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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. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
high frequency transformer
leakage flux
Class 200 transformers
Low
2. Used to increase the magnetic flux in a transformer
Voltage
current related to turns ratio law
central magnetic core
Choke coil
3. 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.
Voltage - Current
Step-up
fuse
Low
4. Anything above 600 volts is _____?
rating
High voltage
Class 200 transformers
an iron core and coil
5. 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 of wire in the primary and secondary coils
shell core
continuous path
Exciting
6. 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
Low
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Choke coil
7. 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
dielectric oil
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Eddy
8. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
Current
primary coil
Exciting
Eh - lH = Ex - lX
9. 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.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
eddy currents
leg(s)
10. The 3 principle components of a transformer
phase
X1 - X2...
eddy currents
primary coil - secondary coil - central magnetic core
11. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Electromagnetic Induction.
the number of turns of wire in the primary and secondary coils
Distribution transformer
shell core
12. Two coils wound on a closed iron core form a ________.
Simple Transformer
fault
variable transformers
Eh/Ex=Th/Tx
13. 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.
5
Exciting
directly proportional
Voltage
14. Transformer losses are classified as _____ and _____.
How a transformer works
variable transformers
closed-ended core
Copper Losses - Core Losses
15. It refers to the direction of current flow in a closed circuit.
Distribution transformer
Hysteresis - Eddy - Current
polarity
highly permeable material - iron or stalloy
16. The capacity of a transformer is rated in ____ _____.
ammeter
Kilovolt -- Amperes (kVA)
Low
closed-ended core
17. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Simple Transformer
directly proportional
The ratio of useful power output to its total power input.
Step-up
18. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
current related to voltage law
magnetic field
air core
19. 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
open-ended core
by using silicon iron core
directly proportional
secondary coil
20. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Voltage
Same
open-ended core
Measuring
21. The terminals of the high voltage winding are marked _____.
leg(s)
wigginton
The ratio of useful power output to its total power input.
H1 - h2...
22. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
air core
How a transformer works
secondary coil
primary coil
23. A transformer primary (H) that has 400 turns is wound to step the voltage down from 240 volts to 120 volts. The number or turns (TX) required in the secondary (X) winding is _____.
Primary
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Voltage
24. Core losses are _____ loss and _____ - _____ loss.
leakage flux
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Hysteresis - Eddy - Current
Simple Transformer
25. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
primary winding
eddy currents
Same
variable
26. Hysteresis Loss can be reduced by using a core with this feature
leakage flux
rated KVA of a transformer
primary winding
low rententivity
27. Reference to a jumper or conductor - to or from a piece of electrical equipment.
step-up (high voltage) transformers - step down transformer - autotransformer
Measuring
dielectric oil
leg(s)
28. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
class 400 transformers
the number of turns of wire in the primary and secondary coils
flux
central magnetic core
29. The winding to which voltage is supplied is called the _____ winding.
Same
Copper Losses - Core Losses
Primary
Measuring
30. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
open-ended core
rated KVA of a transformer
Primary
variable
31. An instrument used to measure electrical current.
die to leakage flux
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
ammeter
by using silicon iron core
32. The entire transformer is placed in a metal tank then immersed in ________.
central magnetic core
Copper Losses - Core Losses
Hysteresis
dielectric oil
33. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Autotransformer
Exciting Current
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
saturable reactor
34. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
die to leakage flux
hysteresis losses (lagging losses)
step-up (high voltage) transformers - step down transformer - autotransformer
a magnetic field that varies quickly in direction and stregnth
35. Determines if the transformer is a step up or step down transformer
eddy currents
Autotransformer
the number of turns of wire in the primary and secondary coils
flux leakage
36. 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.
closed-ended core
shell core
Electromagnet
37. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
directly proportional
electromagnetic mutual induction without loosing too much energy
magnetic field
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
38. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
The ratio of useful power output to its total power input.
saturable reactor
Eddy
silicon steel
39. 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.
polarity
Exciting
constant current transfomers
rated KVA of a transformer
40. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
CORE: Core losses are caused by eddy currents set up by the magnetic field.
How a transformer works
Distribution transformer
air core
41. The winding to which the load is connected is called the _____ winding.
wigginton
Hysteresis - Eddy - Current
Secondary
variable transformers
42. The terminals of the low voltage winding are marked _____.
magnetic field
X1 - X2...
saturable reactor
flux
43. The 3 types of transformer power loss
High voltage
fuse
shell core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
44. How the voltage and the number of turns are related for the voltage related to turn ratio
saturable reactor
Distribution transformer
Class 200 transformers
directly proportional
45. Connected to earth or to some conducting body which serves in place of the earth.
magnetic flux
hysteresis losses (lagging losses)
voltage ralated to turns ratio
grounded (Earthed)
46. has a laminated iron core (layers of metal plates)
primary coil - secondary coil - central magnetic core
open-ended core
closed-ended core
thin copper wire coated with insulated material (shellac or enamel)
47. 3 types of transformers
dielectric oil
step-up (high voltage) transformers - step down transformer - autotransformer
primary coil - secondary coil - central magnetic core
Secondary
48. A partial or total local failure in the insulation or continuity of a conductor.
high frequency transformer
Low
fault
Hysteresis - Eddy - Current
49. With no load on the secondary winding - a small current flows in the primary called _____ _____.
voltage ralated to turns ratio
How a transformer works
Exciting Current
Kilovolt -- Amperes (kVA)
50. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
secondary coil
die to leakage flux
saturable reactor
Voltage - Current