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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. Hysteresis Loss can be reduced by using a core with this feature
low rententivity
primary coil - secondary coil - central magnetic core
primary coil
Low
2. How coils serve as the primary and secondary windings for an autotransformer
a magnetic field that varies quickly in direction and stregnth
central magnetic core
secondary coil
one coils serves as the primary and secondary windings
3. The number of turns can be adjusted in these types of transformers
open-ended core
Vs Ip = Vp Is
variable transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
4. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
silicon steel
step-up (high voltage) transformers - step down transformer - autotransformer
Measuring Equipment
Low
5. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
closed-ended core
polarity
closed-ended core
Low
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.
fault
Electromagnet
step-up (high voltage) transformers - step down transformer - autotransformer
air core
7. The relationship between current and voltage in the coils are inverse
wigginton
rating
current related to voltage law
primary coil - secondary coil - central magnetic core
8. An electromagnetic device that operates on the principle of self induction. It uses AC.
rating
Choke coil
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
air core
9. It refers to the direction of current flow in a closed circuit.
by using silicon iron core
transformers efficiency
Low
polarity
10. both coils in this core are heavily insulated
one coils serves as the primary and secondary windings
Transformer
closed-ended core
High voltage
11. Used to increase the magnetic flux in a transformer
highly permeable material - iron or stalloy
transformers efficiency law
central magnetic core
Volt-Amperes (Eh-lh=ExLx)
12. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Step-down
hysteresis losses (lagging losses)
leg(s)
eddy currents
13. 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 _____.
class 400 transformers
Distribution transformer
leakage flux
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
14. Waste of power known as transformer loss - often produced by closed-ended core
constant current transfomers
high frequency transformer
eddy currents
Insulates - cools transformer by convection - dissipates heat
15. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
an iron core and coil
variable transformers
rated KVA of a transformer
16. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Exciting Current
continuous path
Distribution transformer
primary winding
17. With no load on the secondary winding - a small current flows in the primary called _____ _____.
central magnetic core
shell core
variable
Exciting Current
18. Copper loss is known as _____ loss.
Copper Losses - Core Losses
leg(s)
H1 - h2...
19. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
dielectric oil
the number of turns in the coil
wigginton
primary coil
20. The voltage induced in the coil is directly proportional to this
constant current transfomers
the number of turns in the coil
Exciting
High voltage
21. What is a rotation meter?
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
leg(s)
Secondary
Autotransformer
22. A designated limit of operating characteristics based on definite conditions.
Low
primary coil
the number of turns in the coil
rating
23. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Secondary
Secondary
transformers efficiency law
Eddy
24. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
open-ended core
rated KVA of a transformer
Electromagnetic Induction.
high frequency transformer
25. The total numbre of lines or force issuing from a pole. (north or south)
How a transformer works
Copper Losses - Core Losses
closed-ended core (square/doughnut shaped)
magnetic flux
26. Core losses are _____ loss and _____ - _____ loss.
leakage flux
primary coil - secondary coil - central magnetic core
Hysteresis - Eddy - Current
air core
27. The winding of a transformer to which electrical energy is supplied.
open-ended core
X1 - X2...
rating
primary winding
28. Refers to the transformer's ability to avoid power loss (heat)
leg(s)
transformers efficiency
High voltage
Low
29. This type of core is moderately efficient due to closing the core and layering design which reduces power loss from less leakage flux which provides a continuous path for magnetic flux and an increase in field strength
a magnetic field that varies quickly in direction and stregnth
polarity
voltage ralated to turns ratio
closed-ended core
30. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
central magnetic core
short circuit
shell core
thin copper wire coated with insulated material (shellac or enamel)
31. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Electromagnetic Induction.
closed-ended core (square/doughnut shaped)
How a transformer works
ammeter
32. Is concentrated in the metal core
variable
Primary
die to leakage flux
magnetic field
33. 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
Eh - lH = Ex - lX
flux leakage
coercivity
saturable reactor
34. 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.
voltage ralated to turns ratio
closed-ended core
grounded system
primary winding
35. A single electrical circuit.
Same
grounded (Earthed)
open-ended core
phase
36. The 3 types of transformer power loss
Hysteresis
open-ended core
Copper Losses - Core Losses
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
37. 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.
current related to voltage law
Exciting
the number of turns of wire in the primary and secondary coils
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
38. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
voltage ralated to turns ratio
5
open-ended core
39. A ___________ transformer is a continuously adjustable Autotransformer.
Class 200 transformers
voltage ralated to turns ratio
variable
dielectric oil
40. Anything above 600 volts is _____?
shell core
Step-down
closed-ended core
High voltage
41. A transformer loses less than _% in energy
phase
magnetic field
voltage ralated to turns ratio
5
42. The simplest type of transformer core
air core
variable
flux leakage
directly proportional
43. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
central magnetic core
Same
Step-down
Hysteresis
44. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
class 400 transformers
change the input voltage
continuous path
Exciting Current
45. A simple design has a core within each coil
open-ended core
Hysteresis - Eddy - Current
grounded system
shell core
46. 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.
high frequency transformer
Volt-Amperes (Eh-lh=ExLx)
Transformer
47. The formula for the current related to voltage law
grounded system
Vs Ip = Vp Is
thin copper wire coated with insulated material (shellac or enamel)
Same
48. The current related to turns ratio law
Ip Ns = Is Np
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Electromagnetic Induction.
Class 200 transformers
49. How coercivity is minimized
Voltage - Current
Low
by using silicon iron core
Class 200 transformers
50. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
secondary coil
Vs Ns = Vp Np
continuous path
Eh/Ex=Th/Tx
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