BRAINWAVE - Knowledge Centre for Electrical Engineering

2013-04-15T14:56:00.002+05:30

APED Manuals

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Transformers: Basics, Maintenance and Diagnostics

2013-04-09T17:52:00.001+05:30

Transformers: Basics, Maintenance and Diagnostics

CONTENTS

1. Introduction......................................................................... 1

2. Introduction to Transformers .............................................. 1

2.1 Principle of Operation................................................ 3

2.2 Transformer Action.................................................... 4

2.3 Transformer Voltage and Current.............................. 8

2.4 The Magnetic Circuit ................................................. 10

2.5 Core Losses................................................................ 13

2.6 Copper Losses............................................................ 13

2.7 Transformer Rating.................................................... 14

2.8 Percent Impedance ..................................................... 14

2.9 Internal Forces ........................................................... 16

2.10 Autotransformers ....................................................... 17

2.11 Instrument Transformers............................................ 18

2.12 Potential Transformers............................................... 19

2.13 Current Transformers................................................. 20

2.14 Transformer Taps....................................................... 22

2.15 Transformer Bushings................................................ 23

2.16 Transformer Polarity.................................................. 24

2.17 Single-Phase Transformer Connections for

Typical Service to Buildings................................... 25

2.18 Parallel Operation of Single-Phase Transformers

for Additional Capacity........................................... 26

2.19 Three-Phase Transformer Connections...................... 28

2.20 Wye and Delta Connections....................................... 28

2.21 Three-Phase Connections Using

Single-Phase Transformers ..................................... 29

2.22 Paralleling Three-Phase Transformers....................... 32

2.23 Methods of Cooling ................................................... 35

2.24 Oil-Filled – Self-Cooled Transformers...................... 36

2.25 Forced-Air and Forced-Oil-Cooled

Transformers ......................................................... 36

2.26 Transformer Oil ......................................................... 37

Contents (continued)

2. Introduction to Transformers (continued)

2.27 Conservator System ................................................... 38

2.28 Oil-Filled, Inert-Gas System...................................... 39

2.29 Indoor Transformers .................................................. 41

3. Routine Maintenance ......................................................... 42

3.1 Introduction to Reclamation Transformers................ 42

3.2 Transformer Cooling Methods Introduction.............. 44

3.3 Dry-Type Transformers ............................................. 45

3.3.1 Potential Problems and Remedial

Actions for Dry-Type Transformer

Cooling Systems ......................................... 47

3.4 Liquid-Immersed Transformers ................................. 48

3.4.1. Liquid-Immersed, Air-Cooled ....................... 48

3.4.2 Liquid-Immersed, Air-Cooled/Forced

Liquid-Cooled ............................................. 50

3.4.3 Liquid-Immersed, Water-Cooled................... 51

3.4.4 Liquid-Immersed, Forced Liquid-Cooled...... 52

3.4.5 Potential Problems and Remedial Actions

for Liquid-Filled Transformer

Cooling Systems ......................................... 52

3.4.5.1 Leaks ............................................... 52

3.4.5.2 Cleaning Radiators.......................... 53

3.4.5.3 Plugged Radiators ........................... 53

3.4.5.4 Sludge Formation............................ 53

3.4.5.5 Valve Problems............................... 54

3.4.5.6 Mineral Deposits............................. 54

3.4.5.7 Low Oil Level ................................. 54

3.4.6 Cooling System Inspections........................... 54

4. Oil-Filled Transformer Inspections..................................... 56

4.1 Transformer Tank ...................................................... 57

4.2 Top Oil Thermometers............................................... 57

Contents (continued)

4. Oil-Filled Transformer Inspections (continued)

4.3 Winding Temperature Thermometers........................ 58

4.3.1 Temperature Indicators Online ...................... 60

4.3.2 Temperature Indicators Offline...................... 60

4.4 Oil Level Indicators ................................................... 61

4.5 Pressure Relief Devices ............................................. 62

4.5.1 Newer Pressure Relief Devices...................... 63

4.5.2 Older Pressure Relief Devices ....................... 66

4.6 Sudden Pressure Relay............................................... 67

4.6.1 Testing Suggestion......................................... 69

4.7 Buchholz Relay (Found Only on Transformers

with Conservators) .................................................. 69

4.8 Transformer Bushings: Testing and

Maintenance of High-Voltage Bushings................. 72

4.9 Oil Preservation Sealing Systems .............................. 76

4.9.1 Sealing Systems Types .................................. 77

4.9.1.1 Free Breathing................................. 77

4.9.1.2 Sealed or Pressurized Breathing ..... 77

4.9.1.3 Pressurized Inert Gas Sealed

System.......................................... 78

4.9.2 Gas Pressure Control Components ................ 81

4.9.2.1 High-Pressure Gauge ...................... 81

4.9.2.2 High-Pressure Regulator................. 81

4.9.2.3 Low-Pressure Regulator.................. 82

4.9.2.4 Bypass Valve Assembly ................. 82

4.9.2.5 Oil Sump......................................... 82

4.9.2.6 Shutoff Valves ................................ 83

4.9.2.7 Sampling and Purge Valve.............. 83

4.9.2.8 Free Breathing Conservator ............ 83

4.9.2.9 Conservator with Bladder or

Diaphragm Design ....................... 84

4.10 Auxiliary Tank Sealing System ................................. 90

Contents (continued)

5. Gaskets................................................................................ 91

5.1 Sealing (Mating) Surface Preparation........................ 92

5.2 Cork-Nitrile................................................................ 93

5.3 Cork-Neoprene........................................................... 94

5.4 Nitrile “NBR” ............................................................ 95

5.4.1 Viton .............................................................. 95

5.5 Gasket Sizing for Standard Groove Depths ............... 97

5.6 Rectangular Nitrile Gaskets ....................................... 99

5.7 Bolting Sequences to Avoid Sealing Problems ......... 103

6. Transformer Oils................................................................. 105

6.1 Transformer Oil Functions......................................... 105

6.1.1 Dissolved Gas Analysis ................................. 105

6.1.2 Key Gas Method ............................................ 109

6.1.2.1 Four-Condition DGA Guide

(IEEE C57-104) ........................... 109

6.1.3 Sampling Intervals and Recommended

Actions ........................................................ 113

6.1.4 Atmospheric Gases ........................................ 117

6.1.5 Dissolved Gas Software................................. 117

6.1.6 Temperature ................................................... 122

6.1.7 Gas Mixing..................................................... 122

6.1.8 Gas Solubility................................................. 123

6.1.9 Diagnosing a Transformer Problem

Using Dissolved Gas Analysis and

the Duval Triangle ...................................... 125

6.1.9.1 Origin of the Duval Triangle........... 125

6.1.9.2 How to Use the Duval Triangle ...... 125

6.1.9.3 Expertise Needed ............................ 131

6.1.9.4 Rogers Ratio Method of DGA........ 131

6.1.10 Carbon Dioxide/Carbon Monoxide Ratio...... 138

6.1.11 Moisture Problems......................................... 141

Contents (continued)

