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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. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
the number of turns of wire in the primary and secondary coils
Current
Low
Electromagnet
2. The capacity of a transformer is rated in ____ _____.
central magnetic core
directly proportional
Secondary
Kilovolt -- Amperes (kVA)
3. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
The ratio of useful power output to its total power input.
transformers efficiency law
Primary
high frequency transformer
4. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
low rententivity
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Hysteresis
Eh - lH = Ex - lX
5. 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
rated KVA of a transformer
Step-up
rating
open-ended core
6. 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.
an iron core and coil
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Secondary
silicon steel
7. 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
continuous path
primary coil - secondary coil - central magnetic core
current related to turns ratio law
leakage flux
8. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
open-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
constant current transfomers
9. Used to increase the magnetic flux in a transformer
electromagnetic mutual induction without loosing too much energy
die to leakage flux
central magnetic core
Eh - lH = Ex - lX
10. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Insulates - cools transformer by convection - dissipates heat
shell core
grounded system
highly permeable material - iron or stalloy
11. Waste of power known as transformer loss - often produced by closed-ended core
continuous path
eddy currents
hysteresis losses (lagging losses)
Class 200 transformers
12. The terminals of the low voltage winding are marked _____.
X1 - X2...
voltage ralated to turns ratio
Class 200 transformers
rated KVA of a transformer
13. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
polarity
X1 - X2...
by using silicon iron core
current related to turns ratio law
14. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
flux
primary coil
Voltage
rating
15. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
Transformer
Class 200 transformers
closed-ended core
16. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
Autotransformer
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
short circuit
CORE: Core losses are caused by eddy currents set up by the magnetic field.
17. 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
primary coil
5
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
18. 3 types of transformers
change the input voltage
step-up (high voltage) transformers - step down transformer - autotransformer
central magnetic core
Choke coil
19. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
coercivity
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
central magnetic core
change the input voltage
20. An electromagnetic device that operates on the principle of self induction. It uses AC.
eddy currents
phase
primary coil
Choke coil
21. The number of turns can be adjusted in these types of transformers
transformers efficiency law
Simple Transformer
Measuring
variable transformers
22. A simple design has a core within each coil
saturable reactor
dielectric oil
coercivity
open-ended core
23. It refers to the direction of current flow in a closed circuit.
polarity
primary winding
flux
Hysteresis
24. Connected to earth or to some conducting body which serves in place of the earth.
one coils serves as the primary and secondary windings
secondary coil
grounded (Earthed)
CORE: Core losses are caused by eddy currents set up by the magnetic field.
25. How the voltage and the number of turns are related for the voltage related to turn ratio
Secondary
polarity
Ip Ns = Is Np
directly proportional
26. Anything above 600 volts is _____?
Step-up
fault
directly proportional
High voltage
27. 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 _____.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
one coils serves as the primary and secondary windings
Primary
High voltage
28. The simplest type of transformer core
air core
Vs Ns = Vp Np
variable
high frequency transformer
29. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
Volt-Amperes (Eh-lh=ExLx)
class 400 transformers
30. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
secondary coil
phase
silicon steel
H1 - h2...
31. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
short circuit
voltage ralated to turns ratio
Voltage
the number of turns of wire in the primary and secondary coils
32. Refers to the transformer's ability to avoid power loss (heat)
Volt-Amperes (Eh-lh=ExLx)
Step-up
Exciting Current
transformers efficiency
33. The formula for the voltage related to turns ratio
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Vs Ns = Vp Np
current related to voltage law
Step-down
34. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
flux
Class 200 transformers
dielectric oil
35. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
central magnetic core
leg(s)
rated KVA of a transformer
Copper Losses - Core Losses
36. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
leg(s)
low rententivity
CORE: Core losses are caused by eddy currents set up by the magnetic field.
primary coil
37. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
change the input voltage
flux
hysteresis losses (lagging losses)
Vs Ip = Vp Is
38. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
one coils serves as the primary and secondary windings
Volt-Amperes (Eh-lh=ExLx)
air core
the number of turns in the coil
39. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
the number of turns in the coil
a magnetic field that varies quickly in direction and stregnth
coercivity
40. 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.
rated KVA of a transformer
Electromagnet
Low
by varying the size of the applied DC
41. 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.
closed-ended core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
constant current transfomers
open-ended core
42. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
flux
Primary
class 400 transformers
primary coil
43. 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.
Vs Ns = Vp Np
Simple Transformer
silicon steel
44. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
closed-ended core
Eh - lH = Ex - lX
Distribution transformer
class 400 transformers
45. A single electrical circuit.
phase
dielectric oil
Primary
Measuring Equipment
46. The winding to which voltage is supplied is called the _____ winding.
a magnetic field that varies quickly in direction and stregnth
5
ratio of a transformer
Primary
47. _____ currents are reduced by laminating the core.
a magnetic field that varies quickly in direction and stregnth
Eddy
change the input voltage
48. The formula for the current related to voltage law
class 400 transformers
Vs Ip = Vp Is
leakage flux
an iron core and coil
49. A transformer loses less than _% in energy
5
polarity
closed-ended core (square/doughnut shaped)
magnetic flux
50. Two coils wound on a closed iron core form a ________.
Simple Transformer
Voltage
Step-up
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.