ANALYSIS OF VERY FAST TRANSIENT OVERVOLTAGES IN GIS AND ITS MITIGATION TECHNIQUES

INTRODUCTION GAS INSULATED SUBSTATIONS

CONT…

ADVANTAGES OF GIS

COMPONENTS

SOFTWARE USED: ATP-EMTP

CIRCUIT UNDER STUDY

EXPERIMENTAL VFTO SET-UP BUS DUCT SETUP TO ANALYSE VFTO

1. Non communicating insulator

2. Communicating insulator 3. Gas filling port4. Conductor5. Gap 6. Capacitive divider port7. Dish end8. 291Ø, 225mm long9. 291Ø, 450mm long10. 291Ø, 1040mm long11. Viewing port

EMTP MODELLING OF GIS COMPONENTS The capacitance per unit length

The internal inductance of the conductor   Surge Impedance(Zo) & Velocity of wave (v)

 

CIRCUIT DIAGRAM FOR EMTP ANALYSIS

RESULTS & DISCUSSIONS

FIG : VOLTAGE WAVEFORM AT AD06 WHEN DISCONNECTOR OR CIRCUIT BREAKER IS OPERATED

CONT…

FIG : VOLTAGE WAVEFORM AT BS17 WHEN DISCONNECTOR-A IS OPERATED

Vpeak= 423 kV Tr= 29 ns

Vpeak= 495 kV Tr= 25.2 ns

FIG : VOLTAGE WAVEFORM AT BS17 WHEN DISCONNECTOR-B IS OPERATED

CONT…

FIG : VOLTAGE WAVEFORM AT BS17 WHEN CIRCUIT BREAKER IS OPERATED

CONT…

Vpeak= 495 kV Tr= 25.2 ns

MEASURED VFTO WAVEFORM FROM EXPERIMENTAL SET-UP.

EFFECTS OF VFTO

TRANSFORMER SF6 INSULATION DISCONNECTORS & BREAKERS ENCLOSURE BUSHIINGS CABLES SECONDARY EQUIPMENT

1. RC-FILTER

MITIGATION TECHNIQUES

Vp= 23.5 kV

Tr= 312.5ns

Vp= 27.2kV

Tr= 303ns

2. CAPACITOR

CONCLUSION

Generation of VFTO can cause high non-uniform voltage distributions in the windings.

It is necessary to mitigate the VFTO Usage of Both RC-Filter & Simple capacitor

will give satisfactory results