prEN IEC 62855:2021

Nuclear power plants - Electrical power systems - Electrical power systems analysis

IEC 62855 provides the electrotechnical engineering guidelines for analysis of AC and DC electrical power systems in nuclear power plants (NPPs) in order to demonstrate that the power sources and the distribution systems have the capability for safe operation and shut down of the NPP, bringing it to a controlled state after an anticipated operational occurrence or accident conditions and finally reaching a safe state. The analytical studies discussed in this document provide assurance that the design bases are satisfied to meet their functional requirements under the conditions produced by the applicable design basis events. The studies provide assurance that the electrical power system is capable of supporting safety functions during all required plant conditions. NOTE The safety functions are described in IAEA Specific Safety Requirements SSR-2/1 related to the design of the nuclear power plants.. Analytical studies validate the robustness and adequacy of design margins and demonstrate the capability of electrical power systems to support plant operation for normal, abnormal, degraded and accident conditions. The analyses are used to verify that the electrical power system can withstand minor disturbances and that the consequences of major disturbances or failures do not degrade the capability of the electrical power systems to support safe shutdown of the plant and maintain the plant in shutdown condition. The analyses are performed with one or more of • simulation tools (software and hardware) that have been verified and validated, • hand calculations, and • tests. This document provides guidance on the types of analyses required to demonstrate that the plant's auxiliary power system can perform the required safety functions. This document does not provide specific details on how the analysis should be conducted. This document does not cover digital controllers (such as controllers for rectifiers, inverters, sequencers and electrical protection devices) used in electrical power systems. IEC 61513 gives recommendations that apply to the electronic controls and protective elements of the electrical power systems. This document does not include environmental conditions (i.e. temperature, humidity, etc.) or external events (seismic, flooding, fire, high energy electromagnetic pulse, etc.) that may impact equipment sizing or protection requirements. The external events lightning and geomagnetic storms are included. This document does not cover additional or unique requirements for stand-alone power system, such as power supplies for security measures in NPPs. Pertinent clauses of this document may be used as a guideline for such systems. Redundancy in the power system design can increase the availability of electrical power to critical plant equipment. Performing a probabilistic risk assessment (PRA) is a method of assessing system availability and optimizing design for high reliability. This document does not cover improving the reliability of NPP electrical power systems using statistical or diverse and redundant schemes. Requirements for safeguards of personnel involved with installation, maintenance and operation of electrical systems and general personal safety are outside the scope of this document. General guidance for lightning protection of equipment is provided in relevant clauses of this document. This document is intended to be used: • for verification of the design of new nuclear power plants, • for demonstrating the adequacy and impact of major modifications of electrical power systems in operating nuclear power plants, and • where there is a requirement to assess and establish operating limits and constraints for existing plants. Pertinent parts of this document can be used as guidance for decommissioning stages.

Kernkraftwerke - Elektrische Stromversorgung - Analyse der Stromversorgung

Centrales nucléaires de puissance – Systèmes d’alimentation électrique – Analyse des systèmes d’alimentation électrique

L'IEC 62855:2016 donne les directives en matière d'ingénierie électrotechnique pour l'analyse des systèmes électriques de puissance en courant alternatif (CA) et en courant continu (CC) des centrales nucléaires (CNPE). Il s'agit de démontrer que les sources de puissance et le système de distribution électrique peuvent garantir le fonctionnement et l'arrêt sûr de la centrale, de manière à atteindre un état contrôlé après un incident de fonctionnement prévu, puis un état sûr. La présente norme a pour objectif d'être utilisée: - pour vérifier la conception des nouvelles centrales nucléaires de puissance; - pour démontrer la pertinence et l'impact de modifications majeures apportées aux systèmes électriques des CNPE en exploitation; - lorsque les centrales existantes font l'objet d'une exigence d'évaluation et d'établissement des limites ainsi que des contraintes de fonctionnement.

Jedrske elektrarne - Elektroenergetski sistemi - Analiza elektroenergetskih sistemov

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN IEC 62855:2021
01-maj-2021
Jedrske elektrarne - Elektroenergetski sistemi - Analiza elektroenergetskih
sistemov

Nuclear power plants - Electrical power systems - Electrical power systems analysis

Kernkraftwerke - Elektrische Stromversorgung - Analyse der Stromversorgung

Centrales nucléaires de puissance – Systèmes d’alimentation électrique – Analyse des

systèmes d’alimentation électrique
Ta slovenski standard je istoveten z: prEN IEC 62855:2021
ICS:
27.120.20 Jedrske elektrarne. Varnost Nuclear power plants. Safety
oSIST prEN IEC 62855:2021 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN IEC 62855:2021
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oSIST prEN IEC 62855:2021
EUROPEAN STANDARD DRAFT
prEN IEC 62855
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2021
ICS 27.120.20
English Version
Nuclear power plants - Electrical power systems - Electrical
power systems analysis
(IEC 62855:2016)

Centrales nucléaires de puissance - Systèmes Kernkraftwerke - Elektrische Stromversorgung - Analyse

d'alimentation électrique - Analyse des systèmes der Stromversorgung
d'alimentation électrique (IEC 62855:2016)
(IEC 62855:2016)
This draft European Standard is submitted to CENELEC members for enquiry.
Deadline for CENELEC: 2021-05-28.
The text of this draft consists of the text of IEC 62855:2016 (45A/1094/FDIS).

