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. Defined as the ratio of the power output to the power input (in a closed circuit containing resistance)
fault
transformers efficiency law
Low
constant current transfomers
2. How a variable degree of core saturation is accomplished in a saturable reactor?
Vs Ip = Vp Is
Volt-Amperes (Eh-lh=ExLx)
Secondary
by varying the size of the applied DC
3. Instrument transformers reduce high voltages and currents to safe - usable values for the operation of _____ _____.
saturable reactor
current related to turns ratio law
Measuring Equipment
primary winding
4. 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 _____.
Secondary
Eh/Ex=Th/Tx = (240/120 = 400/Tx) - 240 TX = 48000 - Tx = 48000/240 = 200 turns
High voltage
5. The simplest type of transformer core
air core
the number of turns in the coil
magnetic field
an iron core and coil
6. A choke coil uses this to induce current
variable transformers
an iron core and coil
Distribution transformer
transformers efficiency law
7. The 3 types of transformer power loss
central magnetic core
transformers efficiency
copper losses (I2R); hysteresis losses (lagging losses); and eddy current losses (swirling currents)
rated KVA of a transformer
8. A transformer loses less than _% in energy
Secondary
Choke coil
phase
5
9. Is concentrated in the metal core
Step-down
air core
magnetic field
Kilovolt -- Amperes (kVA)
10. To prevent injury to personnel when servicing any equipment connected to a current transformer - the secondary winding must be ____ - _____.
open-ended core
Short Circuited: Unless the secondary winding is short-circuited - a high open circuit voltage that can be dangerous will exist.
Low
Transformer
11. A variable transformer is a continuously adjustable _____ - has the primary winding and secondary winding electrically connected.
central magnetic core
Autotransformer
closed-ended core (square/doughnut shaped)
Class 200 transformers
12. 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
Secondary
variable transformers
polarity
13. 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
short circuit
closed-ended core
Current
open-ended core
14. The volt-amperes of the primary of a transformer is equal to the _____ - _____ output of the transformer.
Step-down
Volt-Amperes (Eh-lh=ExLx)
electromagnetic mutual induction without loosing too much energy
primary coil - secondary coil - central magnetic core
15. Modern; extremely efficient-more effective coupling between primary and secondary coils; smaller and lighter
Kilovolt -- Amperes (kVA)
rating
high frequency transformer
fuse
16. This is the most advanced and most efficient type of tansformer; it is commonly used in x-ray equipment
transformers efficiency law
shell core
Primary
Step-down
17. Central magnetic core made of
constant current transfomers
Step-down
fault
highly permeable material - iron or stalloy
18. Used to increase the magnetic flux in a transformer
highly permeable material - iron or stalloy
one coils serves as the primary and secondary windings
by using silicon iron core
central magnetic core
19. _____ currents are reduced by laminating the core.
step-up (high voltage) transformers - step down transformer - autotransformer
Eddy
Eh - lH = Ex - lX
phase
20. 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
H1 - h2...
primary winding
Secondary
21. The winding to which the load is connected is called the _____ winding.
Primary
Autotransformer
CORE: Core losses are caused by eddy currents set up by the magnetic field.
Secondary
22. The output rating of a transformer is based upon the maximum _____ the transformer is capable of carrying without exceeding a certain temperature rise.
Secondary
phase
Current
leakage flux
23. Provides the ratio between the applied primary voltage and the induced secondary voltage as result of the turns ratio
Aire core -open ended core -closed ended core (square/doughnut shaped) -shell core
Exciting Current
eddy currents
voltage ralated to turns ratio
24. Kind of wire is the secondary coil in a transformer
current related to turns ratio law
phase
Transformer
thin copper wire coated with insulated material (shellac or enamel)
25. 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)
by varying the size of the applied DC
Electromagnet
low rententivity
26. The output side it develops AC by electromagnetic mutual induction - Secondary voltage is induced in this coil
Secondary
secondary coil
rating
high frequency transformer
27. A magnetic field changing with respect to the conductor will generate a _____ in the conductor.
Secondary
central magnetic core
open-ended core
Voltage
28. The entire transformer is placed in a metal tank then immersed in ________.
directly proportional
dielectric oil
Voltage
thin copper wire coated with insulated material (shellac or enamel)
29. Copper loss is known as _____ loss.
Voltage
air core
Hysteresis - Eddy - Current
30. The voltage induced in the coil is directly proportional to this
Secondary
the number of turns in the coil
Step-down
highly permeable material - iron or stalloy
31. Insulated primary and secondary coils are in close proximity to each other - no iron core and very innefficient
constant current transfomers
air core
by varying the size of the applied DC
Eddy
32. If the transformer is used as a _____ transformer - the low voltage winding is the primary.
Step-up
eddy currents
Same
electromagnetic mutual induction without loosing too much energy
33. The current flowing through the primary winding - in response to the applied primary voltage - sets this up
Same
a magnetic field that varies quickly in direction and stregnth
rated KVA of a transformer
the number of turns of wire in the primary and secondary coils
34. has a laminated iron core (layers of metal plates)
shell core
closed-ended core
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
5
35. The transformer winding to which the load is connected is called the _____ winding.
Secondary
open-ended core
the number of turns in the coil
Electromagnet
36. 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
Eddy
X1 - X2...
Vs Ns = Vp Np
37. What is a rotation meter?
the number of turns of wire in the primary and secondary coils
Copper Losses - Core Losses
A small three-phase meter used to determine the direction of phase rotation on circuits or transformer banks.
closed-ended core
38. The current related to turns ratio law
Insulates - cools transformer by convection - dissipates heat
Vs Ns = Vp Np
Ip Ns = Is Np
The ratio of useful power output to its total power input.
39. Reference to a jumper or conductor - to or from a piece of electrical equipment.
secondary coil
die to leakage flux
leg(s)
by varying the size of the applied DC
40. This type of transformer power loss is caused by the continually changing AC current movement which constantly magnetizes/demagnetizes/re-magnetizes
dielectric oil
Voltage
class 400 transformers
hysteresis losses (lagging losses)
41. It refers to the direction of current flow in a closed circuit.
Low
polarity
grounded (Earthed)
X1 - X2...
42. A ___________ transformer is a continuously adjustable Autotransformer.
Measuring
primary coil - secondary coil - central magnetic core
variable
grounded (Earthed)
43. The turns of both windings are cut by the same flux; therefore the induced emf in each turn of both windings is the _____.
Same
silicon steel
Simple Transformer
closed-ended core
44. Refers to the transformer's ability to avoid power loss (heat)
transformers efficiency
closed-ended core (square/doughnut shaped)
polarity
rating
45. A single electrical circuit.
Ip Ns = Is Np
primary coil - secondary coil - central magnetic core
phase
central magnetic core
46. A transformer is a device that has no moving parts and that transfers energy from one circuit to another by _____.
continuous path
Measuring Equipment
magnetic flux
Electromagnetic Induction.
47. Determines if the transformer is a step up or step down transformer
5
the number of turns in the coil
current related to turns ratio law
the number of turns of wire in the primary and secondary coils
48. The output which can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature limitations.
grounded (Earthed)
flux leakage
rated KVA of a transformer
transformers efficiency
49. How coercivity is minimized
Voltage - Current
variable
dielectric oil
by using silicon iron core
50. Two coils wound on a closed iron core form a ________.
Simple Transformer
low rententivity
Eh/Ex=Th/Tx
flux