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