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Test your basic knowledge |
Transformers
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Study First
Subject
:
engineering
Instructions:
Answer 50 questions in 15 minutes.
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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. Copper loss is known as _____ loss.
dielectric oil
ammeter
constant current transfomers
2. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
polarity
flux
Step-up
3. How coercivity is minimized
die to leakage flux
a magnetic field that varies quickly in direction and stregnth
by using silicon iron core
secondary coil
4. Divergence of the magnetic field causes this
Secondary
closed-ended core
Autotransformer
leakage flux
5. The transformer winding to which voltage is supplied is called the _____ winding.
transformers efficiency
Primary
Secondary
air core
6. The entire transformer is placed in a metal tank then immersed in ________.
transformers efficiency
Vs Ip = Vp Is
dielectric oil
7. The formula for the voltage related to turns ratio
coercivity
primary winding
Eh - lH = Ex - lX
Vs Ns = Vp Np
8. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
leg(s)
High voltage
electromagnetic mutual induction without loosing too much energy
9. has a laminated iron core (layers of metal plates)
variable
closed-ended core
Measuring Equipment
open-ended core
10. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
CORE: Core losses are caused by eddy currents set up by the magnetic field.
coercivity
wigginton
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
11. 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)
Eh - lH = Ex - lX
flux leakage
Exciting Current
wigginton
12. 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.
Hysteresis - Eddy - Current
Electromagnet
voltage ralated to turns ratio
13. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
silicon steel
central magnetic core
Voltage
thin copper wire coated with insulated material (shellac or enamel)
14. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
ratio of a transformer
voltage ralated to turns ratio
primary coil
by using silicon iron core
15. An electromagnetic device that operates on the principle of self induction. It uses AC.
electromagnetic mutual induction without loosing too much energy
Hysteresis
Choke coil
16. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
Vs Ns = Vp Np
current related to turns ratio law
leg(s)
Voltage - Current
17. 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
transformers efficiency
directly proportional
How a transformer works
an iron core and coil
18. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
Choke coil
rated KVA of a transformer
a magnetic field that varies quickly in direction and stregnth
class 400 transformers
19. Determines if the transformer is a step up or step down transformer
Eh - lH = Ex - lX
the number of turns of wire in the primary and secondary coils
Ip Ns = Is Np
variable
20. How coils serve as the primary and secondary windings for an autotransformer
Vs Ns = Vp Np
one coils serves as the primary and secondary windings
high frequency transformer
open-ended core
21. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
5
directly proportional
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Eddy
22. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
constant current transfomers
5
directly proportional
Eh/Ex=Th/Tx
23. A large amount of power wasted with the open-ended core
High voltage
die to leakage flux
variable transformers
Kilovolt -- Amperes (kVA)
24. _____ currents are reduced by laminating the core.
an iron core and coil
constant current transfomers
closed-ended core (square/doughnut shaped)
Eddy
25. The winding to which voltage is supplied is called the _____ winding.
Class 200 transformers
Primary
Hysteresis
26. With no load on the secondary winding - a small current flows in the primary called _____ _____.
phase
secondary coil
Step-down
Exciting Current
27. both coils in this core are heavily insulated
rating
air core
closed-ended core
one coils serves as the primary and secondary windings
28. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
highly permeable material - iron or stalloy
Distribution transformer
one coils serves as the primary and secondary windings
Secondary
29. A ___________ transformer is a continuously adjustable Autotransformer.
variable
Vs Ns = Vp Np
electromagnetic mutual induction without loosing too much energy
phase
30. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
directly proportional
Low
continuous path
31. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Step-down
Autotransformer
phase
dielectric oil
32. What is a rotation meter?
open-ended core
Voltage
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Copper Losses - Core Losses
33. 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.
primary winding
leakage flux
polarity
Secondary
34. The number of turns can be adjusted in these types of transformers
variable transformers
Exciting
dielectric oil
magnetic flux
35. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Distribution transformer
silicon steel
shell core
grounded system
36. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
air core
Transformer
flux
37. Two coils wound on a closed iron core form a ________.
primary winding
grounded (Earthed)
Simple Transformer
38. Kind of wire is the secondary coil in a transformer
Transformer
current related to turns ratio law
thin copper wire coated with insulated material (shellac or enamel)
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
39. 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
variable transformers
Eh/Ex=Th/Tx
open-ended core
5
40. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
one coils serves as the primary and secondary windings
air core
Distribution transformer
short circuit
41. An instrument used to measure electrical current.
Exciting Current
Secondary
ammeter
step-up (high voltage) transformers - step down transformer - autotransformer
42. A designated limit of operating characteristics based on definite conditions.
Ip Ns = Is Np
high frequency transformer
transformers efficiency
rating
43. 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.
Choke coil
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
eddy currents
constant current transfomers
44. 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.
Copper Losses - Core Losses
grounded system
low rententivity
change the input voltage
45. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
electromagnetic mutual induction without loosing too much energy
Insulates - cools transformer by convection - dissipates heat
Voltage - Current
class 400 transformers
46. Connected to earth or to some conducting body which serves in place of the earth.
highly permeable material - iron or stalloy
current related to turns ratio law
grounded (Earthed)
Step-down
47. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Step-down
polarity
CORE: Core losses are caused by eddy currents set up by the magnetic field.
How a transformer works
48. 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
How a transformer works
short circuit
Hysteresis
step-up (high voltage) transformers - step down transformer - autotransformer
49. The formula for the current related to voltage law
Electromagnetic Induction.
rated KVA of a transformer
Vs Ip = Vp Is
voltage ralated to turns ratio
50. 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
variable
Simple Transformer
H1 - h2...
saturable reactor
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