Functional Requirements from AC and DC grids to DC grid ... · ↗VSC HVDC is receiving massive...

© PROMOTioN – Progress on Meshed HVDC Offshore Transmission Networks

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 691714.

Functional Requirements from AC and DC grids to DC grid protection Dirk Van Hertem KU Leuven and EnergyVille

25-10-2016

© T

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CONTENTS

• Promotion project

• DC grid protection and WP4 of promotion

• System and Components Constraints

• Expected performance

• First suggestions for functional requirements

03.05.16 2

© T

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Promotion Horizon 2020 project (2016-2019)

WP14

Project

Manage

ment

WP13

Dissem

ination

WP1 – Requirements for meshed offshore grids

WP2 –

Grid

Topology

&

Converter

s

WP3 –

WTG-

Converter

Interactio

n

WP4 DC Grid

protection

system

development

WP5 Test

environm

ent for

HVDC

circuit

breakers

WP6

HVDC CB

performa

nce

characteri

zation

WP7

Regulatio

n and

Financin

g WP8

Wind farm

demonstrators

WP9

Demonstration

of DC grid

protection

WP 10

Circuit Breaker

performance

demonstration

WP 11 – Harmonization towards standardisation

WP 12 – Deployment plan for future European offshore grid development



Towards an HVDC grids with the most appropriate, cost effective, multi-vendor protection system

Busbar fault

Pole-to-ground fault

DC CB

Converter (with/without fault blocking capability)

DC Circuit Breaker

Relay

DC Disconnector

Vendor D

Vendor C

Vendor B

Vendor A

Busbar

Cable



↗VSC HVDC is receiving massive attention from industry, especially for offshore connections and interconnectors

↗DC grids are seen as a logical evolution ↗Offering redundancy

↗Possible cost savings

↗DC grids require protection

↗Current VSC HVDC protection: at the AC side ↗ not a good solution for the future pan-European grid

DC grids and DC grid protection

03.05.16 5



↗to develop a set of functional requirements for various DC grids: from small scale to large overlay grids and for a variety of system configurations and converter topologies

↗to analyse a wide range of DC grid protection philosophies on a common set of metrics

↗to identify the best performing methods for the systems under study

↗to develop detailed protection methodologies for the selected methods

↗to develop configurable multi-purpose HVDC protection IEDs to enable testing of the methodologies

↗to investigate the key influencing parameters of protection systems on the cost-benefit evaluation

WP4: develop multi-vendor protection systems

03.05.16 6



↗Protection system: What to protect? ↗Humans

↗System

↗Components

↗For the AC system: ↗After single fault, selective protection system clears fault

↗Backup protection if that fails

↗Protection operates in 60 – 200 ms

↗Operated N-1: no single credible fault/contingency causes large sustained outage ↗ Expected behavior at a single line fault

↗ Expected behavior at busbar fault

↗ Expected behavior at fault at lower levels (e.g. distribution)

↗ Fault ride through behavior of wind farm

↗3 GW / 1.8 GW / … maximum loss of infeed

What are our expectations of DC grid protection?

03.05.16 7



↗What about the DC grid? ↗Same as AC?

↗Which reliability?

↗Are the limits (delays, power loss,…) the same?

↗What are relevant faults at the DC side ↗ Pole to pole?

↗ Pole to ground?

↗ Busbar?

↗What is the accepted behavior at the DC side

↗AND the connecting AC systems ↗ Continental Europe, Ireland, offshore wind, offshore load

↗Do we expect the same for all systems? ↗ Small --> medium --> large

What are our expectations of DC grid protection?

03.05.16 8



↗Type (a) line protection : impact only on the faulty line

↗Type (b) line+ protection : impact on the faulty line and on the closest MMC converter

↗Type (c) open grid protection : impact of all the breakers at a bus

↗Type (d) grid splitting protection : impact only on the faulty zone

↗Type (e) low-speed HVDC grid protection : impact on the entire grid

Overview: Fault clearing strategies (zones-impact)



Functional requirements?

03.05.16 10

System and components

constraints

Expected performance for DC

grids (small, medium and large)

• Various DC faults

Functional requirements

for DC grids

• Current technology

• What is the limit now?

• What is the limit in 2050?



