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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. A simple design has a core within each coil
open-ended core
leg(s)
Hysteresis
2. A designated limit of operating characteristics based on definite conditions.
rating
ammeter
silicon steel
voltage ralated to turns ratio
3. both coils in this core are heavily insulated
ratio of a transformer
Eh - lH = Ex - lX
Secondary
closed-ended core
4. The voltage induced in the coil is directly proportional to this
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
variable transformers
Step-down
the number of turns in the coil
5. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
magnetic flux
a magnetic field that varies quickly in direction and stregnth
rating
closed-ended core
6. How a variable degree of core saturation is accomplished in a saturable reactor?
Class 200 transformers
current related to voltage law
transformers efficiency law
by varying the size of the applied DC
7. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
grounded system
Hysteresis
Current
8. Copper loss is known as _____ loss.
closed-ended core
The ratio of useful power output to its total power input.
die to leakage flux
9. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
closed-ended core
highly permeable material - iron or stalloy
Electromagnetic Induction.
10. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
5
rated KVA of a transformer
grounded (Earthed)
Choke coil
11. How coercivity is minimized
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
dielectric oil
shell core
by using silicon iron core
12. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
voltage ralated to turns ratio
highly permeable material - iron or stalloy
Volt-Amperes (Eh-lh=ExLx)
magnetic flux
13. 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
closed-ended core
current related to turns ratio law
dielectric oil
Exciting
14. It refers to the direction of current flow in a closed circuit.
variable transformers
Step-down
polarity
Voltage
15. The capacity of a transformer is rated in ____ _____.
Kilovolt -- Amperes (kVA)
phase
step-up (high voltage) transformers - step down transformer - autotransformer
ammeter
16. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Autotransformer
ammeter
magnetic flux
voltage ralated to turns ratio
17. 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 _____.
The ratio of useful power output to its total power input.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Measuring Equipment
electromagnetic mutual induction without loosing too much energy
18. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
silicon steel
class 400 transformers
Volt-Amperes (Eh-lh=ExLx)
Primary
19. 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
Primary
How a transformer works
CORE: Core losses are caused by eddy currents set up by the magnetic field.
closed-ended core
20. The winding to which the load is connected is called the _____ winding.
H1 - h2...
electromagnetic mutual induction without loosing too much energy
Secondary
saturable reactor
21. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
primary winding
by using silicon iron core
Secondary
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
22. Waste of power known as transformer loss - often produced by closed-ended core
eddy currents
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Exciting
rated KVA of a transformer
23. 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.
Exciting
Current
an iron core and coil
change the input voltage
24. The 3 types of transformer power loss
Autotransformer
current related to turns ratio law
Exciting Current
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
25. The current related to turns ratio law
an iron core and coil
Ip Ns = Is Np
change the input voltage
26. 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.
class 400 transformers
central magnetic core
Primary
Electromagnet
27. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
H1 - h2...
Transformer
short circuit
Low
28. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
Eh/Ex=Th/Tx
leg(s)
Voltage - Current
primary coil
29. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
phase
continuous path
air core
30. 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
Measuring Equipment
central magnetic core
fault
31. Refers to the transformer's ability to avoid power loss (heat)
air core
transformers efficiency
Measuring Equipment
class 400 transformers
32. A partial or total local failure in the insulation or continuity of a conductor.
Secondary
saturable reactor
fault
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
33. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
air core
coercivity
closed-ended core (square/doughnut shaped)
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
34. An instrument used to measure electrical current.
Simple Transformer
Electromagnetic Induction.
ammeter
closed-ended core
35. The formula for the current related to voltage law
die to leakage flux
Vs Ip = Vp Is
How a transformer works
36. The winding to which voltage is supplied is called the _____ winding.
leg(s)
rating
Primary
Voltage
37. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
variable
X1 - X2...
CORE: Core losses are caused by eddy currents set up by the magnetic field.
38. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Vs Ip = Vp Is
flux leakage
secondary coil
39. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
H1 - h2...
Eh/Ex=Th/Tx
closed-ended core
central magnetic core
40. A transformer is a device that either increases or decreases alternating current and voltage using this principle
secondary coil
electromagnetic mutual induction without loosing too much energy
saturable reactor
closed-ended core
41. A ___________ transformer is a continuously adjustable Autotransformer.
polarity
Low
magnetic field
variable
42. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
by using silicon iron core
Voltage - Current
leakage flux
43. A single electrical circuit.
Autotransformer
phase
Exciting Current
Secondary
44. Is concentrated in the metal core
open-ended core
magnetic field
High voltage
closed-ended core (square/doughnut shaped)
45. 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.
Low
Secondary
the number of turns of wire in the primary and secondary coils
by varying the size of the applied DC
46. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
polarity
Eh/Ex=Th/Tx
air core
47. has a laminated iron core (layers of metal plates)
closed-ended core
Insulates - cools transformer by convection - dissipates heat
variable transformers
highly permeable material - iron or stalloy
48. A large amount of power wasted with the open-ended core
eddy currents
ammeter
die to leakage flux
central magnetic core
49. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Current
High voltage
leg(s)
hysteresis losses (lagging losses)
50. What does transformer efficiency mean?
Primary
magnetic flux
The ratio of useful power output to its total power input.
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