciting
37. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
Measuring Equipment
silicon steel
Autotransformer
secondary coil
38. both coils in this core are heavily insulated
grounded (Earthed)
Hysteresis - Eddy - Current
eddy currents
closed-ended core
39. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
variable transformers
Ip Ns = Is Np
high frequency transformer
40. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
wigginton
Electromagnet
rating
41. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Choke coil
air core
coercivity
current related to voltage law
42. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
fuse
closed-ended core
43. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
Exciting Current
Same
magnetic field
44. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Primary
Transformer
transformers efficiency law
Autotransformer
45. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
coercivity
Vs Ip = Vp Is
flux leakage
ratio of a transformer
46. A single electrical circuit.
phase
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
primary coil
electromagnetic mutual induction without loosing too much energy
47. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
an iron core and coil
Step-up
by varying the size of the applied DC
Eddy
48. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
closed-ended core (square/doughnut shaped)
How a transformer works
voltage ralated to turns ratio
rated KVA of a transformer
49. Function of the dielectric oil
primary coil
Insulates - cools transformer by convection - dissipates heat
Volt-Amperes (Eh-lh=ExLx)
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
50. Used to increase the magnetic flux in a transformer
central magnetic core
Eh/Ex=Th/Tx
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Primary