Guideline for planning of HVDC systems - Part 1: HVDC systems with line-commutated converters

IEC TR 63179-1:2020 (E) provides guidelines for the selection of a high-voltage directive current (HVDC) system with line-commutated converters (LCC), hereafter referred to as HVDC system, for the purposes of HVDC system planning. It covers the guidelines on the requirements for integrating HVDC systems in AC power networks, selection of rated voltage and power, overloads, circuit configuration, expandability, comparison of technical, economic, regulatory, political, social and environmental factors, etc.
This document is applicable for planning an HVDC system. This guideline is not exhaustive and it is possible that there will be other specific aspects, particular to a specific HVDC project, which will also need to be considered.

General Information

Status
Published
Publication Date
20-Apr-2020
Current Stage
PPUB - Publication issued
Completion Date
21-Apr-2020
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IEC TR 63179-1
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Guideline for planning of HVDC systems –
Part 1: HVDC systems with line-commutated converters
IEC TR 63179-1:2020-04 (en)
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IEC TR 63179-1
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Guideline for planning of HVDC systems –
Part 1: HVDC systems with line-commutated converters
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.200; 29.240.01 ISBN 978-2-8322-8208-3

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63179-1:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 6

4 General ........................................................................................................................... 6

5 Comparison between HVDC and AC alternatives ............................................................. 8

5.1 Consideration of overall network planning ............................................................... 8

5.1.1 Overall network planning ................................................................................. 8

5.1.2 Connection topologies for HVDC systems ........................................................ 8

5.2 Comparison of transmission capacity ...................................................................... 9

5.3 Comparison of operation requirements .................................................................... 9

5.3.1 Comparison of system fault and stability .......................................................... 9

5.3.2 Comparison of voltage regulation and reactive power compensation ................ 9

5.4 Comparison of cost ............................................................................................... 10

5.5 Comparison of other aspects ................................................................................ 11

6 HVDC solutions ............................................................................................................. 11

6.1 Main circuit topologies .......................................................................................... 11

6.1.1 General ......................................................................................................... 11

6.1.2 Monopolar HVDC transmission system .......................................................... 12

6.1.3 Bipolar HVDC transmission system ................................................................ 12

6.1.4 Rigid bipolar HVDC system ............................................................................ 12

6.2 Main equipment .................................................................................................... 13

6.2.1 General ......................................................................................................... 13

6.2.2 Converter ...................................................................................................... 13

6.2.3 AC filtering equipment ................................................................................... 14

6.3 Key DC rating parameters ..................................................................................... 14

6.3.1 Rated DC power ............................................................................................ 14

6.3.2 Rated DC voltage .......................................................................................... 15

6.3.3 Rated DC current ........................................................................................... 16

6.4 Line conductor ...................................................................................................... 16

6.5 Station sites and transmission line routes ............................................................. 17

6.5.1 Converter station sites ................................................................................... 17

6.5.2 Electrode station sites ................................................................................... 18

6.5.3 Overhead line route ....................................................................................... 18

6.5.4 Submarine cable route ................................................................................... 18

6.5.5 Land cable route ............................................................................................ 19

6.6 Interface requirements between AC network and HVDC ........................................ 19

6.7 Requirements of HVDC control system ................................................................. 20

6.7.1 Requirements for basic control and protection ............................................... 20

6.7.2 Supplementary control ................................................................................... 20

7 Analysis of security of supply and stability for DC alternatives ....................................... 21

7.1 Requirements for power network connection criteria ............................................. 21

7.1.1 General requirements for AC/DC power network ............................................ 21

7.1.2 Short-circuit ratio (SCR) of the AC system connected with single DC

system ........................................................................................................... 21

7.1.3 Short-circuit ratio of the AC system connected with multi-infeed DC

system ........................................................................................................... 22

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IEC TR 63179-1:2020 © IEC 2020 – 3 –

7.1.4 Effective inertia constant of AC/DC power network ........................................ 23

7.2 Stability of AC power system due to HVDC alternatives ........................................ 24

7.2.1 Stability analysis for AC power system .......................................................... 24

7.2.2 Analysis of sub-synchronous torsional interactions (SSTI) between

HVDC and nearby turbine-generator .............................................................. 24

