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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. 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.
Eh/Ex=Th/Tx
leakage flux
Secondary
high frequency transformer
2. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
Eddy
Ip Ns = Is Np
Vs Ip = Vp Is
3. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
closed-ended core
shell core
short circuit
Exciting Current
4. The transformer winding to which voltage is supplied is called the _____ winding.
wigginton
step-up (high voltage) transformers - step down transformer - autotransformer
the number of turns of wire in the primary and secondary coils
Primary
5. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
magnetic flux
voltage ralated to turns ratio
shell core
6. Central magnetic core made of
constant current transfomers
short circuit
highly permeable material - iron or stalloy
ratio of a transformer
7. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
The ratio of useful power output to its total power input.
Eh - lH = Ex - lX
eddy currents
leakage flux
8. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Transformer
Hysteresis
continuous path
9. How coercivity is minimized
Simple Transformer
change the input voltage
step-up (high voltage) transformers - step down transformer - autotransformer
by using silicon iron core
10. 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.
flux
constant current transfomers
H1 - h2...
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
11. A ___________ transformer is a continuously adjustable Autotransformer.
flux
variable
voltage ralated to turns ratio
the number of turns of wire in the primary and secondary coils
12. _____ currents are reduced by laminating the core.
Electromagnet
Eddy
magnetic field
current related to turns ratio law
13. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
die to leakage flux
Exciting Current
14. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
How a transformer works
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
15. Determines if the transformer is a step up or step down transformer
the number of turns of wire in the primary and secondary coils
coercivity
silicon steel
Simple Transformer
16. Transformer losses are classified as _____ and _____.
Insulates - cools transformer by convection - dissipates heat
Ip Ns = Is Np
Exciting
Copper Losses - Core Losses
17. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
Choke coil
central magnetic core
high frequency transformer
18. Two coils wound on a closed iron core form a ________.
Simple Transformer
Kilovolt -- Amperes (kVA)
Primary
grounded system
19. Both the primary and secondary coils in a transformer are arranged around this
Secondary
class 400 transformers
central magnetic core
high frequency transformer
20. The capacity of a transformer is rated in ____ _____.
Kilovolt -- Amperes (kVA)
closed-ended core (square/doughnut shaped)
secondary coil
transformers efficiency law
21. The 4 types of transformer cores
class 400 transformers
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
short circuit
flux leakage
22. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
die to leakage flux
Step-down
Transformer
by using silicon iron core
23. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
Vs Ip = Vp Is
die to leakage flux
Primary
24. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Voltage - Current
closed-ended core
closed-ended core
Current
25. The terminals of the low voltage winding are marked _____.
Autotransformer
Primary
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
X1 - X2...
26. 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)
leakage flux
wigginton
Transformer
Voltage
27. The 3 principle components of a transformer
primary coil - secondary coil - central magnetic core
flux
magnetic flux
28. The entire transformer is placed in a metal tank then immersed in ________.
The ratio of useful power output to its total power input.
dielectric oil
continuous path
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
29. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
transformers efficiency
Low
central magnetic core
30. Divergence of the magnetic field causes this
leakage flux
voltage ralated to turns ratio
current related to voltage law
Measuring
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.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Primary
grounded system
Vs Ip = Vp Is
32. Used to increase the magnetic flux in a transformer
Low
central magnetic core
polarity
by using silicon iron core
33. The formula for the voltage related to turns ratio
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Vs Ns = Vp Np
the number of turns in the coil
34. Connected to earth or to some conducting body which serves in place of the earth.
grounded (Earthed)
current related to voltage law
primary winding
silicon steel
35. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
flux leakage
air core
an iron core and coil
Insulates - cools transformer by convection - dissipates heat
36. 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.
closed-ended core
polarity
fuse
Exciting
37. A designated limit of operating characteristics based on definite conditions.
Exciting Current
rating
Choke coil
Copper Losses - Core Losses
38. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Ip Ns = Is Np
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
39. How a variable degree of core saturation is accomplished in a saturable reactor?
Choke coil
by varying the size of the applied DC
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Primary
40. The terminals of the high voltage winding are marked _____.
air core
grounded system
High voltage
H1 - h2...
41. An electromagnetic device that operates on the principle of self induction. It uses AC.
primary winding
silicon steel
grounded (Earthed)
Choke coil
42. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Distribution transformer
step-up (high voltage) transformers - step down transformer - autotransformer
dielectric oil
fuse
43. What is a rotation meter?
phase
Insulates - cools transformer by convection - dissipates heat
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
transformers efficiency
44. 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
Primary
Simple Transformer
continuous path
closed-ended core
45. The current related to turns ratio law
Ip Ns = Is Np
flux leakage
5
Class 200 transformers
46. Copper loss is known as _____ loss.
flux
flux leakage
primary coil - secondary coil - central magnetic core
47. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
eddy currents
Step-down
flux leakage
CORE: Core losses are caused by eddy currents set up by the magnetic field.
48. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Transformer
air core
flux
step-up (high voltage) transformers - step down transformer - autotransformer
49. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Electromagnet
Step-up
transformers efficiency
transformers efficiency law
50. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
saturable reactor
5
Step-down