Components of DC grid protection: influencing eachother

03.05.16 11

Protection

equipment

Control equipment

Power system components

Converters

Switchgear

Fault current limiters

System controls

Communications

Relays/Algorithms

Measurements

Communications

Restoration



↗Selectivity & speed ↗E.g., maximum portion of the

grid which can be disconnected

↗Maximum time for which grid can be disconnected

↗Backup protection ↗Lower probability, but higher

impact

↗Robustness towards system changes

System functional requirements lead to requirements for protection

↗Suitable protection philosophies ↗Selective

↗Partly selective

↗Non-selective

↗Suitable fault clearing strategies



↗Protection algorithms ↗Speed

↗Selectivity

↗Sensitivity

↗Reliability

↗Breakers ↗Speed

↗ Interruption capability

↗Energy absorption capability

↗Fault current limiters ↗Di/dt …

Protection requirements lead to requirements for protection components

↗Suitable candidates ↗Protection algorithms

↗ Non-unit

↗ Unit/Pilot

↗Breakers: Mechanical, Hybrid

↗ Inductors/SFCL/…



• Potential Faults/events: • AC faults (single-phase-to-ground, three-phase-to-ground)

• Outage of a converter

• DC line faults (pole-to-ground, pole-to-pole)

• DC busbar faults

• Potential effects on the AC & DC systems: • DC system: overvoltage, under voltage, overcurrent, DC grid

instability, DC overload

• AC system: overvoltage, under voltage, overcurrent, AC grid instability (transient stability, small signal stability, frequency stability), AC overload

• what is acceptable?

Why relevant? Faults occur and they influence the total system



DC Line (pole-to-ground) fault: example 1

15

Test system: 3-terminal bipolar with metallic return DC Power during and after pole-to-ground fault

Utilizing fast selective DC protection (fault clearing ~5ms):

DC system:

• Possible overload post fault clearing

AC system:

• Very short transients

Conv1

Conv3

Conv2

100km

150km




03.05.16 16

Utilizing AC circuit breaker for fault clearing (fault clearing 2~3 cycles):

DC system:

• Outage of the whole DC system

• Possible large fault currents depending on grounding configuration

AC system:

• See multiple short-circuit faults once converters are blocked

• Possible instability

AC2

AC1

Conv1

Conv2

Conv3

Conv4

Conv5

Fault

Conv blkAC sees SC faults

Fault cleared

DC restart

t

P PAC1

some ms

40~60 ms

hundreds ms




03.05.16 17

Utilizing converters with fault blocking capability:

DC system:

• Outage of the whole DC system

AC system:

• Short interruption

• Possible instability

o Asynchronous AC systems

o Synchronous AC systems

Synchronized

AC systems

ω ω

AC2

AC1

Conv1

Conv2

Conv3

Conv4

Conv5

FaultConv Blk

DC restart

t

P PAC1

some ms

tens ms?



HVDC converter outage: influence on ac frequency and generator rotor angles

03.05.16 18

Simplified representation of ac system:

• Equivalent synchronous generator (SGeq) with inertia constant H

• Droop control action is neglected within the considered time frame (0-0.2s)

• HVDC converter outage = Load step on synchronous generator


This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 691714. 03.05.16 19

1

3

579

47,5

48

48,5

49

49,5

50

H [s]

Fre

qu

en

cy [H

z]

ΔP [pu]

For ΔT = 0.1 s

47,5-48 48-48,5 48,5-49 49-49,5 49,5-50

1

2

3

4

5

6

7

8

9

10

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9 1

H [

s]

Fre

qu

en

cy [H

z ]

ΔP [pu]

00.25

0.5

0.75

1

49

49,2

49,4

49,6

49,8

50

ΔP

[p

u]

Fre

qu

en

cy [H

z]

ΔT [s]

For H = 5s

49-49,2 49,2-49,4 49,4-49,6 49,6-49,8 49,8-50

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

0,0

2

0,0

4

0,0

6

0,0

8

0,1

0,1

2

0,1

4

0,1

6

0,1

8

0,2

ΔP

[p

u]

Fre

qu

en

cy [H

z]

ΔT [s]



↗Maximum loss of power infeed and duration:

Constraints from synchronous AC Systems

03.05.16 20

∆P

t

Pmax

fewms

> hundreds ms

Maximum allowed

permanent loss

Tens -100 ms

P1

P2

Pzone2 < Pmax

Pzone1 < P2

Zone 1FB

Zone 2ACCB

DC Disconnector

DC circuit breaker

Full bridge MMC

AC

AC

AC circuit breaker

Half bridge MMC



↗Maximum temporary power loss and duration ↗at a node

↗ to a synchronous zone

↗ to a control area

↗Voltage support requirement

Constraints from asynchronous AC Systems

03.05.16 21



↗Point-to-point HVDC offshore links ↗AC fault ride-through: hundreds ms (e.g. 384 ms for 30% Vremaining GB [1])

↗DC faults are protected using AC circuit breakers: 2~3 cycles

↗Constraints to DC grids: ↗Fault interruption: within 2 ~3 cycles

↗Converter DC LVRT capability?

Constraints from wind farms

03.05.16 22

F1

DC

chopper

F2ACCBACCB

F2

[1] A. J. Beddard and U. Oj, “Factors Affecting the Reliability of VSC-HVDC for the Connection of

Offshore Windfarms,” PhD thesis, 2014.



↗Converter (for all types of converters): ↗Udc at the converter terminal

↗ Normal operation: 90% - 110%

↗ Minimum voltage and duration for a converter has to stay unblocked: 0.8pu hundreds ms?

