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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. Anything above 600 volts is _____?
Exciting
Primary
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
High voltage
2. The winding of a transformer to which electrical energy is supplied.
magnetic field
electromagnetic mutual induction without loosing too much energy
constant current transfomers
primary winding
3. Both the primary and secondary coils in a transformer are arranged around this
an iron core and coil
central magnetic core
Secondary
ammeter
4. The 4 types of transformer cores
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
fuse
flux
primary coil - secondary coil - central magnetic core
5. 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.
Secondary
Exciting
Eh/Ex=Th/Tx
saturable reactor
6. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
rating
Step-up
ratio of a transformer
continuous path
7. The transformer winding to which the load is connected is called the _____ winding.
the number of turns of wire in the primary and secondary coils
Primary
5
Secondary
8. Copper loss is known as _____ loss.
central magnetic core
Eddy
Class 200 transformers
9. The total numbre of lines or force issuing from a pole. (north or south)
one coils serves as the primary and secondary windings
hysteresis losses (lagging losses)
magnetic flux
class 400 transformers
10. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
air core
the number of turns of wire in the primary and secondary coils
Hysteresis - Eddy - Current
11. 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
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Hysteresis
rated KVA of a transformer
How a transformer works
12. Two coils wound on a closed iron core form a ________.
Secondary
low rententivity
Current
Simple Transformer
13. The relationship between current and voltage in the coils are inverse
leakage flux
current related to voltage law
Voltage - Current
Insulates - cools transformer by convection - dissipates heat
14. A large amount of power wasted with the open-ended core
Vs Ns = Vp Np
Volt-Amperes (Eh-lh=ExLx)
the number of turns of wire in the primary and secondary coils
die to leakage flux
15. Used to increase the magnetic flux in a transformer
central magnetic core
the number of turns of wire in the primary and secondary coils
saturable reactor
the number of turns in the coil
16. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
primary winding
high frequency transformer
grounded system
17. The simplest type of transformer core
Vs Ip = Vp Is
air core
Low
Vs Ns = Vp Np
18. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
current related to voltage law
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
shell core
19. The turns ratio between the windings (primary & secondary) of a transformer unless otherwise specified.
ratio of a transformer
Exciting Current
central magnetic core
Hysteresis - Eddy - Current
20. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
Distribution transformer
Electromagnetic Induction.
rating
saturable reactor
21. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
polarity
Eh - lH = Ex - lX
central magnetic core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
22. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
shell core
X1 - X2...
Electromagnet
hysteresis losses (lagging losses)
23. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
rated KVA of a transformer
fault
Same
shell core
24. closed core with a top and bottom. It directs the magnetic field towards the primary and secondary coils and increases the field stregnth
Hysteresis
closed-ended core (square/doughnut shaped)
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Class 200 transformers
25. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
voltage ralated to turns ratio
low rententivity
secondary coil
leakage flux
26. 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.
high frequency transformer
coercivity
constant current transfomers
Voltage
27. 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.
5
step-up (high voltage) transformers - step down transformer - autotransformer
Secondary
the number of turns in the coil
28. With no load on the secondary winding - a small current flows in the primary called _____ _____.
Primary
Exciting Current
Copper Losses - Core Losses
The ratio of useful power output to its total power input.
29. The capacity of a transformer is rated in ____ _____.
class 400 transformers
polarity
Kilovolt -- Amperes (kVA)
Ip Ns = Is 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
Hysteresis
Transformer
low rententivity
eddy currents
31. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
highly permeable material - iron or stalloy
closed-ended core
the number of turns of wire in the primary and secondary coils
a magnetic field that varies quickly in direction and stregnth
32. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Volt-Amperes (Eh-lh=ExLx)
CORE: Core losses are caused by eddy currents set up by the magnetic field.
leakage flux
33. 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
a magnetic field that varies quickly in direction and stregnth
Copper Losses - Core Losses
flux
Class 200 transformers
34. The magnetic lines of force that flow from the north pole of a magnet and return to the south pole.
flux
Low
primary winding
rated KVA of a transformer
35. How coils serve as the primary and secondary windings for an autotransformer
die to leakage flux
one coils serves as the primary and secondary windings
open-ended core
variable
36. The current related to turns ratio law
Ip Ns = Is Np
phase
coercivity
Choke coil
37. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
Transformer
by varying the size of the applied DC
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
Eh/Ex=Th/Tx
38. 3 types of transformers
ratio of a transformer
flux
saturable reactor
step-up (high voltage) transformers - step down transformer - autotransformer
39. Kind of wire is the secondary coil in a transformer
Low
thin copper wire coated with insulated material (shellac or enamel)
closed-ended core
fault
40. A transformer loses less than _% in energy
Step-down
Class 200 transformers
grounded (Earthed)
5
41. If the transformer is used as a _____ transformer - the high voltage winding is the primary.
leg(s)
ammeter
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
Step-down
42. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
variable transformers
Same
grounded (Earthed)
Voltage
43. Reference to a jumper or conductor - to or from a piece of electrical equipment.
leg(s)
Exciting
polarity
Copper Losses - Core Losses
44. A single electrical circuit.
air core
phase
ammeter
eddy currents
45. A simple design has a core within each coil
a magnetic field that varies quickly in direction and stregnth
leakage flux
open-ended core
directly proportional
46. An abnormal connection of relative low resistance - whether made accidentally or intentionally - between two point of different potential in a circuit.
an iron core and coil
short circuit
grounded (Earthed)
open-ended core
47. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
saturable reactor
Step-down
class 400 transformers
Measuring
48. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Electromagnetic Induction.
Measuring Equipment
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
49. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
leg(s)
polarity
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.
50. The winding to which voltage is supplied is called the _____ winding.
the number of turns in the coil
Primary
Same
secondary coil