7.2.3 Analysis for multi-infeed HVDC links .............................................................. 25

8 Economic comparison among the alternatives ............................................................... 25

8.1 General ................................................................................................................. 25

8.2 Main factors to be considered ............................................................................... 25

8.3 Indexes to be considered ...................................................................................... 26

8.4 Sensitivity analysis ............................................................................................... 26

8.5 Economic conclusion for recommended solution ................................................... 26

9 Study conclusions and recommended solution ............................................................... 26

Bibliography .......................................................................................................................... 28

Figure 1 – Phases during integration of a new HVDC system into the power network .............. 7

Figure 2 – Procedure for planning an HVDC system ............................................................... 8

Figure 3 – Cost versus distance ............................................................................................ 11

Table 1 – Typical overhead bipolar HVDC project for power transmission ............................. 15

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– 4 – IEC TR 63179-1:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDELINE FOR PLANNING OF HVDC SYSTEMS –
Part 1: HVDC systems with line-commutated converters
FOREWORD

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example "state of the art".
IEC TR 63179-1, which is a Technical Report, has been prepared by IEC technical

committee 115: High Voltage Direct Current (HVDC) transmission for DC voltages above

100 kV.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
115/216/DTR 115/230/RVDTR

Full information on the voting for the approval of this Technical Report can be found in the

report on voting indicated in the above table.
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IEC TR 63179-1:2020 © IEC 2020 – 5 –

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this document will remain unchanged until the

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– 6 – IEC TR 63179-1:2020 © IEC 2020
GUIDELINE FOR PLANNING OF HVDC SYSTEMS –
Part 1: HVDC systems with line-commutated converters
1 Scope

This document provides guidelines for the selection of a high-voltage directive current (HVDC)

system with line-commutated converters (LCC), hereafter referred to as HVDC system, for the

purposes of HVDC system planning. It covers the guidelines on the requirements for

integrating HVDC systems in AC power networks, selection of rated voltage and power,

overloads, circuit configuration, expandability, comparison of technical, economic, regulatory,

political, social and environmental factors, etc. This document is applicable for planning an

HVDC system.

This guideline is not exhaustive and it is possible that there will be other specific aspects,

particular to a specific HVDC project, which will also need to be considered.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.
IEC 60633, High-voltage direct current (HVDC) transmission – Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60633 apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org
• ISO Online browsing platform: available at http://www.iso.org/obp
4 General

The HVDC system development and integration cycle may be described in terms of six

phases, as shown in Figure 1.

The main task of HVDC system planning is to develop and select an HVDC scheme based on

the conclusions of power network development planning where the network requirements are

defined. HVDC system planning uses as a minimum the total transmission capacity and range

of connection points previously determined by power network development planning, taking

into account current and future conditions of the power system, environment, and other

contributing factors.

There is a certain degree of repetition and iteration between HVDC system planning and

system design (refer to Figure 1). For the purpose of project feasibility study and scheme

comparison, some investigation would be carried out during the system planning phase, the

detailed studies and final design would be accomplished during the system design phase.

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IEC TR 63179-1:2020 © IEC 2020 – 7 –
Figure 1 – Phases during integration of a new HVDC system into the power network
The work contents and procedure for planning of an HVDC system are as follows:

a) compare HVDC and AC solutions at high level according to the specific requirements (see

Clause 5);

b) when HVDC is the only technically feasible solution, or the use of an HVDC scheme has

overwhelming advantages, a number of alternative HVDC solutions could be investigated

(see Clause 6). When both HVDC and AC alternatives are technically feasible and neither

of them has overwhelming advantages, further analysis is required to confirm the
preferred solution;

c) verify the security of supply and stability of each alternative (see Clause 7);

d) compare the economic efficiency of alternative solutions (see Clause 8);
e) present the recommended solution (see Clause 9).
The above steps in the planning of an HVDC system are shown in Figure 2.
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– 8 – IEC TR 63179-1:2020 © IEC 2020
Figure 2 – Procedure for planning an HVDC system
5 Comparison between HVDC and AC alternatives
5.1 Consideration of overall network planning
5.1.1 Overall network planning

