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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. Transformer losses are classified as _____ and _____.
wigginton
rating
Copper Losses - Core Losses
central magnetic core
2. A transformer is a device that either increases or decreases alternating current and voltage using this principle
electromagnetic mutual induction without loosing too much energy
Eh - lH = Ex - lX
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
wigginton
3. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
continuous path
Current
Distribution transformer
dielectric oil
4. 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
Eh - lH = Ex - lX
voltage ralated to turns ratio
open-ended core
How a transformer works
5. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
class 400 transformers
Step-down
air core
fuse
6. Copper loss is known as _____ loss.
continuous path
Step-up
phase
7. The capacity of a transformer is rated in ____ _____.
Hysteresis - Eddy - Current
Exciting
Kilovolt -- Amperes (kVA)
primary coil - secondary coil - central magnetic core
8. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
closed-ended core
short circuit
air core
grounded system
9. It refers to the direction of current flow in a closed circuit.
one coils serves as the primary and secondary windings
polarity
fuse
dielectric oil
10. 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
Hysteresis
Insulates - cools transformer by convection - dissipates heat
Eh/Ex=Th/Tx
magnetic flux
11. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
saturable reactor
Copper Losses - Core Losses
flux
Eh - lH = Ex - lX
12. The entire transformer is placed in a metal tank then immersed in ________.
primary coil
Primary
dielectric oil
closed-ended core
13. 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.
grounded system
fault
Electromagnet
Simple Transformer
14. A partial or total local failure in the insulation or continuity of a conductor.
directly proportional
How a transformer works
fault
low rententivity
15. 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.
variable transformers
primary coil - secondary coil - central magnetic core
Secondary
open-ended core
16. 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.
high frequency transformer
continuous path
Copper Losses - Core Losses
Electromagnet
17. 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.
electromagnetic mutual induction without loosing too much energy
constant current transfomers
voltage ralated to turns ratio
current related to turns ratio law
18. Core losses are _____ loss and _____ - _____ loss.
leg(s)
Secondary
Hysteresis - Eddy - Current
highly permeable material - iron or stalloy
19. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
constant current transfomers
eddy currents
Secondary
20. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
by varying the size of the applied DC
the number of turns of wire in the primary and secondary coils
Eddy
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
21. The voltage induced in the coil is directly proportional to this
Hysteresis
How a transformer works
the number of turns in the coil
an iron core and coil
22. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
primary winding
Voltage - Current
closed-ended core
open-ended core
23. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Autotransformer
Secondary
dielectric oil
flux
24. How coercivity is minimized
variable transformers
fuse
by using silicon iron core
one coils serves as the primary and secondary windings
25. 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
Voltage - Current
variable transformers
open-ended core
step-up (high voltage) transformers - step down transformer - autotransformer
26. 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
secondary coil
continuous path
Choke coil
Ip Ns = Is Np
27. 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.
Transformer
Ip Ns = Is Np
leg(s)
28. A single electrical circuit.
Exciting
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
variable
phase
29. The formula for the voltage related to turns ratio
X1 - X2...
Eddy
rated KVA of a transformer
Vs Ns = Vp Np
30. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
closed-ended core (square/doughnut shaped)
Measuring
Primary
the number of turns in the coil
31. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Current
Low
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
high frequency transformer
32. Divergence of the magnetic field causes this
Exciting
voltage ralated to turns ratio
closed-ended core (square/doughnut shaped)
leakage flux
33. How the voltage and the number of turns are related for the voltage related to turn ratio
class 400 transformers
X1 - X2...
highly permeable material - iron or stalloy
directly proportional
34. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
rated KVA of a transformer
Voltage
Current
constant current transfomers
35. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
silicon steel
short circuit
shell core
Eh/Ex=Th/Tx
36. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Exciting Current
low rententivity
transformers efficiency law
Autotransformer
37. Determines if the transformer is a step up or step down transformer
the number of turns of wire in the primary and secondary coils
grounded (Earthed)
Secondary
H1 - h2...
38. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Simple Transformer
change the input voltage
39. A designated limit of operating characteristics based on definite conditions.
rating
leg(s)
eddy currents
variable transformers
40. A transformer loses less than _% in energy
5
Secondary
variable transformers
die to leakage flux
41. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
Voltage - Current
low rententivity
closed-ended core (square/doughnut shaped)
42. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
change the input voltage
constant current transfomers
an iron core and coil
43. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
shell core
secondary coil
Autotransformer
a magnetic field that varies quickly in direction and stregnth
44. 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
Class 200 transformers
transformers efficiency law
a magnetic field that varies quickly in direction and stregnth
secondary coil
45. What does transformer efficiency mean?
Current
Ip Ns = Is Np
by varying the size of the applied DC
The ratio of useful power output to its total power input.
46. A large amount of power wasted with the open-ended core
leakage flux
air core
Low
die to leakage flux
47. Reference to a jumper or conductor - to or from a piece of electrical equipment.
the number of turns of wire in the primary and secondary coils
The ratio of useful power output to its total power input.
5
leg(s)
48. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Hysteresis
high frequency transformer
Current
Step-down
49. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
flux
ammeter
class 400 transformers
50. The formula for the current related to voltage law
The ratio of useful power output to its total power input.
fault
Same
Vs Ip = Vp Is