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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. 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
the number of turns of wire in the primary and secondary coils
Eh/Ex=Th/Tx
X1 - X2...
2. 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.
saturable reactor
Volt-Amperes (Eh-lh=ExLx)
Secondary
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
3. Determines if the transformer is a step up or step down transformer
Exciting
eddy currents
Hysteresis - Eddy - Current
the number of turns of wire in the primary and secondary coils
4. A single electrical circuit.
phase
step-up (high voltage) transformers - step down transformer - autotransformer
closed-ended core (square/doughnut shaped)
secondary coil
5. A transformer is a device that either increases or decreases alternating current and voltage using this principle
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Electromagnet
Vs Ip = Vp Is
electromagnetic mutual induction without loosing too much energy
6. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
flux leakage
Voltage
Low
7. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
one coils serves as the primary and secondary windings
the number of turns of wire in the primary and secondary coils
Current
How a transformer works
8. The simplest type of transformer core
the number of turns in the coil
Voltage
air core
ammeter
9. What is a rotation meter?
variable
open-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
directly proportional
10. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
Ip Ns = Is Np
high frequency transformer
silicon steel
the number of turns in the coil
11. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
thin copper wire coated with insulated material (shellac or enamel)
closed-ended core
current related to voltage law
Eh/Ex=Th/Tx
12. The terminals of the high voltage winding are marked _____.
by varying the size of the applied DC
H1 - h2...
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
wigginton
13. 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.
thin copper wire coated with insulated material (shellac or enamel)
constant current transfomers
Electromagnet
Vs Ip = Vp Is
14. Transformer losses are classified as _____ and _____.
Copper Losses - Core Losses
saturable reactor
hysteresis losses (lagging losses)
die to leakage flux
15. It refers to the direction of current flow in a closed circuit.
step-up (high voltage) transformers - step down transformer - autotransformer
polarity
H1 - h2...
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
16. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Distribution transformer
current related to turns ratio law
Voltage
fuse
17. How coils serve as the primary and secondary windings for an autotransformer
one coils serves as the primary and secondary windings
fault
Voltage - Current
coercivity
18. Two coils wound on a closed iron core form a ________.
Simple Transformer
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
silicon steel
Measuring Equipment
19. The 4 types of transformer cores
primary coil - secondary coil - central magnetic core
Kilovolt -- Amperes (kVA)
central magnetic core
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
20. The shape of the core of the transformer ensures a ______________ for the magnetic flux with maximum concentration within the core and minimum leakage of the air
Secondary
highly permeable material - iron or stalloy
rated KVA of a transformer
continuous path
21. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
leakage flux
the number of turns of wire in the primary and secondary coils
Copper Losses - Core Losses
22. An instrument used to measure electrical current.
voltage ralated to turns ratio
ammeter
Vs Ns = Vp Np
Volt-Amperes (Eh-lh=ExLx)
23. Is concentrated in the metal core
high frequency transformer
magnetic field
Secondary
voltage ralated to turns ratio
24. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
silicon steel
shell core
Class 200 transformers
rated KVA of a transformer
25. How coercivity is minimized
electromagnetic mutual induction without loosing too much energy
Transformer
by using silicon iron core
Hysteresis - Eddy - Current
26. 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.
saturable reactor
grounded system
Step-up
shell core
27. _____ currents are reduced by laminating the core.
Eddy
the number of turns in the coil
short circuit
open-ended core
28. The winding to which the load is connected is called the _____ winding.
variable transformers
closed-ended core
Autotransformer
Secondary
29. The formula for the voltage related to turns ratio
saturable reactor
primary coil - secondary coil - central magnetic core
Exciting
Vs Ns = Vp Np
30. 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
Eh/Ex=Th/Tx
hysteresis losses (lagging losses)
Hysteresis
How a transformer works
31. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
Low
Secondary
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Step-down
32. A transformer loses less than _% in energy
5
die to leakage flux
Measuring
Primary
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
an iron core and coil
Copper Losses - Core Losses
Insulates - cools transformer by convection - dissipates heat
How a transformer works
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
Choke coil
class 400 transformers
Class 200 transformers
open-ended core
35. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
an iron core and coil
air core
Step-down
Eddy
36. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
transformers efficiency law
rated KVA of a transformer
rating
leg(s)
37. Function of the dielectric oil
open-ended core
Insulates - cools transformer by convection - dissipates heat
Eddy
magnetic field
38. 3 types of transformers
step-up (high voltage) transformers - step down transformer - autotransformer
directly proportional
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
wigginton
39. The entire transformer is placed in a metal tank then immersed in ________.
Measuring Equipment
constant current transfomers
dielectric oil
Ip Ns = Is Np
40. 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.
fuse
primary winding
air core
one coils serves as the primary and secondary windings
41. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
secondary coil
Volt-Amperes (Eh-lh=ExLx)
short circuit
leakage flux
42. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
Autotransformer
directly proportional
polarity
the number of turns in the coil
43. 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 _____.
variable transformers
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Secondary
saturable reactor
44. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
Electromagnet
primary winding
Kilovolt -- Amperes (kVA)
ratio of a transformer
45. 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.
flux leakage
current related to voltage law
Exciting
central magnetic core
46. How the voltage and the number of turns are related for the voltage related to turn ratio
leg(s)
X1 - X2...
directly proportional
Voltage
47. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Hysteresis - Eddy - Current
ammeter
secondary coil
48. Kind of wire is the secondary coil in a transformer
phase
thin copper wire coated with insulated material (shellac or enamel)
primary winding
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
49. The relationship between current and voltage in the coils are inverse
Hysteresis - Eddy - Current
Measuring Equipment
current related to voltage law
variable
50. The transformer winding to which voltage is supplied is called the _____ winding.
Autotransformer
Kilovolt -- Amperes (kVA)
Primary
wigginton