If this draft becomes a European Standard, CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which

stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CENELEC in three official versions (English, French, German).

A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to

the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the

Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to

provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and

shall not be referred to as a European Standard.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Project: 73226 Ref. No. prEN IEC 62855:2021 E
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oSIST prEN IEC 62855:2021
prEN IEC 62855:2021 (E)
European foreword

This document (prEN IEC 62855:2021) consists of the text of document IEC 62855:2016, prepared by

IEC/TC 45 "Instrumentation, control and electrical power systems of nuclear facilities"

This document is currently submitted to the CENELEC Enquiry.
The following dates are proposed:
• latest date by which the existence of this document (doa) dor + 6 months
has to be announced at national level
• latest date by which this document has to be (dop) dor + 12 months
implemented at national level by publication of an
identical national standard or by endorsement

• latest date by which the national standards (dow) dor + 36 months (to be confirmed

conflicting with this document have to be withdrawn or modified when voting)

As stated in the nuclear safety directive 2009/71/EURATOM, Chapter 1, Article 2, item 2, Member States

are not prevented from taking more stringent safety measures in the subject-matter covered by the

Directive, in compliance with Community law.

In a similar manner, this European standard does not prevent Member States from taking more stringent

nuclear safety and/or security measures in the subject-matter covered by this standard.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60038 NOTE Harmonized as EN 60038
IEC 60364-5-52 NOTE Harmonized as HD 60364-5-52
IEC 60880 NOTE Harmonized as EN 60880
IEC 60964 NOTE Harmonized as EN IEC 60964
IEC 61225 NOTE Harmonized as EN IEC 61225
IEC 61508-1 NOTE Harmonized as EN 61508-1
IEC 61508-2 NOTE Harmonized as EN 61508-2
IEC 61508-3 NOTE Harmonized as EN 61508-3
IEC 61508-4 NOTE Harmonized as EN 61508-4
IEC 61513 NOTE Harmonized as EN 61513
IEC 62003 NOTE Harmonized as EN IEC 62003
IEC 62138 NOTE Harmonized as EN IEC 62138
IEC 62271-200 NOTE Harmonized as EN 62271-200
IEC 62305-1 NOTE Harmonized as EN 62305-1
IEC 62305-3 NOTE Harmonized as EN 62305-3
IEC 62305-4 NOTE Harmonized as EN 62305-4
IEC 62340 NOTE Harmonized as EN 62340
IEC 62566 NOTE Harmonized as EN 62566
IEC 62645 NOTE Harmonized as EN IEC 62645
IEC 63046 NOTE Harmonized as prEN IEC 63046 to be published
ISO/IEC 27001 NOTE Harmonized as EN ISO/IEC 27001
ISO/IEC 27002 NOTE Harmonized as EN 16495
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oSIST prEN IEC 62855:2021
IEC 62855
Edition 1.0 2016-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Electrical power systems – Electrical power systems
analysis
Centrales nucléaires de puissance – Systèmes d’alimentation électrique –
Analyse des systèmes d’alimentation électrique
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-3589-8

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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oSIST prEN IEC 62855:2021
– 2 – IEC 62855:2016  IEC 2016
CONTENTS

FOREWORD ......................................................................................................................... 5

INTRODUCTION ................................................................................................................... 7

1 Scope .......................................................................................................................... 10

2 Normative references................................................................................................... 11

3 Terms and definitions .................................................................................................. 11

4 Symbols and abbreviations .......................................................................................... 12

5 Electrical power system analyses ................................................................................. 13

5.1 Overview of typical studies .................................................................................. 13

5.1.1 Transient stability analyses .......................................................................... 13

5.1.2 Load flow studies ......................................................................................... 13

5.1.3 Transient and dynamic studies ..................................................................... 13

5.1.4 Short circuit studies ..................................................................................... 14

5.1.5 Electrical protection coordination and selectivity ........................................... 14

5.1.6 Lightning protection studies .......................................................................... 14

5.2 Applicability of analyses to different plant states .................................................. 14

5.2.1 General ....................................................................................................... 14

5.2.2 Recommendations ....................................................................................... 14

5.3 Selection, verification and validation of analytical tools ........................................ 15

5.3.1 General ....................................................................................................... 15

5.3.2 Recommendations ....................................................................................... 16

5.4 Electrical power system model ............................................................................. 17

5.5 Grid and NPP connection .................................................................................... 17

5.6 Updating of system analyses ............................................................................... 17

5.7 Prerequisites for the performance of electrical studies ......................................... 17

5.8 Acceptance requirements .................................................................................... 18

6 Off-site power transient stability analyses ..................................................................... 18

6.1 General ............................................................................................................... 18

