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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. 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)
wigginton
flux
rated KVA of a transformer
Kilovolt -- Amperes (kVA)
2. both coils in this core are heavily insulated
low rententivity
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
closed-ended core
fault
3. The total numbre of lines or force issuing from a pole. (north or south)
H1 - h2...
rated KVA of a transformer
Hysteresis
magnetic flux
4. Divergence of the magnetic field causes this
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
leakage flux
Ip Ns = Is Np
closed-ended core
5. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
air core
by varying the size of the applied DC
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
CORE: Core losses are caused by eddy currents set up by the magnetic field.
6. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Distribution transformer
closed-ended core
electromagnetic mutual induction without loosing too much energy
7. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
magnetic field
primary coil
air core
Current
8. An electromagnetic device that operates on the principle of self induction. It uses AC.
closed-ended core
Voltage
change the input voltage
Choke coil
9. It refers to the direction of current flow in a closed circuit.
Insulates - cools transformer by convection - dissipates heat
flux
polarity
Eh - lH = Ex - lX
10. Anything above 600 volts is _____?
High voltage
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Voltage - Current
Ip Ns = Is Np
11. The transformer winding to which voltage is supplied is called the _____ winding.
eddy currents
ratio of a transformer
Primary
Vs Ns = Vp Np
12. This core is more efficient than the air core because the iron core in each coil intensifies the magnetic flux in both primary and secondary coils when they become magnetized as current flows through each set of coils
continuous path
open-ended core
How a transformer works
highly permeable material - iron or stalloy
13. Central magnetic core made of
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Volt-Amperes (Eh-lh=ExLx)
Eddy
highly permeable material - iron or stalloy
14. An instrument used to measure electrical current.
eddy currents
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Low
ammeter
15. 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.
variable
Primary
Electromagnet
Step-up
16. 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.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Current
fuse
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
17. The winding to which the load is connected is called the _____ winding.
polarity
one coils serves as the primary and secondary windings
Secondary
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
18. How a variable degree of core saturation is accomplished in a saturable reactor?
dielectric oil
by varying the size of the applied DC
die to leakage flux
Hysteresis - Eddy - Current
19. Transformer losses are classified as _____ and _____.
an iron core and coil
Copper Losses - Core Losses
Simple Transformer
20. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
open-ended core
flux
step-up (high voltage) transformers - step down transformer - autotransformer
voltage ralated to turns ratio
21. How coercivity is minimized
hysteresis losses (lagging losses)
open-ended core
Low
by using silicon iron core
22. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
Choke coil
constant current transfomers
variable
23. The 3 types of transformer power loss
grounded (Earthed)
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
X1 - X2...
highly permeable material - iron or stalloy
24. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
coercivity
rated KVA of a transformer
Voltage - Current
Eh - lH = Ex - lX
25. 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
Measuring
Volt-Amperes (Eh-lh=ExLx)
closed-ended core
Voltage - Current
26. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Eh - lH = Ex - lX
Current
silicon steel
fuse
27. The characteristic that requires energy to carry out the constant reorientation of the magnetic dipoles in the hysteresis loss
coercivity
silicon steel
Copper Losses - Core Losses
flux
28. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Hysteresis - Eddy - Current
open-ended core
Measuring Equipment
CORE: Core losses are caused by eddy currents set up by the magnetic field.
29. The 4 types of transformer cores
dielectric oil
Hysteresis
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Secondary
30. The transformer winding to which the load is connected is called the _____ winding.
Secondary
Autotransformer
Choke coil
5
31. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Secondary
closed-ended core (square/doughnut shaped)
electromagnetic mutual induction without loosing too much energy
Electromagnet
32. A choke coil uses this to induce current
X1 - X2...
an iron core and coil
Exciting Current
saturable reactor
33. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
Volt-Amperes (Eh-lh=ExLx)
Hysteresis
current related to turns ratio law
Voltage
34. Hysteresis Loss can be reduced by using a core with this feature
silicon steel
low rententivity
Low
Secondary
35. How the voltage and the number of turns are related for the voltage related to turn ratio
continuous path
thin copper wire coated with insulated material (shellac or enamel)
Distribution transformer
directly proportional
36. The simplest type of transformer core
open-ended core
silicon steel
air core
Voltage - Current
37. Determines if the transformer is a step up or step down transformer
Eddy
the number of turns of wire in the primary and secondary coils
The ratio of useful power output to its total power input.
Hysteresis
38. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Electromagnetic Induction.
flux leakage
transformers efficiency law
How a transformer works
39. A simple design has a core within each coil
open-ended core
grounded system
an iron core and coil
leg(s)
40. 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
Hysteresis
Copper Losses - Core Losses
change the input voltage
Kilovolt -- Amperes (kVA)
41. The 3 principle components of a transformer
current related to turns ratio law
Voltage - Current
primary coil - secondary coil - central magnetic core
rated KVA of a transformer
42. Refers to the transformer's ability to avoid power loss (heat)
primary coil - secondary coil - central magnetic core
continuous path
CORE: Core losses are caused by eddy currents set up by the magnetic field.
transformers efficiency
43. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
continuous path
Exciting Current
Transformer
central magnetic core
44. Used to increase the magnetic flux in a transformer
central magnetic core
transformers efficiency law
Hysteresis
Distribution transformer
45. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
High voltage
Kilovolt -- Amperes (kVA)
Step-down
Electromagnet
46. A designated limit of operating characteristics based on definite conditions.
by varying the size of the applied DC
class 400 transformers
rating
wigginton
47. Waste of power known as transformer loss - often produced by closed-ended core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
short circuit
eddy currents
continuous path
48. 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.
grounded system
Exciting
continuous path
change the input voltage
49. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
Voltage - Current
fuse
rated KVA of a transformer
variable
50. A transformer which when supplied from a constant potential source automatically maintans a constant current in its secondary circuit under varying conditions of load impedance. Used on series street light circuits.
constant current transfomers
saturable reactor
change the input voltage
hysteresis losses (lagging losses)