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.