6.2 Recommendation ................................................................................................ 18

6.3 Acceptance requirements .................................................................................... 18

7 AC on-site power system analyses ............................................................................... 18

7.1 General ............................................................................................................... 18

7.2 Load flow studies ................................................................................................ 19

7.2.1 General ....................................................................................................... 19

7.2.2 Recommendations ....................................................................................... 19

7.2.3 Acceptance requirements ............................................................................. 19

7.3 Transient studies ................................................................................................. 19

7.3.1 General ....................................................................................................... 19

7.3.2 Faulted conditions ........................................................................................ 19

7.3.3 Bus transfer studies ..................................................................................... 20

7.3.4 Motor starting and reacceleration studies ...................................................... 21

7.3.5 House load operation ................................................................................... 22

7.3.6 Voltage disturbances .................................................................................... 22

7.3.7 Voltage surge caused by switching and malfunctions .................................... 23

7.3.8 Load sequencer studies ............................................................................... 23

7.3.9 Frequency studies ........................................................................................ 24

7.4 Fault studies ....................................................................................................... 24

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IEC 62855:2016  IEC 2016 – 3 –

7.4.1 Short-circuit studies ..................................................................................... 24

7.4.2 Earth fault (degraded insulation) studies ....................................................... 25

7.5 Electrical protection coordination studies ............................................................. 25

7.5.1 Recommendations ....................................................................................... 25

7.5.2 Acceptance requirements ............................................................................. 26

8 DC system and uninterruptible AC system analyses ..................................................... 26

8.1 Load flow studies ................................................................................................ 26

8.1.1 General ....................................................................................................... 26

8.1.2 Recommendations ....................................................................................... 26

8.1.3 Acceptance requirements ............................................................................. 27

8.2 Transient studies ................................................................................................. 27

8.2.1 Rectifier ....................................................................................................... 27

8.2.2 Inverter/UPS and bypass switch ................................................................... 27

8.3 Fault studies ....................................................................................................... 28

8.3.1 Short circuit studies ..................................................................................... 28

8.3.2 Earth fault (degraded insulation) studies ....................................................... 28

8.4 Electrical protection coordination studies ............................................................. 28

8.4.1 Recommendations ....................................................................................... 28

8.4.2 Acceptance requirements ............................................................................. 29

9 Miscellaneous analyses ............................................................................................... 29

9.1 Lightning protection studies ................................................................................. 29

9.1.1 General ....................................................................................................... 29

9.1.2 Recommendation ......................................................................................... 29

9.1.3 Acceptance requirements ............................................................................. 30

9.2 Electromagnetic compatibility .............................................................................. 30

9.2.1 General ....................................................................................................... 30

9.2.2 Recommendation ......................................................................................... 30

9.3 Harmonic studies ................................................................................................ 30

9.3.1 General ....................................................................................................... 30

9.3.2 Recommendation ......................................................................................... 30

9.4 Geomagnetic induced current (GIC) ..................................................................... 30

9.5 Ferroresonance studies ....................................................................................... 30

Annex A (informative) Establishment of design bases for nuclear power plant

electrical power systems ..................................................................................................... 31

A.1 Overview............................................................................................................. 31

A.2 Site electrical characteristics ............................................................................... 34

A.2.1 General ....................................................................................................... 34

A.2.2 Grid disturbances ......................................................................................... 35

A.2.3 Short circuit power ....................................................................................... 35

A.2.4 Lightning protection and insulation coordination ............................................ 36

A.2.5 Earthing characteristics ................................................................................ 36

A.3 Plant electrical characteristics ............................................................................. 37

A.3.1 General ....................................................................................................... 37

A.3.2 Main generator characteristics ...................................................................... 37

A.3.3 Standby AC power sources and alternate AC source ..................................... 37

A.3.4 DC power sources ........................................................................................ 39

A.4 Conceptual electrical design criteria .................................................................... 39

A.4.1 General ....................................................................................................... 39

A.4.2 Capacity of power sources ........................................................................... 39

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– 4 – IEC 62855:2016  IEC 2016

A.4.3 Protection coordination ................................................................................ 39

A.4.4 Voltage transients and interruptions ............................................................. 40

A.4.5 Capability for bus transfer ............................................................................ 40

A.4.6 Capability for motor start and reacceleration ................................................. 40

A.4.7 System earthing ........................................................................................... 40

