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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. With no load on the secondary winding - a small current flows in the primary called _____ _____.
closed-ended core
transformers efficiency law
Exciting Current
rating
2. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
step-up (high voltage) transformers - step down transformer - autotransformer
closed-ended core (square/doughnut shaped)
closed-ended core
change the input voltage
3. 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 _____.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
low rententivity
phase
4. A simple design has a core within each coil
high frequency transformer
constant current transfomers
flux
open-ended core
5. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
short circuit
The ratio of useful power output to its total power input.
low rententivity
polarity
6. An instrument used to measure electrical current.
the number of turns in the coil
ammeter
constant current transfomers
dielectric oil
7. The relationship between current and voltage in the coils are inverse
Secondary
5
air core
current related to voltage law
8. Anything above 600 volts is _____?
High voltage
Low
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
central magnetic core
9. Determines if the transformer is a step up or step down transformer
one coils serves as the primary and secondary windings
the number of turns of wire in the primary and secondary coils
Voltage
short circuit
10. 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.
Kilovolt -- Amperes (kVA)
primary winding
fuse
11. The formula for the current related to voltage law
Autotransformer
primary coil
Vs Ip = Vp Is
eddy currents
12. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
Measuring Equipment
Voltage
Step-up
13. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
air core
High voltage
Voltage
Autotransformer
14. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
one coils serves as the primary and secondary windings
Primary
Low
primary coil
15. 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.
central magnetic core
continuous path
Exciting
Simple Transformer
16. The capacity of a transformer is rated in ____ _____.
flux leakage
primary coil
Kilovolt -- Amperes (kVA)
step-up (high voltage) transformers - step down transformer - autotransformer
17. both coils in this core are heavily insulated
Electromagnet
H1 - h2...
closed-ended core
Eh - lH = Ex - lX
18. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
continuous path
Eh/Ex=Th/Tx
fuse
voltage ralated to turns ratio
19. The transformer winding to which voltage is supplied is called the _____ winding.
Voltage
one coils serves as the primary and secondary windings
closed-ended core
Primary
20. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
voltage ralated to turns ratio
flux
High voltage
21. A large amount of power wasted with the open-ended core
transformers efficiency law
die to leakage flux
Step-down
grounded (Earthed)
22. How coils serve as the primary and secondary windings for an autotransformer
magnetic field
Hysteresis - Eddy - Current
saturable reactor
one coils serves as the primary and secondary windings
23. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
X1 - X2...
wigginton
change the input voltage
24. 3 types of transformers
saturable reactor
transformers efficiency
How a transformer works
step-up (high voltage) transformers - step down transformer - autotransformer
25. _____ currents are reduced by laminating the core.
air core
Eddy
shell core
Autotransformer
26. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Choke coil
leakage flux
Electromagnetic Induction.
Hysteresis - Eddy - Current
27. Waste of power known as transformer loss - often produced by closed-ended core
eddy currents
the number of turns in the coil
grounded system
change the input voltage
28. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Hysteresis
Vs Ip = Vp Is
Same
29. Copper loss is known as _____ loss.
transformers efficiency
die to leakage flux
Vs Ip = Vp Is
30. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
central magnetic core
Step-up
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Measuring Equipment
31. 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.
constant current transfomers
rated KVA of a transformer
open-ended core
low rententivity
32. 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
Secondary
How a transformer works
flux
Insulates - cools transformer by convection - dissipates heat
33. The winding to which the load is connected is called the _____ winding.
Simple Transformer
constant current transfomers
short circuit
Secondary
34. Central magnetic core made of
highly permeable material - iron or stalloy
closed-ended core (square/doughnut shaped)
High voltage
magnetic flux
35. Divergence of the magnetic field causes this
Step-up
Measuring
leakage flux
Copper Losses - Core Losses
36. 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
voltage ralated to turns ratio
closed-ended core
leakage flux
37. An electromagnetic device that operates on the principle of self induction. It uses AC.
Transformer
die to leakage flux
Choke coil
Eh/Ex=Th/Tx
38. Reference to a jumper or conductor - to or from a piece of electrical equipment.
wigginton
Autotransformer
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
leg(s)
39. Used to increase the magnetic flux in a transformer
step-up (high voltage) transformers - step down transformer - autotransformer
Class 200 transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
central magnetic core
40. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
X1 - X2...
polarity
Same
Current
41. What does transformer efficiency mean?
phase
The ratio of useful power output to its total power input.
magnetic field
constant current transfomers
42. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Choke coil
current related to voltage law
Eh - lH = Ex - lX
short circuit
43. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
hysteresis losses (lagging losses)
change the input voltage
air core
Ip Ns = Is Np
44. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
air core
Hysteresis - Eddy - Current
dielectric oil
45. The simplest type of transformer core
ammeter
air core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
5
46. A transformer is a device that either increases or decreases alternating current and voltage using this principle
electromagnetic mutual induction without loosing too much energy
Class 200 transformers
Step-down
magnetic flux
47. 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.
variable
Transformer
Electromagnet
Class 200 transformers
48. A designated limit of operating characteristics based on definite conditions.
Primary
Vs Ns = Vp Np
primary winding
rating
49. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
rated KVA of a transformer
central magnetic core
How a transformer works
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
50. Function of the dielectric oil
Distribution transformer
Hysteresis - Eddy - Current
Same
Insulates - cools transformer by convection - dissipates heat