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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. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
eddy currents
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Electromagnetic Induction.
X1 - X2...
2. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
dielectric oil
ratio of a transformer
transformers efficiency law
directly proportional
3. A test instrument used to indicate low voltage potentials in the range of 110 to 600 volts either alternating or direct current. (slang term: wiggy)
fault
primary winding
a magnetic field that varies quickly in direction and stregnth
wigginton
4. The number of turns can be adjusted in these types of transformers
Vs Ip = Vp Is
variable transformers
open-ended core
central magnetic core
5. A large amount of power wasted with the open-ended core
dielectric oil
die to leakage flux
CORE: Core losses are caused by eddy currents set up by the magnetic field.
the number of turns of wire in the primary and secondary coils
6. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
wigginton
Eh/Ex=Th/Tx
H1 - h2...
silicon steel
7. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Simple Transformer
Vs Ip = Vp Is
Step-down
highly permeable material - iron or stalloy
8. 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)
Measuring Equipment
rating
silicon steel
9. The loss of power required to reverse the core magnatism each time the current reverses. This loss is caused by friction between the molecules of iron as these particles are aligned first in one direction and the in the opposite direct as current dir
Hysteresis
Primary
5
current related to voltage law
10. A transformer is a device that either increases or decreases alternating current and voltage using this principle
die to leakage flux
electromagnetic mutual induction without loosing too much energy
a magnetic field that varies quickly in direction and stregnth
fuse
11. Kind of wire is the secondary coil in a transformer
Transformer
change the input voltage
central magnetic core
thin copper wire coated with insulated material (shellac or enamel)
12. The total numbre of lines or force issuing from a pole. (north or south)
secondary coil
magnetic flux
CORE: Core losses are caused by eddy currents set up by the magnetic field.
rated KVA of a transformer
13. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Copper Losses - Core Losses
Same
fuse
primary coil
14. Connected to earth or to some conducting body which serves in place of the earth.
grounded (Earthed)
dielectric oil
Hysteresis
silicon steel
15. The simplest type of transformer core
Electromagnetic Induction.
current related to voltage law
air core
Exciting
16. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
closed-ended core (square/doughnut shaped)
secondary coil
Eddy
Low
17. 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.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Primary
Eh/Ex=Th/Tx
constant current transfomers
18. A designated limit of operating characteristics based on definite conditions.
rating
High voltage
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Low
19. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
short circuit
flux leakage
transformers efficiency law
secondary coil
20. A simple design has a core within each coil
Step-down
Kilovolt -- Amperes (kVA)
open-ended core
air core
21. The 3 types of transformer power loss
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Eddy
Vs Ip = Vp Is
Copper Losses - Core Losses
22. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
leg(s)
Insulates - cools transformer by convection - dissipates heat
polarity
23. 3 types of transformers
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Distribution transformer
fuse
step-up (high voltage) transformers - step down transformer - autotransformer
24. The terminals of the high voltage winding are marked _____.
leg(s)
Eddy
Autotransformer
H1 - h2...
25. An instrument used to measure electrical current.
closed-ended core
wigginton
ammeter
step-up (high voltage) transformers - step down transformer - autotransformer
26. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
flux
central magnetic core
Current
eddy currents
27. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
Insulates - cools transformer by convection - dissipates heat
Step-up
Volt-Amperes (Eh-lh=ExLx)
28. Divergence of the magnetic field causes this
magnetic flux
leakage flux
a magnetic field that varies quickly in direction and stregnth
transformers efficiency
29. A transformer loses less than _% in energy
polarity
rated KVA of a transformer
constant current transfomers
5
30. Waste of power known as transformer loss - often produced by closed-ended core
eddy currents
grounded (Earthed)
Distribution transformer
31. Two coils wound on a closed iron core form a ________.
Exciting Current
current related to turns ratio law
Simple Transformer
Secondary
32. Reference to a jumper or conductor - to or from a piece of electrical equipment.
Eh/Ex=Th/Tx
change the input voltage
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
leg(s)
33. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
highly permeable material - iron or stalloy
Voltage - Current
primary winding
34. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
an iron core and coil
Class 200 transformers
Measuring
current related to turns ratio law
35. The formula for the current related to voltage law
electromagnetic mutual induction without loosing too much energy
Ip Ns = Is Np
Vs Ip = Vp Is
5
36. 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 _____.
Vs Ns = Vp Np
class 400 transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
fuse
37. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Voltage - Current
Secondary
flux
a magnetic field that varies quickly in direction and stregnth
38. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
air core
hysteresis losses (lagging losses)
dielectric oil
class 400 transformers
39. 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
open-ended core
the number of turns of wire in the primary and secondary coils
step-up (high voltage) transformers - step down transformer - autotransformer
40. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
closed-ended core (square/doughnut shaped)
rating
Exciting Current
41. A choke coil uses this to induce current
fault
eddy currents
an iron core and coil
voltage ralated to turns ratio
42. Copper loss is known as _____ loss.
voltage ralated to turns ratio
grounded system
change the input voltage
43. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
Simple Transformer
phase
Kilovolt -- Amperes (kVA)
44. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
directly proportional
Electromagnetic Induction.
short circuit
flux leakage
45. The capacity of a transformer is rated in ____ _____.
Secondary
Kilovolt -- Amperes (kVA)
closed-ended core
current related to voltage law
46. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Eddy
Vs Ns = Vp Np
low rententivity
Step-up
47. Central magnetic core made of
highly permeable material - iron or stalloy
Secondary
Copper Losses - Core Losses
directly proportional
48. The relationship between current and voltage in the coils are inverse
by using silicon iron core
the number of turns in the coil
current related to voltage law
Vs Ip = Vp Is
49. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
coercivity
air core
closed-ended core (square/doughnut shaped)
Transformer
50. What does transformer efficiency mean?
grounded system
flux
The ratio of useful power output to its total power input.
flux leakage