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Transformers
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Subject
:
engineering
Instructions:
Answer 50 questions in 15 minutes.
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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. 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 _____.
central magnetic core
silicon steel
Hysteresis
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
2. The 3 types of transformer power loss
Copper Losses - Core Losses
leg(s)
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Secondary
3. 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
rating
eddy currents
continuous path
Choke coil
4. What does transformer efficiency mean?
Hysteresis - Eddy - Current
The ratio of useful power output to its total power input.
Eddy
hysteresis losses (lagging losses)
5. An electromagnetic device that operates on the principle of self induction. It uses AC.
flux leakage
grounded system
Choke coil
class 400 transformers
6. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Ip Ns = Is Np
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Step-up
primary coil - secondary coil - central magnetic core
7. A single electrical circuit.
ammeter
phase
Exciting
die to leakage flux
8. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
hysteresis losses (lagging losses)
Electromagnet
Autotransformer
9. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Vs Ns = Vp Np
Choke coil
low rententivity
Measuring
10. 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
fuse
Choke coil
open-ended core
polarity
11. A simple design has a core within each coil
shell core
variable transformers
open-ended core
fuse
12. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
High voltage
low rententivity
Distribution transformer
secondary coil
13. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Current
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Copper Losses - Core Losses
wigginton
14. A designated limit of operating characteristics based on definite conditions.
highly permeable material - iron or stalloy
primary coil - secondary coil - central magnetic core
rating
CORE: Core losses are caused by eddy currents set up by the magnetic field.
15. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
variable
thin copper wire coated with insulated material (shellac or enamel)
transformers efficiency law
Measuring Equipment
16. The winding to which the load is connected is called the _____ winding.
polarity
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Secondary
central magnetic core
17. 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
fault
die to leakage flux
Voltage
18. Anything above 600 volts is _____?
grounded system
Copper Losses - Core Losses
High voltage
air core
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
rated KVA of a transformer
magnetic field
primary winding
saturable reactor
20. The total numbre of lines or force issuing from a pole. (north or south)
phase
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
fault
magnetic flux
21. A large amount of power wasted with the open-ended core
die to leakage flux
Measuring Equipment
polarity
Kilovolt -- Amperes (kVA)
22. 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.
Copper Losses - Core Losses
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Secondary
Vs Ns = Vp Np
23. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Hysteresis
Exciting Current
fault
24. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
a magnetic field that varies quickly in direction and stregnth
central magnetic core
Same
leg(s)
25. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Choke coil
short circuit
How a transformer works
the number of turns in the coil
26. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
highly permeable material - iron or stalloy
Current
Same
Eddy
27. The terminals of the low voltage winding are marked _____.
primary coil - secondary coil - central magnetic core
shell core
leakage flux
X1 - X2...
28. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Simple Transformer
flux
Ip Ns = Is Np
Volt-Amperes (Eh-lh=ExLx)
29. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Autotransformer
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Measuring Equipment
30. Both the primary and secondary coils in a transformer are arranged around this
Vs Ip = Vp Is
central magnetic core
step-up (high voltage) transformers - step down transformer - autotransformer
fuse
31. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Measuring
Eh - lH = Ex - lX
Vs Ns = Vp Np
the number of turns in the coil
32. The formula for the voltage related to turns ratio
an iron core and coil
Measuring Equipment
voltage ralated to turns ratio
Vs Ns = Vp Np
33. Reference to a jumper or conductor - to or from a piece of electrical equipment.
constant current transfomers
Primary
leg(s)
coercivity
34. Copper loss is known as _____ loss.
Class 200 transformers
leakage flux
low rententivity
35. How coercivity is minimized
closed-ended core (square/doughnut shaped)
by using silicon iron core
Same
saturable reactor
36. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Exciting
flux
secondary coil
short circuit
37. Kind of wire is the secondary coil in a transformer
How a transformer works
thin copper wire coated with insulated material (shellac or enamel)
magnetic field
Secondary
38. 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)
CORE: Core losses are caused by eddy currents set up by the magnetic field.
rated KVA of a transformer
transformers efficiency law
wigginton
39. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
flux leakage
Measuring Equipment
magnetic flux
ratio of a transformer
40. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
rating
grounded system
Primary
41. 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
variable transformers
Simple Transformer
How a transformer works
class 400 transformers
42. The voltage induced in the coil is directly proportional to this
Secondary
the number of turns in the coil
5
Eh/Ex=Th/Tx
43. Central magnetic core made of
Secondary
one coils serves as the primary and secondary windings
highly permeable material - iron or stalloy
change the input voltage
44. A transformer is a device that either increases or decreases alternating current and voltage using this principle
electromagnetic mutual induction without loosing too much energy
H1 - h2...
directly proportional
class 400 transformers
45. Transformers with 4800 volt primaries and 120/240 volt secondaries - either pole or subway type - with two secondary windings terminating at internal links which provide for parallel operation of the secondary windings at 120 volts or series operatio
constant current transfomers
directly proportional
Class 200 transformers
central magnetic core
46. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
H1 - h2...
hysteresis losses (lagging losses)
Low
the number of turns of wire in the primary and secondary coils
47. Hysteresis Loss can be reduced by using a core with this feature
air core
change the input voltage
low rententivity
48. A choke coil uses this to induce current
rated KVA of a transformer
an iron core and coil
H1 - h2...
eddy currents
49. Used to increase the magnetic flux in a transformer
Hysteresis
current related to turns ratio law
class 400 transformers
central magnetic core
50. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
thin copper wire coated with insulated material (shellac or enamel)
Secondary
saturable reactor
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