6. Transformer Oils (continued)

6.1 Transformer Oil Functions (continued)

6.1.11 Moisture Problems (continued)

6.1.11.1 Dissolved Moisture in

Transformer Oil ........................... 145

6.1.11.2 Moisture in Transformer

Insulation...................................... 146

7. Transformer Oil Tests that Should Be Completed

Annually with the Dissolved Gas Analysis ............... 150

7.1 Dielectric Strength ..................................................... 150

7.1.1 Interfacial Tension ......................................... 151

7.2 Acid Number.............................................................. 152

7.3 Test for Oxygen Inhibitor .......................................... 153

7.4 Power Factor .............................................................. 154

7.5 Oxygen....................................................................... 155

7.6 Furans......................................................................... 155

7.7 Oil Treatment Specification....................................... 159

7.7.1 Taking Oil Samples for DGA........................ 160

7.7.1.1 DGA Oil Sample Container ............ 162

7.7.1.2 Taking the Sample .......................... 163

8. Silicone Oil-Filled Transformers ........................................ 167

8.1 Background ................................................................ 167

8.2 Carbon Monoxide in Silicone Transformers.............. 170

8.3 Comparison of Silicone Oil and Mineral

Oil Transformers..................................................... 170

8.4 Gas Limits.................................................................. 171

8.5 Physical Test Limits................................................... 175

9. Transformer Testing ......................................................... 176

9.1 DC Winding Resistance Measurement ...................... 176

9.2 Core Insulation Resistance and Inadvertent

Core Ground Test (Megger®) ................................ 178

Contents (continued)

9. Transformer Testing (continued)

9.3 Doble Tests on Insulation .......................................... 180

9.3.1 Insulation Power Factor Test ......................... 180

9.3.2 Capacitance Test ............................................ 180

9.3.3 Excitation Current Test .................................. 181

9.3.4 Bushing Tests................................................. 182

9.3.5 Percent Impedance/Leakage

Reactance Test ............................................ 182

9.3.6 Sweep Frequency Response

Analysis Tests ............................................. 183

9.4 Visual Inspection ....................................................... 186

9.4.1 Background .................................................... 186

9.4.2 Oil Leaks........................................................ 187

9.4.3 Oil Pumps....................................................... 187

9.4.4 Fans and Radiators......................................... 188

9.4.5 Age................................................................. 188

9.4.6 Infrared Temperature Analysis ...................... 189

9.4.7 IR for Transformer Tanks .............................. 189

9.4.8 IR for Surge Arresters.................................... 190

9.4.9 IR for Bushings .............................................. 190

9.4.10 IR for Radiators and Cooling Systems........... 191

9.4.11 Corona Scope Scan ........................................ 193

9.5 Ultrasonic and Sonic Fault Detection ........................ 193

9.5.1 Background .................................................... 193

9.5.2 Process ........................................................... 194

9.6 Vibration Analysis ..................................................... 194

9.6.1 Background .................................................... 194

9.6.2 Process ........................................................... 195

9.7 Turns Ratio Test ......................................................... 195

9.7.1 Background .................................................... 195

9.7.2 Process ........................................................... 195

9.8 Estimate of Paper Deterioration (Online) .................. 196

9.8.1 CO2 and CO Accumulated Total

Gas Values .................................................. 196

9. Transformer Testing (continued)

9.8 Estimate of Paper Deterioration (Online) (continued)

9.8.2 CO2/CO Ratio ................................................ 196

9.9 Estimate of Paper Deterioration (Offline

During Internal Inspection)..................................... 197

9.9.1 Degree of Polymerization (DP) ..................... 197

9.9.1.1 Background ..................................... 197

9.9.1.2 Process ............................................ 198

9.9.2 Internal Inspection ......................................... 198

9.9.2.1 Background ..................................... 198

9.9.2.2 Transformer Borescope................... 200

9.10 Transformer Operating History.................................. 200

9.11 Transformer Diagnostics/Condition

Assessment Summary ............................................. 201

Appendix: Hydroplant Risk Assessment –

Transformer Condition Assessment.................................... 205

References ................................................................................. 231

Acronyms and Abbreviations ................................................... 235

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The Art and Science of Protective Relaying

2013-04-09T17:46:00.000+05:30

The Art and Science of Protective Relaying

- C Russel Mason

CONTENTS

1. The philosophy of protective relaying

What is protective relaying?

The function of protective relaying

Fundamental principles of protective relaying

- primary relaying

- back-up relaying

- protection against other abnormal conditions

Functional characteristics of protective relaying

- sensitivity, selectivity, and speed

- reliability

How do protective relays operate?

2. Fundamental relay-operating principles and characteristics

General considerations

- operating principles

- definitions of operation

- operation indicators

- seal-in and holding coils, and seal-in relays

- adjustment of pickup or reset

- time delay and its definitions

Single-quantity relays of the electromagnetic-attraction type

- operating principle

- ratio of reset to pickup

- tendency toward vibration

Directional relays of the electromagnetic attraction type

- operating principle

- efficiency

- ratio of continuous thermal capacity to pickup

Induction-type relays–general operating principles

- the production of actuating force

- types of actuating structure

Single-quantity induction relays

- torque control

- effect of frequency

- effect of d-c offset

- ratio of reset to pickup

Directional induction relays

- torque relations in terms of actuating quantities

- the significance of the term “directional”

