SUBJECTS
|
BROWSE
|
CAREER CENTER
|
POPULAR
|
JOIN
|
LOGIN
Business Skills
|
Soft Skills
|
Basic Literacy
|
Certifications
About
|
Help
|
Privacy
|
Terms
|
Email
Search
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. How a variable degree of core saturation is accomplished in a saturable reactor?
the number of turns in the coil
closed-ended core (square/doughnut shaped)
by varying the size of the applied DC
Voltage
2. 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.
silicon steel
Electromagnetic Induction.
Electromagnet
phase
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)
wigginton
continuous path
primary coil
How a transformer works
4. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
leg(s)
Copper Losses - Core Losses
by using silicon iron core
5. 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
fault
constant current transfomers
central magnetic core
6. has a laminated iron core (layers of metal plates)
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Eh/Ex=Th/Tx
closed-ended core
open-ended core
7. 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.
the number of turns in the coil
Low
Secondary
class 400 transformers
8. The terminals of the low voltage winding are marked _____.
X1 - X2...
closed-ended core (square/doughnut shaped)
Transformer
highly permeable material - iron or stalloy
9. Two coils wound on a closed iron core form a ________.
variable transformers
step-up (high voltage) transformers - step down transformer - autotransformer
one coils serves as the primary and secondary windings
Simple Transformer
10. 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.
wigginton
primary coil
primary coil - secondary coil - central magnetic core
11. _____ currents are reduced by laminating the core.
Current
Eddy
die to leakage flux
flux
12. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Exciting Current
Voltage - Current
grounded system
Current
13. Divergence of the magnetic field causes this
Eddy
leakage flux
continuous path
secondary coil
14. The total numbre of lines or force issuing from a pole. (north or south)
fault
magnetic flux
grounded (Earthed)
Volt-Amperes (Eh-lh=ExLx)
15. The 3 types of transformer power loss
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
grounded (Earthed)
variable transformers
flux
16. Anything above 600 volts is _____?
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
High voltage
variable transformers
Voltage
17. The simplest type of transformer core
air core
an iron core and coil
coercivity
silicon steel
18. The 3 principle components of a transformer
flux
Voltage - Current
primary coil
primary coil - secondary coil - central magnetic core
19. A partial or total local failure in the insulation or continuity of a conductor.
directly proportional
leakage flux
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
fault
20. How coercivity is minimized
by using silicon iron core
Simple Transformer
leakage flux
coercivity
21. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Current
Step-down
High voltage
closed-ended core (square/doughnut shaped)
22. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
rated KVA of a transformer
transformers efficiency
Autotransformer
constant current transfomers
23. The current related to turns ratio law
shell core
flux leakage
Ip Ns = Is Np
constant current transfomers
24. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
variable transformers
silicon steel
change the input voltage
dielectric oil
25. A single electrical circuit.
open-ended core
ammeter
open-ended core
phase
26. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
primary coil
Vs Ip = Vp Is
secondary coil
coercivity
27. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
directly proportional
magnetic flux
Secondary
Measuring
28. Transformer losses are classified as _____ and _____.
open-ended core
thin copper wire coated with insulated material (shellac or enamel)
Copper Losses - Core Losses
Vs Ns = Vp Np
29. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
The ratio of useful power output to its total power input.
wigginton
Eh - lH = Ex - lX
transformers efficiency
30. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Electromagnetic Induction.
magnetic field
How a transformer works
directly proportional
31. The terminals of the high voltage winding are marked _____.
Electromagnetic Induction.
Copper Losses - Core Losses
H1 - h2...
Vs Ns = Vp Np
32. Connected to earth or to some conducting body which serves in place of the earth.
grounded (Earthed)
Primary
Class 200 transformers
air core
33. Function of the dielectric oil
high frequency transformer
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
low rententivity
Insulates - cools transformer by convection - dissipates heat
34. The winding of a transformer to which electrical energy is supplied.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
primary coil - secondary coil - central magnetic core
primary winding
Low
35. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
Exciting Current
grounded (Earthed)
shell core
36. The formula for the voltage related to turns ratio
phase
secondary coil
Vs Ns = Vp Np
Vs Ip = Vp Is
37. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
High voltage
Ip Ns = Is Np
Same
shell core
38. An electromagnetic device that operates on the principle of self induction. It uses AC.
How a transformer works
Hysteresis
hysteresis losses (lagging losses)
Choke coil
39. Is concentrated in the metal core
wigginton
flux
magnetic field
current related to voltage law
40. The winding to which the load is connected is called the _____ winding.
Secondary
magnetic flux
Vs Ip = Vp Is
saturable reactor
41. How the voltage and the number of turns are related for the voltage related to turn ratio
polarity
Measuring
directly proportional
Eh - lH = Ex - lX
42. An instrument used to measure electrical current.
ammeter
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
open-ended core
rated KVA of a transformer
43. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
silicon steel
change the input voltage
current related to turns ratio law
central magnetic core
44. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
closed-ended core (square/doughnut shaped)
Step-down
short circuit
highly permeable material - iron or stalloy
45. A simple design has a core within each coil
voltage ralated to turns ratio
open-ended core
eddy currents
Autotransformer
46. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
The ratio of useful power output to its total power input.
Ip Ns = Is Np
eddy currents
Eh/Ex=Th/Tx
47. Used to increase the magnetic flux in a transformer
directly proportional
central magnetic core
air core
Secondary
48. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
X1 - X2...
the number of turns in the coil
49. Copper loss is known as _____ loss.
Ip Ns = Is Np
voltage ralated to turns ratio
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
50. The 4 types of transformer cores
Eh - lH = Ex - lX
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Secondary
Step-up