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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. _____ currents are reduced by laminating the core.
fuse
phase
short circuit
Eddy
2. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
voltage ralated to turns ratio
closed-ended core
ratio of a transformer
Eh - lH = Ex - lX
3. Divergence of the magnetic field causes this
leakage flux
coercivity
wigginton
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
4. A ___________ transformer is a continuously adjustable Autotransformer.
rating
X1 - X2...
Voltage - Current
variable
5. 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
closed-ended core
Electromagnetic Induction.
Transformer
an iron core and coil
6. Is concentrated in the metal core
magnetic field
Vs Ns = Vp Np
polarity
fault
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)
closed-ended core
Voltage - Current
Step-down
8. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Low
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
closed-ended core (square/doughnut shaped)
one coils serves as the primary and secondary windings
9. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
air core
Copper Losses - Core Losses
Current
Autotransformer
10. The current related to turns ratio law
by varying the size of the applied DC
magnetic field
Copper Losses - Core Losses
Ip Ns = Is Np
11. 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)
air core
Measuring Equipment
wigginton
Hysteresis - Eddy - Current
12. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
primary winding
high frequency transformer
magnetic flux
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
13. Copper loss is known as _____ loss.
Volt-Amperes (Eh-lh=ExLx)
step-up (high voltage) transformers - step down transformer - autotransformer
High voltage
14. Determines if the transformer is a step up or step down transformer
secondary coil
the number of turns of wire in the primary and secondary coils
closed-ended core
change the input voltage
15. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
the number of turns in the coil
primary coil
current related to turns ratio law
16. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
transformers efficiency law
Measuring Equipment
change the input voltage
primary coil - secondary coil - central magnetic core
17. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
Distribution transformer
grounded (Earthed)
Measuring
18. 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
X1 - X2...
Low
Secondary
Hysteresis
19. With no load on the secondary winding - a small current flows in the primary called _____ _____.
thin copper wire coated with insulated material (shellac or enamel)
Exciting Current
central magnetic core
the number of turns in the coil
20. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
fuse
directly proportional
Current
open-ended core
21. both coils in this core are heavily insulated
wigginton
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
closed-ended core
variable
22. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx
Exciting
phase
Secondary
23. The 3 principle components of a transformer
closed-ended core (square/doughnut shaped)
voltage ralated to turns ratio
primary coil - secondary coil - central magnetic core
Ip Ns = Is Np
24. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
a magnetic field that varies quickly in direction and stregnth
short circuit
step-up (high voltage) transformers - step down transformer - autotransformer
primary winding
25. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
an iron core and coil
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Step-down
fault
26. A partial or total local failure in the insulation or continuity of a conductor.
rated KVA of a transformer
fault
saturable reactor
Secondary
27. The formula for the current related to voltage law
Exciting
grounded (Earthed)
Vs Ip = Vp Is
open-ended core
28. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
by varying the size of the applied DC
Electromagnetic Induction.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
die to leakage flux
29. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
open-ended core
step-up (high voltage) transformers - step down transformer - autotransformer
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
30. Refers to the transformer's ability to avoid power loss (heat)
transformers efficiency
fuse
fault
directly proportional
31. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
grounded (Earthed)
Measuring Equipment
continuous path
ratio of a transformer
32. It refers to the direction of current flow in a closed circuit.
fuse
hysteresis losses (lagging losses)
polarity
Hysteresis - Eddy - Current
33. The number of turns can be adjusted in these types of transformers
continuous path
variable transformers
transformers efficiency law
rated KVA of a transformer
34. The relationship between current and voltage in the coils are inverse
current related to voltage law
The ratio of useful power output to its total power input.
by using silicon iron core
Voltage - Current
35. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
flux
central magnetic core
High voltage
primary coil
36. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
high frequency transformer
X1 - X2...
Volt-Amperes (Eh-lh=ExLx)
shell core
37. An electromagnetic device that operates on the principle of self induction. It uses AC.
ratio of a transformer
Choke coil
short circuit
dielectric oil
38. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
a magnetic field that varies quickly in direction and stregnth
5
coercivity
39. A large amount of power wasted with the open-ended core
a magnetic field that varies quickly in direction and stregnth
Hysteresis
die to leakage flux
step-up (high voltage) transformers - step down transformer - autotransformer
40. Anything above 600 volts is _____?
Electromagnet
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Measuring
High voltage
41. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
a magnetic field that varies quickly in direction and stregnth
Simple Transformer
Electromagnetic Induction.
Exciting
42. A transformer is a device that either increases or decreases alternating current and voltage using this principle
air core
electromagnetic mutual induction without loosing too much energy
low rententivity
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
43. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Exciting
Step-up
44. Function of the dielectric oil
central magnetic core
polarity
the number of turns in the coil
Insulates - cools transformer by convection - dissipates heat
45. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
grounded (Earthed)
closed-ended core (square/doughnut shaped)
Step-up
46. The transformer winding to which the load is connected is called the _____ winding.
Electromagnetic Induction.
closed-ended core (square/doughnut shaped)
central magnetic core
Secondary
47. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
grounded (Earthed)
Transformer
Secondary
Step-down
48. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
electromagnetic mutual induction without loosing too much energy
voltage ralated to turns ratio
continuous path
49. Two coils wound on a closed iron core form a ________.
fault
closed-ended core (square/doughnut shaped)
continuous path
Simple Transformer
50. What does transformer efficiency mean?
the number of turns in the coil
5
The ratio of useful power output to its total power input.
ratio of a transformer
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