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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 terminals of the high voltage winding are marked _____.
Autotransformer
Primary
X1 - X2...
H1 - h2...
2. A transformer loses less than _% in energy
5
saturable reactor
Electromagnetic Induction.
ammeter
3. Kind of wire is the secondary coil in a transformer
Eh/Ex=Th/Tx
thin copper wire coated with insulated material (shellac or enamel)
current related to voltage law
Same
4. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
secondary coil
High voltage
Same
current related to turns ratio law
5. The current related to turns ratio law
central magnetic core
Ip Ns = Is Np
Hysteresis - Eddy - Current
6. The 4 types of transformer cores
transformers efficiency
wigginton
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Volt-Amperes (Eh-lh=ExLx)
7. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
closed-ended core (square/doughnut shaped)
Measuring Equipment
open-ended core
Choke coil
8. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Eh/Ex=Th/Tx
closed-ended core
Measuring Equipment
closed-ended core
9. Two coils wound on a closed iron core form a ________.
a magnetic field that varies quickly in direction and stregnth
Simple Transformer
Autotransformer
polarity
10. Refers to the transformer's ability to avoid power loss (heat)
Electromagnet
air core
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
transformers efficiency
11. How the voltage and the number of turns are related for the voltage related to turn ratio
directly proportional
Measuring
Low
low rententivity
12. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
Simple Transformer
primary coil
shell core
voltage ralated to turns ratio
13. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Step-down
phase
closed-ended core (square/doughnut shaped)
ammeter
14. The winding to which the load is connected is called the _____ winding.
Eh/Ex=Th/Tx
flux leakage
Step-down
Secondary
15. 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.
Volt-Amperes (Eh-lh=ExLx)
primary winding
fuse
Measuring
16. The entire transformer is placed in a metal tank then immersed in ________.
voltage ralated to turns ratio
dielectric oil
Measuring Equipment
Eddy
17. The terminals of the low voltage winding are marked _____.
Exciting Current
short circuit
Secondary
X1 - X2...
18. 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)
magnetic field
wigginton
leg(s)
open-ended core
19. The 3 principle components of a transformer
Hysteresis - Eddy - Current
The ratio of useful power output to its total power input.
ratio of a transformer
primary coil - secondary coil - central magnetic core
20. Core losses are _____ loss and _____ - _____ loss.
Hysteresis - Eddy - Current
Eh - lH = Ex - lX
How a transformer works
flux
21. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
electromagnetic mutual induction without loosing too much energy
primary coil - secondary coil - central magnetic core
Eh - lH = Ex - lX
22. The formula for the voltage related to turns ratio
coercivity
leakage flux
5
Vs Ns = Vp Np
23. The simplest type of transformer core
air core
the number of turns of wire in the primary and secondary coils
one coils serves as the primary and secondary windings
5
24. 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
CORE: Core losses are caused by eddy currents set up by the magnetic field.
primary winding
leg(s)
open-ended core
25. Divergence of the magnetic field causes this
leakage flux
Primary
by using silicon iron core
26. Reference to a jumper or conductor - to or from a piece of electrical equipment.
grounded (Earthed)
open-ended core
ammeter
leg(s)
27. How a variable degree of core saturation is accomplished in a saturable reactor?
Low
How a transformer works
by varying the size of the applied DC
constant current transfomers
28. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Step-down
Electromagnetic Induction.
Vs Ns = Vp Np
High voltage
29. 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.
transformers efficiency
magnetic field
grounded system
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
30. A ___________ transformer is a continuously adjustable Autotransformer.
coercivity
Volt-Amperes (Eh-lh=ExLx)
The ratio of useful power output to its total power input.
variable
31. Waste of power known as transformer loss - often produced by closed-ended core
Voltage
eddy currents
coercivity
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
32. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Kilovolt -- Amperes (kVA)
voltage ralated to turns ratio
Low
Measuring
33. For a step up and step down transformer if the turns ratio is constant this is the only way to change the output voltage
fault
phase
change the input voltage
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
34. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
constant current transfomers
the number of turns in the coil
magnetic flux
Volt-Amperes (Eh-lh=ExLx)
35. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
Exciting
Hysteresis
Low
36. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Volt-Amperes (Eh-lh=ExLx)
closed-ended core
Insulates - cools transformer by convection - dissipates heat
air core
37. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
short circuit
silicon steel
fault
5
38. An electromagnetic device that operates on the principle of self induction. It uses AC.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Choke coil
Current
primary coil - secondary coil - central magnetic core
39. 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
variable transformers
Measuring
Hysteresis
thin copper wire coated with insulated material (shellac or enamel)
40. The winding of a transformer to which electrical energy is supplied.
Kilovolt -- Amperes (kVA)
Current
Primary
primary winding
41. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Voltage
flux leakage
High voltage
rating
42. A transformer is a device that either increases or decreases alternating current and voltage using this principle
silicon steel
Eh - lH = Ex - lX
electromagnetic mutual induction without loosing too much energy
class 400 transformers
43. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Volt-Amperes (Eh-lh=ExLx)
ratio of a transformer
Exciting Current
variable transformers
44. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
eddy currents
phase
transformers efficiency law
Volt-Amperes (Eh-lh=ExLx)
45. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
Hysteresis
a magnetic field that varies quickly in direction and stregnth
Ip Ns = Is Np
Eh/Ex=Th/Tx
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.
Ip Ns = Is Np
Exciting
class 400 transformers
Secondary
47. 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
secondary coil
closed-ended core
Vs Ip = Vp Is
variable transformers
48. Copper loss is known as _____ loss.
closed-ended core
Primary
Eh/Ex=Th/Tx
49. Both the primary and secondary coils in a transformer are arranged around this
a magnetic field that varies quickly in direction and stregnth
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Exciting
central magnetic core
50. Function of the dielectric oil
continuous path
current related to turns ratio law
change the input voltage
Insulates - cools transformer by convection - dissipates heat