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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. Divergence of the magnetic field causes this
the number of turns of wire in the primary and secondary coils
grounded (Earthed)
leakage flux
shell core
2. The transformer winding to which the load is connected is called the _____ winding.
Hysteresis
Low
Secondary
a magnetic field that varies quickly in direction and stregnth
3. The formula for the voltage related to turns ratio
closed-ended core
Distribution transformer
Vs Ns = Vp Np
H1 - h2...
4. The terminals of the high voltage winding are marked _____.
Low
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Vs Ip = Vp Is
H1 - h2...
5. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Secondary
Eddy
coercivity
How a transformer works
6. 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
Current
Same
Hysteresis
Eddy
7. A simple design has a core within each coil
open-ended core
central magnetic core
Secondary
Same
8. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
a magnetic field that varies quickly in direction and stregnth
electromagnetic mutual induction without loosing too much energy
How a transformer works
secondary coil
9. Is concentrated in the metal core
eddy currents
grounded (Earthed)
magnetic field
Simple Transformer
10. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Secondary
Step-up
variable
voltage ralated to turns ratio
11. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
short circuit
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Class 200 transformers
12. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Exciting
Primary
Voltage - Current
voltage ralated to turns ratio
13. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Exciting
short circuit
coercivity
variable
14. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
one coils serves as the primary and secondary windings
low rententivity
grounded (Earthed)
closed-ended core (square/doughnut shaped)
15. Used to increase the magnetic flux in a transformer
Simple Transformer
closed-ended core (square/doughnut shaped)
Insulates - cools transformer by convection - dissipates heat
central magnetic core
16. The voltage induced in the coil is directly proportional to this
phase
the number of turns in the coil
Hysteresis
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
17. A partial or total local failure in the insulation or continuity of a conductor.
closed-ended core (square/doughnut shaped)
Insulates - cools transformer by convection - dissipates heat
Exciting
fault
18. A ___________ transformer is a continuously adjustable Autotransformer.
variable
voltage ralated to turns ratio
transformers efficiency law
X1 - X2...
19. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
short circuit
the number of turns of wire in the primary and secondary coils
directly proportional
20. With no load on the secondary winding - a small current flows in the primary called _____ _____.
magnetic flux
a magnetic field that varies quickly in direction and stregnth
voltage ralated to turns ratio
Exciting Current
21. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
by using silicon iron core
Eddy
magnetic field
Same
22. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Eh - lH = Ex - lX
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Electromagnet
Voltage - Current
23. Waste of power known as transformer loss - often produced by closed-ended core
central magnetic core
Distribution transformer
eddy currents
closed-ended core
24. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
air core
step-up (high voltage) transformers - step down transformer - autotransformer
flux
primary winding
25. 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
magnetic field
Class 200 transformers
closed-ended core
highly permeable material - iron or stalloy
26. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
short circuit
Measuring
Step-down
high frequency transformer
27. 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)
the number of turns of wire in the primary and secondary coils
Distribution transformer
wigginton
How a transformer works
28. Transformer losses are classified as _____ and _____.
an iron core and coil
by using silicon iron core
Copper Losses - Core Losses
hysteresis losses (lagging losses)
29. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
fault
Autotransformer
The ratio of useful power output to its total power input.
30. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
continuous path
current related to voltage law
low rententivity
Autotransformer
31. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
constant current transfomers
Measuring
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Primary
32. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
low rententivity
The ratio of useful power output to its total power input.
Eddy
rated KVA of a transformer
33. The total numbre of lines or force issuing from a pole. (north or south)
the number of turns of wire in the primary and secondary coils
Secondary
magnetic flux
step-up (high voltage) transformers - step down transformer - autotransformer
34. 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
Current
one coils serves as the primary and secondary windings
phase
35. Two coils wound on a closed iron core form a ________.
Simple Transformer
Class 200 transformers
directly proportional
silicon steel
36. A transformer loses less than _% in energy
Low
5
variable transformers
wigginton
37. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
a magnetic field that varies quickly in direction and stregnth
Hysteresis
fuse
highly permeable material - iron or stalloy
38. Reference to a jumper or conductor - to or from a piece of electrical equipment.
variable
Eddy
leg(s)
Eh/Ex=Th/Tx
39. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
shell core
Kilovolt -- Amperes (kVA)
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Primary
40. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
the number of turns of wire in the primary and secondary coils
Eddy
rating
Distribution transformer
41. Both the primary and secondary coils in a transformer are arranged around this
Exciting
Step-down
Vs Ip = Vp Is
central magnetic core
42. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
magnetic flux
an iron core and coil
silicon steel
high frequency transformer
43. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Low
constant current transfomers
Hysteresis - Eddy - Current
electromagnetic mutual induction without loosing too much energy
44. The simplest type of transformer core
H1 - h2...
air core
Autotransformer
Exciting Current
45. The formula for the current related to voltage law
Eh - lH = Ex - lX
step-up (high voltage) transformers - step down transformer - autotransformer
Vs Ip = Vp Is
a magnetic field that varies quickly in direction and stregnth
46. 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
Hysteresis - Eddy - Current
open-ended core
continuous path
air core
47. The 3 principle components of a transformer
flux leakage
highly permeable material - iron or stalloy
primary coil - secondary coil - central magnetic core
by varying the size of the applied DC
48. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
Vs Ns = Vp Np
CORE: Core losses are caused by eddy currents set up by the magnetic field.
current related to turns ratio law
Secondary
49. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
air core
Hysteresis
high frequency transformer
50. How a variable degree of core saturation is accomplished in a saturable reactor?
central magnetic core
magnetic flux
Same
by varying the size of the applied DC