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HVDC Technology

Phil Sheppard

Head of Network Strategy

Alternating Current (AC) Direct Current (DC)

Was developed to allow power transfer

at higher voltage (to minimise losses)

Power flows depending on system

impedance (limited control over

powerflow)

Worldwide choice of power

transmission technology (at different

frequencies)

Conventional power generation is AC

Power system was initially a DC system!

More cost effective for longer power transmission

Allows control of power at different routes

Allows connection of different synchronised AC zones zones (even at different frequencies)

AC vs DC Power Transmission

IGBT based Voltage Source

Operable in AC grids with low short

circuit levels

Independent control of P&Q

Power reversal and Fast Ramp Up/Down

Capability

Harmonics only seen at Switching

Frequency (xkHz)

Smaller converter station

Can energise an AC network (black start

capability)

Thyristors based Line Commutated

Converter

Lower converter losses

Less critical DC line-to-ground faults

Filter Switching Required for Different

Dispatch Levels

Commutation Failure and Operation in

Weak Networks

Larger converter station

Can only operate in an energised AC

network

Voltage Source Converter

(VSC)

Current Source Converter

(CSC)

HVDC Technologies

CSC and VSC

4

Basslink

(Tasmania

2005) LCC

500MW

Transbay

(USA 2010)

VSC 400 MW

Caprivi Link

(Namibia

2009) VSC

300MW

Borwin 1

(Germany

2009) VSC

400 MW

Inelfe (France

– Spain 2013)

VSC 1000MW

KII Channel

(Japan 2000)

LCC 2800MW

Skagerrak 4

(Norway

2014) VSC

700MW

Sapei (Italy

2011) LCC

800MW

North East

Agra (India

2015)

8000MW

Xiangjiaba -

Shanghai

(China 2011)

LCC 6400MW

Western Link

(UK 2016)

LCC 2200MW

Jinping Sunan

(China 2013)

LCC 7200MW

Worldwide HVDC experience

5

Present AC interconnector capacity limited by stability constraint

2.2 GW DC Link (subsea) from Scotland to England

To further increase the capacity to over 6 GW

To enhance system stability (power control, POD)

Why not AC?

Expensive Option Compared to DC

Long Lead Time

Visual Impact

Two DC links of smaller capacity would be expensive

Technology: Line Commutated Current:

2.2 GW and higher HVDC converters are based on proven technology

(Current Source Converter)

Offer a short-term rating (to 2.4GW)

Low losses and no black start requirement favour CSC design

DC cables of 600kV rating is a significant benefit (first in the world).

Use of HVDC Technology in GB

6

Given the size of the Round 3

windfarms, an integrated solution

in comparison to radial offers 25%

reduced overall Cost (including the

onshore reinforcements required)

Fault detection

Fault Isolation

- Lack of DC Breakers

Converter control co-ordination

Power reversal

Integrated Offshore Windfarms

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Operating in an islanded network with

low system strength (short circuit

level)

Windfarm/Converter Control

DC/AC Faults

(detection/isolation/system recovery)

Loss of Array

Power Sharing (multiple DC Links)

Power Quality

System Frequency

Loss of infeed

Low Voltage Ride Through

Frequency Control

System Stability

Voltage Control

Power Oscillations

Power Reversal

Power Quality

SSR/SSTI

Control Interaction

Power System Studies for HVDC

Projects – long list…!

8

Improvements in the

design of DC breaker

which allows for

better “meshed” DC

networks (multi-

terminal)

VSC converter design

to reduce the losses

Ancillary services

from DC links such as

Rapid Frequency

Response, Power

Oscillation Damping

Multi-vendor Control platform for

multi-terminal development

Innovations in the world of DC

Technology

HVDC R&D in National Grid

Over 30 live R&D projects on

HVDC technology

Working closely with UK and

International Universities and

Manufacturers

One of World’s leading

Transmission companies in

HVDC modelling

9

Results from IOTP indicate the overall

benefits are in order of £1billion for the

current connection programme (2017

onwards)

If projects connect after 2020 improved

technology should be available and a

further benefit up to £2billion can be

potentially achieved

Results currently present only comparison

of capital costs

Cost Benefit Analysis, which includes

operational cost considerations is

underway

Current work shows the Integrated

offshore concept bring overall benefits

Local Boundary EC3

P1

P2

P3

P4

P5P6

2030 TEC

Doggerbank

Creyke Beck

(CREB4)

Lackenby

(LACK4)

Tod Point

(new s/s)

Local Boundary EC7

1 GW

1 GW

ONSHORE AREA OFFSHORE AREA

1.8 GW

Killingholme

(KILL4)

Walpole

(WALP4)

Local Boundary EC1

P1

Hornsea

1 GW

1 GW

1.8GW *P5b

Bramford

(BRAM4)

P1a

P2a

Norwich Main

(NORM4)

Local Boundary EC5

East Anglia

Bacton

(new s/s)

P3

2GW

P5a

P2b

P1b

P3a

P3b

1.8GW

P6a

P6b

P6cP4a

P4b

1.8GW*

Lowestoft

(new s/s)

1.2GW

1GW

Boundary B9

(2800MW)

Boundary B7

(3500MW)

Boundary B7a

(3400MW)

Boundary B8

(2700MW)

Boundary B6

(2500MW)

P4

1.8GW

Onshore

Actions:

+ QB Opt

(1 x 200MW)

(3 x 300MW)

(2 x 500MW)

P2

(7 x 300MW)

(1GW)

(1GW)

Bootstrap

2.5GW

Onshore

Actions:

+ QB Opt

Benefits of East Coast Integration

Potential North Sea offshore grid

12

HVDC Technology

Search:

national grid high

voltage direct current

fact sheet