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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. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
current related to voltage law
transformers efficiency
CORE: Core losses are caused by eddy currents set up by the magnetic field.
secondary coil
2. How a variable degree of core saturation is accomplished in a saturable reactor?
Primary
flux
Secondary
by varying the size of the applied DC
3. 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
variable transformers
closed-ended core
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
4. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Low
short circuit
Measuring Equipment
Exciting Current
5. The number of turns can be adjusted in these types of transformers
the number of turns in the coil
silicon steel
How a transformer works
variable transformers
6. 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
Low
Vs Ns = Vp Np
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
closed-ended core
7. Determines if the transformer is a step up or step down transformer
secondary coil
Voltage
flux
the number of turns of wire in the primary and secondary coils
8. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
How a transformer works
constant current transfomers
primary coil - secondary coil - central magnetic core
9. Kind of wire is the secondary coil in a transformer
step-up (high voltage) transformers - step down transformer - autotransformer
air core
silicon steel
thin copper wire coated with insulated material (shellac or enamel)
10. Transformer losses are classified as _____ and _____.
Secondary
ratio of a transformer
Copper Losses - Core Losses
closed-ended core
11. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
change the input voltage
Secondary
die to leakage flux
Electromagnetic Induction.
12. Connected to earth or to some conducting body which serves in place of the earth.
Low
grounded (Earthed)
flux
primary winding
13. Core losses are _____ loss and _____ - _____ loss.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
rated KVA of a transformer
Hysteresis - Eddy - Current
14. The transformer winding to which the load is connected is called the _____ winding.
current related to voltage law
ratio of a transformer
step-up (high voltage) transformers - step down transformer - autotransformer
Secondary
15. 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
the number of turns in the coil
continuous path
Choke coil
Distribution transformer
16. 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
phase
primary winding
current related to voltage law
17. The transformer winding to which voltage is supplied is called the _____ winding.
magnetic flux
saturable reactor
Primary
die to leakage flux
18. An instrument used to measure electrical current.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
X1 - X2...
ammeter
19. 3 types of transformers
Secondary
Class 200 transformers
step-up (high voltage) transformers - step down transformer - autotransformer
Secondary
20. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
primary coil
Current
hysteresis losses (lagging losses)
Hysteresis
21. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
directly proportional
hysteresis losses (lagging losses)
ammeter
transformers efficiency
22. A part of a circuit made of a low melting point material so that it will melt and break the circuit when a specified current exceeded. Always the weakest point in the circuit.
The ratio of useful power output to its total power input.
Distribution transformer
dielectric oil
fuse
23. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
eddy currents
thin copper wire coated with insulated material (shellac or enamel)
Measuring Equipment
Ip Ns = Is Np
24. Is concentrated in the metal core
by using silicon iron core
Distribution transformer
magnetic field
wigginton
25. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
die to leakage flux
central magnetic core
Same
polarity
26. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Eddy
Electromagnetic Induction.
class 400 transformers
flux leakage
27. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Simple Transformer
Step-up
transformers efficiency law
Kilovolt -- Amperes (kVA)
28. What is a rotation meter?
an iron core and coil
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
grounded system
the number of turns of wire in the primary and secondary coils
29. 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.
Electromagnetic Induction.
Exciting
step-up (high voltage) transformers - step down transformer - autotransformer
hysteresis losses (lagging losses)
30. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
grounded (Earthed)
an iron core and coil
Class 200 transformers
high frequency transformer
31. Copper loss is known as _____ loss.
air core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Eh - lH = Ex - lX
32. Central magnetic core made of
Measuring Equipment
Exciting
highly permeable material - iron or stalloy
fuse
33. 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
the number of turns of wire in the primary and secondary coils
open-ended core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
saturable reactor
34. The 3 types of transformer power loss
magnetic field
by using silicon iron core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Measuring Equipment
35. Divergence of the magnetic field causes this
leakage flux
How a transformer works
open-ended core
current related to turns ratio law
36. 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
central magnetic core
Hysteresis
Step-up
coercivity
37. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
step-up (high voltage) transformers - step down transformer - autotransformer
ratio of a transformer
Low
primary coil
38. The 3 principle components of a transformer
primary coil - secondary coil - central magnetic core
central magnetic core
Eh - lH = Ex - lX
eddy currents
39. The terminals of the high voltage winding are marked _____.
Eddy
H1 - h2...
fuse
magnetic flux
40. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
High voltage
an iron core and coil
transformers efficiency law
Current
41. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
change the input voltage
X1 - X2...
thin copper wire coated with insulated material (shellac or enamel)
Low
42. A simple design has a core within each coil
Same
air core
Kilovolt -- Amperes (kVA)
open-ended core
43. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
transformers efficiency
variable transformers
grounded system
44. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
primary coil - secondary coil - central magnetic core
Distribution transformer
change the input voltage
45. A transformer loses less than _% in energy
Copper Losses - Core Losses
closed-ended core (square/doughnut shaped)
5
silicon steel
46. How coercivity is minimized
closed-ended core
fault
step-up (high voltage) transformers - step down transformer - autotransformer
by using silicon iron core
47. Waste of power known as transformer loss - often produced by closed-ended core
thin copper wire coated with insulated material (shellac or enamel)
variable
ammeter
eddy currents
48. The winding to which voltage is supplied is called the _____ winding.
Primary
short circuit
rating
Step-up
49. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Voltage
magnetic flux
Choke coil
50. A designated limit of operating characteristics based on definite conditions.
constant current transfomers
rating
air core
Copper Losses - Core Losses