- the polarizing quantity of a directional relay

- the operating characteristic of a directional relay

- the “constant-product” characteristic

- effect of d-c offset and other transients

The universal relay-torque equation

3. Current, voltage, directional, current (or voltage)-balance, and differential relays

General protective-relay features

Overcurrent, undercurrent, overvoltage and undervoltage relays

D-C directional relays

A-C directional relays

Current (or voltage) – balance relays

Differential relays

4. Distance relays

The impedance-type distance relay

The modified impedance-type distance relay

The reactance-type distance relay

The mho-type distance relay

General considerations applicable to all distance relays

5. Wire-pilot relays

Why current-differential relaying is not used

Purpose of a pilot

Tripping and blocking pilots

D-C wire-pilot relaying

Additional fundamental considerations

A-C wire-pilot relaying

6. Carrier-current-pilot and microwave-pilot relays

The carrier-current pilot

The microwave pilot

Phase-comparison relaying

Directional-comparison relaying

Looking ahead

7. Current transformers

Types of current transformers

Calculation of C.T accuracy

Polarity and connections

8. Voltage transformers

Accuracy of potential transformers

Capacitance potential devices

The use of low-tension voltage

Polarity and connections

9. Methods for analyzing generalizing, and visualizing relay response

The R-X diagram

Short circuits

Power swings and loss of synchronism

Response of polyphase directional relays to positive- and negative-phase-sequence volt-amperes

Response of single-phase directional relays to short circuits

Phase-sequence filters

10 A.C generator and motor protection

Generator protection

11. Transformer protection

Power transformers and power auto transformers

Step voltage regulators

Grounding transformers

Electric arc-furnace transformers

Power-rectifier transformers

12 bus protection

Protection by back-up relays

The fault bus1

Directional-comparison relaying

Current-differential relaying with over current relays

Partial-differential relaying

Current-differential relaying with percentage-differential relays

Voltage-differential relaying with “linear couplers”

Current-differential relaying with over voltage relays

Combined power-transformer and bus protection

The value of bus sectionalizing

Back-up protection for bus faults

Grounding the secondaries of differentially connected CT’s

Once-a-shift testing of differential-relaying equipment

13. Line protection with over current relays

How to set inverse-time-over current relays for coordination

Arc and ground resistance

Effect of loop circuits on over current relay adjustments

Effect of system on choice of inverseness of relay characteristic

The use of instantaneous over current relays

An incidental advantage of instantaneous over current relaying

Overreach of instantaneous over current relays

The directional feature

Use of two versus three relays for phase-fault protection

Single-phase versus poly phase directional-over current relays

How to prevent single-phase directional over current-relay mis-operation during ground faults

Adjustment of ground versus phase relays

Effect of limiting the magnitude of ground-fault current

Transient C.T errors

Detection of ground faults in ungrounded systems

Effect of ground-fault neutralizers on line relaying

The effect of open phases not accompanied by a short circuit

The effect of open phases accompanied by short circuits

Polarizing the directional units of ground relays

Negative-phase-sequence directional units for ground-fault relaying

Current-balance and power-balance relaying

Automatic reclosing

Restoration of service to distribution feeders after prolonged outages

Coordinating with fuses A-C and capacitor tripping

14. Line protection with distance relays

The choice between impedance, reactance, or mho

The adjustment of distance relays

The effect of arcs on distance-relay operation

The effect of intermediate current sources on distance-relay operation

Overreach because of offset current waves

Overreach of ground distance relays for phase faults

Use of low-tension voltage

Use of low-tension current

Effect of power-transformer magnetizing-current inrush on distance-relay operation

The connections of ground distance relays

Operation when PT fuses blow

Purposeful tripping on loss of synchronism

Blocking tripping on loss of synchronism

Automatic reclosing

Effect of presence of expulsion protective gaps

Effect of a series capacitor

Cost-reduction schemes for distance relaying

Electronic distance relays

15. Line protection with pilot relays

Wire-pilot relaying

Obtaining adequate sensitivity

The protection of multi terminal lines

Current-transformer requirements

Back-up protection

Carrier-current-pilot relaying

Phase comparison

Directional comparison

Combined phase and directional comparison

All-electronic directional-comparison equipment

High-speed reclosing

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2013-01-05T15:27:00.000+05:30

Electricity in Andhra Pradesh

AP Power Generation - 15933.09 MW

APGENCO Private Central Govt.

8924.9MW 3619.29 MW 3115.74MW

56% 22.7% 19.55%

APGENCO - 8924.86 MW 56%

Thermal Hydel Wind Solar Gas Other

5092.5MW 3829.4MW 2MW 1MW 0MW 0MW

57% 42.9%

Formed on 1^stFebruary, 1999.

3rd Largest producer of electricity in India. (1.NTPC 2.MAHAGENCO)

Total No.of Employees: 10889 (as per 2008)

APTRIPCO - 1.2 MW

Mini Hydel

1.2MW

Joint Sector - 272 MW 1.7%

A.P.G.P.C.L – Gas - 272MW

Private Sector (in MW) - 3619.29 MW 22.7%

Thermal Mini Hydel Wind Solar Gas Co-Gen/Biomass/Bagasse Mini Power Plants Other

0 105.64 256.29 25.75 2494.7 540.8 74.31 121.8

0% 2.91% 7.08% 0.71% 68.92% 14.94% 2.05% 3.36%

Central Govt. Contribution - 3115.74 MW 19.55%

APTRANSCO

Transmission Lines

400 KV - 3307.88 Circuit Kilo Meters

220 KV - 13633.99 Circuit Kilo Meters

132 KV - 15954.95 Circuit Kilo Meters

Sub Stations

400 KV - 10

220 KV - 111

132 KV - 310

Formed on 1^stFebruary, 1999.

