SUBJECTS
|
BROWSE
|
CAREER CENTER
|
POPULAR
|
JOIN
|
LOGIN
Business Skills
|
Soft Skills
|
Basic Literacy
|
Certifications
About
|
Help
|
Privacy
|
Terms
|
Email
Search
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
saturable reactor
How a transformer works
variable transformers
2. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Volt-Amperes (Eh-lh=ExLx)
rating
closed-ended core
polarity
3. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
open-ended core
closed-ended core
Step-down
air core
4. Core losses are _____ loss and _____ - _____ loss.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
Copper Losses - Core Losses
Hysteresis - Eddy - Current
coercivity
5. What does transformer efficiency mean?
The ratio of useful power output to its total power input.
step-up (high voltage) transformers - step down transformer - autotransformer
Electromagnetic Induction.
6. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
Exciting Current
transformers efficiency law
grounded (Earthed)
Measuring Equipment
7. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
Electromagnet
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
low rententivity
hysteresis losses (lagging losses)
8. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
secondary coil
Step-up
central magnetic core
variable
9. Divergence of the magnetic field causes this
one coils serves as the primary and secondary windings
Choke coil
Copper Losses - Core Losses
leakage flux
10. 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
eddy currents
polarity
Insulates - cools transformer by convection - dissipates heat
11. A transformer rated at 500KVA and below used for voltage transformation on the distribuition system.
Exciting Current
phase
primary coil - secondary coil - central magnetic core
Distribution transformer
12. The winding of a transformer to which electrical energy is supplied.
leg(s)
primary winding
the number of turns in the coil
Vs Ns = Vp Np
13. Function of the dielectric oil
Insulates - cools transformer by convection - dissipates heat
step-up (high voltage) transformers - step down transformer - autotransformer
secondary coil
variable
14. 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
a magnetic field that varies quickly in direction and stregnth
Secondary
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
15. Both the primary and secondary coils in a transformer are arranged around this
central magnetic core
highly permeable material - iron or stalloy
variable transformers
dielectric oil
16. 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
central magnetic core
grounded system
variable transformers
17. The formula for the voltage related to turns ratio
Vs Ns = Vp Np
class 400 transformers
short circuit
H1 - h2...
18. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
Measuring Equipment
Copper Losses - Core Losses
closed-ended core
polarity
19. 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)
wigginton
Hysteresis - Eddy - Current
central magnetic core
Electromagnet
20. Hysteresis Loss can be reduced by using a core with this feature
Electromagnetic Induction.
by varying the size of the applied DC
CORE: Core losses are caused by eddy currents set up by the magnetic field.
low rententivity
21. The capacity of a transformer is rated in ____ _____.
Exciting
Voltage
Kilovolt -- Amperes (kVA)
H1 - h2...
22. 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.
a magnetic field that varies quickly in direction and stregnth
Exciting
magnetic flux
by varying the size of the applied DC
23. Two coils wound on a closed iron core form a ________.
primary coil - secondary coil - central magnetic core
Simple Transformer
flux leakage
Class 200 transformers
24. 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
How a transformer works
Secondary
Electromagnetic Induction.
H1 - h2...
25. The 3 principle components of a transformer
air core
primary coil - secondary coil - central magnetic core
grounded (Earthed)
Vs Ns = Vp Np
26. The relationship between current and voltage in the coils are inverse
fault
current related to voltage law
central magnetic core
by using silicon iron core
27. It refers to the direction of current flow in a closed circuit.
an iron core and coil
polarity
Vs Ip = Vp Is
28. Some losses occur in all transformers. These losses are classified as copper losses and _____ losses.
Choke coil
saturable reactor
Electromagnet
CORE: Core losses are caused by eddy currents set up by the magnetic field.
29. Transformers designed for 4800 volt primary operation - but the secondaries are connected 240/480 volts. Winding ratio is 10:1
Voltage
class 400 transformers
low rententivity
5
30. 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)
H1 - h2...
transformers efficiency
silicon steel
31. A transformer loses less than _% in energy
How a transformer works
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
eddy currents
5
32. _____ shows that the voltages across the windings of a transformer are directly proportional to the turns in each winding.
grounded (Earthed)
Measuring
flux leakage
Eh/Ex=Th/Tx
33. both coils in this core are heavily insulated
high frequency transformer
The ratio of useful power output to its total power input.
Eh - lH = Ex - lX
closed-ended core
34. _____ shows that the voltamperes of the primary of a transformer equal the voltamperes of the secondary of a transformer.
Electromagnet
Eh - lH = Ex - lX
the number of turns of wire in the primary and secondary coils
Ip Ns = Is Np
35. ___________ is often used in laminated cores - increases electrical resistance which decreases eddy currents
Vs Ip = Vp Is
closed-ended core (square/doughnut shaped)
silicon steel
Class 200 transformers
36. How coils serve as the primary and secondary windings for an autotransformer
Measuring Equipment
Insulates - cools transformer by convection - dissipates heat
How a transformer works
one coils serves as the primary and secondary windings
37. The energy is always transferred without a change in frequency - but usually with changes in _____ and _____.
Voltage - Current
the number of turns of wire in the primary and secondary coils
die to leakage flux
variable
38. 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.
Exciting
Electromagnet
die to leakage flux
primary coil
39. An instrument used to measure electrical current.
ammeter
closed-ended core (square/doughnut shaped)
silicon steel
5
40. The relationship between amperage flowing through the coils and the number of turns on individual coils is inverse
current related to turns ratio law
current related to voltage law
Kilovolt -- Amperes (kVA)
phase
41. A designated limit of operating characteristics based on definite conditions.
Voltage
the number of turns in the coil
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
rating
42. What is a rotation meter?
transformers efficiency law
Primary
magnetic field
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
43. A single electrical circuit.
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
phase
open-ended core
Ip Ns = Is Np
44. Central magnetic core made of
an iron core and coil
highly permeable material - iron or stalloy
die to leakage flux
Eddy
45. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
secondary coil
transformers efficiency
shell core
46. The entire transformer is placed in a metal tank then immersed in ________.
How a transformer works
rating
Autotransformer
dielectric oil
47. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
rating
Eh/Ex=Th/Tx
Autotransformer
Electromagnetic Induction.
48. 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
Measuring
Class 200 transformers
short circuit
open-ended core
49. Determines if the transformer is a step up or step down transformer
Insulates - cools transformer by convection - dissipates heat
air core
the number of turns of wire in the primary and secondary coils
current related to voltage law
50. Is concentrated in the metal core
magnetic field
closed-ended core
step-up (high voltage) transformers - step down transformer - autotransformer
low rententivity