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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. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
current related to voltage law
air core
wigginton
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 _____.
the number of turns in the coil
How a transformer works
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
silicon steel
3. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
current related to turns ratio law
by varying the size of the applied DC
Simple Transformer
4. It refers to the direction of current flow in a closed circuit.
high frequency transformer
variable transformers
polarity
by varying the size of the applied DC
5. The transformer winding to which voltage is supplied is called the _____ winding.
Choke coil
fault
Primary
Electromagnetic Induction.
6. The winding to which the load is connected is called the _____ winding.
variable transformers
Kilovolt -- Amperes (kVA)
silicon steel
Secondary
7. A transformer is a device that either increases or decreases alternating current and voltage using this principle
saturable reactor
electromagnetic mutual induction without loosing too much energy
Electromagnetic Induction.
Vs Ns = Vp Np
8. How a variable degree of core saturation is accomplished in a saturable reactor?
directly proportional
flux
How a transformer works
by varying the size of the applied DC
9. A designated limit of operating characteristics based on definite conditions.
a magnetic field that varies quickly in direction and stregnth
eddy currents
rating
flux leakage
10. An instrument used to measure electrical current.
ammeter
Kilovolt -- Amperes (kVA)
Vs Ip = Vp Is
voltage ralated to turns ratio
11. The terminals of the low voltage winding are marked _____.
Hysteresis - Eddy - Current
flux leakage
Hysteresis
X1 - X2...
12. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
secondary coil
5
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
transformers efficiency law
13. A transformer loses less than _% in energy
Primary
Electromagnetic Induction.
Ip Ns = Is Np
5
14. Waste of power known as transformer loss - often produced by closed-ended core
Vs Ip = Vp Is
polarity
eddy currents
secondary coil
15. 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
eddy currents
class 400 transformers
Distribution transformer
16. Hysteresis Loss can be reduced by using a core with this feature
Autotransformer
variable
low rententivity
polarity
17. The relationship between current and voltage in the coils are inverse
current related to voltage law
Copper Losses - Core Losses
a magnetic field that varies quickly in direction and stregnth
Step-down
18. Used to increase the magnetic flux in a transformer
central magnetic core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
low rententivity
Exciting
19. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
continuous path
the number of turns of wire in the primary and secondary coils
X1 - X2...
rated KVA of a transformer
20. A choke coil uses this to induce current
Transformer
by varying the size of the applied DC
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
an iron core and coil
21. Core losses are _____ loss and _____ - _____ loss.
primary coil - secondary coil - central magnetic core
Secondary
Electromagnet
Hysteresis - Eddy - Current
22. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
closed-ended core
Exciting Current
short circuit
flux leakage
23. Two coils wound on a closed iron core form a ________.
Simple Transformer
How a transformer works
current related to voltage law
hysteresis losses (lagging losses)
24. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
X1 - X2...
shell core
Ip Ns = Is Np
Volt-Amperes (Eh-lh=ExLx)
25. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
open-ended core
Low
Electromagnet
secondary coil
26. Anything above 600 volts is _____?
Eddy
directly proportional
ammeter
High voltage
27. The winding to which voltage is supplied is called the _____ winding.
electromagnetic mutual induction without loosing too much energy
directly proportional
Primary
28. The winding of a transformer to which electrical energy is supplied.
fault
grounded system
primary winding
the number of turns of wire in the primary and secondary coils
29. _____ currents are reduced by laminating the core.
Hysteresis - Eddy - Current
one coils serves as the primary and secondary windings
central magnetic core
Eddy
30. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
5
Current
Vs Ns = Vp Np
Secondary
31. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
voltage ralated to turns ratio
Same
5
rating
32. 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
Secondary
leg(s)
continuous path
magnetic field
33. Determines if the transformer is a step up or step down transformer
Autotransformer
short circuit
rating
the number of turns of wire in the primary and secondary coils
34. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
step-up (high voltage) transformers - step down transformer - autotransformer
Kilovolt -- Amperes (kVA)
closed-ended core
35. The capacity of a transformer is rated in ____ _____.
thin copper wire coated with insulated material (shellac or enamel)
Kilovolt -- Amperes (kVA)
Eh/Ex=Th/Tx
class 400 transformers
36. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Exciting Current
saturable reactor
Volt-Amperes (Eh-lh=ExLx)
variable
37. An electromagnetic device that operates on the principle of self induction. It uses AC.
Copper Losses - Core Losses
an iron core and coil
rated KVA of a transformer
Choke coil
38. Is concentrated in the metal core
magnetic field
Current
primary coil - secondary coil - central magnetic core
The ratio of useful power output to its total power input.
39. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
current related to voltage law
transformers efficiency law
Voltage - Current
central magnetic core
40. 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)
low rententivity
Electromagnetic Induction.
wigginton
flux
41. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
grounded system
Ip Ns = Is Np
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
42. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
secondary coil
class 400 transformers
Same
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
43. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Simple Transformer
flux
Transformer
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
44. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
class 400 transformers
directly proportional
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
electromagnetic mutual induction without loosing too much energy
45. The current related to turns ratio law
Simple Transformer
Kilovolt -- Amperes (kVA)
continuous path
Ip Ns = Is Np
46. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
ratio of a transformer
the number of turns of wire in the primary and secondary coils
continuous path
47. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
grounded (Earthed)
Primary
Eddy
Eh - lH = Ex - lX
48. 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
polarity
leakage flux
open-ended core
closed-ended core
49. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
CORE: Core losses are caused by eddy currents set up by the magnetic field.
transformers efficiency law
Autotransformer
a magnetic field that varies quickly in direction and stregnth
50. The formula for the voltage related to turns ratio
The ratio of useful power output to its total power input.
directly proportional
Vs Ns = Vp Np