AP-DISCOMs

Transmission Lines

33 KV - 4154.65 Kilo Meters

11 KV - 282495.21 Kilo Meters

LT - 553730.11 Kilo Meters

Sub Stations

33 KV - 4119

Formed on 1^stApril, 2000. (Formation of 4 DISCOMs 1.APCPDCL 2.APEPDCL. 3.APNPDCL 4.APSPDCL)

Electrical Engineering Objective Questions

2012-07-13T00:23:00.000+05:30

Electrical Machines Objective Questions

BRAINWAVE

GATE-2012

Electrical Machines

Max. Marks: 45(Q.1 – Q.45 1 Mark) Max. Time: 90 Min.s

1.For understanding the behaviour of a transformer, the following laws may be called for

1. Lenz’s law 2. Newton’s second law 3. Faraday’s laws of electromagnetic induction 4. Ohm’s law 5. Fleming’s right hand rule 6. Right hand grip rule

From these the correct answer is

(a) 1,3,4 (b) 2,3,4,5 (c) 1,3,4,5,6 (d) 1,3,4,6

2.In an ideal transformer, if K is some constant, then supply voltage V, in terms of its magnetizing current I_m can be expressed as

(a) jKfI_m (b) jKf/I_m (c) –jKfI_m (d) –jKf/I_m

3.A transformer has sometimes two or more ratings depending upon the use of

(a) the cooling techniques (b) the type of windings

(c) the type of core (d) the type of insulation

4.A transformer at no load excited at rated voltage. Now a cut is made in the transformer yoke thus creating a small air gap. With this, the transformer core flux

(a) will decrease and magnetizing current Im will increase

(b) will remain constant and Im will increase

(c) as well as Im both will increase

(d) as well as Im both will decrease

5.If the secondary winding of an ideal transformer shown in the circuit has 40 turns, the number of turns in the primary winding for maximum power transfer to the 2 resistor will be

(a) 20 (b) 40 (c) 80 (d) 160

6.In a single phase transformer, polarities of terminals a & b at any instant are shown in the fig. At the same instant,

(a) c is +ve, d is +ve and flux is clockwise (cw) (b) c is -ve, d is +ve and flux is counter clockwise (ccw)

(c) c is -ve, d is +ve and flux is clockwise (cw) (d) c is +ve, d is -ve and flux is counter clockwise (ccw)

7.CRGO laminations in a transformer are used to minimise

(a) eddy current loss (b) hysteresis loss (c) both eddy current and hysteresis losses (d) ohmic loss

8.If a transformer primary is energised from a square wave voltage source, then its output voltage will be

(a) zero (b) a sine wave (c) a triangular wave (d) a pulsed wave

9. The no load current in a transformer lags the applied voltage by

(a) 90⁰ (b) about 75⁰ (c) 0⁰ (d) about 110⁰

10. The leakage flux in a transformer depends upon

(a) the applied voltage (b) the frequency (c) the load current (d) the mutual flux

11. The useful flux of a transformer is 1 Wb. When it is loaded at 0.8 p.f lag, then its mutual flux

(a) may decrease to 0.8Wb (b) may increase to 1.01 Wb

(c) remains constant (d) may decrease to 0.99 Wb

12.Two transformers of the same type, using the same grade of iron and conductor materials are designed to work at the same flux and current densities; but the linear dimensions of one are two times those of the other in all respects. Then the ratio of kVA ratings of the two transformers closely equals

(a) 16 (b) 8 (c) 4 (d) 2

13.A 220/440 V, 50Hz, 5 kVA, single phase transformer operates on 220 V, 40 Hz supply with secondary open circuited. Then

(a) both eddy current & hysteresis looses decrease (b) both eddy current & hysteresis looses increase

(c) eddy current loss remains the same but hysteresis loss increase

(d) eddy current loss increases but hysteresis loss remains the same

14.The hysteresis & eddy current losses of a single phase transformer working on 200 V, 50 Hz supply are P_h & P_e respectively. The percentage decrease in these, when operated on a 160 V, 40 Hz supply are

(a) 32, 36 (b) 20, 36 (c) 25, 50 (d) 40, 80

15.The maximum efficiency for a transformer occurs at 80% of full load. Its core loss is P_c and ohmic loss is P_oh. For this transformer, the ratio Pc/Poh is

(a) 0.8 (b) 1.25 (c) 0.64 (d) 0.8944

16. Frequency of the supply voltage to a transformer at no load is increased but the supply voltage is held constant. With this

(1) eddy current loss remains constant but hysteresis loss increases

(2) eddy current loss remains constant but hysteresis loss decreases

(3) magnetizing current increases but core loss current decreases

(4) both magnetizing and core loss currents decrease

From these, the correct answer is

(a) 2,3 (b) 2,4 (c) 1,3 (d) 1,4

17.The applied voltage to a transformer primary is increased keeping V/f constant. With this, the core loss will

(a) decrease & magnetizing current Im will increase (b) increase & Im will also increase

(c) remain constant & Im will also remain constant (d) increase & Im will remain constant

18. As the load on a transformer is increased, the core losses

(a) decrease slightly (b) increase slightly

(c) remain constant (d) may increase or decrease slightly depending upon the nature of load

19. Can a 50 Hz transformer be used for 25 Hz, if the input voltage is maintained constant at the rated value corresponding to 50 Hz?

(a) Yes. Since the voltage is constant, current levels will not change

(b) No. Flux will be doubled which will drive the core to excessive saturation

(c) No. Owing to decreased reactance of transformer, input current will be doubled at load

(d) Yes. At constant voltage, insulation will not be overstressed

20. In a transformer, if primary leakage impedance is neglected then

1. magnetizing current lags the applied voltage V₁ by 900

2. Core loss current lags V₁ by 900

3. Exciting current lags V₁ by 900

4.core loss current is in phase with V₁

5.Exciting current lags V₁ by about 800

6. Magnetizing current lags V₁ by about 800

From these, the correct statements are

(a) 1,4,5 (b) 3,4,6 (c) 1,4 (d) 1,2,6

21. A transformer secondary is connected to pure resistive load. The power factor on the primary side will be

(a) Near about .95 lead (b) near about .095 lag (c) zero (d) unity

22. A 50 Hz transformer having equal hysteresis and eddy current losses at rated excitation is operated at 45 Hz at 90% of rated voltage compared to rated operating point, the core loss under this condition

(a) reduces by 10% (b) reduces by 19% (c) reduces by 14.5% (d)Remains unchanged

23. In a 1-phase transformer, the magnitude of leakage reactance is twice that of resistance of both primary and secondary. With secondary short circuited, the input p.f is

(a) 1/√2 (b) 1/√5 (c) 2/√5 (d) 1/√3

24. A multimeter, for measuring resistance is connected to one terminal of primary and the other terminal of secondary. The multimeter reading would be

(a) zero (b) infinity (c) zero or infinity (d) equal to the resistance of the windings

25. For given base voltage and base volt amperes, the per unit leakage impedance of a transformer is x. What will be the per unit leakage impedance of this transformer when the voltage and volt-ampere bases are both doubled?

