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Test your basic knowledge |
Transformers
Start Test
Study First
Subject
:
engineering
Instructions:
Answer 50 questions in 15 minutes.
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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 turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
polarity
step-up (high voltage) transformers - step down transformer - autotransformer
secondary coil
ratio of a transformer
2. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
flux leakage
closed-ended core (square/doughnut shaped)
Ip Ns = Is Np
eddy currents
3. A single electrical circuit.
Vs Ns = Vp Np
primary coil - secondary coil - central magnetic core
Measuring
phase
4. has a laminated iron core (layers of metal plates)
closed-ended core
ratio of a transformer
directly proportional
Eh - lH = Ex - lX
5. Determines if the transformer is a step up or step down transformer
one coils serves as the primary and secondary windings
transformers efficiency law
the number of turns of wire in the primary and secondary coils
High voltage
6. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Measuring
variable
7. A choke coil uses this to induce current
die to leakage flux
dielectric oil
an iron core and coil
magnetic field
8. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
open-ended core
coercivity
Volt-Amperes (Eh-lh=ExLx)
Step-down
9. 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.
Electromagnet
Exciting
a magnetic field that varies quickly in direction and stregnth
the number of turns in the coil
10. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
high frequency transformer
primary coil - secondary coil - central magnetic core
Voltage - Current
voltage ralated to turns ratio
11. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
open-ended core
Ip Ns = Is Np
primary coil - secondary coil - central magnetic core
12. The entire transformer is placed in a metal tank then immersed in ________.
dielectric oil
Step-up
closed-ended core
wigginton
13. A part of a circuit made of a low melting point material so that it will melt and break the circuit when a specified current exceeded. Always the weakest point in the circuit.
central magnetic core
Hysteresis
Secondary
fuse
14. Anything above 600 volts is _____?
High voltage
Hysteresis
Electromagnet
15. The terminals of the low voltage winding are marked _____.
a magnetic field that varies quickly in direction and stregnth
by varying the size of the applied DC
X1 - X2...
closed-ended core
16. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
current related to turns ratio law
H1 - h2...
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Volt-Amperes (Eh-lh=ExLx)
17. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
fault
change the input voltage
directly proportional
X1 - X2...
18. Waste of power known as transformer loss - often produced by closed-ended core
open-ended core
open-ended core
air core
eddy currents
19. Used to increase the magnetic flux in a transformer
Hysteresis - Eddy - Current
by varying the size of the applied DC
central magnetic core
primary winding
20. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Choke coil
Transformer
magnetic field
21. 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.
saturable reactor
Step-up
Electromagnet
constant current transfomers
22. 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 _____.
Secondary
Same
central magnetic core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
23. The winding of a transformer to which electrical energy is supplied.
Primary
ammeter
coercivity
primary winding
24. 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
by varying the size of the applied DC
ammeter
short circuit
Hysteresis
25. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
variable transformers
Measuring
hysteresis losses (lagging losses)
low rententivity
26. Copper loss is known as _____ loss.
Insulates - cools transformer by convection - dissipates heat
Autotransformer
Distribution transformer
27. Core losses are _____ loss and _____ - _____ loss.
magnetic flux
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Hysteresis - Eddy - Current
Vs Ns = Vp Np
28. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
secondary coil
Electromagnet
Primary
29. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
transformers efficiency
Step-down
open-ended core
How a transformer works
30. The simplest type of transformer core
Eh - lH = Ex - lX
air core
variable
phase
31. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Vs Ns = Vp Np
Hysteresis - Eddy - Current
primary coil
Autotransformer
32. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
by varying the size of the applied DC
Distribution transformer
saturable reactor
Low
33. Transformer losses are classified as _____ and _____.
X1 - X2...
saturable reactor
Copper Losses - Core Losses
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
34. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eddy
Eh - lH = Ex - lX
one coils serves as the primary and secondary windings
central magnetic core
35. A designated limit of operating characteristics based on definite conditions.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
directly proportional
rating
Step-up
36. 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
coercivity
Step-down
Eddy
37. A partial or total local failure in the insulation or continuity of a conductor.
coercivity
fault
Step-up
primary coil
38. How coils serve as the primary and secondary windings for an autotransformer
coercivity
one coils serves as the primary and secondary windings
Simple Transformer
closed-ended core
39. With no load on the secondary winding - a small current flows in the primary called _____ _____.
dielectric oil
silicon steel
eddy currents
Exciting Current
40. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
secondary coil
Step-up
fault
41. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Vs Ip = Vp Is
closed-ended core (square/doughnut shaped)
Current
Low
42. A transformer loses less than _% in energy
5
die to leakage flux
Step-down
Autotransformer
43. The terminals of the high voltage winding are marked _____.
High voltage
H1 - h2...
step-up (high voltage) transformers - step down transformer - autotransformer
central magnetic core
44. A large amount of power wasted with the open-ended core
class 400 transformers
Volt-Amperes (Eh-lh=ExLx)
grounded system
die to leakage flux
45. A simple design has a core within each coil
open-ended core
Secondary
electromagnetic mutual induction without loosing too much energy
5
46. 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)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
High voltage
a magnetic field that varies quickly in direction and stregnth
wigginton
47. both coils in this core are heavily insulated
Vs Ip = Vp Is
voltage ralated to turns ratio
Primary
closed-ended core
48. 3 types of transformers
high frequency transformer
step-up (high voltage) transformers - step down transformer - autotransformer
electromagnetic mutual induction without loosing too much energy
How a transformer works
49. What does transformer efficiency mean?
open-ended core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
The ratio of useful power output to its total power input.
Secondary
50. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
secondary coil
Current
central magnetic core
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