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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. Copper loss is known as _____ loss.
transformers efficiency law
Primary
current related to voltage law
2. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
magnetic field
class 400 transformers
directly proportional
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
3. With no load on the secondary winding - a small current flows in the primary called _____ _____.
electromagnetic mutual induction without loosing too much energy
Voltage
voltage ralated to turns ratio
Exciting Current
4. The relationship between current and voltage in the coils are inverse
current related to voltage law
saturable reactor
Ip Ns = Is Np
Eh/Ex=Th/Tx
5. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Simple Transformer
magnetic flux
CORE: Core losses are caused by eddy currents set up by the magnetic field.
coercivity
6. Hysteresis Loss can be reduced by using a core with this feature
Eh/Ex=Th/Tx
low rententivity
How a transformer works
magnetic field
7. The capacity of a transformer is rated in ____ _____.
low rententivity
5
Kilovolt -- Amperes (kVA)
High voltage
8. The winding to which the load is connected is called the _____ winding.
Secondary
eddy currents
Vs Ip = Vp Is
Autotransformer
9. Is concentrated in the metal core
Secondary
class 400 transformers
closed-ended core (square/doughnut shaped)
magnetic field
10. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
eddy currents
transformers efficiency law
Low
central magnetic core
11. Transformer losses are classified as _____ and _____.
step-up (high voltage) transformers - step down transformer - autotransformer
Simple Transformer
Copper Losses - Core Losses
12. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
hysteresis losses (lagging losses)
Vs Ip = Vp Is
Hysteresis - Eddy - Current
magnetic field
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 _____.
wigginton
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
change the input voltage
central magnetic core
14. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
H1 - h2...
Autotransformer
How a transformer works
15. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
The ratio of useful power output to its total power input.
Voltage
Autotransformer
5
16. has a laminated iron core (layers of metal plates)
ratio of a transformer
the number of turns of wire in the primary and secondary coils
closed-ended core
variable transformers
17. The terminals of the high voltage winding are marked _____.
H1 - h2...
fuse
one coils serves as the primary and secondary windings
magnetic field
18. The entire transformer is placed in a metal tank then immersed in ________.
Measuring Equipment
H1 - h2...
dielectric oil
Ip Ns = Is Np
19. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
X1 - X2...
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Distribution transformer
Exciting
20. The 3 principle components of a transformer
saturable reactor
silicon steel
primary coil - secondary coil - central magnetic core
Vs Ip = Vp Is
21. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
X1 - X2...
Low
Electromagnet
Exciting
22. The winding to which voltage is supplied is called the _____ winding.
a magnetic field that varies quickly in direction and stregnth
Primary
primary coil
The ratio of useful power output to its total power input.
23. Function of the dielectric oil
low rententivity
Hysteresis
Insulates - cools transformer by convection - dissipates heat
voltage ralated to turns ratio
24. 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
high frequency transformer
closed-ended core
Secondary
Simple Transformer
25. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Voltage - Current
rating
silicon steel
change the input voltage
26. Central magnetic core made of
highly permeable material - iron or stalloy
open-ended core
Copper Losses - Core Losses
current related to turns ratio law
27. 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)
leg(s)
Autotransformer
wigginton
a magnetic field that varies quickly in direction and stregnth
28. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
directly proportional
the number of turns in the coil
Voltage
a magnetic field that varies quickly in direction and stregnth
29. A single electrical circuit.
flux
constant current transfomers
Hysteresis
phase
30. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
secondary coil
rated KVA of a transformer
central magnetic core
Exciting
31. 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.
Primary
Electromagnet
magnetic field
Exciting
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.
high frequency transformer
die to leakage flux
fuse
33. How the voltage and the number of turns are related for the voltage related to turn ratio
Exciting
directly proportional
low rententivity
Choke coil
34. What does transformer efficiency mean?
Eddy
primary coil - secondary coil - central magnetic core
The ratio of useful power output to its total power input.
continuous path
35. Used to increase the magnetic flux in a transformer
Choke coil
magnetic flux
by using silicon iron core
central magnetic core
36. Connected to earth or to some conducting body which serves in place of the earth.
closed-ended core
air core
grounded (Earthed)
by varying the size of the applied DC
37. The simplest type of transformer core
Voltage - Current
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
air core
electromagnetic mutual induction without loosing too much energy
38. Divergence of the magnetic field causes this
Voltage - Current
leakage flux
Step-up
open-ended core
39. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Current
the number of turns in the coil
Choke coil
air core
40. A partial or total local failure in the insulation or continuity of a conductor.
Ip Ns = Is Np
variable
Secondary
fault
41. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Choke coil
Electromagnetic Induction.
Low
short circuit
42. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
secondary coil
primary coil
constant current transfomers
ratio of a transformer
43. _____ currents are reduced by laminating the core.
Eddy
Current
Same
Measuring
44. A large amount of power wasted with the open-ended core
fault
Choke coil
eddy currents
die to leakage flux
45. The 4 types of transformer cores
Voltage - Current
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
electromagnetic mutual induction without loosing too much energy
grounded (Earthed)
46. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
Step-down
Simple Transformer
open-ended core
Electromagnetic Induction.
47. Reference to a jumper or conductor - to or from a piece of electrical equipment.
Vs Ns = Vp Np
primary coil - secondary coil - central magnetic core
leg(s)
directly proportional
48. 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
Measuring
saturable reactor
fault
49. The voltage induced in the coil is directly proportional to this
How a transformer works
Transformer
current related to voltage law
the number of turns in the coil
50. Both the primary and secondary coils in a transformer are arranged around this
Vs Ip = Vp Is
die to leakage flux
central magnetic core
rated KVA of a transformer
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