(a) 0.5x (b) 2x (c) 4x (d) x

26. At 50 Hz operation, a single phase transformer has hysteresis loss of 200 W and eddy current loss of 100 W. Its core loss at 60 Hz operation will be

(a) 432 W (b) 408 W (c) 384 W (d) 360 W

27. In a transformer, eddy current loss is 100 W which is half of the total core loss. If both the thickness of laminations and frequency are increased by 10%, the new core loss would be

(a) 256.41 W (b) 231 W (c) 267.41 W (d) 242 W

28. A 220 V, 50 Hz transformer with 0.35 mm thick laminations has eddy current loss of 120 W which is two third of the total core loss at no load. If this transformer is built with 0.7 mm thick laminations and is worked from 110 V, 25 Hz, then total no load loss would be

(a) 150 W (b) 510 W (c) 200 W (d) 45 W

29. A transformer fed from an alternator at 230 V, 50 Hz has eddy current loss of 50 W and hysteresis loss of 100 W. If the speed of the prime mover driving the alternator drops to 80% of its previous speed, then eddy current and hysteresis losses in the transformer would be

(a) 40 W, 80 W (b) 32 W, 80 W (c) 32 W, 64 W (d) 40 W, 64 W

30. Two windings of a transformer are indicated by terminals AB and CD as shown in fig. When a voltage of 110 V is applied across AB with CD short circuited, a voltage of 200 V appears across AC. The turns ratio from CD to AB is

(a) 3 (b) 1 (c) 3 or 1 (d) 2 or 1

31. A 400V/200/200V, 50Hz three winding transformer is connected as shown fig. The reading of the voltmeter V will be

(a) 0V (b) 400V (c) 600V (d) 800V

32. A transformer has leakage impedance of Z_e= r_e+jx_e. Its maximum voltage regulation occurs at a power factor of

(a) r_e/x_e leading (b)r_e/z_e lagging (c) x_e/z_e leading (d)r_e/z_e leading

33.A transformer has leakage impedance of Z_e= r_e+jx_e. Zero voltage regulation for this transformer occurs at a power factor of

(a) r_e/x_e leading (b)r_e/z_e lagging (c) x_e/z_e leading (d)r_e/z_e leading

34.A 1-phase transformer has p.u. leakage impedance of 0.02+j0.04. Its regulation at power factor 0.8 lagging and 0.8 leading are respectively

(a) 4%, 0.8% (b) 4%, -0.8% (c) 2.4%,-0.8% (d) 4%,-1%

35.The voltage regulation of transformer is mainly influenced by

(a) no-load current and load power factor (b) winding resistance and load power factor

(c) leakage fluxes and load power factor (d) winding resistance and core loss

36.A 1-phase transformer has a maximum efficiency of 90% at full load unity p.f. Efficiency at half load at the same p.f is

(a) 86.7% (b) 88.26% (c) 88.9% (d) 87.8%

37. full-load voltage regulation of a power transformer is zero when power factor of the load is near

(a)unity and leading (b) zero and leading

(c) Zero and lagging (d) unity and lagging

38. The voltage regulation of transformer at full load 0.8 pf lagging is 4%.Its voltage regulation at full-load 0.8pf leading

(a) will be positive (b) will be negative (c) may be positive (d)may be negative

39. The voltage regulation of transformer depend on its

1. Equivalent reactance 2.equivalent resistance 3. Load power factor

4. transformer size 5.load current

From these, the correct answer is

(a) 1 , 2 ,3 ,5 (b)1, 2, 3, 4, 5 (c) 1, 2, 4, 5 (d) 1, 2, 3, 4

40. The voltage regulation of a transformer at full load and 0.8 pf lagging is 2.5%.The voltage regulation at full load 0.8 leading will be

(a) -2.5% (b) zero (c) -0.9% (d) 2.5%

41.The efficiency of a transformer at full load and 0.8 pf lag is 90%.its efficiency at full load 0.8 pf leading will be

(a) Somewhat less than 90% (b) somewhat more than 90%

(c) 90% (d) 91%

42.Transformer maximum efficiency ,for a constant load current, occurs at

(a) at unity (b)zero pf leading (c) zero pf lagging (d) unity pf

43. Transformer at no –load behaves like

(a) a resistor, pf=0 (b) an inductive reactor, pf=0.2lagging

(c) a capacitive reactor, pf=0.2 leading (d) an inductive reactor, pf=0.8 lagging

44.which of the following statements are incorrect

1. Maximum voltage regulation of a transformer occurs at leading power factor

2. voltage regulation of a transformer is the maximum when load power factor (lagging) angle has the same value as the angle of equivalent impedance

3. voltage regulation of a transformer at zero power factor is always zero

4.voltage regulation of a transformer can be negative at leading power factor

Select the correct answer using the code given bellow:

(a) 1 and 3 (b) 2 and 3 (c) 2and 4 (d) 1 and 4

45.A transformer designed for operation of 60Hz supply is worked on 50Hz supply system without change its voltage and current ratings. When compared with full load efficiency at 60Hz, the transformer efficiency on full load at 50Hz will

(a)increases marginally (b) increases by a factor of 1.2

(c) remain unaltered (d) decreases marginally

* Source: Electrical Machinery by P.S.Bimbhra (My Favourite)

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My Favourite Volumes

2012-07-12T23:54:00.001+05:30

Lessons in Electric Circuits

Volume – 2 (A.C)

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My Favourite Volumes

2012-07-12T23:50:00.000+05:30

Lessons in Electric Circuits

Volume – 1 (D.C)

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Transformer

2012-07-12T23:40:00.000+05:30

Best Practice Manual - Transformer

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Caste System and Problems

2012-06-16T18:11:00.000+05:30

CASTE PROBLEM IN INDIA

(This article is a chapter from the book, "Swami Vivekananda On India and Her Problems". )

"I have a message for the world, which I will deliver without fear and care for the future. To the reformers I will point out that I am a greater reformer than any one of them. They want to reform only little bits. I want root-and-branch reform."

- Swami Vivekananda

Caste in Society and Not in Religion
The Underlying Idea of the Caste System
Inequality of Privilege Vitiates the System
Untouchability - A Superstitious Accretion
Solution of the Caste Problem

CASTE IN SOCIETY AND NOT IN RELIGION

Though our castes and our institutions are apparently linked with our religion, they are not so. These institutions have been necessary to protect us as a nation, and when this necessity for self-preservation will no more exist, they will die a natural death. In religion there is no caste. A man from the highest caste and a man from the lowest may become a monk in India and the two castes become equal. The caste system is opposed to the religion of Vedanta.

