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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. 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
thin copper wire coated with insulated material (shellac or enamel)
closed-ended core
Copper Losses - Core Losses
Current
2. The 3 principle components of a transformer
Simple Transformer
Electromagnet
primary coil - secondary coil - central magnetic core
silicon steel
3. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
class 400 transformers
4. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
Transformer
high frequency transformer
Step-down
saturable reactor
5. The voltage induced in the coil is directly proportional to this
Simple Transformer
Hysteresis
fault
the number of turns in the coil
6. 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.
Same
short circuit
closed-ended core (square/doughnut shaped)
Exciting
7. A large amount of power wasted with the open-ended core
die to leakage flux
Primary
transformers efficiency
CORE: Core losses are caused by eddy currents set up by the magnetic field.
8. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
open-ended core
Volt-Amperes (Eh-lh=ExLx)
Measuring Equipment
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
9. _____ currents are reduced by laminating the core.
highly permeable material - iron or stalloy
Class 200 transformers
Eddy
Exciting Current
10. The capacity of a transformer is rated in ____ _____.
Kilovolt -- Amperes (kVA)
short circuit
Copper Losses - Core Losses
primary coil
11. The winding to which the load is connected is called the _____ winding.
Transformer
Secondary
ratio of a transformer
dielectric oil
12. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
Eddy
saturable reactor
grounded system
13. has a laminated iron core (layers of metal plates)
grounded (Earthed)
Eh/Ex=Th/Tx
closed-ended core
Voltage
14. Is concentrated in the metal core
Volt-Amperes (Eh-lh=ExLx)
magnetic field
shell core
transformers efficiency
15. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
hysteresis losses (lagging losses)
fuse
grounded system
coercivity
16. The 3 types of transformer power loss
primary winding
variable
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
leakage flux
17. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Volt-Amperes (Eh-lh=ExLx)
primary coil - secondary coil - central magnetic core
Choke coil
Step-up
18. Both the primary and secondary coils in a transformer are arranged around this
central magnetic core
silicon steel
air core
Ip Ns = Is Np
19. 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
variable transformers
Choke coil
Same
20. 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
The ratio of useful power output to its total power input.
an iron core and coil
continuous path
CORE: Core losses are caused by eddy currents set up by the magnetic field.
21. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx
current related to voltage law
5
Step-up
22. Used to increase the magnetic flux in a transformer
How a transformer works
central magnetic core
transformers efficiency law
secondary coil
23. 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
Hysteresis
closed-ended core
dielectric oil
flux leakage
24. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
silicon steel
constant current transfomers
Vs Ns = Vp Np
Low
25. The terminals of the high voltage winding are marked _____.
variable transformers
H1 - h2...
Voltage - Current
Exciting Current
26. The formula for the current related to voltage law
high frequency transformer
Secondary
Vs Ip = Vp Is
short circuit
27. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
The ratio of useful power output to its total power input.
Distribution transformer
Secondary
CORE: Core losses are caused by eddy currents set up by the magnetic field.
28. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
transformers efficiency law
Vs Ns = Vp Np
coercivity
H1 - h2...
29. Two coils wound on a closed iron core form a ________.
Simple Transformer
an iron core and coil
Vs Ip = Vp Is
eddy currents
30. What is a rotation meter?
voltage ralated to turns ratio
Autotransformer
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
fuse
31. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
rated KVA of a transformer
Choke coil
Eh - lH = Ex - lX
CORE: Core losses are caused by eddy currents set up by the magnetic field.
32. 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.
grounded (Earthed)
open-ended core
Electromagnet
central magnetic core
33. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
grounded (Earthed)
die to leakage flux
34. A partial or total local failure in the insulation or continuity of a conductor.
fault
primary coil
Insulates - cools transformer by convection - dissipates heat
Primary
35. Divergence of the magnetic field causes this
The ratio of useful power output to its total power input.
leakage flux
secondary coil
phase
36. A choke coil uses this to induce current
Voltage - Current
class 400 transformers
an iron core and coil
ammeter
37. The current related to turns ratio law
polarity
fuse
Ip Ns = Is Np
Class 200 transformers
38. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
eddy currents
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
open-ended core
current related to turns ratio law
39. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
closed-ended core
by varying the size of the applied DC
central magnetic core
40. Reference to a jumper or conductor - to or from a piece of electrical equipment.
electromagnetic mutual induction without loosing too much energy
leg(s)
by varying the size of the applied DC
die to leakage flux
41. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
Primary
Exciting Current
class 400 transformers
42. The terminals of the low voltage winding are marked _____.
The ratio of useful power output to its total power input.
X1 - X2...
primary coil
Measuring Equipment
43. A simple design has a core within each coil
open-ended core
Low
X1 - X2...
eddy currents
44. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
eddy currents
Copper Losses - Core Losses
rated KVA of a transformer
current related to turns ratio law
45. An electromagnetic device that operates on the principle of self induction. It uses AC.
leg(s)
closed-ended core
Choke coil
Distribution transformer
46. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Volt-Amperes (Eh-lh=ExLx)
High voltage
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Eh - lH = Ex - lX
47. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
air core
current related to voltage law
transformers efficiency law
48. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Autotransformer
air core
secondary coil
dielectric oil
49. 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)
transformers efficiency law
variable transformers
ratio of a transformer
wigginton
50. 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
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Autotransformer
Volt-Amperes (Eh-lh=ExLx)