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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. Function of the dielectric oil
variable transformers
Insulates - cools transformer by convection - dissipates heat
Choke coil
2. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
grounded system
X1 - X2...
Voltage - Current
change the input voltage
3. 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 _____.
voltage ralated to turns ratio
primary coil
The ratio of useful power output to its total power input.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
4. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
air core
class 400 transformers
open-ended core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
5. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx
closed-ended core
Step-up
one coils serves as the primary and secondary windings
6. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Copper Losses - Core Losses
Hysteresis - Eddy - Current
Vs Ns = Vp Np
Eh - lH = Ex - lX
7. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
current related to turns ratio law
Distribution transformer
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
8. Refers to the transformer's ability to avoid power loss (heat)
Secondary
constant current transfomers
open-ended core
transformers efficiency
9. How a variable degree of core saturation is accomplished in a saturable reactor?
fault
high frequency transformer
Secondary
by varying the size of the applied DC
10. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Eh - lH = Ex - lX
Secondary
Volt-Amperes (Eh-lh=ExLx)
phase
11. A large amount of power wasted with the open-ended core
shell core
die to leakage flux
Voltage - Current
Measuring
12. The shape of the core of the transformer ensures a ______________ for the magnetic flux with maximum concentration within the core and minimum leakage of the air
closed-ended core
continuous path
constant current transfomers
flux leakage
13. The transformer winding to which voltage is supplied is called the _____ winding.
Exciting Current
Primary
rated KVA of a transformer
Step-up
14. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
ratio of a transformer
Vs Ns = Vp Np
Electromagnetic Induction.
primary winding
15. A transformer which when supplied from a constant potential source automatically maintans a constant current in its secondary circuit under varying conditions of load impedance. Used on series street light circuits.
constant current transfomers
Electromagnet
Eh/Ex=Th/Tx
Exciting
16. A designated limit of operating characteristics based on definite conditions.
rating
How a transformer works
open-ended core
electromagnetic mutual induction without loosing too much energy
17. Reference to a jumper or conductor - to or from a piece of electrical equipment.
closed-ended core
leg(s)
Hysteresis
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
18. Waste of power known as transformer loss - often produced by closed-ended core
central magnetic core
flux
eddy currents
silicon steel
19. The entire transformer is placed in a metal tank then immersed in ________.
dielectric oil
X1 - X2...
High voltage
directly proportional
20. It refers to the direction of current flow in a closed circuit.
Exciting
polarity
flux
highly permeable material - iron or stalloy
21. 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
H1 - h2...
Electromagnet
open-ended core
the number of turns in the coil
22. An electromagnetic device that operates on the principle of self induction. It uses AC.
electromagnetic mutual induction without loosing too much energy
wigginton
Volt-Amperes (Eh-lh=ExLx)
Choke coil
23. Copper loss is known as _____ loss.
Primary
magnetic flux
transformers efficiency law
24. The winding to which voltage is supplied is called the _____ winding.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
highly permeable material - iron or stalloy
Primary
Eh - lH = Ex - lX
25. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
leakage flux
Hysteresis
hysteresis losses (lagging losses)
voltage ralated to turns ratio
26. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
the number of turns in the coil
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Simple Transformer
closed-ended core
27. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
X1 - X2...
silicon steel
dielectric oil
electromagnetic mutual induction without loosing too much energy
28. 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.
Hysteresis
Secondary
by using silicon iron core
Current
29. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
transformers efficiency
constant current transfomers
Current
air core
30. How the voltage and the number of turns are related for the voltage related to turn ratio
Eh/Ex=Th/Tx
dielectric oil
low rententivity
directly proportional
31. 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.
high frequency transformer
Electromagnet
phase
CORE: Core losses are caused by eddy currents set up by the magnetic field.
32. The terminals of the high voltage winding are marked _____.
by varying the size of the applied DC
Measuring Equipment
H1 - h2...
ratio of a transformer
33. Determines if the transformer is a step up or step down transformer
transformers efficiency
the number of turns of wire in the primary and secondary coils
Current
Measuring
34. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
transformers efficiency law
Measuring
current related to voltage law
35. The terminals of the low voltage winding are marked _____.
fuse
magnetic flux
wigginton
X1 - X2...
36. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
flux leakage
Autotransformer
Step-down
constant current transfomers
37. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
electromagnetic mutual induction without loosing too much energy
the number of turns in the coil
Choke coil
air core
38. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
flux leakage
polarity
Hysteresis
voltage ralated to turns ratio
39. The relationship between current and voltage in the coils are inverse
Hysteresis - Eddy - Current
dielectric oil
Secondary
current related to voltage law
40. both coils in this core are heavily insulated
Secondary
closed-ended core
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
the number of turns of wire in the primary and secondary coils
41. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Exciting
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
central magnetic core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
42. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
one coils serves as the primary and secondary windings
Exciting Current
X1 - X2...
Step-up
43. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Eddy
Eh - lH = Ex - lX
coercivity
Voltage
44. A ___________ transformer is a continuously adjustable Autotransformer.
leg(s)
variable
Electromagnet
low rententivity
45. The winding to which the load is connected is called the _____ winding.
thin copper wire coated with insulated material (shellac or enamel)
open-ended core
short circuit
Secondary
46. Both the primary and secondary coils in a transformer are arranged around this
constant current transfomers
central magnetic core
Secondary
variable
47. A single electrical circuit.
Ip Ns = Is Np
phase
magnetic flux
fault
48. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
short circuit
current related to voltage law
grounded system
49. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
the number of turns of wire in the primary and secondary coils
ammeter
current related to turns ratio law
Current
50. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
one coils serves as the primary and secondary windings
transformers efficiency
shell core
continuous path