↗ Iarm of the converter ↗ IGBT (maximum instantaneous current limit):

↗ 2 [pu] on maximum dc value allowed by IGBT

↗ Future technology: SiC, GaN?

↗ Diode/thyristors

↗ Surge withstand capability [kA2t]

Constraints from DC grid components

03.05.16 23

DC fault ride through capability

Udc/Udcn

t

tUV,blkUmin,blk

100%110%

90%

When a converter is allowed to be blocked and tripped



↗DC Circuit Breakers: constraints to relay speed


03.05.16 24

Energy absorption branch

Auxiliary branch

Main branchRCBCurrent limiter

Imax

tbr,otbr,t tint tc

∆tbr,t ∆tbr,int ∆tbr,rcb

Parameter Unit Typical value Foreseeable values(2030-2050)

Breaker tripping delay [ms] Hybrid: 2-3 ms,

Mechanical: 5-10

ms

Fault current

interruption capability [kA]

Hybrid: 5-10 kA,

Mechanical: 10-16

kA

Energy absorption

capability [MJ] ~ 10 MJ

Bypass delay [ms] ?

Residual current

interruption capability [kA] 0.1 kA

Maximum current rate

of rise [kA/s] 3-5 kA/s

Maximum breaker

surge arrestor voltage [pu] 1.5

Rated voltage [kV] 320 500?

Structure of a DC circuit breaker

Fault interruption process

Currently collecting inputs for different components



↗Cable constraints [3]:

WP4.1 Investigation and evaluation of fault detection and selectivity methods, towards functional requirements


03.05.16 25

Parameter Unit Typical value

Foreseeable values(2030-2050)

Remarks

Lightning impulse withstand level

[pu] 2,1 (same polarity)

Lightning impulse withstand level

Switching impulse withstand level

[pu] 1,2 (opposite polarity)

Switching impulse withstand level

Maximum continuous dc voltage (applied during type and routine test)

[pu] 1,85 Maximum continuous dc voltage (applied during type and routine test for 15minutes)

Thermal overload limit

[pu] ?

[3] Cigre WG B1.32 - Recommendations for testing DC extruded cable systems for power transmission at a rated

voltage up to 500 kV

t

U0

2.1 [pu]

t

U0

-1.2 [pu]



• Stress on AC and DC system

• AC side system fault ride through capability

• DC side voltage capability

• Chicken and egg problem: DC grid design depends on what we expect from its operations and operational expectations depend on the system in place

• What do we want as behavior? What is acceptable?

Towards Functional Requirements of DC Grids

26

∆P

t

Pmax

5ms Few hundreds ms

Allowed power outage – time requirement Pmax: allowed maximum permanent loss

Allowed voltage deviations (source: cigre B4-56)



Questions?

27

COPYRIGHT PROMOTioN – Progress on Meshed HVDC Offshore Transmission

Networks

MAIL [email protected] WEB www.promotion-offshore.net

The opinions in this presentation are those of the author and do not

commit in any way the European Commission

PROJECT COORDINATOR DNV GL, Kema Nederland BV

Utrechtseweg 310, 6812 AR Arnhem, The Netherlands

Tel +31 26 3 56 9111

Web www.dnvgl.com/energy

CONTACT

PARTNERS Kema Nederland BV, ABB AB, KU Leuven, KTH Royal

Institute of Technology, EirGrid plc, SuperGrid Institute,

Deutsche WindGuard GmbH, Mitsubishi Electric Europe

B.V., Affärsverket Svenska kraftnät, Alstom Grid UK Ltd

(Trading as GE Grid Solutions), University of Aberdeen,

Réseau de Transport d‘Électricité, Technische Universiteit

Delft, Statoil ASA, TenneT TSO B.V., German OFFSHORE

WIND ENERGY Foundation, Siemens AG, Danmarks

Tekniske Universitet, Rheinisch-Westfälische Technische

Hochschule Aachen, Universitat Politècnica de València,

Forschungsgemeinschaft für. Elektrische Anlagen und

Stromwirtschaft e.V., Dong Energy Wind Power A/S, The

Carbon Trust, Tractebel Engineering S.A., European

University Institute, Iberdrola Renovables Energía, S.A.,

European Association of the Electricity Transmission &

Distribution Equipment and Services Industry, University of

Strathclyde, ADWEN Offshore, S.L., Prysmian,

Rijksuniversiteit Groningen, MHI Vestas Offshore Wind AS,

Energinet.dk, Scottish Hydro Electric Transmission plc

APPENDIX



DISCLAIMER & PARTNERS

03.05.16 28

mailto:[email protected]



http://www.promotion-offshore.net/



http://www.dnvgl.com/energy

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Functional Requirements from AC and DC grids to DC grid ... · ↗VSC HVDC is receiving massive...

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