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HVDC Switch gear and Protection (CB)
Introduction
• Commercial success – after 1980
• Alternative to 3Ø, 50 hz, AC
• Applications
• Long 2 terminal bipolar high power HVDC systems
• Back to back HVDC coupling stations
• Long high power submarine cable links
• Multi terminal HVDC interconnection between AC systems
HVDC
links
around the
world.
HVDC Links in
India
Protection and Switch gear requirements
• Different from AC
• Integrated with thyristor convertor control
• Normal operation – thyristor control
• Single pole faults – AC circuit breakers are tripped
• At present HVDC systems are without HVDC CB’s in DC poles.
Converter Transformer for HVDC lines
Control
• By tap changing of converter transformers
• Thyristor control of converter valves
MRTB
• Metallic return transfer breaker
• To interrupt earth return currents
Barrier for expansion of HVDC
• Lack of Circuit Breakers
• One of the most important hindrance
• Present CB costs too much
Artificial current zero
• Produced by LC oscillations
• DC has no natural current zeroes
• Breaker interrupts at artificial current zeroes
Schematic of DC switching system
Energy equation
Commutation Principle
Control of dI/dt and dV/dt
• Lsat is connected in series to reduce dI/dt
• R-C1 in parallel to reduce dV/dt
• Resistance R across load side
• Switching Stress Factor
Complete HVDC switching system
Types of HVDC circuit Breakers
• Identified with reference to –
• Switching time
• Current to be interrupted
• Switching energy
• Voltage at which current is interrupted
• TRV
• Eg:- type A CB, Type B CB (based on operating time)
Solid State Circuit Breakers
• To lower on state losses.
• No failure – Current flows through GCT
• Failure – Semiconductors switched off.
• TRV – Varistor starts conducting.
• Demagnetizes line inductance.
Hybrid HVDC Circuit Breaker
• Hybrid of mechanical actuator and IGBT.
• Have very low losses and is ultra fast.
• Normal operation – current flows through mechanical breaker & power
electronics breaker in series.( least resistance).
Fault operation of Hybrid
HVDC Circuit Breaker
• 3 stages
• Power electronics breaker is tripped.
• High resistance path for current.
• Mechanical breaker is fired.
• Main power electronics completes
breaking process.
ABB announcing invention of HVDC Circuit Breaker
Ultra-fast mechatronic circuit breaker for HVDC by
Alstom
Thank You
References
• Switchgear Protection and Power Systems by Sunil S. Rao
• Wikipedia
• DC circuit breakers and their use in HVDC grids by N Kostoulas
• The Hybrid HVDC Circuit Breaker at new.abb.com