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Test your basic knowledge |
Transformers
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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 characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Primary
coercivity
Copper Losses - Core Losses
2. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
Measuring Equipment
Measuring
Same
3. The current related to turns ratio law
Ip Ns = Is Np
one coils serves as the primary and secondary windings
low rententivity
leakage flux
4. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
low rententivity
dielectric oil
closed-ended core
Voltage - Current
5. Transformer losses are classified as _____ and _____.
Eh - lH = Ex - lX
rated KVA of a transformer
closed-ended core
Copper Losses - Core Losses
6. The formula for the voltage related to turns ratio
Secondary
central magnetic core
directly proportional
Vs Ns = Vp Np
7. 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 _____.
transformers efficiency
ammeter
Class 200 transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
8. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
continuous path
Copper Losses - Core Losses
fuse
Same
9. 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 using silicon iron core
Hysteresis
polarity
open-ended core
10. 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.
grounded system
directly proportional
high frequency transformer
constant current transfomers
11. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
open-ended core
a magnetic field that varies quickly in direction and stregnth
open-ended core
flux leakage
12. The transformer winding to which the load is connected is called the _____ winding.
rated KVA of a transformer
Secondary
the number of turns of wire in the primary and secondary coils
wigginton
13. The 3 types of transformer power loss
wigginton
low rententivity
Copper Losses - Core Losses
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
14. How coercivity is minimized
by using silicon iron core
transformers efficiency law
air core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
15. A single electrical circuit.
Eh/Ex=Th/Tx
phase
the number of turns in the coil
magnetic field
16. 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
Vs Ip = Vp Is
primary coil
How a transformer works
High voltage
17. Determines if the transformer is a step up or step down transformer
the number of turns of wire in the primary and secondary coils
voltage ralated to turns ratio
ratio of a transformer
closed-ended core (square/doughnut shaped)
18. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
X1 - X2...
Low
current related to turns ratio law
Secondary
19. 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
primary coil - secondary coil - central magnetic core
phase
high frequency transformer
saturable reactor
20. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
voltage ralated to turns ratio
short circuit
hysteresis losses (lagging losses)
grounded (Earthed)
21. _____ currents are reduced by laminating the core.
air core
rated KVA of a transformer
Eddy
a magnetic field that varies quickly in direction and stregnth
22. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Current
low rententivity
change the input voltage
Autotransformer
23. A ___________ transformer is a continuously adjustable Autotransformer.
leakage flux
an iron core and coil
variable
electromagnetic mutual induction without loosing too much energy
24. A simple design has a core within each coil
phase
open-ended core
leakage flux
thin copper wire coated with insulated material (shellac or enamel)
25. A transformer loses less than _% in energy
saturable reactor
Transformer
5
Eddy
26. Core losses are _____ loss and _____ - _____ loss.
Eh - lH = Ex - lX
primary coil
Hysteresis - Eddy - Current
CORE: Core losses are caused by eddy currents set up by the magnetic field.
27. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
fuse
Choke coil
Distribution transformer
secondary coil
28. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
X1 - X2...
Distribution transformer
Hysteresis
29. What does transformer efficiency mean?
primary coil
current related to voltage law
The ratio of useful power output to its total power input.
fault
30. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
shell core
central magnetic core
class 400 transformers
magnetic field
31. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
transformers efficiency law
shell core
Electromagnet
directly proportional
32. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
current related to voltage law
Distribution transformer
short circuit
33. both coils in this core are heavily insulated
Same
Ip Ns = Is Np
shell core
closed-ended core
34. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
magnetic field
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
air core
Measuring
35. 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
Copper Losses - Core Losses
Current
Secondary
36. The winding of a transformer to which electrical energy is supplied.
primary winding
Hysteresis - Eddy - Current
grounded (Earthed)
grounded system
37. An instrument used to measure electrical current.
primary coil - secondary coil - central magnetic core
ammeter
central magnetic core
38. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
primary winding
Primary
closed-ended core
39. 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)
low rententivity
Exciting Current
secondary coil
40. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
short circuit
constant current transfomers
secondary coil
Primary
41. Waste of power known as transformer loss - often produced by closed-ended core
fault
hysteresis losses (lagging losses)
eddy currents
air core
42. How the voltage and the number of turns are related for the voltage related to turn ratio
coercivity
fault
Eddy
directly proportional
43. A choke coil uses this to induce current
an iron core and coil
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Autotransformer
Secondary
44. The simplest type of transformer core
Class 200 transformers
air core
shell core
Eh/Ex=Th/Tx
45. The 3 principle components of a transformer
change the input voltage
thin copper wire coated with insulated material (shellac or enamel)
primary coil - secondary coil - central magnetic core
open-ended core
46. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
air core
5
constant current transfomers
high frequency transformer
47. The entire transformer is placed in a metal tank then immersed in ________.
Secondary
dielectric oil
wigginton
48. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
transformers efficiency law
central magnetic core
Distribution transformer
Eh/Ex=Th/Tx
49. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
open-ended core
a magnetic field that varies quickly in direction and stregnth
Measuring Equipment
Voltage - Current
50. 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
primary winding
class 400 transformers
Voltage - Current
closed-ended core
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