Caste is a social custom, and all our great preachers have tried to break it down. From Buddhism downwards, every sect has preached against caste, and every time it has only riveted the chains. Beginning from Buddha to Rammohan Ray, everyone made the mistake of holding caste to be a religious institution and tried to pull down religion and caste altogether, and failed.

In spite of all the ravings of the priests, caste is simply a crystallized social institution, which after doing its service is now filling the atmosphere of India with its stench, and it can only be removed by giving back to people their lost social individuality. Caste is simply the outgrowth of the political institutions of India; it is a hereditary trade guild. Trade competition with Europe has broken caste more than any teaching.

THE UNDERLYING IDEA OF THE CASTE SYSTEM

The older I grow, the better I seem to think of caste and such other time-honored institutions of India. There was a time when I used to think that many of them were useless and worthless, but the older I grow, the more I seem to feel a difference in cursing any one of them, for each one of them is the embodiment of the experience of centuries.

A child of but yesterday, destined to die the day after tomorrow, comes to me and asks me to change all my plans and if I hear the advice of that baby and change all my surroundings according to his ideas I myself should be a fool, and no one else. Much of the advice that is coming to us from different countries is similar to this. Tell these wiseacres, "I will hear you when you have made a stable society yourselves. You cannot hold on to one idea for two days, you quarrel and fail; you are born like moths in the spring and die like them in five minutes. You come up like bubbles and burst like bubbles too. First form a stable society like ours. First make laws and institutions that remains undiminished in their power through scores of centuries. Then will be the time to talk on the subject with you, but till then, my friend, you are only a giddy child."

Caste is a very good thing. Caste is the plan we want to follow. What caste really is, not one in a million understands. There is no country in the world without caste. Caste is based throughout on that principle. The plan in India is to make everybody Brahmana, the Brahmana being the ideal of humanity. If you read the history of India you will find that attempts have always been made to raise the lower classes. Many are the classes that have been raised. Many more will follow till the whole will become Brahmana. That is the plan.

Our ideal is the Brahmana of spiritual culture and renunciation. By the Brahmana ideal what do I mean? I mean the ideal Brahmana-ness in which worldliness is altogether absent and true wisdom is abundantly present. That is the ideal of the Hindu race. Have you not heard how it is declared he, the Brahmana, is not amenable to law, that he has no law, that he is not governed by kings, and that his body cannot be hurt? That is perfectly true. Do not understand it in the light thrown upon it by interested and ignorant fools, but understand it in the light of the true and original Vedantic conception.. If the Brahmana is he who has killed all selfishness and who lives to acquire and propagate wisdom and the power of love - if a country is altogether inhabited by such Brahmanas, by men and women who are spiritual and moral and good, is it strange to think of that country as being above and beyond all law? What police, what Military are necessary to govern them? Why should any one govern them at all? Why should they live under a government? They are good and noble, and they are the men of God; these are our ideal Brahmanas, and we read that in the SatyaYuga there was only one caste, and that was the Brahmana. We read in the Mahabharata that the whole world was in the beginning peopled with Brahmanas, and that as they began to degenerate they became divided into different castes, and that when the cycle turns round they will all go back to that Brahmanical origin.

The son of a Brahmana is not necessarily always a Brahmana; though there is every possibility of his being one, he may not become so. The Brahmana caste and the Brahmana quality are two distinct things.

As there are sattva, rajas and tamas - one or other of these gunas more or less - in every man, so the qualities which make a Brahmana, Kshatriya, Vaishya or a Shudra are inherent in every man, more or less. But at time one or other of these qualities predominates in him in varying degrees and is manifested accordingly. Take a man in his different pursuits, for example : when he is engaged in serving another for pay, he is in Shudra-hood; when he is busy transacting some some piece of business for profit, on his account, he is a Vaishya; when he fights to right wrongs then the qualities of a Kshatriya come out in him; and when he meditates on God, or passes his time in conversation about Him, then he is a Brahmana. Naturally, it is quite possible for one to be changed from one caste into another. Otherwise, how did Viswamitra become a Brahmana and Parashurama a Kshatriya?

The means of European civilization is the sword; of the Aryans, the division into different varnas. This system of division into varnas is the stepping-stone to civilization, making one rise higher and higher in proportion to one's learning and culture. In Europe, it is everywhere victory to the strong and death to the weak. In the land of Bharata (India), every social rule is for the protection of the weak.

Such is our ideal of caste, as meant for raising all humanity slowly and gently towards the realization of the great ideal of spiritual man, who is non-resisting, calm, steady, worshipful, pure and meditative. In that ideal there is God.

We believe in Indian caste as one of the greatest social institutions that the Lord gave to man. We also believe that through the unavoidable defects, foreign persecutions, and above all, the monumental ignorance and pride of many Brahmanas who do not deserve the name, have thwarted in many ways, the legitimate fructification of this glorious Indian institution, it has already worked wonders for the land of Bharata and it destined to lead Indian humanity to its goal.

Caste should not go; but should be readjusted occasionally. Within the old structure is to be life enough for the building of two hundred thousand new ones. It is sheer nonsense to desire the abolition of caste.

INEQUALITY OF PRIVILEGE VITIATES THE SYSTEM

It is in the nature of society to form itself into groups; and what will go will be these privileges! Caste is a natural order. I can perform one duty in social life, and you another; you can govern a country, and I can mend a pair of old shoes, but that is no reason why you are greater than I, for can you mend my shoes? Can I govern the country? I am clever in mending shoes, you are clever in reading Vedas, that is no reason why you should trample on my head; why if one commits murder should he be praised and if another steals an apple why should he be hanged? This will have to go.

Caste is good. That is only natural way of solving life. Men must form themselves into groups, and you cannot get rid of that. Wherever you go there will be caste. But that does not mean that there should be these privileges. They should be knocked on the head. If you teach Vedanta to the fisherman, he will say, "I am as good a man as you, I am a fisherman, you are a philosopher, but I have the same God in me, as you have in you." And that is what we want, no privilege for anyone, equal chances for all; let everyone be taught that the Divine is within, and everyone will work out his own salvation. The days of exclusive privileges and exclusive claims are gone, gone for ever from the soil of India.

