2011-03-24_session1_carlbarker_hvdc as a bulk power transfer system

7/29/2019 2011-03-24_Session1_CarlBarker_HVDC as a Bulk Power Transfer System

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GRID

Chief Engineer, Systems

Offshore Wind Training Seminar - March 2011

Session 1:

HVDC as a bulk power transfer system

Carl Barker


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HVDC as a bulk power transfer system March 2011 - P 3

Friends of the SuperGrid (FOSG)

Connection Capacity(GW)

Dogger Germany Offshore 10

Dogger Norfolk Bank 5

Dogger Firth of Forth 5

Dogger Norway 5

Germany Offshore - Munich 10

London Norfolk Bank 5

Norfolk Bank BelgiumOffshore

2

SuperNode

Belgium Offshore 2

Dogger - Hornsea 10

Germany Offshore 10

Norfolk Bank 5

Munich 10

Firth of Forth 5Figure 1: SuperGrid Phase 1

Figure 2: Interconnection and SuperNode Cap

Source: FOSG Position paper on the EC Communication for a European Infrastructure Package, Dec 2010


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Why DC Transmission?

HVDC transmission is the correct technology forbulk submarine energy transfer.

AC

DC

Charges and Discharges

Every Half Cycle

Only Charges the Cable Once


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Why DC Transmission?

Basic Structure of VSC Transmission System

t

Idc

t

ii

Iact

i

Iac

Idc= V1- V2R

DC transmissionline

Q1 Q2P

VSC VSC

Station 1 Station 2

V1 V2

IC1

Network

1

Network

2


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Agenda

Why DC Transmission? Page 3

Offshore Grids Page 7

DC Grid Control Page 14

DC Grid Protection Page 24

DC Grid Fault Clearance Page 34

DC Grid Standardisation Page 43


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Offshore DC Grids

Definition:

DC Grids Multiple converters connecting AC powernetworks to a DC power network

DC Grids Permit the economic transfer of power overburied cables reducing environmental impact

DC Grids Permits economic bulk transfer over large

distances DC Grids Reduce the number of AC/DC Conversions

therefore reduce losses


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132kV

400V400V400V

11kV11kV

400V400V400V

11kV11kV

DC Grid Configurations: Point-to-point System


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132kV

400V400V400V

11kV11kV

400V400V400V

11kV11kV

DC Grid Configurations: Meshed System


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132kV

400V400V400V

11kV11kV

400V400V400V

11kV11kV

DC Grid Configurations: Radial System


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HVDC connections

Grid connection

Cable +/-320kV DC

or similar

DC Converter

Station

HVAC cable

Onshore Offshore

MV array

cabling to

WTG

MV array

cabling to

WTG


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Platform Switchgear Arrangement

AC

DC

To Adjacent

Platform

To Shore

Station

To Adjacent

Platform


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Agenda








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Two-terminal VSC Control

Basic Converter control of a two-terminal VSC

Converter 1 Converter 2

Converter 3

Converter 4

Slack bus


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DC Grid Control

Will a single utility / system owner be prepared to act asthe slack bus for all other interconnected systems?

Converter 1 Converter 2

Converter 3

Converter 4

Slack bus


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Comparison of AC and DC parameters

AC PARAMETER DC PARAMETERFrequency

Target DC Voltage

Vdc Voltage Change

))sin(V(

Voltage Change

V

Impedance of Connection

)X( Resistance of Connection

R

Real Power X

sinVV

Real Power

R

VV


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A typical VSC converter slope

characteristic

a*

Vdc

-Idc +Idc

IMPORT(A)

EXPORT(A)

VdcMAX

(A)

VdcMIN

(A)

LRSP

Vdc/IdcSlope(A)

-Idc

MAX(A)

+Idc

MAX(A)

-Idc IMPORT

LIMIT(A)

+Idc EXPORT

LIMIT(A)

VAa

b

c

d

d*


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A basic controller for DC converter

in a multi-terminal HVDC scheme

DispatchCentreConverter

Station

Controller

Porder

LRSP

Idcmax Limit

slopedc

dc

I

V

Vdc

MAX

V

X

Vorder

Limits

Vdc

MIN

Vorder

Idc measured

Iorder

Limits

Idcmin Limit

Idc measured

LRSP

Porder


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A two-terminal VSC Grid with power

flow from terminal A to terminal B

Vdc

-Idc +Idc

IMPORT(A)

EXPORT(A)

VdcMAX

(A)

VdcMIN

(A)

LRSP

OP

VA

VB

IMPORT

(B)

EXPORT

(B)

VdcMAX

(B)

VdcMIN

(B)


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A change in power demand compensated

by a new power dispatch

Vdc

+Idc

EXPORT

(A)

OP2

VA1

VB2

IMPORT

(B)

VdcMAX

(B)

VdcMIN

(B)

OP1

Vdc

+Idc

EXPORT

(A)

OP2

VA3

VB3

IMPORT

(B)

VdcMAX

(B)

VdcMIN

(B)

OP1

Constant

Pdc Line

OP3


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A three-terminal DC grid

OPB

Vdc

-Idc +Idc

LRSP

OPC OPA

IBIC IA = IB+ IC

IMPORT

(A)

EXPORT

(A)

IMPORT (B)

IMPORT (C- - )

EXPORT (B)

EXPORT (C- - )


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Voltage Optimiser

OPB

Vdc

-Idc +Idc

LRSP

OPC OPA

IBI

CIA

= IB+

IC

IMPORT

(A)

