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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
closed-ended core
Voltage - Current
voltage ralated to turns ratio
secondary coil
2. 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 _____.
Low
polarity
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
closed-ended core (square/doughnut shaped)
3. 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.
ammeter
H1 - h2...
open-ended core
Secondary
4. With no load on the secondary winding - a small current flows in the primary called _____ _____.
step-up (high voltage) transformers - step down transformer - autotransformer
Copper Losses - Core Losses
Exciting Current
short circuit
5. An instrument used to measure electrical current.
ammeter
closed-ended core
Secondary
closed-ended core
6. The 3 principle components of a transformer
low rententivity
Exciting
primary coil - secondary coil - central magnetic core
High voltage
7. Both the primary and secondary coils in a transformer are arranged around this
current related to turns ratio law
central magnetic core
primary winding
How a transformer works
8. A partial or total local failure in the insulation or continuity of a conductor.
Insulates - cools transformer by convection - dissipates heat
rated KVA of a transformer
High voltage
fault
9. The terminals of the low voltage winding are marked _____.
Secondary
fault
X1 - X2...
flux leakage
10. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
magnetic field
Exciting Current
Eh/Ex=Th/Tx
Current
11. Waste of power known as transformer loss - often produced by closed-ended core
Current
H1 - h2...
eddy currents
Hysteresis
12. The voltage induced in the coil is directly proportional to this
ammeter
closed-ended core (square/doughnut shaped)
the number of turns in the coil
high frequency transformer
13. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
flux leakage
Current
Volt-Amperes (Eh-lh=ExLx)
14. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
directly proportional
primary coil
magnetic flux
Vs Ns = Vp Np
15. What does transformer efficiency mean?
an iron core and coil
Distribution transformer
low rententivity
The ratio of useful power output to its total power input.
16. Kind of wire is the secondary coil in a transformer
grounded system
Copper Losses - Core Losses
short circuit
thin copper wire coated with insulated material (shellac or enamel)
17. A transformer loses less than _% in energy
wigginton
5
Insulates - cools transformer by convection - dissipates heat
leakage flux
18. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
shell core
transformers efficiency
Choke coil
19. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
primary coil - secondary coil - central magnetic core
Simple Transformer
flux leakage
20. _____ currents are reduced by laminating the core.
Volt-Amperes (Eh-lh=ExLx)
grounded (Earthed)
Eddy
primary coil
21. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
coercivity
CORE: Core losses are caused by eddy currents set up by the magnetic field.
by using silicon iron core
Measuring
22. The 4 types of transformer cores
silicon steel
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Voltage
wigginton
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
Class 200 transformers
Step-up
polarity
How a transformer works
24. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
Volt-Amperes (Eh-lh=ExLx)
flux leakage
primary coil
25. A designated limit of operating characteristics based on definite conditions.
rating
thin copper wire coated with insulated material (shellac or enamel)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
directly proportional
26. both coils in this core are heavily insulated
Autotransformer
Secondary
closed-ended core
change the input voltage
27. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
class 400 transformers
Distribution transformer
How a transformer works
28. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
one coils serves as the primary and secondary windings
ratio of a transformer
by varying the size of the applied DC
the number of turns in the coil
29. 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.
grounded system
Current
Vs Ns = Vp Np
fuse
30. Divergence of the magnetic field causes this
Insulates - cools transformer by convection - dissipates heat
leakage flux
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Measuring Equipment
31. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
change the input voltage
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Same
grounded system
32. 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
fault
primary winding
Class 200 transformers
33. Function of the dielectric oil
closed-ended core
magnetic flux
Insulates - cools transformer by convection - dissipates heat
The ratio of useful power output to its total power input.
34. 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
closed-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
by varying the size of the applied DC
35. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Secondary
fuse
Choke coil
CORE: Core losses are caused by eddy currents set up by the magnetic field.
36. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
transformers efficiency law
air core
flux leakage
Primary
37. Copper loss is known as _____ loss.
High voltage
primary coil
fuse
38. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
by using silicon iron core
Insulates - cools transformer by convection - dissipates heat
silicon steel
Step-up
39. A choke coil uses this to induce current
open-ended core
an iron core and coil
silicon steel
variable
40. A simple design has a core within each coil
open-ended core
variable
Choke coil
Distribution transformer
41. 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
transformers efficiency law
open-ended core
die to leakage flux
shell core
42. The formula for the current related to voltage law
Vs Ip = Vp Is
one coils serves as the primary and secondary windings
Low
short circuit
43. The winding to which the load is connected is called the _____ winding.
central magnetic core
Secondary
Voltage - Current
44. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
Secondary
highly permeable material - iron or stalloy
coercivity
45. 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
closed-ended core
Class 200 transformers
Vs Ip = Vp Is
variable transformers
46. Is concentrated in the metal core
Class 200 transformers
magnetic field
leakage flux
current related to turns ratio law
47. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
Eh/Ex=Th/Tx
eddy currents
air core
48. 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.
leakage flux
constant current transfomers
Step-down
Vs Ns = Vp Np
49. Anything above 600 volts is _____?
High voltage
high frequency transformer
X1 - X2...
class 400 transformers
50. Central magnetic core made of
leakage flux
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
highly permeable material - iron or stalloy
High voltage