A.4.8 Capability of electrical equipment ................................................................. 41

A.4.9 Electromagnetic interference ........................................................................ 41

A.4.10 Geomagnetic induced currents ..................................................................... 41

A.4.11 Ferroresonance ............................................................................................ 41

A.5 Conceptual nuclear design criteria ....................................................................... 42

A.5.1 General ....................................................................................................... 42

A.5.2 Reliability and availability, single failure criterion .......................................... 42

A.5.3 Common cause failures (CCF) and common mode failures (CMF) ................. 43

A.6 Design bases analysis ......................................................................................... 43

A.6.1 General ....................................................................................................... 43

A.6.2 Voltage ........................................................................................................ 44

A.6.3 Sizing of safety standby AC power sources ................................................... 45

A.6.4 Frequency.................................................................................................... 46

A.6.5 Electrical consumers’ databases and power balances ................................... 46

Annex B (informative) Guidelines for analytical studies ....................................................... 48

B.1 Analytical studies methodology ............................................................................ 48

B.1.1 General ....................................................................................................... 48

B.1.2 Process ....................................................................................................... 48

B.2 Example of detailed level ..................................................................................... 50

B.2.1 Purpose ....................................................................................................... 50

B.2.2 Analysis and basics ..................................................................................... 50

B.2.3 Minimum required data ................................................................................. 51

B.2.4 Contribution of the study .............................................................................. 51

Annex C (informative) Verification of design bases and equipment specification .................. 52

Annex D (informative) Example of plant specific acceptance criteria ................................... 55

Bibliography ....................................................................................................................... 56

Figure A.1 – Input and process to determine the specific electrical design bases for a

nuclear power plant and verification analyses ...................................................................... 32

Figure A.2 – Relationship of the plant electrical power system, the off-site electrical

power system and the on-site electrical power system for a nuclear power plant .................. 33

Figure A.3 – Relationship of power supplies important to safety, safety power supplies,

and the preferred power supply for a nuclear power plant .................................................... 34

Figure A.4 – Typical voltage design bases ........................................................................... 44

Figure B.1 – Overview of analytical studies ......................................................................... 48

Figure B.2 – Phenomena .................................................................................................... 49

Table C.1 – AC on-site power system analyses ................................................................... 52

Table C.2 – DC system and uninterruptible AC system analyses .......................................... 53

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oSIST prEN IEC 62855:2021
IEC 62855:2016  IEC 2016 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
NUCLEAR POWER PLANTS –
ELECTRICAL POWER SYSTEMS –
ELECTRICAL POWER SYSTEMS ANALYSIS
FOREWORD

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International Standard IEC 62855 has been prepared by subcommittee 45A: Instrumentation,

control and electrical systems of nuclear facilities, of IEC technical committee 45: Nuclear

instrumentation.
The text of this document is based on the following documents:
FDIS Report on voting
45A/1094/FDIS 45A/1100/RVD

Full information on the voting for the approval of this document can be found in the report on

voting indicated in the above table.

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

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oSIST prEN IEC 62855:2021
– 6 – IEC 62855:2016  IEC 2016

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

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
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that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
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oSIST prEN IEC 62855:2021
IEC 62855:2016  IEC 2016 – 7 –
INTRODUCTION
a) Technical background, main issues and organisation of the Standard

The principal function of the electrical power system is to support the safe operation of a

nuclear power plant (NPP) in all modes of operation. A subset of the electrical power system

is essential for supporting nuclear safety functions at various voltage levels. This subset is

critical for all plant states and events requiring plant cool-down in a controlled manner. A

reliable power system is critical for maintaining control to power, control and monitor plant

safety functions. This is required to support the barriers that prevent radiological releases

during design basis accidents and design extension conditions.
International Standards and National safety codes provide guidance on acceptable

requirements for safe and reliable operation of electrical distribution systems. Compliance

with these safety codes and standards generally provides reasonable assurance for the

correct electrical functionality and capability of these systems in the nuclear power plant

(NPP).

The design basis of the electrical power systems in a NPP should be established by

consideration of the following elements:

• nuclear design criteria, defence in depth approach, safety classification, design basis

conditions (DBC) and design extension conditions (DEC);

• requirements for transmission system operating limits, grid safety, grid code, plant

performance and operating limits;
• architecture and specification of the electrical power systems;

• sizing of main components and systems such as unit auxiliary and standby transformers,

switchgear, cables, motors and standby alternating current (AC) and direct current (DC)

power sources;
• load allocations and load power balance;
• load flow calculations;
• coordination of characteristics (voltage, current and short circuit current);
• support system requirements during postulated DBCs;
• design verification including verification analyses.

An example of design bases considerations for electrical power systems is provided in

informative Annex A.

Guidelines and an example of analytical methods are detailed in informative Annex B. The

relationship between analyses and verif
...