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Internet site: MENU-DRIVEN GRAPHICAL USER INTERFACE (GUI) PROGRAMS-Performance from Transformer equivalent circuit |
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MENU-DRIVEN GRAPHICAL USER INTERFACE (GUI) PROGRAMS- by Prof. H. Sadat. -The transformer program obtains the transformer equivalent circuit from open-circuit and short-circuit tests. It also finds the transformer performance characteristics using the transformer parameters. In the induction motor program the parameters of the equivalent circuit can be entered on the circuit diagram. The program draws the Thevenin's equivalent circuit. Performance characteristics are then obtained for the specified slip and the torque slip curve is plotted on the screen. The analysis can be repeated for different slips. A GUI program deals with the design of a first-order controller in the forward path of a closed-loop control system. This GUI program designs the following controllers: Proportional, phase-lag, phase-lead, PD,PI, and PID controllers. To run the controller design program at the MATLABprompt type>> rldesigngui
TRANSFORMERS -OBJECTIVE TYPE QUESTIONS
Ans: (b)
2. The use of higher flux density in transformer design
a) reduces the transformer weight per kVA
b) increases the weight/kVA
c) increases the weight/kW
Ans. a
3. The conservator is used in a transformer because
a) it supplies oil to the transformer whenever needed
b) protects the transformer from damage when oil expands due to rise in temperature
c) it provides fresh air and cools down the oil.
Ans. b
4. Which of the following has the highest efficiency?
a) dc shunt motor
b) transformer
c) induction motor
d) synchronous motor
Ans. b
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S. No. |
Type test |
Purpose |
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1 |
Measurement of winding resistance |
To know resistance of winding utilized |
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2 |
Measurement of voltage ratio and check of voltage vector relationship |
To know correct voltage ratio at each tap and to check vector symbol (To ascertain phase displacement) |
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3 |
Measurement of impedance voltage/ short-circuit impedance (principal tapping) and load loss |
To know copper (load) loss and impedance voltage |
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4 |
Measurement of no-load loss and current |
To know core loss & excitation current |
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5 |
Measurement of insulation resistance |
To check insulation strength |
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6 |
Dielectric tests (Lightning impulse on line terminals |
To verify impulse voltage withstand capacity of insulation (Line terminal to earth & other winding) |
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7 |
Temperature rise test |
To check temperature rise of transformer under loading conditions |
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8 |
Tests on on-load tap changer (where appropriate) |
To ensure proper operation of OLTC |
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S. No. |
Special test |
Purpose |
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1 |
Dielectric test (Modified impulse test on Neutral |
To verify impulse voltage withstand capacity of insulation (Neutral terminal to earth & other winding) |
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2 |
Measurement of zero sequence impedance of 3-phase transformers |
To check zero sequence impedance of 3-phase transformers |
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3 |
Short circuit test |
To ensure mechanical strength under short circuit condition |
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4 |
Measurement of acoustic noise level |
To measure sound level produced by transformer during rated excitation under no-load condition |
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5 |
Measurement of harmonics of the no-load current |
To measure harmonics of the no-load current |
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6 |
Measurement of power taken by fans & oil pumps |
To know power consumption of fans & oil pumps |
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S. No. |
Routine test |
Purpose |
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Type Tests 1,2,3,4,5,6, and 9 will also be the Routine Tests. In addition, the following Dielectric tests will be performed as a Routine test |
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Dielectric Tests
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SAMPLE CRITERIA: Each power transformer to be tested
INSULATING OILS [IS: 335-1983 OR IEC: 296-1982]
There are no specific lit
of type/routine /acceptance tests to be performed on manufactured insulating
oil. However, the manufacturer shall verify the following characteristics by
carrying out relevant tests on the insulating oil.
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S. No. |
Property |
As per IS: 335 (Un-inhibited) |
As per IEC: 296 |
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Un-inhibited |
Inhibited -IA |
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1 |
Appearance |
Clear & transparent
and free from suspended matter or sediments |
Clear & transparent
and free from suspended matter or sediments |
Clear & transparent
and free from suspended matter or sediments |
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2 |
Density g/cm3 |
0.89 at 270C |
< 0.895 at 200
C |
< 0.895 at 200
C |
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3 |
Kinematic viscosity at 270
Max. |
27 cSt at 270C |
16.5 cSt at 40 0C |
16.5 cSt at 40 0C |
|
4 |
Interfacial tension Min. |
0.04 N/m at 270C |
0.04 N/m at 250C |
0.04 N/m at 250C |
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5 |
Flash point Pansky-Marten (closed)
Min |
1400C |
1400C |
1400C |
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6 |
Pour point Max. |
-90 C |
-300 C |
-300 C |
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7 |
Neutralization value ·
Total acidity Max. ·
Inorganic
acidity/alkalinity |
0.03mg KOH/g Nil |
0.03mg KOH/g Nil |
0.03mg KOH/g Nil |
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8 |
Corrosive sulpher |
Non-corrosive |
Non-corrosive |
Non-corrosive |
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9 |
Electric Strength
(Breakdown voltage) Min. ·
New unfiltered oil ·
After filtration |
30 kV (RMS) 50 kV (RMS) |
30 kV (RMS) 50 kV (RMS) |
30 kV (RMS) 50 kV (RMS) |
|
10 |
Dielectric dissipation
factor( tand) at 900 Max. |
0.005 |
0.005 |
0.005 |
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11 |
Specific resistivity ·
At 900 Min. ·
At 27 0 Min. |
30x 1018
ohm-cm 500x 1018
ohm-cm |
- - |
- - |
|
12 |
Oxidation stability ·
Neutralization
value after oxidation Max. ·
Total sludge after
oxidation Max. |
0.40 mg KOH/g 0.10% by weight |
0.40 mg KOH/g 0.10% by weight |
No limit |
SAMPLING CRITERIA
As per IS:6855-1973 OR
relevant specification of equipment
where oil is required.