UNTOUCHABILITY - A SUPERSTITIOUS ACCRETION

Formerly the characteristic of the noble-minded was - (tribhuvanamupakara shrenibhih priyamanah) "to please the whole universe by one's numerous acts of service", but now it is - I am pure and the whole world is impure. "Don't touch me!" "Don't touch me!" The whole world is impure, and I alone am pure! Lucid Brahmajnana! Bravo! Great God! Nowadays, Brahman is neither in the recesses of the heart, nor in the highest heaven, nor in all beings - now He is in the cooking pot!

We are orthodox Hindus, but we refuse entirely to identify ourselves with "Don't- touchism". That is not Hinduism; it is in none of our books; it is an orthodox superstition, which has interfered with national efficiency all along the line. Religion has entered in the cooking pot. The present religion of the Hindus is neither the path of Knowledge or Reason - it is "Don't-touchism". - "Don't touch me", "Don't touch me" - that exhausts its description.

"Don't touchism" is a form of mental disease. Beware! All expansion is life, all contraction is death. All love is expansion, all selfishness is contraction. Love is therefore the only law of life. See that you do not lose your lives in this dire irreligion of "Don't- touchism". Must the teaching (Atmavat sarvabhuteshu) - "Looking upon all beings as your own self" - be confined to books alone? How will they grant salvation who cannot feed a hungry mouth with a crumb of bread? How will those, who become impure at the mere breath of others, purify others?

We must cease to tyrannize. To what a ludicrous state are we brought! If a bhangi comes to anybody as a bhangi, he would be shunned as the plague; but no sooner does he get a cupful of water poured upon his head with some muttering of prayers by a padri, and get a coat to his back, no matter how threadbare, and come into the room of the most orthodox Hindu, I don't see the man who then dare refuse him a chair and a hearty shake of hands! Irony can go no farther.

Just see, for want of sympathy from the Hindus, thousands of pariahs in Madras are turning Christians. Don't think that this is simply due to the pinch of hunger; it is because they do not get any sympathy from us. We are day and night calling out to them "Don't touch us! Don't touch us!" Is there any compassion or kindliness of heart in the country? Only a class of "Don't-touchists" ; kick such customs out! I sometimes feel the urge to break the barriers of "Don't-touchism", go at once and call out, "Come all who are poor, miserable, wretched and downtrodden", and to bring them all together. Unless they rise, the Mother will not awake.

Each Hindu, I say, is a brother to every other, and it is we, who have degraded them by our outcry, "Don't touch", "Don't touch!" And so the whole country has been plunged to the utmost depths of meanness, cowardice and ignorance. These men have to be lifted; words of hope and faith have to be proclaimed to them. We have to tell them, "You are also men like us and you have all the rights that we have."

SOLUTION OF THE CASTE PROBLEM

Our solution of the caste question is not degrading those who are already high up, is not running amuck through food and drink, is not jumping out of our own limits in order to have more enjoyment, but it comes by every one of us fulfilling the dictates of our Vedantic religion, by our attaining spirituality and by our becoming ideal Brahmana. There is a law laid on each one of you in this land by your ancestors, whether you are Aryans, or non-Aryans, rishis or Brahmanas or the very lowest outcaste. The command is the same to you all, that you must make progress without stopping, and that from the highest man to the lowest pariah, every one in this country has to try and become the ideal Brahmana. This Vedantic idea is applicable not only here but over the whole world.

The Brahmana-hood is the ideal of humanity in India as wonderfully put forward by Shankaracharya at the beginning of his commentary on the Gita, where he speaks about the reason for Krishna's coming as a preacher for the preservation of Brahmana- hood, of Brahmana-ness. That was the great end. This Brahmana, the man of God, he who has known Brahman, the ideal man, the perfect man, must remain, he must not go. And with all the defects of the caste now, we know that we must all be ready to give to the Brahmanas this credit, that from them have come more men with real Brahmana-ness in them than from all the other castes. We must be bold enough, must be brave enough to speak their defects, but at the same time we must give credit that is due to them.

Therefore, it is no use fighting among the castes. What good will it do? It will divide us all the more, weaken us all the more, degrade us all the more. The solution is not by bringing down the higher, but by raising the lower up to the level of the higher. And that is the line of work that is found in all our books, in spite of what you may hear from some people whose knowledge of their own Scriptures and whose capacity to understand the mighty plans of the ancients are only zero. What is the plan? The ideal at the one end is the Brahmana and the ideal at the other end is the chandala, and the whole work is to raise the chandala up to the Brahmana. Slowly and slowly you will find more and more privileges granted to them.

I regret that in modern times there should be so much discussion between the castes. This must stop. It is useless on both sides, especially on the side of the higher caste, the Brahmana, the day for these privileges and exclusive claims is gone. The duty of every aristocracy is to dig its own grave, and the sooner it does so, the better. The more he delays, the more it will fester and the worse death it will die. It is the duty of the Brahmana, therefore, to work for the salvation of the rest of mankind, in India. If he does that and so long as he does that, he is a Brahmana.

Any one who claims to be a Brahmana, then, should prove his pretensions, first by manifesting that spirituality, and next by raising others to the same status. We earnestly entreat the Brahmanas not to forget the ideal of India - the production of a universe of Brahmanas, pure as purity, good as God Himself : this was at the beginning, says the Mahabharata and so will it be in the end.

It seems that most of the Brahmanas are only nursing a false pride of birth; and any schemer, native or foreign, who can pander to this vanity and inherent laziness, by fulsome sophistry, appears to satisfy more.

Beware Brahmanas, this is the sign of death! Arise and show your manhood, your Brahmana-hood, by raising the non-Brahmanas around you - not in the spirit of a master - not with the rotten canker of egoism crawling with superstitions and charlatanry of East and West - but in the spirit of a servant.

To the Brahmanas I appeal, that they must work hard to raise the Indian people by teaching them what they know, by giving out the culture that they have accumulated for centuries. It is clearly the duty of the Brahmanas of India to remember what real Brahmana-hood is. As Manu says, all these privileges and honors are given to the Brahmana because, "with him is the treasury of virtue". He must open that treasury and distribute to the world.

