Transformer
What would be the secondary current of a step-down
transformer with a turns raito of 1.74:1, a primary voltage of
11kV and secondary impedance of 316 ohms?
60.6 Amps
622 Amps
34.8 Amps
20 Amps
Effective cooling of a transformer will:
increase the power rating
of the transformer
Reduces the percentage
impedance of the transformer
Minimise eddy currents
in the transformer core
help maintain the primary
voltage of the transformer
Laminated transformer cores are constructed using materials containing what?
Copper
Stainless steel
Iron
Aluminium
Which two voltages at no-load determine Voltage regulation?
The secondary voltage at no-load
and at full load
The primary voltage to
secondary voltage
the secondary voltages at
different temperatures
the secondary voltage of
two different transformers
Which 2 of the following methods are used to insulate LV (dry) transformers?
Cast resin (CRT)
Cellulose insulation with
mineral oil
Mineral oil only
Vacuum pressure impregnated
(VPI)
What is a typical rated output of a current transformer?
1A or 3A
5A or 10A
1A or 5A
3A or 10A
Which 2 of the following are possible causes of secondary voltage variations
in a transformer
Increased load
Primary voltage fluctuation
Back emf
Incorrect connections
Which 3 are typical applications of an autotransformer?
Reducing starting voltages of synchronous
and induction motors
Changing speed of a.c. fans
Increasing current for spot
welders
Dropping voltages
in d.c. circuits
Compensate for volt-drops
in long cable runs
What is a safety risk if the common section of an autotransformer is open cicuited
Primary voltage will
increase to load value
The secondary current might reach
short circuit values
Primary current may equal
secondary current
The secondary voltage could
become equal to the primary voltage
The secondary voltage of a transformer is produced by the principles of?
Mutual induction
Electrostatic induction
Self-induction
Current induction
What is the effect of the circulating currents that result if two transformers are
incorrectly paralleled
Increase the output current
supplied to the load
Overheat the
transformer windings
Double the secondary
winding voltages
Increase the power
factor of the load
Lamination style ( Circle)
Toroid
Core
Shell
Lamination style ( Sqaure)
Shell
Core
Toroir
Lamination style (Split sqaure)
Shell
Core
Toroid
What test is used to determine the variable (copper) losses of a transformer
Secondary load test
Insulation test
No-load test
Short circuit test
Which of the following tests can be used to determine fixed (iron) losses of a transformer
Insulation test
Short circuit test
No-load test
Secondary load test
What is the percentage impedance of a 4 MVA, 33kV transformer that has 2.31V primary voltage during a short circuit test
21%
7%
33%
57%
Which 2 are affected by the percentage impedance (z%) value of a transformer?
Voltage regulation
Turns ratio
Transformer output rating
Prospective short-circuit current
What test is used to determine percentage impedance of a transformer?
Full load test
Short circuit test
Open circuit test
Insulation test
Which 2 of the following are disadvantages of an auto transformer?
Only useful for moderately smaller voltage changes
Complexity of construction
No electrical isolation between the windings
Increased cost
Larger short circuit current
An isolating transformer installed in accordance to AS/NZS 3000 must have?
The primary winding separated from the secondary winding by double insulation
Both legs of the primary winding connected to the secondary winding
An earthed metal shield installed between windings and bonded to both windings
One leg of the primary winding connected to the secondary winding
Nameplate
Fitted with external cooling fans?
105A
Secondary voltage
6.1%
Primary voltage
11kV
Impedance%
Star
Primary winding connection
440V
Secondary winding
No
Secondary Current
No.
Fitted with oil pumps.
Delta
Power rating
2000KVA
Phasor diagram
Ie
Secondary voltage
Iu
Energy loss current
V2
Magnetizing current
( 0 ) with( | )in middle
Flux
V1
No load current
Io
Primary voltage
Which three of the following statements about transmission and distribution transformers are true?
Distribution transformers step up voltage from transmission lines to distribution lines
Output voltages of a transmission transformer is generally 400V three phase and 230V single phase
The voltages in transmission lines are generally higher than those in distribution lines
Distribution transformers are generally rated less than 200Mva
Transmission transformers step up voltage from generation plant to transmission lines
Transmission transformers are generally rated less than 200MVA
What is the typical output rating of a potential transformer used for monitoring high voltage?
110 Volts
220 Volts
12 Volts
120 Volts
Which 6 are common applications of a transformers?
Compensate for volt drop in long cables
Measure values higher than the range of standard meters
To step down the voltage from transmission lines to distribution lines
To step down the voltage for small appliances
Electrically connect circuits to share loads
Step up voltages to reduce power losses in transmission lines
Step up current to power large loads
Magnetically connect circuits that are physically seperated
Electrically isolate circuits in high-risk environments
Which 4 are recommended precautions for the connection and disconnection of potential (instrument) transformers
The PT should be tested and inspected to ensure compliance with specifications before use
The primary and secondary must be electrically interconnected to ensure mutual induction
The secondary side of the potential transformer must never be short-circuited
The load on the secondary should be wihtin the capacity of the transformer rating
The primary and the circuit under test must be connected in parellel
The secondary should always be open circuit unless an ammeter is connected across the terminals
Which 3 are reasons for connecting transformers in parallel
Improve the power factor of the load
Increase the load capacity
Allow maintenance to occur
Ensure continuity of supple in case of equipment failure
Which 3 are power losses in a transformer
Copper (I2R) losses in the winding
Friction in the induced voltage
Eddy current in the core
Hysteresis loss in the magnetic circuit
Load current in the secondary winding
Which 2 are considered "natural" cooling of transformers?
Convection circulation surrounding air
Circulation of air fans
Convection circulating oil through cooling tubes
Circulation of oil by pumps
Which insulation methods are the most preferred to insulation HV (wet) transformers
Mineral only
Vacuum pressure impregnated (VPI)
Cast resin (CRT)
Cellulose insulation with mineral oil
What are 3 advantages of an autotransformer
Smaller in size compared to double wound transformers of the same VA rating
More efficient for the same VA rating
Improved safety due to common section of winding
Reduced cost
Increased short-circuit performance
Stronger construction
Which 4 of the following are recommended precautions for the connection and disconnection of current (instrument) transformers
The secondary side of the current transformer must be short-circuited before the load is removed
The secondary should always be open circuit unless an ammeter is connected across the terminals
The primary and secondary must be electrically interconnected to ensure mutual induction
The polarity connection must be correct
The secondary circuit of current transformer should not be connected with relay protection device
The secondary circuit should have a protective grounding point
{"name":"Transformer", "url":"https://www.quiz-maker.com/QPREVIEW","txt":"What would be the secondary current of a step-down transformer with a turns raito of 1.74:1, a primary voltage of 11kV and secondary impedance of 316 ohms?, Effective cooling of a transformer will:, Laminated transformer cores are constructed using materials containing what?","img":"https://www.quiz-maker.com/3012/images/ogquiz.png"}
More Quizzes
How much do you know about chatGPT?
747
Socials Quiz
520
Which doTERRA® Citrus Oil Are You?
840
ICJC AWARD CATEGORIES VOTING PAGE (ACJ-OAU)
630
Which ‘Peppa Pig’ Character Is Actually You?
15846
James And The Giant Peach - Novel Quiz
1586
KUIZ HARI GURU ASiS 2020 ( LEVEL 1)
11615
Idioms and Hyperboles
630
Cuanto me conosi
1167
Is Affiliate Marketing A GOOD choice for You?
630
Info Security Chapter 2
20100
Overview of Orphans
420