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3.0 Types of Fault Conditions There are three main types of fault viz: overheating of windings, core and joints, partial discharges: and arcing. 3.1 Overheating Overheating metallic parts heat up the surrounding regions such as paper insulating tapes and oil. This leads to thermal deterioration of these materials. Thermal degradation of paper produces carbon dioxide, carbon monoxide and water. The ratio of carbon dioxide to carbon monoxide is typically five: but if the ratio falls below three, there is indication of severe overheating of the paper, Oil degradation produces a number of hydro-carbon gases such as methane, ethane, ethylene. and acetylene. Methane and ethane are decomposition products that appear above 120 (1 C: ethylene appears above 150°C while acetylene is a high temperature product, appearing at several hundred degrees centigrade Some hydrogen is also produced alongwith the hydro-carbons gases. The proportion of the various hydrocarbons varies with temperature. This is the basis of the well known Ratio Code introduced several years ago by Dorenberg and R.R. Rogers. 3.2 Partial Discharge The second type of fault condition is partial discharge which occurs due to ionization of oil in highly stressed areas where gas/vapour filled voids are present or the insulation is containing moisture. The main product during partial discharge is hydrogen, though small amounts of methane and other gases would also be present depending upon thermal degradation. The disintegration of oil and cellulose due to partial discharge is characterized by the removal of the outer hydrogen atoms to form hydrogen gas. The remaining molecular framework polymerizes and long » chain products such as waxes are formed. Thermal degradation is a more predictable phenomenon which involves the break-up of chemical bonds. Cellulose decomposes ultimately to CO. CO2 and water-, oil break up into lower molecular hydro-carbons. 3.3 Arcing The third type of fault condition is arcing. Arcing can occur between leads, between lead and coil and between other highly stressed regions weakened by fault conditions. The high temperatures caused by arcing results in the production of acetylene and hydrogen. 57
3.4 Pattern of generation of gases in transformer is summarized below. FAULT/PATTERN KEY GAS Conductor Overheating C0/C02 (Carbon Oxides) Oil Overheating C2H4 (EthyIene) Partial Discharge Hz (Hydrogen) Arcing . C2H2 (Acetylene) 4.0 Solubility of Gases 4.1 The solubility of gases in oil varies with temperature and pressure. While solubility of H2. N2, CO. O in oil increases with temperature and that of CO2. C2 H2. C2 H4 and C2 H6, decreases with temperature, solubility of CH,. remains essentially constant. All the gases become more soluble in oil with increase in pressure Solubility of gas is one of the factors contributing to the complexities in formulating permissible levels of gases on the basis of service life of a transformer. Table I show solubility of different gases 25° C and at 1 atm. The homogeneity of the gases in the oil is dependent" on the rate of gas generation, access of the fault area to flowing oil, rate of oil mixing and presence of gas blanket. 5. Dissolved Gas Analysis (DGA) 5.1 Dissolved gas analysis (DGA) of the oil of a transformer in operation is a specialized technique to assess the internal condition of the transformer. DGA is performed by Gas Chromatography. The gases extracted from the oil by a suitable apparatus are transferred to the Gas Chromatograph system for analysis. 5.2 The knowledge of solubility of Hydro-carbon and fixed gases at different temperatures, in insulating oils helps in interpretation of gas analysis. The permissible concentration of dissolved gases in the oil of healthy transformer is shown in Table II. The combinations of Gas levels for different types of faults are shown in Table III while Table IV shows the gas composition by volume under arcing fault with participation of various components of solid dielectrics in a transformer. 5.3 While the absolute concentration of fault gases gives an indication of status of insulation of transformer, whereas the relative concentration of these gases provides a clue to the type of fault. For fault diagnosis the method based on Rogers' Analysis is adopted. 5.4 Roger's method: This method holds good for hydro-carbon gases. By evaluating the gas ratios, the type of fault is detected. Four ratios are used viz., Methane/Hydrogen, Ethane/Methane, Ethylene/Ethane and Acetylene/ 58
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PREFACE The book on "Power Supply I
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However transformers of capacity 13
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3. To keep the unbalance on the 3 p
Page 9 and 10: 1.2 POWER SUPPLY FOR SIGNALLING 1.2
Page 11 and 12: locomotives and Electric Multiple U
Page 13 and 14: 2.0 Supply System 2. POWER SUPPLY F
Page 15 and 16: figures. This charge should be real
Page 17 and 18: 2.4 Scrutiny of Bills have a bearin
Page 19 and 20: c) Procedure to be followed in case
Page 21 and 22: In the territorial setup one Subord
Page 23 and 24: 3.2.3 Over load Capacity of Tractio
Page 25 and 26: B. Insulation resistance will conti
Page 27 and 28: 3.3. GUIDING NOTES ON MAINTENANCE 3
Page 29 and 30: f) Fully push home the wedges betwe
Page 31 and 32: eakers/interrupters should also be
Page 33 and 34: A detail history of every battery s
Page 35 and 36: light or bluish grey according to a
Page 37 and 38: (e) Overhaul, bench tests and calib
Page 39 and 40: 3.5. FORTNIGHTLY MAINTENANCE 3.5.1.
