SGM POWER SYSTEM CONSULTANCY
TECH TALK
VCB APPLICATION – MOTOR SWITCHING
CONTACT- SWAGATA MUKHERJEE
EMAIL-swammukherjee@gmail.com Mobile- 8779027847
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VCB APPLICATION – BREAKING CHARACTERISTICS
VCB CURRENT CHOPPING
– When smaller currents are switched, the arc discharge
tends to be instable already before zero, typically at
current levels in the range of 3-8 A in modern vacuum
interrupters.
– This leads to a sudden decay of the load current known as
chopping.
– Chopping current level is a function of load current- lower
the load current- higher the current chopping level.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
VCB APPLICATION – BREAKING CHARACTERISTICS
VCB Cold Breakdown
– After the line frequency current has become zero, the vacuum
gap has to withstand the TRV.
– Amplitude and shape/frequency of TRV depends on chopping
current level and load R-L-C parameters.
– Stray capacitance also plays important role in establishing TRV
shape.
– When the gap is small, gap voltage withstand capability can be
less than TRV across the gap leading to voltage breakdownknown as Cold Breakdown.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
VCB APPLICATION – BREAKING CHARACTERISTICS
VCB HF Current and Voltage Escalation
– Cold breakdown leads to High Frequency current.
– Based on HF current quenching capability there is
possibility of multiple reignitions with successive higher
voltages.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
VCB APPLICATION – MOTOR SWITCHING
•
•
VCB modelled with its characteristics current
chopping, cold breakdown and HF frequency
handling capability.
6.6kV motor and cable modelled along with
stray capacitance.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
VCB APPLICATION – MOTOR SWITCHING
VCB Current Chopping and multiple HF Current
re-ignition
• All A, B and C phase has current chopping.
• C Phase goes through multiple HF Current reignition.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
VCB APPLICATION – MOTOR SWITCHING
Motor Voltage Escalation
• Due to multiple high frequency
current re-ignition, motor
terminal experiences a high
frequency voltage escalation.
• Motor terminal experiences in
excess of 3PU voltage stress.
CONCEPT| FEED| DETAIL|PROPOSAL SUPPORT ONSHORE|OFFSHORE|NEAR SHORE
O&G|LNG|CHEMICAL|NUCLEAR EMTP|ETAP|NUMERICALRELAY ENGINEERING
THANK YOU FOR YOUR ATTENTION.