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. How a variable degree of core saturation is accomplished in a saturable reactor?
variable
Voltage - Current
eddy currents
by varying the size of the applied DC
2. A large amount of power wasted with the open-ended core
die to leakage flux
phase
Vs Ip = Vp Is
Measuring Equipment
3. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
fault
magnetic flux
by varying the size of the applied DC
4. Hysteresis Loss can be reduced by using a core with this feature
transformers efficiency
fuse
low rententivity
rating
5. The relationship between current and voltage in the coils are inverse
closed-ended core (square/doughnut shaped)
one coils serves as the primary and secondary windings
Secondary
current related to voltage law
6. The voltage induced in the coil is directly proportional to this
Choke coil
dielectric oil
Exciting Current
the number of turns in the coil
7. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Electromagnetic Induction.
thin copper wire coated with insulated material (shellac or enamel)
hysteresis losses (lagging losses)
Low
8. The number of turns can be adjusted in these types of transformers
variable transformers
by using silicon iron core
Secondary
the number of turns of wire in the primary and secondary coils
9. 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 varying the size of the applied DC
primary coil - secondary coil - central magnetic core
electromagnetic mutual induction without loosing too much energy
Class 200 transformers
10. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
ammeter
air core
continuous path
Step-down
11. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
change the input voltage
Distribution transformer
Eh/Ex=Th/Tx
Simple Transformer
12. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
open-ended core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
shell core
primary coil - secondary coil - central magnetic core
13. Anything above 600 volts is _____?
High voltage
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.
Copper Losses - Core Losses
14. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
phase
one coils serves as the primary and secondary windings
primary coil
Autotransformer
15. Copper loss is known as _____ loss.
fault
Measuring
Hysteresis - Eddy - Current
16. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Vs Ns = Vp Np
Same
wigginton
electromagnetic mutual induction without loosing too much energy
17. 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 _____.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
voltage ralated to turns ratio
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Transformer
18. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
Vs Ip = Vp Is
CORE: Core losses are caused by eddy currents set up by the magnetic field.
primary coil
shell core
19. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
Electromagnetic Induction.
leg(s)
the number of turns in the coil
20. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Electromagnet
hysteresis losses (lagging losses)
Voltage
air core
21. Both the primary and secondary coils in a transformer are arranged around this
Eh/Ex=Th/Tx
eddy currents
saturable reactor
central magnetic core
22. A single electrical circuit.
high frequency transformer
CORE: Core losses are caused by eddy currents set up by the magnetic field.
phase
closed-ended core
23. The formula for the current related to voltage law
magnetic flux
Vs Ip = Vp Is
step-up (high voltage) transformers - step down transformer - autotransformer
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
24. A simple design has a core within each coil
open-ended core
coercivity
saturable reactor
Volt-Amperes (Eh-lh=ExLx)
25. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Secondary
Step-down
Class 200 transformers
leg(s)
26. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
central magnetic core
air core
Volt-Amperes (Eh-lh=ExLx)
27. 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.
a magnetic field that varies quickly in direction and stregnth
Secondary
H1 - h2...
short circuit
28. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
high frequency transformer
Electromagnet
flux
change the input voltage
29. A partial or total local failure in the insulation or continuity of a conductor.
fault
step-up (high voltage) transformers - step down transformer - autotransformer
Ip Ns = Is Np
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
30. How coils serve as the primary and secondary windings for an autotransformer
closed-ended core
change the input voltage
one coils serves as the primary and secondary windings
dielectric oil
31. Function of the dielectric oil
Same
Insulates - cools transformer by convection - dissipates heat
5
Voltage
32. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
central magnetic core
Kilovolt -- Amperes (kVA)
dielectric oil
33. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Hysteresis
ratio of a transformer
constant current transfomers
Voltage
34. Kind of wire is the secondary coil in a transformer
polarity
thin copper wire coated with insulated material (shellac or enamel)
open-ended core
current related to voltage law
35. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
voltage ralated to turns ratio
ammeter
grounded (Earthed)
36. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
polarity
closed-ended core
Exciting
37. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
coercivity
Electromagnet
polarity
short circuit
38. 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.
highly permeable material - iron or stalloy
ratio of a transformer
Electromagnet
Transformer
39. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
secondary coil
closed-ended core
change the input voltage
40. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Eh/Ex=Th/Tx
CORE: Core losses are caused by eddy currents set up by the magnetic field.
high frequency transformer
rated KVA of a transformer
41. A transformer loses less than _% in energy
ammeter
by using silicon iron core
5
primary coil - secondary coil - central magnetic core
42. The terminals of the low voltage winding are marked _____.
primary winding
How a transformer works
open-ended core
X1 - X2...
43. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
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
flux
Simple Transformer
44. The winding to which voltage is supplied is called the _____ winding.
Exciting
Primary
Ip Ns = Is Np
hysteresis losses (lagging losses)
45. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
Ip Ns = Is Np
Class 200 transformers
saturable reactor
46. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Voltage
ammeter
High voltage
Measuring Equipment
47. What does transformer efficiency mean?
ratio of a transformer
The ratio of useful power output to its total power input.
primary winding
Vs Ns = Vp Np
48. The current related to turns ratio law
Current
Step-up
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Ip Ns = Is Np
49. Determines if the transformer is a step up or step down transformer
the number of turns of wire in the primary and secondary coils
Transformer
current related to turns ratio law
a magnetic field that varies quickly in direction and stregnth
50. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
short circuit
current related to turns ratio law
dielectric oil
Primary