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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. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Choke coil
air core
current related to voltage law
ratio of a transformer
2. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
coercivity
Secondary
Volt-Amperes (Eh-lh=ExLx)
Primary
3. 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
saturable reactor
fuse
closed-ended core
highly permeable material - iron or stalloy
4. A ___________ transformer is a continuously adjustable Autotransformer.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Class 200 transformers
Autotransformer
variable
5. both coils in this core are heavily insulated
short circuit
closed-ended core (square/doughnut shaped)
closed-ended core
primary coil
6. The 3 principle components of a transformer
Exciting
primary coil - secondary coil - central magnetic core
by varying the size of the applied DC
current related to voltage law
7. A partial or total local failure in the insulation or continuity of a conductor.
silicon steel
dielectric oil
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
fault
8. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
closed-ended core (square/doughnut shaped)
Primary
Kilovolt -- Amperes (kVA)
Eh - lH = Ex - lX
9. Hysteresis Loss can be reduced by using a core with this feature
Autotransformer
wigginton
primary winding
low rententivity
10. A transformer is a device that either increases or decreases alternating current and voltage using this principle
an iron core and coil
die to leakage flux
grounded (Earthed)
electromagnetic mutual induction without loosing too much energy
11. Central magnetic core made of
constant current transfomers
The ratio of useful power output to its total power input.
highly permeable material - iron or stalloy
the number of turns of wire in the primary and secondary coils
12. Copper loss is known as _____ loss.
variable
Kilovolt -- Amperes (kVA)
High voltage
13. A simple design has a core within each coil
open-ended core
Choke coil
Ip Ns = Is Np
Hysteresis - Eddy - Current
14. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Step-up
Choke coil
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
closed-ended core (square/doughnut shaped)
15. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Current
closed-ended core (square/doughnut shaped)
Voltage
air core
16. Both the primary and secondary coils in a transformer are arranged around this
Voltage - Current
phase
Class 200 transformers
central magnetic core
17. Anything above 600 volts is _____?
Secondary
High voltage
transformers efficiency
magnetic field
18. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
primary winding
grounded system
step-up (high voltage) transformers - step down transformer - autotransformer
CORE: Core losses are caused by eddy currents set up by the magnetic field.
19. What does transformer efficiency mean?
Vs Ip = Vp Is
Eddy
Copper Losses - Core Losses
The ratio of useful power output to its total power input.
20. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
The ratio of useful power output to its total power input.
Voltage
Eh/Ex=Th/Tx
primary winding
21. The transformer winding to which voltage is supplied is called the _____ winding.
current related to turns ratio law
H1 - h2...
highly permeable material - iron or stalloy
Primary
22. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
flux leakage
polarity
Transformer
secondary coil
23. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
silicon steel
Same
Eh/Ex=Th/Tx
magnetic flux
24. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Autotransformer
Step-down
Distribution transformer
directly proportional
25. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
one coils serves as the primary and secondary windings
class 400 transformers
The ratio of useful power output to its total power input.
26. A transformer loses less than _% in energy
primary winding
open-ended core
Exciting Current
5
27. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
change the input voltage
variable
class 400 transformers
28. The terminals of the high voltage winding are marked _____.
H1 - h2...
5
Kilovolt -- Amperes (kVA)
How a transformer works
29. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
transformers efficiency law
central magnetic core
phase
30. Is concentrated in the metal core
primary coil - secondary coil - central magnetic core
current related to voltage law
magnetic field
Measuring
31. The current related to turns ratio law
an iron core and coil
Primary
Ip Ns = Is Np
closed-ended core (square/doughnut shaped)
32. Two coils wound on a closed iron core form a ________.
5
a magnetic field that varies quickly in direction and stregnth
Secondary
Simple Transformer
33. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Volt-Amperes (Eh-lh=ExLx)
continuous path
one coils serves as the primary and secondary windings
Electromagnetic Induction.
34. Used to increase the magnetic flux in a transformer
secondary coil
Autotransformer
central magnetic core
phase
35. The 3 types of transformer power loss
a magnetic field that varies quickly in direction and stregnth
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
air core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
36. What is a rotation meter?
fault
transformers efficiency law
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
step-up (high voltage) transformers - step down transformer - autotransformer
37. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
closed-ended core (square/doughnut shaped)
Eh - lH = Ex - lX
step-up (high voltage) transformers - step down transformer - autotransformer
38. Reference to a jumper or conductor - to or from a piece of electrical equipment.
transformers efficiency law
flux leakage
leg(s)
Primary
39. 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
Electromagnetic Induction.
current related to voltage law
dielectric oil
40. 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
continuous path
highly permeable material - iron or stalloy
step-up (high voltage) transformers - step down transformer - autotransformer
closed-ended core
41. 3 types of transformers
Hysteresis
Low
step-up (high voltage) transformers - step down transformer - autotransformer
Voltage - Current
42. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Ip Ns = Is Np
transformers efficiency law
Current
silicon steel
43. The total numbre of lines or force issuing from a pole. (north or south)
Eh - lH = Ex - lX
low rententivity
class 400 transformers
magnetic flux
44. Connected to earth or to some conducting body which serves in place of the earth.
Hysteresis - Eddy - Current
grounded (Earthed)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Primary
45. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
primary winding
Choke coil
flux leakage
Voltage - Current
46. Core losses are _____ loss and _____ - _____ loss.
closed-ended core (square/doughnut shaped)
Hysteresis - Eddy - Current
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
central magnetic core
47. 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.
constant current transfomers
Measuring Equipment
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
eddy currents
48. The winding to which the load is connected is called the _____ winding.
Primary
highly permeable material - iron or stalloy
Secondary
primary coil - secondary coil - central magnetic core
49. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
secondary coil
thin copper wire coated with insulated material (shellac or enamel)
Step-up
How a transformer works
50. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
primary winding
step-up (high voltage) transformers - step down transformer - autotransformer
rating