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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. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Measuring
open-ended core
primary coil
Eh - lH = Ex - lX
2. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Autotransformer
rating
Kilovolt -- Amperes (kVA)
electromagnetic mutual induction without loosing too much energy
3. 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.
primary coil - secondary coil - central magnetic core
hysteresis losses (lagging losses)
ammeter
grounded system
4. 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.
the number of turns in the coil
Eh/Ex=Th/Tx
Exciting
Step-down
5. The formula for the current related to voltage law
Volt-Amperes (Eh-lh=ExLx)
Vs Ip = Vp Is
Electromagnetic Induction.
Ip Ns = Is Np
6. 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
air core
Electromagnet
Hysteresis
7. How coercivity is minimized
fault
highly permeable material - iron or stalloy
by using silicon iron core
closed-ended core
8. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
magnetic flux
leg(s)
grounded system
Transformer
9. Transformer losses are classified as _____ and _____.
open-ended core
Vs Ip = Vp Is
by using silicon iron core
Copper Losses - Core Losses
10. The simplest type of transformer core
open-ended core
current related to voltage law
air core
CORE: Core losses are caused by eddy currents set up by the magnetic field.
11. A choke coil uses this to induce current
an iron core and coil
open-ended core
thin copper wire coated with insulated material (shellac or enamel)
primary winding
12. 3 types of transformers
flux
current related to turns ratio law
step-up (high voltage) transformers - step down transformer - autotransformer
Eddy
13. The current related to turns ratio law
Measuring Equipment
Ip Ns = Is Np
Measuring
by varying the size of the applied DC
14. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
Insulates - cools transformer by convection - dissipates heat
one coils serves as the primary and secondary windings
Primary
15. Determines if the transformer is a step up or step down transformer
highly permeable material - iron or stalloy
the number of turns of wire in the primary and secondary coils
Eh - lH = Ex - lX
16. How the voltage and the number of turns are related for the voltage related to turn ratio
Distribution transformer
transformers efficiency law
directly proportional
flux leakage
17. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
fuse
Current
Hysteresis
X1 - X2...
18. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Voltage - Current
secondary coil
leakage flux
central magnetic core
19. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Secondary
closed-ended core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
20. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
central magnetic core
Measuring
silicon steel
low rententivity
21. The winding to which the load is connected is called the _____ winding.
Secondary
Secondary
current related to turns ratio law
flux leakage
22. Waste of power known as transformer loss - often produced by closed-ended core
Eddy
Insulates - cools transformer by convection - dissipates heat
eddy currents
polarity
23. 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
closed-ended core
Autotransformer
the number of turns of wire in the primary and secondary coils
24. Used to increase the magnetic flux in a transformer
primary winding
Low
Eddy
central magnetic core
25. A designated limit of operating characteristics based on definite conditions.
continuous path
rating
Measuring
grounded (Earthed)
26. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
transformers efficiency law
Hysteresis
Eddy
Autotransformer
27. The capacity of a transformer is rated in ____ _____.
rated KVA of a transformer
Autotransformer
Measuring Equipment
Kilovolt -- Amperes (kVA)
28. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Electromagnet
flux
Secondary
flux leakage
29. 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)
central magnetic core
closed-ended core
Measuring
30. The entire transformer is placed in a metal tank then immersed in ________.
dielectric oil
the number of turns in the coil
a magnetic field that varies quickly in direction and stregnth
magnetic field
31. Transformers with 4800 volt primaries and 120/240 volt secondaries - either pole or subway type - with two secondary windings terminating at internal links which provide for parallel operation of the secondary windings at 120 volts or series operatio
an iron core and coil
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
ratio of a transformer
Class 200 transformers
32. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
constant current transfomers
Same
directly proportional
33. 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
change the input voltage
How a transformer works
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
34. Reference to a jumper or conductor - to or from a piece of electrical equipment.
dielectric oil
leg(s)
Measuring Equipment
highly permeable material - iron or stalloy
35. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
air core
directly proportional
Eh/Ex=Th/Tx
Measuring Equipment
36. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
Volt-Amperes (Eh-lh=ExLx)
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
flux
hysteresis losses (lagging losses)
37. _____ currents are reduced by laminating the core.
the number of turns of wire in the primary and secondary coils
secondary coil
Eddy
Electromagnetic Induction.
38. A partial or total local failure in the insulation or continuity of a conductor.
air core
polarity
Hysteresis
fault
39. 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
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Electromagnet
magnetic flux
40. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
grounded system
primary coil
rating
shell core
41. Anything above 600 volts is _____?
rated KVA of a transformer
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
High voltage
Insulates - cools transformer by convection - dissipates heat
42. Is concentrated in the metal core
continuous path
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
magnetic field
Distribution transformer
43. 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 _____.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
How a transformer works
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
polarity
44. It refers to the direction of current flow in a closed circuit.
Exciting Current
polarity
Choke coil
secondary coil
45. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
High voltage
air core
Distribution transformer
Primary
46. An electromagnetic device that operates on the principle of self induction. It uses AC.
Hysteresis
How a transformer works
H1 - h2...
Choke coil
47. Modern; used to control filament circuit; replaced both the rheostat and choke coil; operated on the electromagnetic principle that if an iron core within or near a coil is saturated with magnetic flux by an independed source of direct current - the
The ratio of useful power output to its total power input.
saturable reactor
step-up (high voltage) transformers - step down transformer - autotransformer
Voltage - Current
48. A large amount of power wasted with the open-ended core
die to leakage flux
polarity
Voltage - Current
highly permeable material - iron or stalloy
49. Core losses are _____ loss and _____ - _____ loss.
primary coil
Insulates - cools transformer by convection - dissipates heat
Hysteresis - Eddy - Current
Low
50. has a laminated iron core (layers of metal plates)
Low
air core
closed-ended core
Same