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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 input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
shell core
primary coil
Measuring Equipment
secondary coil
2. The transformer winding to which the load is connected is called the _____ winding.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
variable transformers
Secondary
3. The terminals of the low voltage winding are marked _____.
The ratio of useful power output to its total power input.
air core
the number of turns in the coil
X1 - X2...
4. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
Current
change the input voltage
current related to turns ratio law
5. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
Low
Vs Ip = Vp Is
Exciting Current
6. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
an iron core and coil
open-ended core
closed-ended core
7. Refers to the transformer's ability to avoid power loss (heat)
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Measuring
transformers efficiency
dielectric oil
8. 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.
X1 - X2...
Volt-Amperes (Eh-lh=ExLx)
H1 - h2...
Secondary
9. _____ currents are reduced by laminating the core.
shell core
Measuring
Ip Ns = Is Np
Eddy
10. The formula for the current related to voltage law
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
current related to turns ratio law
Vs Ip = Vp Is
by varying the size of the applied DC
11. 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
saturable reactor
Exciting Current
by using silicon iron core
variable transformers
12. What does transformer efficiency mean?
variable transformers
primary winding
Eddy
The ratio of useful power output to its total power input.
13. Hysteresis Loss can be reduced by using a core with this feature
highly permeable material - iron or stalloy
X1 - X2...
Copper Losses - Core Losses
low rententivity
14. Anything above 600 volts is _____?
High voltage
Secondary
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
15. The current related to turns ratio law
Ip Ns = Is Np
Vs Ns = Vp Np
Secondary
Simple Transformer
16. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Electromagnet
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
primary coil - secondary coil - central magnetic core
rated KVA of a transformer
17. has a laminated iron core (layers of metal plates)
an iron core and coil
Distribution transformer
closed-ended core
magnetic flux
18. The terminals of the high voltage winding are marked _____.
Volt-Amperes (Eh-lh=ExLx)
an iron core and coil
H1 - h2...
transformers efficiency
19. A transformer loses less than _% in energy
closed-ended core
5
step-up (high voltage) transformers - step down transformer - autotransformer
Class 200 transformers
20. 3 types of transformers
primary winding
by using silicon iron core
Voltage - Current
step-up (high voltage) transformers - step down transformer - autotransformer
21. It refers to the direction of current flow in a closed circuit.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
polarity
fault
constant current transfomers
22. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
thin copper wire coated with insulated material (shellac or enamel)
primary coil
fault
23. The number of turns can be adjusted in these types of transformers
Secondary
primary coil - secondary coil - central magnetic core
variable transformers
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
24. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
current related to voltage law
dielectric oil
magnetic field
ratio of a transformer
25. 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.
closed-ended core
by using silicon iron core
Hysteresis - Eddy - Current
26. 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
primary coil
ratio of a transformer
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Class 200 transformers
27. A simple design has a core within each coil
open-ended core
magnetic field
an iron core and coil
Secondary
28. 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
closed-ended core
closed-ended core (square/doughnut shaped)
variable transformers
Distribution transformer
29. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
primary coil
phase
Electromagnetic Induction.
Voltage
30. The entire transformer is placed in a metal tank then immersed in ________.
dielectric oil
shell core
Eh/Ex=Th/Tx
grounded (Earthed)
31. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Eh - lH = Ex - lX
Measuring
Hysteresis - Eddy - Current
Voltage - Current
32. The winding to which voltage is supplied is called the _____ winding.
open-ended core
Primary
Autotransformer
coercivity
33. Current flows through the primary winding in response to primary voltage and sets up a magnetic field that varies in direction and stregnth. under the influence of the changing magnetic field an AC voltage/kv is induced across the secondary coil by e
silicon steel
5
Low
How a transformer works
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.
Current
grounded system
flux leakage
one coils serves as the primary and secondary windings
35. 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.
Step-up
voltage ralated to turns ratio
the number of turns of wire in the primary and secondary coils
Electromagnet
36. Two coils wound on a closed iron core form a ________.
Volt-Amperes (Eh-lh=ExLx)
rated KVA of a transformer
a magnetic field that varies quickly in direction and stregnth
Simple Transformer
37. Central magnetic core made of
central magnetic core
silicon steel
highly permeable material - iron or stalloy
Step-down
38. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
highly permeable material - iron or stalloy
class 400 transformers
dielectric oil
Distribution transformer
39. 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.
Primary
Step-down
Volt-Amperes (Eh-lh=ExLx)
fuse
40. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Voltage - Current
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Primary
high frequency transformer
41. How the voltage and the number of turns are related for the voltage related to turn ratio
primary winding
Exciting Current
directly proportional
Class 200 transformers
42. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Primary
high frequency transformer
silicon steel
43. The winding of a transformer to which electrical energy is supplied.
voltage ralated to turns ratio
Primary
Volt-Amperes (Eh-lh=ExLx)
primary winding
44. Function of the dielectric oil
shell core
Electromagnet
constant current transfomers
Insulates - cools transformer by convection - dissipates heat
45. The simplest type of transformer core
air core
Hysteresis
die to leakage flux
thin copper wire coated with insulated material (shellac or enamel)
46. 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.
low rententivity
the number of turns in the coil
Transformer
Exciting
47. How coercivity is minimized
central magnetic core
by using silicon iron core
Exciting Current
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
48. A ___________ transformer is a continuously adjustable Autotransformer.
Voltage
closed-ended core
variable
Exciting Current
49. The 4 types of transformer cores
the number of turns in the coil
by varying the size of the applied DC
How a transformer works
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
50. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
variable
central magnetic core
air core
Same