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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. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
voltage ralated to turns ratio
The ratio of useful power output to its total power input.
variable
class 400 transformers
2. 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.
grounded system
class 400 transformers
How a transformer works
Vs Ns = Vp Np
3. The winding to which voltage is supplied is called the _____ winding.
Step-down
die to leakage flux
Simple Transformer
Primary
4. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
transformers efficiency
variable transformers
Step-down
closed-ended core
5. Connected to earth or to some conducting body which serves in place of the earth.
Current
leg(s)
grounded (Earthed)
Vs Ip = Vp Is
6. Core losses are _____ loss and _____ - _____ loss.
Hysteresis
Eh/Ex=Th/Tx
Hysteresis - Eddy - Current
primary coil - secondary coil - central magnetic core
7. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
primary winding
silicon steel
hysteresis losses (lagging losses)
8. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
central magnetic core
Eh - lH = Ex - lX
air core
directly proportional
9. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
Step-down
rating
primary coil
electromagnetic mutual induction without loosing too much energy
10. 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.
Secondary
hysteresis losses (lagging losses)
variable transformers
11. How a variable degree of core saturation is accomplished in a saturable reactor?
Secondary
wigginton
How a transformer works
by varying the size of the applied DC
12. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
secondary coil
a magnetic field that varies quickly in direction and stregnth
Transformer
wigginton
13. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
Primary
primary coil
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
14. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
Secondary
closed-ended core
eddy currents
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
15. 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
Current
open-ended core
Vs Ip = Vp Is
16. 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
leg(s)
thin copper wire coated with insulated material (shellac or enamel)
continuous path
Simple Transformer
17. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
open-ended core
Choke coil
Low
continuous path
18. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
an iron core and coil
rated KVA of a transformer
ratio of a transformer
Primary
19. 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)
wigginton
by using silicon iron core
step-up (high voltage) transformers - step down transformer - autotransformer
Exciting
20. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
short circuit
the number of turns in the coil
Eh/Ex=Th/Tx
air core
21. Determines if the transformer is a step up or step down transformer
polarity
Simple Transformer
Class 200 transformers
the number of turns of wire in the primary and secondary coils
22. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
High voltage
hysteresis losses (lagging losses)
rated KVA of a transformer
eddy currents
23. The terminals of the high voltage winding are marked _____.
rating
Eh - lH = Ex - lX
H1 - h2...
Ip Ns = Is Np
24. How coils serve as the primary and secondary windings for an autotransformer
by varying the size of the applied DC
class 400 transformers
Primary
one coils serves as the primary and secondary windings
25. It refers to the direction of current flow in a closed circuit.
open-ended core
air core
polarity
Distribution transformer
26. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Electromagnetic Induction.
flux
primary winding
class 400 transformers
27. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
electromagnetic mutual induction without loosing too much energy
step-up (high voltage) transformers - step down transformer - autotransformer
shell core
Same
28. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
coercivity
How a transformer works
primary coil - secondary coil - central magnetic core
shell core
29. Divergence of the magnetic field causes this
X1 - X2...
leakage flux
shell core
Primary
30. The current related to turns ratio law
ratio of a transformer
Voltage - Current
Ip Ns = Is Np
Eddy
31. The capacity of a transformer is rated in ____ _____.
Kilovolt -- Amperes (kVA)
eddy currents
rating
coercivity
32. 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
How a transformer works
Distribution transformer
primary coil - secondary coil - central magnetic core
33. Copper loss is known as _____ loss.
Vs Ns = Vp Np
Eh/Ex=Th/Tx
CORE: Core losses are caused by eddy currents set up by the magnetic field.
34. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
Eh/Ex=Th/Tx
Step-down
fault
35. 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 _____.
an iron core and coil
fuse
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Secondary
36. A transformer loses less than _% in energy
saturable reactor
rated KVA of a transformer
Volt-Amperes (Eh-lh=ExLx)
5
37. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
closed-ended core (square/doughnut shaped)
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Step-up
open-ended core
38. _____ currents are reduced by laminating the core.
Current
Eddy
voltage ralated to turns ratio
by varying the size of the applied DC
39. The relationship between current and voltage in the coils are inverse
Measuring
by varying the size of the applied DC
current related to voltage law
closed-ended core (square/doughnut shaped)
40. 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.
one coils serves as the primary and secondary windings
fault
41. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
hysteresis losses (lagging losses)
high frequency transformer
High voltage
ammeter
42. A choke coil uses this to induce current
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Autotransformer
primary coil
an iron core and coil
43. 3 types of transformers
coercivity
step-up (high voltage) transformers - step down transformer - autotransformer
current related to turns ratio law
primary coil
44. The formula for the current related to voltage law
high frequency transformer
Vs Ip = Vp Is
Class 200 transformers
silicon steel
45. An electromagnetic device that operates on the principle of self induction. It uses AC.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Choke coil
an iron core and coil
Vs Ns = Vp Np
46. 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
Transformer
How a transformer works
Distribution transformer
X1 - X2...
47. 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
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
transformers efficiency
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Class 200 transformers
48. 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
high frequency transformer
highly permeable material - iron or stalloy
49. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
Step-down
rated KVA of a transformer
Exciting
50. 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.
Autotransformer
eddy currents
voltage ralated to turns ratio
constant current transfomers