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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 relationship between current and voltage in the coils are inverse
fuse
current related to voltage law
H1 - h2...
current related to turns ratio law
2. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
shell core
Eh/Ex=Th/Tx
Eh - lH = Ex - lX
silicon steel
3. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
the number of turns in the coil
closed-ended core
hysteresis losses (lagging losses)
The ratio of useful power output to its total power input.
4. The simplest type of transformer core
air core
a magnetic field that varies quickly in direction and stregnth
primary coil
closed-ended core
5. A transformer loses less than _% in energy
5
Electromagnetic Induction.
Voltage
variable transformers
6. 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
primary winding
closed-ended core
silicon steel
Current
7. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
step-up (high voltage) transformers - step down transformer - autotransformer
Insulates - cools transformer by convection - dissipates heat
Voltage
high frequency transformer
8. It refers to the direction of current flow in a closed circuit.
open-ended core
highly permeable material - iron or stalloy
grounded (Earthed)
polarity
9. 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
saturable reactor
polarity
flux leakage
rated KVA of a transformer
10. A choke coil uses this to induce current
an iron core and coil
Secondary
Measuring Equipment
Vs Ip = Vp Is
11. The formula for the voltage related to turns ratio
coercivity
Secondary
X1 - X2...
Vs Ns = Vp Np
12. Autotransformers are not safe when they supply a _____ voltage from a high voltage source.
continuous path
closed-ended core (square/doughnut shaped)
Low
short circuit
13. The terminals of the high voltage winding are marked _____.
H1 - h2...
Voltage
Eddy
Step-down
14. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
the number of turns of wire in the primary and secondary coils
class 400 transformers
coercivity
Distribution transformer
15. How a variable degree of core saturation is accomplished in a saturable reactor?
rating
by varying the size of the applied DC
Distribution transformer
leg(s)
16. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
Copper Losses - Core Losses
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
air core
Distribution transformer
17. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Step-down
Exciting
18. The formula for the current related to voltage law
Exciting
Insulates - cools transformer by convection - dissipates heat
the number of turns in the coil
Vs Ip = Vp Is
19. Is concentrated in the metal core
class 400 transformers
magnetic field
the number of turns in the coil
Step-down
20. How coils serve as the primary and secondary windings for an autotransformer
fuse
Exciting
shell core
one coils serves as the primary and secondary windings
21. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
low rententivity
Secondary
H1 - h2...
a magnetic field that varies quickly in direction and stregnth
22. 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
open-ended core
coercivity
low rententivity
Transformer
23. _____ currents are reduced by laminating the core.
Eddy
rated KVA of a transformer
variable transformers
Hysteresis
24. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
Eh - lH = Ex - lX
silicon steel
secondary coil
25. 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.
voltage ralated to turns ratio
rating
grounded system
Ip Ns = Is Np
26. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
a magnetic field that varies quickly in direction and stregnth
constant current transfomers
one coils serves as the primary and secondary windings
27. 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
magnetic flux
change the input voltage
How a transformer works
28. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
short circuit
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Step-down
grounded (Earthed)
29. 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
thin copper wire coated with insulated material (shellac or enamel)
Hysteresis
magnetic field
continuous path
30. 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.
air core
fuse
Insulates - cools transformer by convection - dissipates heat
Electromagnet
31. The 3 types of transformer power loss
Voltage - Current
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Primary
X1 - X2...
32. The input side that attaches to the AC supply it recieves the electrical energy or incoming voltage
primary coil
5
Measuring
Eh - lH = Ex - lX
33. A simple design has a core within each coil
X1 - X2...
Electromagnet
voltage ralated to turns ratio
open-ended core
34. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Current
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
5
transformers efficiency
35. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
ammeter
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Autotransformer
The ratio of useful power output to its total power input.
36. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ equipment.
Measuring
shell core
grounded (Earthed)
Current
37. To minimize ________ in transformer construction - the primary and secondary windings are placed on the same leg(s) of the core.
Distribution transformer
Kilovolt -- Amperes (kVA)
coercivity
flux leakage
38. The transformer winding to which the load is connected is called the _____ winding.
Secondary
flux
fault
39. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
flux
central magnetic core
rating
Eh - lH = Ex - lX
40. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
ammeter
flux
by varying the size of the applied DC
rating
41. The winding of a transformer to which electrical energy is supplied.
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
CORE: Core losses are caused by eddy currents set up by the magnetic field.
primary winding
Measuring Equipment
42. How coercivity is minimized
Volt-Amperes (Eh-lh=ExLx)
primary coil - secondary coil - central magnetic core
the number of turns in the coil
by using silicon iron core
43. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Volt-Amperes (Eh-lh=ExLx)
Exciting Current
an iron core and coil
central magnetic core
44. 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
grounded system
directly proportional
magnetic field
Class 200 transformers
45. An instrument used to measure electrical current.
constant current transfomers
Primary
variable transformers
ammeter
46. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
The ratio of useful power output to its total power input.
transformers efficiency
closed-ended core
47. The transformer winding to which voltage is supplied is called the _____ winding.
Secondary
closed-ended core
by using silicon iron core
Primary
48. Divergence of the magnetic field causes this
closed-ended core
leakage flux
Choke coil
short circuit
49. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Primary
class 400 transformers
fuse
Exciting Current
50. The total numbre of lines or force issuing from a pole. (north or south)
magnetic flux
polarity
magnetic field
Electromagnet