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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 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
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Voltage
flux leakage
2. Core losses are _____ loss and _____ - _____ loss.
Transformer
Primary
Hysteresis - Eddy - Current
shell core
3. 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.
the number of turns in the coil
Secondary
step-up (high voltage) transformers - step down transformer - autotransformer
central magnetic core
4. The terminals of the low voltage winding are marked _____.
The ratio of useful power output to its total power input.
directly proportional
X1 - X2...
Distribution transformer
5. It refers to the direction of current flow in a closed circuit.
air core
rated KVA of a transformer
polarity
the number of turns of wire in the primary and secondary coils
6. 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
rating
How a transformer works
closed-ended core
eddy currents
7. 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)
Distribution transformer
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
wigginton
Eddy
8. Two coils wound on a closed iron core form a ________.
flux
Simple Transformer
saturable reactor
wigginton
9. 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.
hysteresis losses (lagging losses)
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
grounded system
X1 - X2...
10. The voltage induced in the coil is directly proportional to this
the number of turns in the coil
variable
Choke coil
magnetic field
11. Is concentrated in the metal core
magnetic field
by using silicon iron core
polarity
primary winding
12. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
electromagnetic mutual induction without loosing too much energy
grounded system
high frequency transformer
Same
13. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
Step-up
primary coil
grounded system
high frequency transformer
14. The winding to which the load is connected is called the _____ winding.
Primary
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
air core
Secondary
15. The formula for the current related to voltage law
Vs Ip = Vp Is
closed-ended core
grounded system
rating
16. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
Kilovolt -- Amperes (kVA)
magnetic field
Eddy
hysteresis losses (lagging losses)
17. Reference to a jumper or conductor - to or from a piece of electrical equipment.
Secondary
eddy currents
variable transformers
leg(s)
18. How coils serve as the primary and secondary windings for an autotransformer
Secondary
coercivity
one coils serves as the primary and secondary windings
19. Central magnetic core made of
highly permeable material - iron or stalloy
closed-ended core (square/doughnut shaped)
grounded system
Same
20. How a variable degree of core saturation is accomplished in a saturable reactor?
highly permeable material - iron or stalloy
rated KVA of a transformer
by varying the size of the applied DC
magnetic field
21. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
electromagnetic mutual induction without loosing too much energy
flux leakage
Eh - lH = Ex - lX
22. The 3 types of transformer power loss
Measuring
saturable reactor
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
current related to voltage law
23. The simplest type of transformer core
leg(s)
wigginton
Primary
air core
24. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
How a transformer works
Copper Losses - Core Losses
open-ended core
25. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
transformers efficiency
Eh - lH = Ex - lX
silicon steel
hysteresis losses (lagging losses)
26. The total numbre of lines or force issuing from a pole. (north or south)
Ip Ns = Is Np
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
central magnetic core
magnetic flux
27. 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
central magnetic core
continuous path
flux leakage
Measuring Equipment
28. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
closed-ended core (square/doughnut shaped)
Step-up
current related to voltage law
Measuring
29. What is a rotation meter?
fuse
Vs Ip = Vp Is
central magnetic core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
30. 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.
magnetic flux
Exciting
Voltage
31. Function of the dielectric oil
Hysteresis
Insulates - cools transformer by convection - dissipates heat
fuse
primary winding
32. The 3 principle components of a transformer
primary coil - secondary coil - central magnetic core
Primary
wigginton
closed-ended core (square/doughnut shaped)
33. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
closed-ended core
wigginton
short circuit
ratio of a transformer
34. A transformer is a device that either increases or decreases alternating current and voltage using this principle
electromagnetic mutual induction without loosing too much energy
phase
Low
Insulates - cools transformer by convection - dissipates heat
35. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
primary winding
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
class 400 transformers
Low
36. A simple design has a core within each coil
How a transformer works
open-ended core
Electromagnetic Induction.
the number of turns of wire in the primary and secondary coils
37. The 4 types of transformer cores
ammeter
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
air core
rating
38. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
flux
open-ended core
fuse
current related to turns ratio law
39. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
secondary coil
Voltage
Step-up
voltage ralated to turns ratio
40. A stationary device for transferring alternating current electrical energy from one circuit to another circuit by electromagnetic means.
Transformer
grounded system
The ratio of useful power output to its total power input.
dielectric oil
41. The current related to turns ratio law
short circuit
Ip Ns = Is Np
air core
Exciting Current
42. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
flux
rated KVA of a transformer
leg(s)
short circuit
43. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Exciting Current
open-ended core
Primary
transformers efficiency
44. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
air core
Hysteresis
Measuring
Voltage
45. 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
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Electromagnet
saturable reactor
constant current transfomers
46. Determines if the transformer is a step up or step down transformer
High voltage
ratio of a transformer
Step-down
the number of turns of wire in the primary and secondary coils
47. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
variable
one coils serves as the primary and secondary windings
Kilovolt -- Amperes (kVA)
Volt-Amperes (Eh-lh=ExLx)
48. 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.
the number of turns in the coil
step-up (high voltage) transformers - step down transformer - autotransformer
Electromagnet
highly permeable material - iron or stalloy
49. 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.
current related to voltage law
Electromagnetic Induction.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
fuse
50. The winding to which voltage is supplied is called the _____ winding.
die to leakage flux
Primary
by varying the size of the applied DC
Same