03-10-2010, 12:54 PM
TRANSFORMER PROTECTION USING DIGITAL NUMERIC RELAY
12-10-2010, 05:47 PM
TRNSFORMER PROTECTION.ppt (Size: 41 KB / Downloads: 161) TRANSFORMER PROTECTION Prepared by:MUHAMMAD ALI10-M.Sc-EE-32 Protection Schemes Protection Schemes Percentage Differential Protection Over current protection Protection against magnetizing Inrush Current Oil pressure relief Devices Over Current Relays Over fluxing Protection Protection of Three winding Transformer Types of Faults in Transformer Internal Faults Short circuiting in Transformer windind and Connections Incipient faults Core Faults Regulator Faults External Faults Over loading Percentage Differential Protection Employed for Large Power transformer Protect internal short circuits A transformer is provided with on-load tap changing gear .The C.T. ratio is fixed. When transformer is on-load, there is no-load current in the relay, Therefore, its setting should be greater than no-load current Buchholz Relay Gas actuated relay Detects incipient faults Buchholz Relay gives an alarm when a specific amount of gas is formed. C2 H2 and H2 shows arcing in oil between constructed parts CH4 , C2H4 and H2 indicates hot spot in insulation Oil Pressure Relief devices It is fragile disc. It operates when the pressure exceeds 10 psi but close automatically when the pressure falls below the critical level. Employed for large transformer of rating 2 MVA. Employed for Distribution transformer of 200 kVA Over current Relays Protect transformer of rating 100 kVA and below 5 MVA. Used as overload and fault protection. Over fluxing Protection Magnetic flux increases when voltage increases. Reduction in frequency also increases the flux density. = E K/f = flux, f = frequency, E = applied voltage, K = constant Therefore, to control flux, the ratio E/f is controlled. When E/f exceeds unity, it has to be detected. Protection of Three winding Transformer One of winding is connected to the source of supply. Two windings feed loads at different voltages.
08-10-2012, 12:39 PM
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