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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. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
electromagnetic mutual induction without loosing too much energy
primary coil
saturable reactor
closed-ended core (square/doughnut shaped)
2. has a laminated iron core (layers of metal plates)
closed-ended core
transformers efficiency
Hysteresis
ratio of a transformer
3. A simple design has a core within each coil
open-ended core
current related to voltage law
transformers efficiency law
Eh/Ex=Th/Tx
4. With no load on the secondary winding - a small current flows in the primary called _____ _____.
closed-ended core
Distribution transformer
Exciting Current
transformers efficiency
5. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
by varying the size of the applied DC
Secondary
secondary coil
voltage ralated to turns ratio
6. Refers to the transformer's ability to avoid power loss (heat)
silicon steel
voltage ralated to turns ratio
Low
transformers efficiency
7. 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
rated KVA of a transformer
Kilovolt -- Amperes (kVA)
Voltage
8. How the voltage and the number of turns are related for the voltage related to turn ratio
grounded system
Low
variable
directly proportional
9. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Hysteresis - Eddy - Current
change the input voltage
electromagnetic mutual induction without loosing too much energy
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
10. Copper loss is known as _____ loss.
Simple Transformer
ratio of a transformer
one coils serves as the primary and secondary windings
11. A large amount of power wasted with the open-ended core
die to leakage flux
The ratio of useful power output to its total power input.
Eh - lH = Ex - lX
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
12. 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
X1 - X2...
grounded system
continuous path
secondary coil
13. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
a magnetic field that varies quickly in direction and stregnth
phase
saturable reactor
14. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
silicon steel
Step-down
Eh - lH = Ex - lX
closed-ended core
15. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
continuous path
wigginton
one coils serves as the primary and secondary windings
16. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
fuse
X1 - X2...
Simple Transformer
class 400 transformers
17. How a variable degree of core saturation is accomplished in a saturable reactor?
by varying the size of the applied DC
Same
Vs Ns = Vp Np
18. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
flux leakage
Eh/Ex=Th/Tx
dielectric oil
secondary coil
19. An instrument used to measure electrical current.
highly permeable material - iron or stalloy
ammeter
saturable reactor
Copper Losses - Core Losses
20. 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.
highly permeable material - iron or stalloy
Step-up
constant current transfomers
the number of turns of wire in the primary and secondary coils
21. Both the primary and secondary coils in a transformer are arranged around this
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
saturable reactor
central magnetic core
22. A transformer loses less than _% in energy
5
current related to voltage law
closed-ended core
23. 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 _____.
Simple Transformer
grounded system
central magnetic core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
24. 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
polarity
Hysteresis - Eddy - Current
open-ended core
25. Hysteresis Loss can be reduced by using a core with this feature
Distribution transformer
Secondary
low rententivity
magnetic flux
26. The total numbre of lines or force issuing from a pole. (north or south)
die to leakage flux
Choke coil
Hysteresis
magnetic flux
27. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Secondary
28. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
closed-ended core
electromagnetic mutual induction without loosing too much energy
Step-up
29. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
hysteresis losses (lagging losses)
current related to voltage law
step-up (high voltage) transformers - step down transformer - autotransformer
30. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
ratio of a transformer
by varying the size of the applied DC
Exciting Current
a magnetic field that varies quickly in direction and stregnth
31. 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.
Exciting Current
Exciting
short circuit
grounded system
32. 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.
Insulates - cools transformer by convection - dissipates heat
Secondary
How a transformer works
Voltage - Current
33. The winding to which voltage is supplied is called the _____ winding.
Measuring Equipment
fault
one coils serves as the primary and secondary windings
Primary
34. The transformer winding to which the load is connected is called the _____ winding.
rated KVA of a transformer
Secondary
class 400 transformers
Simple Transformer
35. The formula for the current related to voltage law
closed-ended core (square/doughnut shaped)
Vs Ip = Vp Is
current related to turns ratio law
grounded (Earthed)
36. The terminals of the high voltage winding are marked _____.
Vs Ip = Vp Is
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
phase
H1 - h2...
37. 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)
rating
thin copper wire coated with insulated material (shellac or enamel)
wigginton
electromagnetic mutual induction without loosing too much energy
38. The number of turns can be adjusted in these types of transformers
variable transformers
grounded system
ammeter
magnetic flux
39. 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.
Voltage
one coils serves as the primary and secondary windings
saturable reactor
fuse
40. The transformer winding to which voltage is supplied is called the _____ winding.
closed-ended core (square/doughnut shaped)
Primary
Autotransformer
closed-ended core
41. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Distribution transformer
Simple Transformer
leakage flux
fuse
42. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
step-up (high voltage) transformers - step down transformer - autotransformer
closed-ended core
coercivity
air core
43. The terminals of the low voltage winding are marked _____.
How a transformer works
Transformer
X1 - X2...
coercivity
44. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Current
by varying the size of the applied DC
closed-ended core
one coils serves as the primary and secondary windings
45. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
The ratio of useful power output to its total power input.
low rententivity
46. 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
voltage ralated to turns ratio
air core
current related to voltage law
47. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
shell core
X1 - X2...
closed-ended core (square/doughnut shaped)
48. both coils in this core are heavily insulated
electromagnetic mutual induction without loosing too much energy
open-ended core
highly permeable material - iron or stalloy
closed-ended core
49. A partial or total local failure in the insulation or continuity of a conductor.
fault
How a transformer works
ammeter
X1 - X2...
50. 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
ammeter
open-ended core
an iron core and coil
Hysteresis