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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. How coercivity is minimized
flux
Low
by using silicon iron core
highly permeable material - iron or stalloy
2. has a laminated iron core (layers of metal plates)
primary coil
dielectric oil
closed-ended core
electromagnetic mutual induction without loosing too much energy
3. 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
directly proportional
CORE: Core losses are caused by eddy currents set up by the magnetic field.
closed-ended core
saturable reactor
4. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
hysteresis losses (lagging losses)
Transformer
Measuring
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
5. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx
class 400 transformers
Voltage - Current
Volt-Amperes (Eh-lh=ExLx)
6. Copper loss is known as _____ loss.
shell core
Primary
Step-down
7. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
leakage flux
wigginton
rated KVA of a transformer
the number of turns in the coil
8. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Exciting
low rententivity
Electromagnetic Induction.
Eh - lH = Ex - lX
9. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
Simple Transformer
by using silicon iron core
Copper Losses - Core Losses
10. Core losses are _____ loss and _____ - _____ loss.
secondary coil
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Eddy
Hysteresis - Eddy - Current
11. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
open-ended core
saturable reactor
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
12. 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
How a transformer works
a magnetic field that varies quickly in direction and stregnth
transformers efficiency
flux leakage
13. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
The ratio of useful power output to its total power input.
Volt-Amperes (Eh-lh=ExLx)
X1 - X2...
Distribution transformer
14. A designated limit of operating characteristics based on definite conditions.
rating
Copper Losses - Core Losses
open-ended core
Hysteresis
15. A transformer is a device that either increases or decreases alternating current and voltage using this principle
class 400 transformers
Same
low rententivity
electromagnetic mutual induction without loosing too much energy
16. Anything above 600 volts is _____?
High voltage
voltage ralated to turns ratio
Voltage
hysteresis losses (lagging losses)
17. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
short circuit
Copper Losses - Core Losses
highly permeable material - iron or stalloy
CORE: Core losses are caused by eddy currents set up by the magnetic field.
18. _____ currents are reduced by laminating the core.
ammeter
Eddy
The ratio of useful power output to its total power input.
polarity
19. The entire transformer is placed in a metal tank then immersed in ________.
Electromagnet
thin copper wire coated with insulated material (shellac or enamel)
high frequency transformer
dielectric oil
20. Refers to the transformer's ability to avoid power loss (heat)
shell core
transformers efficiency
open-ended core
high frequency transformer
21. The formula for the current related to voltage law
Vs Ip = Vp Is
X1 - X2...
dielectric oil
open-ended core
22. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
Copper Losses - Core Losses
transformers efficiency law
voltage ralated to turns ratio
secondary coil
23. The voltage induced in the coil is directly proportional to this
Eddy
the number of turns in the coil
variable
primary coil
24. The winding to which voltage is supplied is called the _____ winding.
Vs Ip = Vp Is
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Ip Ns = Is Np
Primary
25. 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
polarity
change the input voltage
fuse
26. The simplest type of transformer core
air core
by varying the size of the applied DC
Eddy
hysteresis losses (lagging losses)
27. Kind of wire is the secondary coil in a transformer
die to leakage flux
thin copper wire coated with insulated material (shellac or enamel)
High voltage
secondary coil
28. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
magnetic flux
Secondary
variable
29. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
by using silicon iron core
variable
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Voltage - Current
30. The terminals of the high voltage winding are marked _____.
primary coil - secondary coil - central magnetic core
shell core
X1 - X2...
H1 - h2...
31. The transformer winding to which the load is connected is called the _____ winding.
one coils serves as the primary and secondary windings
Secondary
Kilovolt -- Amperes (kVA)
Insulates - cools transformer by convection - dissipates heat
32. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Primary
transformers efficiency law
shell core
wigginton
33. 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
air core
Distribution transformer
H1 - h2...
34. Determines if the transformer is a step up or step down transformer
Measuring
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
the number of turns of wire in the primary and secondary coils
The ratio of useful power output to its total power input.
35. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
class 400 transformers
Measuring
open-ended core
saturable reactor
36. Divergence of the magnetic field causes this
leakage flux
a magnetic field that varies quickly in direction and stregnth
The ratio of useful power output to its total power input.
Voltage
37. The 4 types of transformer cores
short circuit
How a transformer works
air core
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
38. A simple design has a core within each coil
closed-ended core
Voltage - Current
transformers efficiency
open-ended core
39. 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.
Primary
class 400 transformers
the number of turns of wire in the primary and secondary coils
40. A large amount of power wasted with the open-ended core
5
leakage flux
die to leakage flux
central magnetic core
41. 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.
Secondary
leakage flux
Ip Ns = Is Np
directly proportional
42. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
electromagnetic mutual induction without loosing too much energy
The ratio of useful power output to its total power input.
hysteresis losses (lagging losses)
Step-up
43. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Hysteresis
the number of turns in the coil
ratio of a transformer
Eh/Ex=Th/Tx
44. 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
saturable reactor
closed-ended core
by varying the size of the applied DC
fault
45. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
dielectric oil
voltage ralated to turns ratio
class 400 transformers
Step-up
46. 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
constant current transfomers
Class 200 transformers
Step-up
rated KVA of a transformer
47. Two coils wound on a closed iron core form a ________.
Step-down
flux
Simple Transformer
Copper Losses - Core Losses
48. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
secondary coil
Low
class 400 transformers
Exciting
49. Central magnetic core made of
closed-ended core (square/doughnut shaped)
electromagnetic mutual induction without loosing too much energy
highly permeable material - iron or stalloy
X1 - X2...
50. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
air core
Same
thin copper wire coated with insulated material (shellac or enamel)
variable transformers