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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. _____ currents are reduced by laminating the core.
Eddy
X1 - X2...
Secondary
2. The winding to which voltage is supplied is called the _____ winding.
Copper Losses - Core Losses
Choke coil
Primary
voltage ralated to turns ratio
3. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
Eh - lH = Ex - lX
the number of turns in the coil
coercivity
fault
4. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
closed-ended core
flux
air core
Current
5. Transformer losses are classified as _____ and _____.
Ip Ns = Is Np
Step-down
flux
Copper Losses - Core Losses
6. The 3 types of transformer power loss
H1 - h2...
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Step-down
air core
7. 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.
low rententivity
Electromagnet
fuse
rating
8. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
Eddy
Hysteresis
rated KVA of a transformer
9. The relationship between current and voltage in the coils are inverse
shell core
current related to voltage law
ratio of a transformer
closed-ended core (square/doughnut shaped)
10. The terminals of the high voltage winding are marked _____.
H1 - h2...
dielectric oil
the number of turns of wire in the primary and secondary coils
Exciting Current
11. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
Current
secondary coil
constant current transfomers
rating
12. Two coils wound on a closed iron core form a ________.
Same
short circuit
Simple Transformer
grounded (Earthed)
13. has a laminated iron core (layers of metal plates)
Electromagnetic Induction.
secondary coil
Simple Transformer
closed-ended core
14. The total numbre of lines or force issuing from a pole. (north or south)
Secondary
low rententivity
magnetic flux
Class 200 transformers
15. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
closed-ended core
change the input voltage
Autotransformer
Voltage - Current
16. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
secondary coil
current related to turns ratio law
air core
primary coil
17. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
hysteresis losses (lagging losses)
by using silicon iron core
change the input voltage
Vs Ns = Vp Np
18. Divergence of the magnetic field causes this
Eddy
leakage flux
central magnetic core
Insulates - cools transformer by convection - dissipates heat
19. The transformer winding to which the load is connected is called the _____ winding.
central magnetic core
Secondary
variable transformers
flux leakage
20. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
central magnetic core
Voltage - Current
wigginton
Simple Transformer
21. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
the number of turns in the coil
phase
Primary
rated KVA of a transformer
22. The capacity of a transformer is rated in ____ _____.
Current
closed-ended core
Kilovolt -- Amperes (kVA)
Electromagnet
23. Determines if the transformer is a step up or step down transformer
flux leakage
H1 - h2...
X1 - X2...
the number of turns of wire in the primary and secondary coils
24. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
transformers efficiency
Step-down
high frequency transformer
hysteresis losses (lagging losses)
25. Core losses are _____ loss and _____ - _____ loss.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Hysteresis - Eddy - Current
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
hysteresis losses (lagging losses)
26. The winding to which the load is connected is called the _____ winding.
Secondary
voltage ralated to turns ratio
Measuring Equipment
Exciting Current
27. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
the number of turns of wire in the primary and secondary coils
magnetic field
Electromagnetic Induction.
28. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Autotransformer
Exciting
Measuring Equipment
low rententivity
29. A partial or total local failure in the insulation or continuity of a conductor.
fault
the number of turns of wire in the primary and secondary coils
central magnetic core
eddy currents
30. An instrument used to measure electrical current.
magnetic field
transformers efficiency law
ammeter
closed-ended core
31. A simple design has a core within each coil
High voltage
short circuit
by varying the size of the applied DC
open-ended core
32. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
Primary
current related to turns ratio law
grounded system
Hysteresis
33. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Distribution transformer
shell core
Choke coil
Exciting Current
34. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
leakage flux
Choke coil
rated KVA of a transformer
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
35. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
central magnetic core
Electromagnet
Kilovolt -- Amperes (kVA)
36. Reference to a jumper or conductor - to or from a piece of electrical equipment.
How a transformer works
high frequency transformer
transformers efficiency law
leg(s)
37. A choke coil uses this to induce current
an iron core and coil
ammeter
primary winding
transformers efficiency
38. It refers to the direction of current flow in a closed circuit.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
air core
Autotransformer
polarity
39. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Eddy
Transformer
central magnetic core
ratio of a transformer
40. Anything above 600 volts is _____?
air core
transformers efficiency law
High voltage
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
41. The 4 types of transformer cores
electromagnetic mutual induction without loosing too much energy
open-ended core
flux leakage
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
42. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
ammeter
an iron core and coil
current related to turns ratio law
Distribution transformer
43. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
by varying the size of the applied DC
closed-ended core
shell core
5
44. 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.
Secondary
open-ended core
Same
Class 200 transformers
45. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
Eddy
silicon steel
a magnetic field that varies quickly in direction and stregnth
46. 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.
fuse
coercivity
central magnetic core
current related to turns ratio law
47. 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.
coercivity
grounded system
closed-ended core
open-ended core
48. Central magnetic core made of
highly permeable material - iron or stalloy
Voltage - Current
central magnetic core
directly proportional
49. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Electromagnetic Induction.
transformers efficiency law
primary winding
Voltage - Current
50. 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)
magnetic flux
step-up (high voltage) transformers - step down transformer - autotransformer
primary winding
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