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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 relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
Exciting Current
primary coil - secondary coil - central magnetic core
current related to turns ratio law
Electromagnet
2. What does transformer efficiency mean?
silicon steel
The ratio of useful power output to its total power input.
air core
voltage ralated to turns ratio
3. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
dielectric oil
Exciting Current
Distribution transformer
eddy currents
4. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
closed-ended core (square/doughnut shaped)
silicon steel
Voltage - Current
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
5. An electromagnetic device that operates on the principle of self induction. It uses AC.
Hysteresis - Eddy - Current
Choke coil
primary coil
fuse
6. Is concentrated in the metal core
flux leakage
closed-ended core
magnetic field
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
7. A partial or total local failure in the insulation or continuity of a conductor.
fault
open-ended core
flux
leakage flux
8. 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
die to leakage flux
closed-ended core
continuous path
an iron core and coil
9. The number of turns can be adjusted in these types of transformers
change the input voltage
Vs Ns = Vp Np
variable transformers
Class 200 transformers
10. When an alternating current is applied to the high-voltage (H) winding of a transformer with no load on the secondary (X) winding - a small current - called the _____ current - flows in the primary.
Exciting
magnetic field
The ratio of useful power output to its total power input.
air core
11. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
ratio of a transformer
step-up (high voltage) transformers - step down transformer - autotransformer
Voltage - Current
phase
12. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
5
Eh/Ex=Th/Tx
leg(s)
13. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
Secondary
Kilovolt -- Amperes (kVA)
highly permeable material - iron or stalloy
14. 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.
rated KVA of a transformer
grounded system
Distribution transformer
current related to voltage law
15. The formula for the current related to voltage law
highly permeable material - iron or stalloy
Vs Ip = Vp Is
5
Kilovolt -- Amperes (kVA)
16. It refers to the direction of current flow in a closed circuit.
polarity
the number of turns in the coil
hysteresis losses (lagging losses)
Secondary
17. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
CORE: Core losses are caused by eddy currents set up by the magnetic field.
hysteresis losses (lagging losses)
Voltage
18. A simple design has a core within each coil
open-ended core
transformers efficiency law
current related to turns ratio law
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
19. The transformer winding to which voltage is supplied is called the _____ winding.
Autotransformer
fault
polarity
Primary
20. The relationship between current and voltage in the coils are inverse
current related to voltage law
Kilovolt -- Amperes (kVA)
leg(s)
Autotransformer
21. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
secondary coil
Step-down
magnetic flux
the number of turns of wire in the primary and secondary coils
22. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
current related to voltage law
H1 - h2...
central magnetic core
hysteresis losses (lagging losses)
23. A choke coil uses this to induce current
an iron core and coil
leakage flux
Step-down
central magnetic core
24. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
Low
variable transformers
flux leakage
25. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
one coils serves as the primary and secondary windings
Distribution transformer
transformers efficiency law
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
26. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Hysteresis
polarity
magnetic field
voltage ralated to turns ratio
27. has a laminated iron core (layers of metal plates)
continuous path
leakage flux
central magnetic core
closed-ended core
28. Central magnetic core made of
Eh - lH = Ex - lX
highly permeable material - iron or stalloy
coercivity
Secondary
29. The winding to which voltage is supplied is called the _____ winding.
Copper Losses - Core Losses
Primary
primary winding
Eddy
30. Reference to a jumper or conductor - to or from a piece of electrical equipment.
a magnetic field that varies quickly in direction and stregnth
leg(s)
Exciting Current
voltage ralated to turns ratio
31. 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
Secondary
open-ended core
directly proportional
Copper Losses - Core Losses
32. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Eh/Ex=Th/Tx
Secondary
flux leakage
silicon steel
33. 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.
closed-ended core
Electromagnet
grounded (Earthed)
electromagnetic mutual induction without loosing too much energy
34. Determines if the transformer is a step up or step down transformer
the number of turns of wire in the primary and secondary coils
Autotransformer
rated KVA of a transformer
Voltage - Current
35. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Volt-Amperes (Eh-lh=ExLx)
continuous path
Measuring
Eh/Ex=Th/Tx
36. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
class 400 transformers
Autotransformer
wigginton
closed-ended core
37. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
an iron core and coil
Secondary
Voltage
one coils serves as the primary and secondary windings
38. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Hysteresis - Eddy - Current
phase
5
ratio of a transformer
39. The transformer winding to which the load is connected is called the _____ winding.
Secondary
Vs Ns = Vp Np
Step-down
polarity
40. The 3 principle components of a transformer
CORE: Core losses are caused by eddy currents set up by the magnetic field.
change the input voltage
primary coil - secondary coil - central magnetic core
central magnetic core
41. An instrument used to measure electrical current.
Eh/Ex=Th/Tx
Eddy
ammeter
Vs Ip = Vp Is
42. The simplest type of transformer core
Voltage
Eddy
air core
change the input voltage
43. Both the primary and secondary coils in a transformer are arranged around this
central magnetic core
continuous path
hysteresis losses (lagging losses)
a magnetic field that varies quickly in direction and stregnth
44. How coils serve as the primary and secondary windings for an autotransformer
by varying the size of the applied DC
one coils serves as the primary and secondary windings
Insulates - cools transformer by convection - dissipates heat
phase
45. 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
silicon steel
continuous path
closed-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
46. The winding of a transformer to which electrical energy is supplied.
Secondary
a magnetic field that varies quickly in direction and stregnth
Eh/Ex=Th/Tx
primary winding
47. Core losses are _____ loss and _____ - _____ loss.
rated KVA of a transformer
Hysteresis - Eddy - Current
Secondary
eddy currents
48. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
grounded (Earthed)
dielectric oil
Low
die to leakage flux
49. A single electrical circuit.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Copper Losses - Core Losses
current related to voltage law
phase
50. Copper loss is known as _____ loss.
Step-up
step-up (high voltage) transformers - step down transformer - autotransformer
Insulates - cools transformer by convection - dissipates heat