When a new line between two areas is planned, the solutions should consider all aspects of

transmission planning, including the current and future power demand, line corridor conditions,

operation and maintenance, energy dispatch and overall cost.
5.1.2 Connection topologies for HVDC systems

When an HVDC system is to be added to AC power networks, there are two typical connection

topologies:
a) HVDC interconnection between two asynchronous AC power networks;

b) embedded HVDC system. An embedded HVDC system is an HVDC link between two parts

of the same AC synchronous transmission system.

In addition, a multi-terminal HVDC link could also be considered both in a) and b) above.

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IEC TR 63179-1:2020 © IEC 2020 – 9 –
5.2 Comparison of transmission capacity

The power transfer between two networks through an AC overhead transmission line is

approximately given by the following expression:
P= sinθ
where
V and V are the voltages at the sending and receiving ends, respectively;
S R
X is the series reactance between the two ends;
θ is the load angle (phase difference between the two voltages).

To ensure that synchronism between the two networks is maintained following major

disturbances, the load angle is kept low during steady state operation. As a result, the power

transfer capability of the AC line is reduced compared to its thermal capability. This problem

does not exist with an HVDC system, as the two networks are decoupled and the power can

be independently controlled by the HVDC system.

For high-voltage AC cable transmission over certain distances, the charging current becomes

a major contributor to the thermal loading of the cable, due to its large shunt capacitance.

This therefore limits the useful load that the AC transmission circuit can carry. With DC

transmission, no charging current problems occur and therefore the useful load is also

generally only limited by the thermal capability of the cable.
5.3 Comparison of operation requirements
5.3.1 Comparison of system fault and stability

Faults causing significant voltage variation or power swings do not transmit across an HVDC

link. They may emerge on the other end of an HVDC link simply as a reduction in power,

without causing severe disturbance on the other end of the HVDC link.

Contrary to AC transmission, HVDC does not significantly increase the short-circuit currents

in both sending and receiving ends of AC power networks.

An HVDC link does not suffer from the power angle stability problems which frequently occur

with long AC transmission lines. Also, an AC transmission line is sensitive to disturbances of

the power balance in AC power networks, and the power flow within connecting AC lines is

not easy to be controlled, whereas the controllability of an HVDC system can be used to

support the stability of the connected AC networks by power runback or runup. Furthermore,

an HVDC link can provide additional benefits, such as possible overload and reduced voltage

operation. However, for a short time during a transient, an AC line may be able to transmit

more power than a DC link, even beyond its steady state thermal capacity, while the transient

overload allowed by the converter stations is usually smaller.
5.3.2 Comparison of voltage regulation and reactive power compensation

An AC transmission line imposes a load-dependent reactive power demand which may impact

the active current rating, and may require reactive power compensation at the terminals, and

at points along the line, to ensure the desired voltage level and adequate active power

transfer capability. While series or shunt compensation can assist transmission through

overhead lines, a technical limit is encountered in the case of transmission through insulated

cables. Even at relatively short distances, the reactive power consumes the greater part of the

current carrying capacity of the cable. Such solutions are possible, but inconvenient.

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– 10 – IEC TR 63179-1:2020 © IEC 2020

HVDC systems do not need this type of compensation and therefore do not present the same

technical limitations in long transmission distance, with no requirement for special

compensation along the line/cable.
5.4 Comparison of cost

The listed items below should be evaluated and compared from a monetary point of view:

a) station costs;
b) line costs;
c) cost due to the adaptation of the existing network;

d) capitalised cost of converter station and DC line losses during the life of the project;

e) operational costs;
f) maintenance costs;
g) decommissioning costs;
h) land acquisition and rights of way.
NOTE The above list is not exhaustive.

For bulk power transfer over long distances, an HVDC transmission project has a lower cost,

whereas an AC transmission project has a lower cost at short distance to transmit the same

power. There exists a "breakeven distance" at which HVDC and AC transmission projects

have the same cost.

