HVDC AND CHALLENGES HVDC AND CHALLENGES

WITH MULTIWITH MULTI--TERMINAL TERMINAL

HVDCHVDC

BY: NARASIMHARAO

ROLL NO:M080164EE

Presentation outlinePresentation outline

� Introduction

� HVDC advantages & disadvantages.

� HVDC configurations

� Multi-terminal HVDC

� Challenges with multi-terminal HVDC

IntroductionIntroduction

� First only 2.5Kw transmitted in 1882 by using direct.

� In 1889 630Kw at 14kv DC.

� Gives why we need to go for HVDC transmission.

� Gives information about configurations in HVDC

� In multi-terminal HVDC converters can be connected in series

or parallel.

� Parallel converters gives more flexibility and lower losses.

� About the challenges with multi-terminal HVDC

� Require isolation switch for isolate converter from the fault or

disturbance.

Why we need HVDC Why we need HVDC

� No charging currents in HVDC.

� DC link between the two systems.

� Less losses in line.

Advantages HVDC over AC SystemAdvantages HVDC over AC System

� Transfer Large power with low cost.

� power transmission and stability between the two

asynchronous ac systems.

� No skin effect & less corona losses.

� Power per conductor is more

disadvantagesdisadvantages

� HVDC require static inverters which are expensive & limited

over load capacity.

� Need good communication between the all the terminals.

� Difficult to design the HVDC breakers

configurationsconfigurations

MultiMulti--terminal HVDC terminal HVDC

� It is more complex.

� Telecommunications require between the stations also large.

This is large scale HVDC systems operation in the world.

IT 2000MW in England transmission.

Challenges with multiChallenges with multi--terminal terminal

HVDC HVDC

� Parallel converters in the same station.

� Multi terminal schemes.

� Disconnection of fault dc line section.

� Isolation of switches without dc current

breaking.

� Isolation by using HVDC breaker.

� Detection and clearing of converter faults.

� Importance of telecommunication.

� Electric and magnetic fields.

Parallel converters in the same stationParallel converters in the same station

� Operation is easy

� No importance to telecommunication is needed.

� The only challenges to secure the continued operation without

risk for the overload if one of the parallel rectifier or inverter

when the telecommunication is out of service.

multimulti--terminal schemes, all terminal schemes, all

converters with similar rating converters with similar rating

� When the converters in different stations there is an increase need for telecommunication.

� Telecommunication is need for

Proper timing of rectifier at dc line fault.

Identification of faulty dc line section.

Actions for clearing faults in converters or line

sections.

� Restoration of power transmission as far as the possible after an outage of converters or dc line section.

� Challenge is that there must be backup function for

power restoration and for preventing the overload of

equipment in the case that the telecommunication is out of

service.

Disconnection of fault dc line sectionDisconnection of fault dc line section

� It possible to isolate fault section and still operate the remaining converters.

� Necessary fault detection and switching or isolating devices

would be need to identify the specific dc line section.

Isolation by switches without dc Isolation by switches without dc

current brakingcurrent braking

� We can use isolators but it take more seconds to perform the

task.

� We need a high speed switch (HSS)

It can perform the task very short times (<150ms)

Isolation by using HVDC breakerIsolation by using HVDC breaker

� It will perform isolation without waiting for zero current.

� An HVDC breaker will have combination of HSS and non

linear resistors.

� In HVDC insulation levels are high.

Importance of telecommunicationImportance of telecommunication

� increases with a number of converters operating in parallel.

� With out proper telecommunication system may lead to

prolonged disturbances.

� It not possible to change the load without telecommunications.

Detection and clearing of converter Detection and clearing of converter

faultsfaults

� We need master controller and sequence in logic VDCOL setting.

� Even when telecommunication is totally out of service , a

well designed multi-terminal system will use special VDCOL

characteristics to detect faults .

Electric and magnetic fieldsElectric and magnetic fields

� HVDC limit increases with decrease in frequency.

� Use larger diameter conductor

corona loss will also decreases as field around the conductor

decreases

ConclusionsConclusions

� we have to run the system even when telecommunication out

of service

� Design high speed HVDC breakers

� Use isolators with high speed switch.

� Design hardware for isolating parts of HVDC transmission systems.

THANK YOU

THANK YOU