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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 output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
low rententivity
secondary coil
rated KVA of a transformer
leakage flux
2. The winding to which voltage is supplied is called the _____ winding.
fault
Ip Ns = Is Np
Primary
thin copper wire coated with insulated material (shellac or enamel)
3. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
open-ended core
flux
open-ended core
air core
4. The 3 types of transformer power loss
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
central magnetic core
Step-down
polarity
5. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Eh/Ex=Th/Tx
Measuring Equipment
Choke coil
Exciting
6. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Measuring
Low
constant current transfomers
5
7. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
thin copper wire coated with insulated material (shellac or enamel)
X1 - X2...
grounded (Earthed)
coercivity
8. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
primary coil - secondary coil - central magnetic core
magnetic flux
Current
Eh - lH = Ex - lX
9. It refers to the direction of current flow in a closed circuit.
polarity
ammeter
open-ended core
constant current transfomers
10. 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.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Electromagnet
the number of turns in the coil
Copper Losses - Core Losses
11. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
open-ended core
Eh - lH = Ex - lX
X1 - X2...
Voltage
12. Waste of power known as transformer loss - often produced by closed-ended core
grounded (Earthed)
by varying the size of the applied DC
CORE: Core losses are caused by eddy currents set up by the magnetic field.
eddy currents
13. Reference to a jumper or conductor - to or from a piece of electrical equipment.
Primary
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Distribution transformer
leg(s)
14. The current related to turns ratio law
grounded (Earthed)
Ip Ns = Is Np
Primary
Exciting
15. What is a rotation meter?
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Measuring
central magnetic core
continuous path
16. A transformer loses less than _% in energy
secondary coil
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
shell core
5
17. Refers to the transformer's ability to avoid power loss (heat)
Exciting
primary coil - secondary coil - central magnetic core
transformers efficiency
X1 - X2...
18. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
leakage flux
voltage ralated to turns ratio
magnetic flux
Hysteresis - Eddy - Current
19. Transformer losses are classified as _____ and _____.
Ip Ns = Is Np
Electromagnet
The ratio of useful power output to its total power input.
Copper Losses - Core Losses
20. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Current
CORE: Core losses are caused by eddy currents set up by the magnetic field.
short circuit
Vs Ip = Vp Is
21. 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.
closed-ended core (square/doughnut shaped)
magnetic field
Exciting
central magnetic core
22. The number of turns can be adjusted in these types of transformers
variable transformers
central magnetic core
transformers efficiency law
magnetic flux
23. The transformer winding to which voltage is supplied is called the _____ winding.
air core
eddy currents
Primary
Measuring Equipment
24. A transformer is a device that either increases or decreases alternating current and voltage using this principle
open-ended core
electromagnetic mutual induction without loosing too much energy
voltage ralated to turns ratio
Secondary
25. Used to increase the magnetic flux in a transformer
central magnetic core
Electromagnetic Induction.
low rententivity
26. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Distribution transformer
Step-up
closed-ended core (square/doughnut shaped)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
27. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
a magnetic field that varies quickly in direction and stregnth
Step-up
Secondary
Eh/Ex=Th/Tx
28. 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
directly proportional
Secondary
Primary
29. The formula for the voltage related to turns ratio
continuous path
transformers efficiency
Primary
Vs Ns = Vp Np
30. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Ip Ns = Is Np
primary coil
grounded system
31. Determines if the transformer is a step up or step down transformer
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
High voltage
H1 - h2...
the number of turns of wire in the primary and secondary coils
32. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
Copper Losses - Core Losses
low rententivity
rated KVA of a transformer
33. An instrument used to measure electrical current.
ammeter
dielectric oil
CORE: Core losses are caused by eddy currents set up by the magnetic field.
continuous path
34. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Choke coil
Eh - lH = Ex - lX
X1 - X2...
one coils serves as the primary and secondary windings
35. Hysteresis Loss can be reduced by using a core with this feature
Choke coil
low rententivity
leakage flux
CORE: Core losses are caused by eddy currents set up by the magnetic field.
36. How coercivity is minimized
rated KVA of a transformer
by using silicon iron core
Vs Ip = Vp Is
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
37. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
voltage ralated to turns ratio
secondary coil
class 400 transformers
transformers efficiency law
38. 3 types of transformers
H1 - h2...
step-up (high voltage) transformers - step down transformer - autotransformer
saturable reactor
rating
39. The terminals of the low voltage winding are marked _____.
Voltage - Current
X1 - X2...
primary winding
closed-ended core
40. The simplest type of transformer core
Eddy
Primary
air core
Electromagnetic Induction.
41. The transformer winding to which the load is connected is called the _____ winding.
eddy currents
class 400 transformers
grounded system
Secondary
42. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
closed-ended core
polarity
class 400 transformers
shell core
43. The formula for the current related to voltage law
Vs Ip = Vp Is
highly permeable material - iron or stalloy
constant current transfomers
transformers efficiency
44. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
How a transformer works
closed-ended core
by varying the size of the applied DC
45. 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
ammeter
Electromagnet
Low
continuous path
46. 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.
X1 - X2...
coercivity
Primary
constant current transfomers
47. The capacity of a transformer is rated in ____ _____.
highly permeable material - iron or stalloy
fuse
Kilovolt -- Amperes (kVA)
variable
48. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
continuous path
silicon steel
leg(s)
X1 - X2...
49. 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.
eddy currents
Vs Ns = Vp Np
grounded system
Voltage - Current
50. Divergence of the magnetic field causes this
Eh/Ex=Th/Tx
leakage flux
Exciting
secondary coil
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