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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. 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.
Step-down
Voltage
Exciting
open-ended core
2. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
closed-ended core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
air core
3. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
directly proportional
closed-ended core
voltage ralated to turns ratio
4. The simplest type of transformer core
air core
leakage flux
hysteresis losses (lagging losses)
Electromagnet
5. How coercivity is minimized
by using silicon iron core
fault
Autotransformer
6. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
closed-ended core (square/doughnut shaped)
7. both coils in this core are heavily insulated
die to leakage flux
closed-ended core
Low
electromagnetic mutual induction without loosing too much energy
8. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
transformers efficiency law
polarity
Voltage
9. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
H1 - h2...
Same
Secondary
Current
10. A partial or total local failure in the insulation or continuity of a conductor.
fault
ratio of a transformer
Vs Ns = Vp Np
high frequency transformer
11. The formula for the voltage related to turns ratio
Voltage
Vs Ns = Vp Np
class 400 transformers
open-ended core
12. The relationship between current and voltage in the coils are inverse
Eh - lH = Ex - lX
Eh/Ex=Th/Tx
by using silicon iron core
current related to voltage law
13. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Current
step-up (high voltage) transformers - step down transformer - autotransformer
Autotransformer
Volt-Amperes (Eh-lh=ExLx)
14. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
air core
central magnetic core
Simple Transformer
15. The capacity of a transformer is rated in ____ _____.
the number of turns of wire in the primary and secondary coils
Kilovolt -- Amperes (kVA)
wigginton
one coils serves as the primary and secondary windings
16. A single electrical circuit.
phase
leg(s)
directly proportional
Secondary
17. has a laminated iron core (layers of metal plates)
open-ended core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
closed-ended core
polarity
18. 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
Volt-Amperes (Eh-lh=ExLx)
electromagnetic mutual induction without loosing too much energy
high frequency transformer
open-ended 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
central magnetic core
saturable reactor
low rententivity
current related to turns ratio law
20. 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)
wigginton
rated KVA of a transformer
High voltage
continuous path
21. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
Copper Losses - Core Losses
a magnetic field that varies quickly in direction and stregnth
Electromagnet
fault
22. Refers to the transformer's ability to avoid power loss (heat)
transformers efficiency
Step-up
variable
directly proportional
23. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
air core
dielectric oil
highly permeable material - iron or stalloy
Measuring Equipment
24. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
rated KVA of a transformer
open-ended core
hysteresis losses (lagging losses)
Primary
25. What is a rotation meter?
rating
class 400 transformers
grounded (Earthed)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
26. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Volt-Amperes (Eh-lh=ExLx)
eddy currents
phase
saturable reactor
27. Waste of power known as transformer loss - often produced by closed-ended core
variable
Eddy
transformers efficiency law
eddy currents
28. The winding to which voltage is supplied is called the _____ winding.
Primary
Insulates - cools transformer by convection - dissipates heat
variable transformers
closed-ended core
29. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Simple Transformer
flux leakage
Electromagnetic Induction.
30. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
open-ended core
by using silicon iron core
H1 - h2...
primary coil
31. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
secondary coil
by varying the size of the applied DC
central magnetic core
short circuit
32. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Exciting Current
CORE: Core losses are caused by eddy currents set up by the magnetic field.
current related to voltage law
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
33. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Eh - lH = Ex - lX
phase
Current
34. _____ currents are reduced by laminating the core.
Eddy
current related to turns ratio law
5
The ratio of useful power output to its total power input.
35. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
magnetic flux
primary winding
Vs Ip = Vp Is
36. How a variable degree of core saturation is accomplished in a saturable reactor?
eddy currents
by varying the size of the applied DC
Secondary
polarity
37. Copper loss is known as _____ loss.
transformers efficiency
polarity
die to leakage flux
38. Central magnetic core made of
by varying the size of the applied DC
Measuring
short circuit
highly permeable material - iron or stalloy
39. The winding to which the load is connected is called the _____ winding.
by using silicon iron core
closed-ended core (square/doughnut shaped)
the number of turns in the coil
Secondary
40. The total numbre of lines or force issuing from a pole. (north or south)
grounded (Earthed)
variable
magnetic flux
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
41. A ___________ transformer is a continuously adjustable Autotransformer.
primary coil - secondary coil - central magnetic core
low rententivity
Low
variable
42. The 3 principle components of a transformer
The ratio of useful power output to its total power input.
fuse
voltage ralated to turns ratio
primary coil - secondary coil - central magnetic core
43. 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
ratio of a transformer
Voltage
wigginton
closed-ended core
44. It refers to the direction of current flow in a closed circuit.
transformers efficiency law
variable transformers
shell core
polarity
45. Divergence of the magnetic field causes this
leakage flux
X1 - X2...
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Low
46. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
H1 - h2...
Eh/Ex=Th/Tx
Distribution transformer
ammeter
47. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
die to leakage flux
Eh - lH = Ex - lX
change the input voltage
Step-up
48. Hysteresis Loss can be reduced by using a core with this feature
Class 200 transformers
low rententivity
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Electromagnetic Induction.
49. 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
Hysteresis - Eddy - Current
class 400 transformers
directly proportional
How a transformer works
50. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
Exciting
Volt-Amperes (Eh-lh=ExLx)
primary coil