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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. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
Hysteresis
Voltage
ammeter
2. 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
rated KVA of a transformer
ammeter
continuous path
Exciting
3. The 4 types of transformer cores
current related to turns ratio law
Eh/Ex=Th/Tx
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
How a transformer works
4. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Autotransformer
electromagnetic mutual induction without loosing too much energy
Distribution transformer
H1 - h2...
5. Hysteresis Loss can be reduced by using a core with this feature
Primary
grounded (Earthed)
The ratio of useful power output to its total power input.
low rententivity
6. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
an iron core and coil
Voltage
variable
7. 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
flux leakage
Ip Ns = Is Np
highly permeable material - iron or stalloy
saturable reactor
8. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
change the input voltage
Volt-Amperes (Eh-lh=ExLx)
Voltage - Current
Class 200 transformers
9. Anything above 600 volts is _____?
by using silicon iron core
High voltage
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Exciting Current
10. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
shell core
high frequency transformer
Low
11. _____ currents are reduced by laminating the core.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
die to leakage flux
Eddy
Primary
12. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
Primary
grounded system
hysteresis losses (lagging losses)
polarity
13. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
wigginton
Electromagnetic Induction.
Distribution transformer
transformers efficiency law
14. Both the primary and secondary coils in a transformer are arranged around this
Primary
central magnetic core
fault
constant current transfomers
15. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
eddy currents
the number of turns of wire in the primary and secondary coils
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
rated KVA of a transformer
16. The simplest type of transformer core
Class 200 transformers
air core
Volt-Amperes (Eh-lh=ExLx)
continuous path
17. The number of turns can be adjusted in these types of transformers
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
highly permeable material - iron or stalloy
variable transformers
the number of turns of wire in the primary and secondary coils
18. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
High voltage
Voltage
Eh/Ex=Th/Tx
an iron core and coil
19. Transformer losses are classified as _____ and _____.
closed-ended core
5
central magnetic core
Copper Losses - Core Losses
20. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Step-down
leakage flux
Vs Ns = Vp Np
Measuring
21. Core losses are _____ loss and _____ - _____ loss.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Hysteresis - Eddy - Current
phase
Same
22. 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
change the input voltage
Hysteresis
wigginton
Eh/Ex=Th/Tx
23. has a laminated iron core (layers of metal plates)
continuous path
closed-ended core
Voltage
the number of turns in the coil
24. A large amount of power wasted with the open-ended core
die to leakage flux
highly permeable material - iron or stalloy
by using silicon iron core
closed-ended core
25. Refers to the transformer's ability to avoid power loss (heat)
transformers efficiency
phase
current related to voltage law
change the input voltage
26. The winding to which voltage is supplied is called the _____ winding.
Primary
secondary coil
electromagnetic mutual induction without loosing too much energy
rating
27. The winding of a transformer to which electrical energy is supplied.
closed-ended core
Current
Eddy
primary winding
28. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
open-ended core
Volt-Amperes (Eh-lh=ExLx)
Secondary
29. With no load on the secondary winding - a small current flows in the primary called _____ _____.
secondary coil
Measuring Equipment
flux leakage
Exciting Current
30. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Low
die to leakage flux
transformers efficiency law
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
31. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
the number of turns in the coil
X1 - X2...
air core
Choke coil
32. 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.
low rententivity
5
short circuit
fuse
33. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
High voltage
by varying the size of the applied DC
step-up (high voltage) transformers - step down transformer - autotransformer
34. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
change the input voltage
primary coil - secondary coil - central magnetic core
Eh/Ex=Th/Tx
35. Divergence of the magnetic field causes this
central magnetic core
Eh - lH = Ex - lX
leakage flux
Voltage - Current
36. The current related to turns ratio law
rating
Eh - lH = Ex - lX
Ip Ns = Is Np
H1 - h2...
37. 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.
Autotransformer
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Secondary
38. The 3 types of transformer power loss
hysteresis losses (lagging losses)
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
an iron core and coil
H1 - h2...
39. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
electromagnetic mutual induction without loosing too much energy
voltage ralated to turns ratio
Measuring Equipment
Eh - lH = Ex - lX
40. The formula for the current related to voltage law
ammeter
grounded (Earthed)
magnetic flux
Vs Ip = Vp Is
41. What is a rotation meter?
leakage flux
one coils serves as the primary and secondary windings
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
X1 - X2...
42. How a variable degree of core saturation is accomplished in a saturable reactor?
an iron core and coil
Secondary
by varying the size of the applied DC
the number of turns in the coil
43. The entire transformer is placed in a metal tank then immersed in ________.
dielectric oil
current related to turns ratio law
Insulates - cools transformer by convection - dissipates heat
a magnetic field that varies quickly in direction and stregnth
44. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
variable
change the input voltage
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
class 400 transformers
45. It refers to the direction of current flow in a closed circuit.
polarity
Hysteresis - Eddy - Current
Distribution transformer
Transformer
46. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Secondary
Distribution transformer
flux leakage
by varying the size of the applied DC
47. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
closed-ended core (square/doughnut shaped)
Insulates - cools transformer by convection - dissipates heat
Distribution transformer
48. Is concentrated in the metal core
high frequency transformer
an iron core and coil
Step-up
magnetic field
49. 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
class 400 transformers
Class 200 transformers
eddy currents
Voltage - Current
50. A ___________ transformer is a continuously adjustable Autotransformer.
magnetic flux
Secondary
wigginton
variable