Page 41 and 42: obstruction and also if the shock a
Page 43 and 44: 2. Test a sample of oil for BDV. 3.
Page 45 and 46: 3. Check if the terminations of the
Page 47 and 48: Fortnightly Schedule: a) Drain wate
Page 49 and 50: d) Measure the IR between auxiliary
Page 51 and 52: TRACTION DISTRIBUTION SCHEDULE OF M
Page 53 and 54: 3.0 Inspection of Traction Sub-stat
Page 55 and 56: 4.0 Switching Stations a) Switch Ya
Page 57 and 58: SI. No . APPLICATION AND INTERPRETA
Page 59: 2.2 Oxidation Carbondioxide is the
Page 63 and 64: TABLE - I SOLUBILITY OF DIFFERENT G
Page 65 and 66: TABLE V ROGER'S METHOD OF DIAGNOSIS
Page 67 and 68: 1.1 Schedules MAINTENANCE OF SF6 CI
Page 69 and 70: Point / Location Tripping Mechanism
Page 71 and 72: 1.0 General Annexure 3.05 MAINTENAC
Page 73 and 74: 1.5 Detailed Check Checking shall b
Page 75 and 76: DESIGN ASPECTS OF TRACTION SUBSTATI
Page 77 and 78: • Characteristics of the locomoti
Page 79 and 80: considerations enlisted in para 4.0
Page 81 and 82: xii) Load losses 135.0 kW xiii) Cur
Page 83 and 84: item Nominal System Voltage 66kV 11
Page 85 and 86: 20 1250 1600 2000 245 31.5 1250 160
Page 87 and 88: i) Three post, centre post rotating
Page 89 and 90: etween live parts and different pot
Page 91 and 92: 4.11.5 Design of grounding system 4
Page 93 and 94: 4.12.2 BIL of various equipments us
Page 95 and 96: (d) High speed inter tripping relay
Page 97 and 98: The relay continuously monitors the
Page 99 and 100: SULFUR HEXAFLUORIDE(SF6) GAS 96 ANN
Page 101 and 102: 5.0 POWER SUPPLY SYSTEM PROTECTION
Page 103 and 104: any one of the two sub-staion throu
Page 105 and 106: fault relay (132KV&25KV side) 4. ID
Page 107 and 108: will be supplied to the successful
Page 109 and 110: detected by normal distance protect
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Just as the requirements of supervi
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The use of hermetically sealed comp
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The configuration used in Railway S
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This may be accomplished by several
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A typical example of commonly used
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7.2.6.2The above sequence of messag
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7.3 SCADA EQUIPMENT 7.3.1 General T
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7.3.10 SCADA Software The operating
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systems are different, the basic fe
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To combat interference, co-ordinate
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e = Er / R were introduced in the v
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It is seen that even if the lines a
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Fig. 8.3 Fig. 8.3 contains a family
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Typical Rail Current Distribution F
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8.8 SUPPRESSION OF INTERFERENCE AT
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Magnetizing current is required to
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REGULATION FOR ELECTRICAL CROSSING
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Kc is cable screening factor and it
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