EXPORT

(A)

IMPORT (B)

IMPORT (C- - )

EXPORT (B)

EXPORT (C- - )

Steady-statetransmissionloss

minimisation

One converterterminal

determines thenew, higher,

LRSP

LRSP ramp can bestopped at anytime


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Agenda








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DC Grid protection

Key issues

Multi-terminal DC cable systems are low inertia systems

A DC fault (voltage on one pole goes to zero) is experiencedsimultaneously throughout the system

Protection system must discriminate the faulted cable section

to allow rapid isolation by switchgear action

Multi-terminal system should return to stable operation, inminimum time with minimum loss of infrastructure


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Protection systems

AC

DC

To

Adjacent

Platform

To

Shore

Station

To

Adjacent

Platform

AC side transducers are conventionalelectromagnetic current transformers

DC side transducers are based on modern

fibre optic current measurement techniques


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Current Transducer Nxt Phase

Fibre optic

measurement head

Polymericinsulators toprotect fibre opticcables

Fibre optic connectionto matching unit


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Protection Zones

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

AC feeder from AC

collector platform


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Protection Zones

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

Transformer differential

zone


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Protection Zones

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

AC DC differential

zone


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Protection Zones

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

DC bus protection

zone


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Protection Zones

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

DC cable over-current

protection zone


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DC cable fault protection

DC bus protection DC bus protection

DC cable protection

Unbalance DCcurrent protection


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Agenda








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Modular Multi-level Converter : Half

link

+ V

- V

+ V

- V

U

Module Output voltage

Lowest component count

Only one possibility of

output voltage polarity

No capability ofsuppressing DC-side faults

i i


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Option 1 Half-bridge converters +

Disconnects

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

= Mechanical Disconnect= AC Circuit Breaker

DC cable fault can not be cleared by half

bridge AC/DC converter

AC circuit breakers on all platforms open toclear the fault

Appropriate disconnects opened to isolatefaulted cable section

Complete multi-terminal scheme is re-started

M d l M l i l l C F ll


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Modular Multi-level Converter : Full

link

+ V

- V

+ V

- V

Same circuit as ALSTOMSTATCOM chain circuit Output DC voltage can be

either polarity Hence can connect as tapto LCC-HVDC link Can also suppress DC sidefaults

U

Module Output voltage

O i 2 F ll b id


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Option 2 Full-bridge converters +

Fast Switches

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

= Fast Isolating Switch= AC Circuit Breaker

DC cable fault can be cleared by full bridge

AC/DC converters

Appropriate fast (30 40ms) isolating switchesopened to isolate faulted cable section

Complete multi-terminal scheme is re-startedin 300 400ms

O ti 3 H lf b id t


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Option 3 Half-bridge converters +

Circuit Breakers

AC

DC

To Adjacent

Platform

To Shore

Station

To AdjacentPlatform

= DC Circuit Breaker= AC Circuit Breaker

DC cable fault can be cleared by the

appropriate DC circuit breaker

No AC/DC converter action is required

No interruption of power flow in the multi-terminal system, except faulted section


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DC Circuit Breaker

Half Bridge power electronic converter

Each pole is equivalent to 1/6th of the main AC/DC converter

Full DC fault current interruption capability

Full DC voltage withstand capability

Operating losses = 0.11% of station power per pole

Coordination is required between the over-current capability ofthe AC DC converter and the time required for the Breaker todetect and interrupt the fault current


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DC Circuit Breaker - Possibilities

There are no commercially available DC circuit breakers at this time,although R&D work is in progress. Possibilities include,

Vacuum

Plasma

Power electronic

Magnetic

Super-conducting

Hybrid of technologies


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TWENTIES project DC Breaker WP

Work package goal: specify and demonstrate the

critical component for multi-terminal grids, the DC

breaker

Candidate technologies:

Collaborative Activities

Mechanical switchHybrid switchPower electronic switch


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Agenda








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Do We Need to Standardise?

Purpose of Standards

Support interoperability

Allowing interconnected systems to be built incrementally

and by different equipment suppliers, thus support

incremental investment plans and avoid stranded assets

Allow separation of cable and converter procurement thus

allowing buyers to take advantage of the increasing

number of HVDC cable manufacturers


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Functional Specifications

AC/DC Converters

HVDC Cables

DC Breakers DC-DC Converters

Dump Resistor

Equipment that should have a common functional specification


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Design Specification

Topology?

Symmetric Monopole Monopole Bipole

DC Voltage (nominal, steady-state and transient range)

Fault Current Contribution

Multi-terminal DC Protection

Multi-terminal DC control

Equipment that should be defined at the initial design stage


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DC Grid Standardisation Activities

International recommendations being created;

CENELEC - Four, five, six terminal grids Cigr B4-52 - Large pan-European grids

Cigr have just approved five further DC grid working groups;

B4-56 Guidelines for the preparation of connection agreements orGrid Codes for HVDC grids

B4-57 Guide for the development of models for HVDC converters in aHVDC grid

B4-58 Devices for load flow control and methodologies for directvoltage control in a meshed HVDC Grid

B4-59 Devices for load flow control and methodologies for directvoltage control in a meshed HVDC Grid

B4-60 Designing HVDC Grids for Optimal Reliability and Availabilityperformance


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2011-03-24_session1_carlbarker_hvdc as a bulk power transfer system

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