The comparison is shown in Figure 3. Many factors contribute to the cost of AC and DC

transmission, including ratings, locations, terrain, losses, etc., therefore the determination of

the actual breakeven distance for a particular transmission system should be carried out on a

case-by-case basis. The breakeven distance of overhead line is typically around 600 km to

800 km. For transmission by submarine cable the breakeven distance is around 40 km to

120 km. It may not be practical to consider AC cables longer than 40 km without some forms

of additional compensation measures, but HVDC links using cables over hundreds of

kilometres are feasible.
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IEC TR 63179-1:2020 © IEC 2020 – 11 –
Figure 3 – Cost versus distance
5.5 Comparison of other aspects

In order to determine the most appropriate power transmission solution, a study and

comparison should be done for AC and HVDC alternatives.

The items listed below may be evaluated and compared from a strategic point of view:

a) political environment;
b) social impact;
c) environmental considerations;
d) transmission capacity and integration in the future power networks;
e) human resources for maintenance management and maintenance work;
f) regulatory and statutory requirements.
NOTE The above list is not exhaustive.
6 HVDC solutions
6.1 Main circuit topologies
6.1.1 General

There are two main types of HVDC system, namely transmission (two-terminal, also referred

to as point-to-point, or multi-terminal, where the different terminals are some distance away

from each other) and back-to-back systems (where the two terminals are in the same location

without an HVDC transmission line or cable).

For HVDC transmission systems, there are two categories, namely monopole and bipole.

For a back-to-back HVDC system, the monopolar configuration is normally used. There may

be more than one monopolar back-to-back converter unit in the same location.
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– 12 – IEC TR 63179-1:2020 © IEC 2020
For the main circuit topologies and their features, refer to IEC 60919-1.
6.1.2 Monopolar HVDC transmission system
6.1.2.1 Monopolar HVDC transmission system with earth return

This is the simplest HVDC transmission system topology. It is one of the most cost-effective

solutions. This topology is generally used as the first stage in construction of a (future) bipolar

system. However, it presents the following disadvantages:
a) a pole outage means that 100 % of power transfer capability is lost;

b) it requires an electrode line and a continuously operable earth electrode at the two ends

of the transmission which involves consideration of issues such as corrosion, magnetic

field effects, etc., and with possible impacts on the environment and on transformers close

to the electrodes.
NOTE Details about electrodes are available in IEC/TS 62344.
6.1.2.2 Monopolar HVDC transmission systems with dedicated metallic return
This topology will generally be used:

a) as the first stage in construction of a bipolar system and if long term flow of earth current

is not desirable during the interim period; or

b) if the HVDC transmission line length is short, where electrode lines and earth electrodes

are not economical; or

c) if the earth resistivity is high enough to impose an unacceptable economic penalty; or

d) if the environmental impact due to earth/sea return, such as dryness of land, sea

temperature rise, emission of dissolved gases, etc., is not acceptable.
6.1.3 Bipolar HVDC transmission system

Bipolar HVDC transmission topology is the most commonly used topology when an HVDC

transmission line connects two HVDC converter stations. The bipolar HVDC system with earth

return may be designed such that when one pole converter is out of service, the healthy pole

may use the faulty pole's high-voltage line as a metallic return.
The advantages of the bipolar topology compared to monopolar are as follows:
a) lower losses for a given transmitted power;

b) a pole outage means only 50 % of the total power transfer capability of the HVDC link is

lost. Owing to this, a bipole HVDC link is compared to a double circuit AC line;

c) overload capability may be incorporated into the rating of each pole, such that when one

pole is out of service the healthy pole may pick up some of the faulted pole power, leading

to some contingency power capability above 50 %, although this is scheme-specific;

d) lower earth current flow.

The disadvantages of this topology (compared to monopolar) include the following:

e) higher converter station costs;
f) more converter station equipment and therefore more land usage.
6.1.4 Rigid bipolar HVDC system

In this topology, there is not neutral connection between both converter stations. Since only

two (pole) conductors exist, no unbalance current between both poles is possible. In case of

interruptio
...

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