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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. A large amount of power wasted with the open-ended core
die to leakage flux
dielectric oil
Measuring Equipment
open-ended core
2. It refers to the direction of current flow in a closed circuit.
grounded system
air core
polarity
primary coil - secondary coil - central magnetic core
3. 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.
Secondary
a magnetic field that varies quickly in direction and stregnth
H1 - h2...
grounded system
4. 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.
silicon steel
Electromagnet
an iron core and coil
fuse
5. Refers to the transformer's ability to avoid power loss (heat)
one coils serves as the primary and secondary windings
current related to voltage law
continuous path
transformers efficiency
6. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
Distribution transformer
Insulates - cools transformer by convection - dissipates heat
Same
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
7. Used to increase the magnetic flux in a transformer
hysteresis losses (lagging losses)
closed-ended core
central magnetic core
Voltage
8. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Hysteresis - Eddy - Current
current related to voltage law
ratio of a transformer
Secondary
9. The transformer winding to which voltage is supplied is called the _____ winding.
polarity
Primary
current related to voltage law
secondary coil
10. The 3 types of transformer power loss
Secondary
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
magnetic flux
Distribution transformer
11. The total numbre of lines or force issuing from a pole. (north or south)
dielectric oil
flux leakage
hysteresis losses (lagging losses)
magnetic flux
12. The current related to turns ratio law
Same
air core
polarity
Ip Ns = Is Np
13. A partial or total local failure in the insulation or continuity of a conductor.
5
fault
H1 - h2...
saturable reactor
14. Hysteresis Loss can be reduced by using a core with this feature
Step-up
fuse
coercivity
low rententivity
15. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
shell core
Vs Ip = Vp Is
Copper Losses - Core Losses
air core
16. A designated limit of operating characteristics based on definite conditions.
X1 - X2...
fuse
rating
wigginton
17. 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
the number of turns of wire in the primary and secondary coils
open-ended core
high frequency transformer
X1 - X2...
18. The winding of a transformer to which electrical energy is supplied.
Voltage
primary winding
Secondary
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
19. The simplest type of transformer core
Kilovolt -- Amperes (kVA)
low rententivity
variable
air core
20. How a variable degree of core saturation is accomplished in a saturable reactor?
die to leakage flux
Voltage - Current
by varying the size of the applied DC
Low
21. Copper loss is known as _____ loss.
thin copper wire coated with insulated material (shellac or enamel)
ratio of a transformer
Exciting
22. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
open-ended core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
transformers efficiency
Choke coil
23. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Secondary
coercivity
Current
closed-ended core
24. 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)
silicon steel
closed-ended core
change the input voltage
25. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
die to leakage flux
Exciting
How a transformer works
closed-ended core (square/doughnut shaped)
26. 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
Primary
Class 200 transformers
a magnetic field that varies quickly in direction and stregnth
fuse
27. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
one coils serves as the primary and secondary windings
ratio of a transformer
Primary
current related to turns ratio law
28. The winding to which the load is connected is called the _____ winding.
Autotransformer
Distribution transformer
Secondary
29. Both the primary and secondary coils in a transformer are arranged around this
central magnetic core
current related to voltage law
Same
an iron core and coil
30. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
Secondary
change the input voltage
ammeter
31. A single electrical circuit.
voltage ralated to turns ratio
phase
ammeter
low rententivity
32. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
current related to voltage law
flux leakage
directly proportional
by using silicon iron core
33. 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
continuous path
ammeter
directly proportional
5
34. Two coils wound on a closed iron core form a ________.
class 400 transformers
phase
Simple Transformer
variable transformers
35. Core losses are _____ loss and _____ - _____ loss.
Current
hysteresis losses (lagging losses)
Hysteresis - Eddy - Current
dielectric oil
36. 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
primary coil
Primary
closed-ended core
How a transformer works
37. The formula for the voltage related to turns ratio
Simple Transformer
Vs Ns = Vp Np
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
short circuit
38. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
thin copper wire coated with insulated material (shellac or enamel)
air core
central magnetic core
low rententivity
39. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Distribution transformer
current related to turns ratio law
polarity
wigginton
40. How coercivity is minimized
transformers efficiency
fuse
by using silicon iron core
electromagnetic mutual induction without loosing too much energy
41. What does transformer efficiency mean?
Secondary
Exciting Current
Step-down
The ratio of useful power output to its total power input.
42. The voltage induced in the coil is directly proportional to this
variable transformers
the number of turns in the coil
air core
saturable reactor
43. Function of the dielectric oil
Step-up
closed-ended core
Insulates - cools transformer by convection - dissipates heat
die to leakage flux
44. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
Voltage - Current
secondary coil
Autotransformer
45. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
How a transformer works
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
step-up (high voltage) transformers - step down transformer - autotransformer
a magnetic field that varies quickly in direction and stregnth
46. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Secondary
Voltage
thin copper wire coated with insulated material (shellac or enamel)
Step-down
47. The relationship between current and voltage in the coils are inverse
current related to turns ratio law
Exciting Current
current related to voltage law
closed-ended core
48. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Voltage - Current
thin copper wire coated with insulated material (shellac or enamel)
electromagnetic mutual induction without loosing too much energy
short circuit
49. Divergence of the magnetic field causes this
flux leakage
leakage flux
leg(s)
fault
50. The 3 principle components of a transformer
Eh - lH = Ex - lX
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
primary winding
primary coil - secondary coil - central magnetic core