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Test your basic knowledge |
Transformers
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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. The entire transformer is placed in a metal tank then immersed in ________.
magnetic field
dielectric oil
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
air core
2. The terminals of the high voltage winding are marked _____.
rated KVA of a transformer
H1 - h2...
grounded (Earthed)
step-up (high voltage) transformers - step down transformer - autotransformer
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
change the input voltage
Transformer
closed-ended core
4. 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.
current related to turns ratio law
primary winding
leakage flux
5. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Measuring Equipment
Current
CORE: Core losses are caused by eddy currents set up by the magnetic field.
6. The winding to which the load is connected is called the _____ winding.
the number of turns of wire in the primary and secondary coils
wigginton
electromagnetic mutual induction without loosing too much energy
Secondary
7. The terminals of the low voltage winding are marked _____.
X1 - X2...
grounded (Earthed)
magnetic field
Distribution transformer
8. A large amount of power wasted with the open-ended core
die to leakage flux
Eh - lH = Ex - lX
grounded (Earthed)
The ratio of useful power output to its total power input.
9. 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
ammeter
one coils serves as the primary and secondary windings
closed-ended core
The ratio of useful power output to its total power input.
10. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
highly permeable material - iron or stalloy
closed-ended core
Measuring
Hysteresis
11. An electromagnetic device that operates on the principle of self induction. It uses AC.
eddy currents
silicon steel
Choke coil
highly permeable material - iron or stalloy
12. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
short circuit
Voltage - Current
class 400 transformers
13. A single electrical circuit.
phase
voltage ralated to turns ratio
Vs Ns = Vp Np
Class 200 transformers
14. Used to increase the magnetic flux in a transformer
How a transformer works
air core
Eh - lH = Ex - lX
central magnetic core
15. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
voltage ralated to turns ratio
Exciting Current
thin copper wire coated with insulated material (shellac or enamel)
primary winding
16. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
5
rating
High voltage
closed-ended core (square/doughnut shaped)
17. A simple design has a core within each coil
open-ended core
Same
Exciting Current
closed-ended core
18. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
air core
polarity
primary winding
Autotransformer
19. Is concentrated in the metal core
Secondary
step-up (high voltage) transformers - step down transformer - autotransformer
magnetic field
Step-up
20. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
rating
variable
How a transformer works
21. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
CORE: Core losses are caused by eddy currents set up by the magnetic field.
wigginton
Voltage - Current
22. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
Eh/Ex=Th/Tx
open-ended core
change the input voltage
23. A designated limit of operating characteristics based on definite conditions.
rating
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
constant current transfomers
Hysteresis
24. 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.
Voltage - Current
short circuit
Exciting
How a transformer works
25. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
highly permeable material - iron or stalloy
Electromagnet
Distribution transformer
central magnetic core
26. has a laminated iron core (layers of metal plates)
How a transformer works
shell core
closed-ended core
leg(s)
27. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
Same
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
change the input voltage
variable
28. 3 types of transformers
primary coil
Exciting
step-up (high voltage) transformers - step down transformer - autotransformer
Autotransformer
29. An instrument used to measure electrical current.
ammeter
change the input voltage
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
flux leakage
30. The 3 types of transformer power loss
Copper Losses - Core Losses
by using silicon iron core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
The ratio of useful power output to its total power input.
31. Central magnetic core made of
highly permeable material - iron or stalloy
Primary
flux
the number of turns in the coil
32. 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
grounded (Earthed)
5
variable transformers
33. 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
variable
Hysteresis
variable transformers
high frequency transformer
34. 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 _____.
wigginton
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
coercivity
Same
35. Kind of wire is the secondary coil in a transformer
variable transformers
thin copper wire coated with insulated material (shellac or enamel)
voltage ralated to turns ratio
Primary
36. both coils in this core are heavily insulated
closed-ended core
Distribution transformer
Autotransformer
directly proportional
37. The number of turns can be adjusted in these types of transformers
variable transformers
wigginton
high frequency transformer
phase
38. The current related to turns ratio law
Insulates - cools transformer by convection - dissipates heat
wigginton
H1 - h2...
Ip Ns = Is Np
39. With no load on the secondary winding - a small current flows in the primary called _____ _____.
leakage flux
Exciting Current
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Low
40. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
Class 200 transformers
class 400 transformers
The ratio of useful power output to its total power input.
transformers efficiency law
41. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Current
shell core
hysteresis losses (lagging losses)
Measuring Equipment
42. Waste of power known as transformer loss - often produced by closed-ended core
highly permeable material - iron or stalloy
Simple Transformer
high frequency transformer
eddy currents
43. 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)
variable
coercivity
wigginton
central magnetic core
44. The simplest type of transformer core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
dielectric oil
fault
air core
45. A transformer loses less than _% in energy
5
hysteresis losses (lagging losses)
Voltage
central magnetic core
46. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
current related to voltage law
polarity
Hysteresis
rated KVA of a transformer
47. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
secondary coil
constant current transfomers
Eh - lH = Ex - lX
magnetic flux
48. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Eh/Ex=Th/Tx
coercivity
current related to voltage law
open-ended core
49. How coercivity is minimized
by using silicon iron core
Secondary
polarity
high frequency transformer
50. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
eddy currents
a magnetic field that varies quickly in direction and stregnth
Simple Transformer
secondary coil
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