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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. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
coercivity
Exciting Current
the number of turns of wire in the primary and secondary coils
2. The terminals of the high voltage winding are marked _____.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Copper Losses - Core Losses
Current
H1 - h2...
3. The total numbre of lines or force issuing from a pole. (north or south)
one coils serves as the primary and secondary windings
magnetic flux
electromagnetic mutual induction without loosing too much energy
silicon steel
4. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
by using silicon iron core
X1 - X2...
high frequency transformer
primary winding
5. Function of the dielectric oil
Transformer
Volt-Amperes (Eh-lh=ExLx)
closed-ended core
Insulates - cools transformer by convection - dissipates heat
6. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Exciting Current
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
the number of turns of wire in the primary and secondary coils
7. Divergence of the magnetic field causes this
electromagnetic mutual induction without loosing too much energy
step-up (high voltage) transformers - step down transformer - autotransformer
continuous path
leakage flux
8. The number of turns can be adjusted in these types of transformers
Low
variable transformers
current related to voltage law
Step-up
9. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
grounded system
silicon steel
X1 - X2...
coercivity
10. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Kilovolt -- Amperes (kVA)
saturable reactor
High voltage
flux leakage
11. Anything above 600 volts is _____?
the number of turns of wire in the primary and secondary coils
wigginton
High voltage
phase
12. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
air core
open-ended core
The ratio of useful power output to its total power input.
13. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
change the input voltage
Current
current related to turns ratio law
air core
14. The 3 principle components of a transformer
grounded system
Hysteresis
primary coil - secondary coil - central magnetic core
Electromagnet
15. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Hysteresis - Eddy - Current
current related to voltage law
voltage ralated to turns ratio
Distribution transformer
16. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Vs Ip = Vp Is
rated KVA of a transformer
dielectric oil
High voltage
17. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
current related to voltage law
low rententivity
class 400 transformers
Eh - lH = Ex - lX
18. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
Low
ammeter
Voltage
19. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
air core
secondary coil
high frequency transformer
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.
Simple Transformer
Secondary
fuse
Measuring
21. Is concentrated in the metal core
Electromagnet
saturable reactor
open-ended core
magnetic field
22. The transformer winding to which the load is connected is called the _____ winding.
Secondary
shell core
Eh/Ex=Th/Tx
5
23. Transformer losses are classified as _____ and _____.
leakage flux
thin copper wire coated with insulated material (shellac or enamel)
Copper Losses - Core Losses
magnetic flux
24. _____ currents are reduced by laminating the core.
Eh/Ex=Th/Tx
Eddy
leakage flux
Volt-Amperes (Eh-lh=ExLx)
25. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
high frequency transformer
secondary coil
highly permeable material - iron or stalloy
by varying the size of the applied DC
26. Kind of wire is the secondary coil in a transformer
High voltage
Step-down
thin copper wire coated with insulated material (shellac or enamel)
Vs Ns = Vp Np
27. A system of conductors in which at least one conductors or point (usually the middle wire or neutral point of a transformer or generator windings) is intentionally grounded either solididly or through a current-limiting device.
wigginton
grounded system
short circuit
leakage flux
28. The current related to turns ratio law
Ip Ns = Is Np
Measuring Equipment
primary winding
Current
29. A simple design has a core within each coil
current related to turns ratio law
a magnetic field that varies quickly in direction and stregnth
open-ended core
The ratio of useful power output to its total power input.
30. 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.
variable
Electromagnet
Eh - lH = Ex - lX
secondary coil
31. The winding to which the load is connected is called the _____ winding.
Class 200 transformers
one coils serves as the primary and secondary windings
Secondary
Voltage - Current
32. The simplest type of transformer core
air core
Measuring
eddy currents
primary coil
33. A large amount of power wasted with the open-ended core
Same
die to leakage flux
5
Exciting Current
34. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
variable transformers
closed-ended core
short circuit
CORE: Core losses are caused by eddy currents set up by the magnetic field.
35. 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)
Simple Transformer
flux leakage
The ratio of useful power output to its total power input.
36. Current flows through the primary winding in response to primary voltage and sets up a magnetic field that varies in direction and stregnth. under the influence of the changing magnetic field an AC voltage/kv is induced across the secondary coil by e
central magnetic core
Secondary
rated KVA of a transformer
How a transformer works
37. Hysteresis Loss can be reduced by using a core with this feature
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Current
5
low rententivity
38. 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)
hysteresis losses (lagging losses)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
wigginton
Hysteresis - Eddy - Current
39. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
phase
Insulates - cools transformer by convection - dissipates heat
hysteresis losses (lagging losses)
Step-up
40. Used to increase the magnetic flux in a transformer
Choke coil
central magnetic core
Current
Exciting
41. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
The ratio of useful power output to its total power input.
class 400 transformers
Voltage
Class 200 transformers
42. Determines if the transformer is a step up or step down transformer
wigginton
rated KVA of a transformer
the number of turns of wire in the primary and secondary coils
magnetic flux
43. What is a rotation meter?
central magnetic core
Hysteresis - Eddy - Current
shell core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
44. A ___________ transformer is a continuously adjustable Autotransformer.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Exciting Current
Choke coil
variable
45. The winding to which voltage is supplied is called the _____ winding.
X1 - X2...
grounded system
Primary
46. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Insulates - cools transformer by convection - dissipates heat
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
H1 - h2...
Measuring
47. Both the primary and secondary coils in a transformer are arranged around this
air core
variable transformers
Voltage - Current
central magnetic core
48. What does transformer efficiency mean?
step-up (high voltage) transformers - step down transformer - autotransformer
The ratio of useful power output to its total power input.
rating
a magnetic field that varies quickly in direction and stregnth
49. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
leg(s)
change the input voltage
polarity
The ratio of useful power output to its total power input.
50. 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
an iron core and coil
highly permeable material - iron or stalloy
Eh - lH = Ex - lX
Class 200 transformers
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