It is true that he was the earliest preacher to the Indian races, he was the first to renounce everything in order to attain to the higher realization of life, before others could reach to the idea. It was not his fault that he marched ahead of the other castes. Why did not the other castes so understand and do as they did? Why did they sit down and be lazy, and let the Brahmanas win the race?

But it is one thing to gain an advantage, and another thing to preserve it for evil use. Whenever power is used for evil it becomes diabolical; it must be used for good only. So this accumulated culture of ages of which the Brahmana has been the trustee, he must now give to the people, and it was because he did not open this treasury to the people, that the Muslims invasion was possible. It was because he did not open this treasury to the people from the beginning, that for a thousand years we have been trodden under the heels of everyone who chose to come to India; it was through that we have become degraded, and the first task must be to break open the cells that hide the wonderful treasures which our common ancestors accumulated; bring them out, and give them to everybody, and the Brahmana must be the first to do it. There is an old superstition in Bengal that if the cobra that bites, sucks out his own poison from the patient, the man must survive. Well then, the Brahmana must suck out his own poison.

To the non-Brahmana castes I say, wait, be not in a hurry. Do not seize every opportunity of fighting the Brahmana, because as I have shown; you are suffering from your own fault. Who told you to neglect spirituality and Sanskrit learning? What have you been doing all this time? Why have you been indifferent? Why do you now fret and fume because somebody else had more brains, more energy, more pluck and go than you? Instead of wasting your energies in vain discussions and quarrels in the newspapers, instead of fighting and quarreling in your own homes - which is sinful - use all your energies in acquiring the culture which the Brahmana has, and the thing is done. Why do you not become Sanskrit scholars? Why do you not spend millions to bring Sanskrit education to all the castes of India? That is the question. The moment you do these things, you are equal to the Brahmana! That is the secret power in India.

The only safety, I tell you men who belong to the lower castes, the only way to raise your condition is to study Sanskrit, and this fighting and writing and frothing against the higher castes is in vain, it does no good, and it creates fight and quarrel, and this race, unfortunately already divided, is going to be divided more and more. The only way to bring about the leveling of castes is to appropriate the culture, the education which is the strength of the higher castes.

Mini Ratna Companies

2012-02-19T10:33:00.001+05:30

Mini Ratna status

Category I

This designation applies to PSEs that have made profits continuously for the last three years or earned a net profit of Rs. 30 crore or more in one of the three years. These miniratnas granted certain autonomy like incurring capital expenditure without government approval up to Rs. 500 crore or equal to their net worth, whichever is lower.

Airports Authority of India

Balmer Lawrie & Co. Limited

Bharat Dynamics Limited

BEML Limited

Bharat Sanchar Nigam Limited

Bridge & Roof Company (India) Limited

Central Warehousing Corporation

Central Coalfields Limited

Chennai Petroleum Corporation Limited

Cochin Shipyard Limited

Container Corporation of India Limited

Dredging Corporation of India Limited

Engineers India Limited

Ennore Port Limited

Garden Reach Shipbuilders & Engineers Limited

Goa Shipyard Limited

Hindustan Copper Limited

HLL Lifecare Limited

Hindustan Newsprint Limited

Hindustan Paper Corporation Limited

Housing and Urban Development Corporation

India Tourism Development Corporation

Indian Railway Catering and Tourism Corporation

IRCON International

Kudremukh Iron Ore Company Ltd.

Mazagon Dock Limited

Mahanadi Coalfields Limited

MOIL Limited

Mangalore Refinery and Petrochemicals Limited

Mishra Dhatu Nigam

Minerals and Metals Trading Corporation of India

MSTC Limited

National Fertilizers Limited

National Seeds Corporation

Pawan Hans Helicopters

NHPC Limited

Northern Coalfields Limited

Numaligarh Refinery Limited

Rashtriya Chemicals & Fertilizers Limited

Satluj Jal Vidyut Nigam

Security Printing and Minting Corporation of India Limited

South Eastern Coalfields Limited

State Trading Corporation of India Limited

Tehri Hydro Development Corporation Limited

Telecommunications Consultants (India) Limited

Western Coalfields Limited

Water & Power Consultancy (India) Limited

Category II

This category include those PSEs which have made profits for the last three years continuously and should have a positive net worth. Category II miniratnas have autonomy to incurring the capital expenditure without government approval up to Rs. 250 crore or up to 50% of their net worth whichever is lower.

Bharat Pumps & Compressors Limited

Broadcast Engineering Consultants (I) Limited

Central Mine Planning & Design Institute Limited

Ed.CIL (India) Limited

Engineering Projects (India) Limited

FCI Aravali Gypsum & Minerals India Limited

Ferro Scrap Nigam Limited

HMT (International) Limited

HSCC (India) Limited

India Trade Promotion Organisation

Indian Medicines & Pharmaceuticals Corporation Limited

M E C O N Limited

National Film Development Corporation Limited

National Small Industries Corporation Limited

P E C Limited

Rajasthan Electronics & Instruments Limited

Maharatna Companies

2012-02-19T10:20:00.000+05:30

Maharatna status

In 2009, the government established the Maharatna status, which raises a company's investment ceiling from Rs. 1,000 crore to Rs. 5,000 crore.The Maharatna firms can now decide on investments of up to 15 per cent of their net worth in a project; the Navaratna companies could invest up to Rs 1,000 crore without explicit government approval.

Criteria

The six criteria for eligibility as Maharatna are:

Having Navratna status.
Listed on Indian stock exchange with minimum prescribed public shareholding under SEBI regulations.
An average annual turnover of more than Rs. 20,000. crore during the last 3 years. Earlier it was Rs 25,000 Crore.
An average annual net worth of more than Rs. 10,000crore during the last 3 years. Earlier it was Rs. 15,000 crore.
An average annual net profit after tax of more than Rs. 2500 crore during the last 3 years. Earlier it was Rs. 5000 crore.
Should have significant global presence/international operations.

List of Maharatna

Navratna Companies

2012-02-19T10:16:00.000+05:30

Navratna status

Navratna was the title given originally to nine Public Sector Enterprises (PSEs), identified by the Government of India in 1997 as having comparative advantages, which allowed them greater autonomy to compete in the global market.The number of PSEs having Navratna status has been raised to 16,The government is likely to accord the coveted status to Engineers India Limited which is under consideration.

List of Navratna