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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. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
fault
CORE: Core losses are caused by eddy currents set up by the magnetic field.
eddy currents
Eddy
2. 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.
Kilovolt -- Amperes (kVA)
coercivity
fuse
The ratio of useful power output to its total power input.
3. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
open-ended core
current related to voltage law
secondary coil
shell core
4. A simple design has a core within each coil
by using silicon iron core
open-ended core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Copper Losses - Core Losses
5. The simplest type of transformer core
Step-down
ammeter
air core
grounded system
6. With no load on the secondary winding - a small current flows in the primary called _____ _____.
a magnetic field that varies quickly in direction and stregnth
change the input voltage
Exciting Current
current related to voltage law
7. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
coercivity
Voltage
Step-down
8. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Low
Ip Ns = Is Np
9. A large amount of power wasted with the open-ended core
die to leakage flux
air core
coercivity
class 400 transformers
10. 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.
Electromagnet
phase
a magnetic field that varies quickly in direction and stregnth
transformers efficiency
11. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
thin copper wire coated with insulated material (shellac or enamel)
central magnetic core
a magnetic field that varies quickly in direction and stregnth
change the input voltage
12. The relationship between current and voltage in the coils are inverse
current related to voltage law
by varying the size of the applied DC
Primary
Autotransformer
13. The total numbre of lines or force issuing from a pole. (north or south)
Step-down
Same
ammeter
magnetic flux
14. 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.
Low
a magnetic field that varies quickly in direction and stregnth
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
grounded system
15. An instrument used to measure electrical current.
ammeter
Voltage - Current
Primary
grounded system
16. The current related to turns ratio law
Ip Ns = Is Np
Volt-Amperes (Eh-lh=ExLx)
highly permeable material - iron or stalloy
coercivity
17. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
class 400 transformers
Choke coil
closed-ended core
Transformer
18. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
magnetic flux
current related to turns ratio law
X1 - X2...
high frequency transformer
19. It refers to the direction of current flow in a closed circuit.
polarity
X1 - X2...
Step-up
variable
20. The winding of a transformer to which electrical energy is supplied.
Autotransformer
primary coil
primary winding
leg(s)
21. The terminals of the low voltage winding are marked _____.
X1 - X2...
closed-ended core
How a transformer works
an iron core and coil
22. Used to increase the magnetic flux in a transformer
Voltage
central magnetic core
silicon steel
air core
23. The winding to which voltage is supplied is called the _____ winding.
the number of turns in the coil
by varying the size of the applied DC
grounded (Earthed)
Primary
24. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Low
How a transformer works
ammeter
shell core
25. The transformer winding to which voltage is supplied is called the _____ winding.
Primary
a magnetic field that varies quickly in direction and stregnth
Transformer
closed-ended core
26. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
The ratio of useful power output to its total power input.
by varying the size of the applied DC
fuse
Voltage - Current
27. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
primary coil - secondary coil - central magnetic core
low rententivity
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
flux
28. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
high frequency transformer
current related to voltage law
grounded (Earthed)
Exciting
29. Refers to the transformer's ability to avoid power loss (heat)
silicon steel
Voltage - Current
Primary
transformers efficiency
30. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
transformers efficiency
Step-down
31. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Class 200 transformers
closed-ended core (square/doughnut shaped)
change the input voltage
primary coil
32. Kind of wire is the secondary coil in a transformer
thin copper wire coated with insulated material (shellac or enamel)
an iron core and coil
low rententivity
current related to turns ratio law
33. What is a rotation meter?
flux leakage
Insulates - cools transformer by convection - dissipates heat
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
saturable reactor
34. 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 200 transformers
5
shell core
thin copper wire coated with insulated material (shellac or enamel)
35. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
grounded (Earthed)
an iron core and coil
Eh/Ex=Th/Tx
die to leakage flux
36. 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
Hysteresis
variable
How a transformer works
one coils serves as the primary and secondary windings
37. A ___________ transformer is a continuously adjustable Autotransformer.
secondary coil
variable
ammeter
Autotransformer
38. An electromagnetic device that operates on the principle of self induction. It uses AC.
Choke coil
X1 - X2...
current related to turns ratio law
Eh/Ex=Th/Tx
39. The 3 principle components of a transformer
transformers efficiency law
primary coil - secondary coil - central magnetic core
saturable reactor
Eddy
40. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
eddy currents
X1 - X2...
directly proportional
41. A transformer is a device that either increases or decreases alternating current and voltage using this principle
primary winding
electromagnetic mutual induction without loosing too much energy
flux leakage
change the input voltage
42. Transformer losses are classified as _____ and _____.
The ratio of useful power output to its total power input.
Distribution transformer
closed-ended core
Copper Losses - Core Losses
43. Copper loss is known as _____ loss.
leakage flux
variable
fuse
44. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Vs Ip = Vp Is
a magnetic field that varies quickly in direction and stregnth
by varying the size of the applied DC
rated KVA of a transformer
45. Anything above 600 volts is _____?
Vs Ns = Vp Np
High voltage
Choke coil
Eh - lH = Ex - lX
46. The winding to which the load is connected is called the _____ winding.
Eh - lH = Ex - lX
Secondary
ammeter
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
47. 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.
Exciting
Class 200 transformers
Electromagnet
Voltage
48. A designated limit of operating characteristics based on definite conditions.
magnetic flux
primary coil - secondary coil - central magnetic core
voltage ralated to turns ratio
rating
49. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
step-up (high voltage) transformers - step down transformer - autotransformer
Voltage
fault
primary coil
50. 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.
fuse
Autotransformer
Secondary
Kilovolt -- Amperes (kVA)