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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. 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
open-ended core
current related to turns ratio law
dielectric oil
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
2. Waste of power known as transformer loss - often produced by closed-ended core
eddy currents
Primary
continuous path
Simple Transformer
3. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
rated KVA of a transformer
grounded (Earthed)
Exciting Current
closed-ended core (square/doughnut shaped)
4. Is concentrated in the metal core
magnetic field
Autotransformer
Primary
Secondary
5. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
eddy currents
Step-up
flux leakage
the number of turns in the coil
6. Copper loss is known as _____ loss.
rated KVA of a transformer
magnetic flux
Secondary
7. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
a magnetic field that varies quickly in direction and stregnth
The ratio of useful power output to its total power input.
Vs Ns = Vp Np
Eh/Ex=Th/Tx
8. An instrument used to measure electrical current.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
ammeter
eddy currents
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
9. A partial or total local failure in the insulation or continuity of a conductor.
continuous path
fault
the number of turns in the coil
Exciting
10. The terminals of the low voltage winding are marked _____.
X1 - X2...
a magnetic field that varies quickly in direction and stregnth
transformers efficiency law
high frequency transformer
11. A single electrical circuit.
phase
leakage flux
flux
Measuring Equipment
12. The current related to turns ratio law
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
class 400 transformers
Step-up
Ip Ns = Is Np
13. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
Kilovolt -- Amperes (kVA)
How a transformer works
primary coil - secondary coil - central magnetic core
14. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
Low
Current
Secondary
15. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
by varying the size of the applied DC
Vs Ns = Vp Np
secondary coil
primary coil
16. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
variable
Same
highly permeable material - iron or stalloy
X1 - X2...
17. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
secondary coil
class 400 transformers
CORE: Core losses are caused by eddy currents set up by the magnetic field.
rated KVA of a transformer
18. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Hysteresis - Eddy - Current
short circuit
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
one coils serves as the primary and secondary windings
19. The terminals of the high voltage winding are marked _____.
flux leakage
fuse
current related to voltage law
H1 - h2...
20. Divergence of the magnetic field causes this
Eh/Ex=Th/Tx
continuous path
Secondary
leakage flux
21. Connected to earth or to some conducting body which serves in place of the earth.
Transformer
silicon steel
grounded (Earthed)
low rententivity
22. How coercivity is minimized
by using silicon iron core
Ip Ns = Is Np
Voltage
closed-ended core
23. 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
Primary
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Secondary
How a transformer works
24. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
X1 - X2...
air core
transformers efficiency law
Distribution transformer
25. The 3 types of transformer power loss
fuse
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
The ratio of useful power output to its total power input.
thin copper wire coated with insulated material (shellac or enamel)
26. both coils in this core are heavily insulated
secondary coil
closed-ended core
Measuring Equipment
an iron core and coil
27. The simplest type of transformer core
by varying the size of the applied DC
constant current transfomers
Measuring
air core
28. has a laminated iron core (layers of metal plates)
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
closed-ended core
Primary
Volt-Amperes (Eh-lh=ExLx)
29. The relationship between current and voltage in the coils are inverse
current related to voltage law
5
one coils serves as the primary and secondary windings
Low
30. A transformer loses less than _% in energy
by varying the size of the applied DC
Vs Ip = Vp Is
5
magnetic field
31. The transformer winding to which the load is connected is called the _____ winding.
rating
Secondary
the number of turns of wire in the primary and secondary coils
dielectric oil
32. 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
highly permeable material - iron or stalloy
Choke coil
How a transformer works
continuous path
33. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
thin copper wire coated with insulated material (shellac or enamel)
ammeter
Step-down
Transformer
34. 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
Copper Losses - Core Losses
Hysteresis
Secondary
variable transformers
35. Hysteresis Loss can be reduced by using a core with this feature
silicon steel
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
change the input voltage
low rententivity
36. 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
Measuring
closed-ended core
Secondary
37. Modern; used to control filament circuit; replaced both the rheostat and choke coil; operated on the electromagnetic principle that if an iron core within or near a coil is saturated with magnetic flux by an independed source of direct current - the
variable transformers
Step-down
saturable reactor
Current
38. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
High voltage
Transformer
Copper Losses - Core Losses
air core
39. _____ currents are reduced by laminating the core.
eddy currents
Eddy
leg(s)
rated KVA of a transformer
40. 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)
Electromagnetic Induction.
wigginton
Secondary
variable
41. Reference to a jumper or conductor - to or from a piece of electrical equipment.
secondary coil
current related to voltage law
leg(s)
Eddy
42. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
directly proportional
Voltage
leakage flux
Step-up
43. A designated limit of operating characteristics based on definite conditions.
phase
Eh/Ex=Th/Tx
directly proportional
rating
44. 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
H1 - h2...
Low
Class 200 transformers
Electromagnet
45. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
Class 200 transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
step-up (high voltage) transformers - step down transformer - autotransformer
46. 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.
fuse
Measuring Equipment
central magnetic core
Electromagnet
47. The capacity of a transformer is rated in ____ _____.
magnetic flux
flux leakage
High voltage
Kilovolt -- Amperes (kVA)
48. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
transformers efficiency law
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Autotransformer
Eh/Ex=Th/Tx
49. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Hysteresis - Eddy - Current
Step-up
one coils serves as the primary and secondary windings
class 400 transformers
50. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
primary coil
eddy currents
by using silicon iron core