SUBJECTS
|
BROWSE
|
CAREER CENTER
|
POPULAR
|
JOIN
|
LOGIN
Business Skills
|
Soft Skills
|
Basic Literacy
|
Certifications
About
|
Help
|
Privacy
|
Terms
|
Email
Search
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 designated limit of operating characteristics based on definite conditions.
Step-up
rating
voltage ralated to turns ratio
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
2. both coils in this core are heavily insulated
closed-ended core
thin copper wire coated with insulated material (shellac or enamel)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
grounded (Earthed)
3. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
central magnetic core
Simple Transformer
step-up (high voltage) transformers - step down transformer - autotransformer
4. 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)
Kilovolt -- Amperes (kVA)
Primary
Step-down
wigginton
5. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Electromagnetic Induction.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
rated KVA of a transformer
Eddy
6. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
coercivity
fuse
Class 200 transformers
magnetic field
7. 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)
Eh - lH = Ex - lX
ammeter
eddy currents
8. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Simple Transformer
saturable reactor
9. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
saturable reactor
change the input voltage
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Current
10. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
Class 200 transformers
Volt-Amperes (Eh-lh=ExLx)
Secondary
silicon steel
11. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
transformers efficiency law
Secondary
Secondary
12. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
Simple Transformer
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
transformers efficiency law
13. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Class 200 transformers
Measuring
silicon steel
Primary
14. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
die to leakage flux
grounded system
Volt-Amperes (Eh-lh=ExLx)
wigginton
15. 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
saturable reactor
an iron core and coil
Primary
16. The winding to which the load is connected is called the _____ winding.
Kilovolt -- Amperes (kVA)
primary winding
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Secondary
17. 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.
Hysteresis - Eddy - Current
High voltage
primary coil - secondary coil - central magnetic core
fuse
18. 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
flux
leg(s)
Step-down
open-ended core
19. The 3 principle components of a transformer
primary coil - secondary coil - central magnetic core
closed-ended core (square/doughnut shaped)
the number of turns in the coil
Autotransformer
20. A transformer primary (H) that has 400 turns is wound to step the voltage down from 240 volts to 120 volts. The number or turns (TX) required in the secondary (X) winding is _____.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
How a transformer works
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
21. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
die to leakage flux
Eh - lH = Ex - lX
closed-ended core
22. The voltage induced in the coil is directly proportional to this
change the input voltage
the number of turns in the coil
closed-ended core
transformers efficiency law
23. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
transformers efficiency
grounded (Earthed)
24. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
flux leakage
by using silicon iron core
open-ended core
25. The current related to turns ratio law
highly permeable material - iron or stalloy
Ip Ns = Is Np
magnetic field
Vs Ns = Vp Np
26. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
closed-ended core (square/doughnut shaped)
ratio of a transformer
primary coil
fault
27. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
a magnetic field that varies quickly in direction and stregnth
thin copper wire coated with insulated material (shellac or enamel)
air core
Eh/Ex=Th/Tx
28. A large amount of power wasted with the open-ended core
Transformer
Eh/Ex=Th/Tx
die to leakage flux
secondary coil
29. 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
transformers efficiency
Hysteresis
rating
high frequency transformer
30. The terminals of the high voltage winding are marked _____.
Measuring
H1 - h2...
X1 - X2...
dielectric oil
31. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
Transformer
an iron core and coil
Voltage
32. The simplest type of transformer core
air core
the number of turns in the coil
transformers efficiency law
Primary
33. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Transformer
Step-down
Same
Electromagnet
34. A partial or total local failure in the insulation or continuity of a conductor.
fault
Voltage - Current
polarity
Copper Losses - Core Losses
35. Copper loss is known as _____ loss.
Same
Distribution transformer
current related to voltage law
36. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Eh - lH = Ex - lX
voltage ralated to turns ratio
flux
37. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
the number of turns of wire in the primary and secondary coils
an iron core and coil
Low
38. Kind of wire is the secondary coil in a transformer
hysteresis losses (lagging losses)
grounded (Earthed)
variable
thin copper wire coated with insulated material (shellac or enamel)
39. Function of the dielectric oil
Class 200 transformers
Eddy
short circuit
Insulates - cools transformer by convection - dissipates heat
40. The formula for the current related to voltage law
Vs Ip = Vp Is
wigginton
Eh - lH = Ex - lX
Electromagnetic Induction.
41. Both the primary and secondary coils in a transformer are arranged around this
Hysteresis - Eddy - Current
grounded system
Distribution transformer
central magnetic core
42. What is a rotation meter?
magnetic flux
central magnetic core
Primary
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
43. A transformer loses less than _% in energy
electromagnetic mutual induction without loosing too much energy
a magnetic field that varies quickly in direction and stregnth
high frequency transformer
5
44. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
low rententivity
shell core
hysteresis losses (lagging losses)
Simple Transformer
45. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
one coils serves as the primary and secondary windings
closed-ended core
transformers efficiency law
electromagnetic mutual induction without loosing too much energy
46. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Measuring Equipment
Simple Transformer
Voltage - Current
Secondary
47. How coercivity is minimized
secondary coil
by using silicon iron core
short circuit
Hysteresis
48. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
secondary coil
constant current transfomers
current related to turns ratio law
dielectric oil
49. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
transformers efficiency law
Hysteresis - Eddy - Current
ratio of a transformer
fuse
50. The terminals of the low voltage winding are marked _____.
Eh - lH = Ex - lX
Hysteresis
voltage ralated to turns ratio
X1 - X2...