Explosive atmospheres - Part 32-1: Electrostatic hazards, guidance

IEC TS 60079-32-1:2013 gives guidance about the equipment, product and process properties necessary to avoid ignition and electrostatic shock hazards arising from static electricity as well as the operational requirements needed to ensure safe use of the equipment, product or process. It can be used in a risk assessment of electrostatic hazards or for the preparation of product family or dedicated product standards for electrical or non-electrical machines or equipment.
The purpose of this document is to provide standard recommendations for the control of static electricity, such as earthing of conductors, reduction of charging and restriction of chargeable areas of insulators. In some cases static electricity plays an integral part of a process, e.g. electrostatic coating, but often it is an unwelcome side effect and it is with the latter that this guidance is concerned. If the standard recommendations given in this document are fulfilled it can be expected that the risk of hazardous electrostatic discharges in an explosive atmosphere is at an acceptably low level.

Atmosphères explosives - Partie 32-1: Dangers électrostatiques – Recommandations

IEC TS 60079-32-1:2013 fournit les recommandations relatives au matériel, au produit et aux propriétés de processus nécessaires pour éviter l'inflammation et les dangers de chocs électrostatiques liés à l'électricité statique, ainsi que les exigences de fonctionnement nécessaires pour garantir l'utilisation en toute sécurité du matériel, du produit ou du processus. Elle peut être utilisée dans le cadre d'une appréciation du risque des dangers électrostatiques ou de l'élaboration de normes de famille de produits ou de normes de produits spécifiques concernant des machines ou des équipements électriques ou non électriques.
L'objet du présent document est de fournir des recommandations normalisées pour le contrôle de l'électricité statique, telles que la mise à la terre des conducteurs, la réduction de l'électrisation et la restriction des zones électrisables des isolateurs. Dans certains cas, l'électricité statique fait partie intégrante d'un processus (revêtement électrostatique, par exemple), mais elle s'accompagne souvent d'un effet secondaire gênant, ce sur quoi portent les présentes recommandations. Si les recommandations normalisées indiquées dans le présent document sont respectées, le risque de décharges électrostatiques dangereuses attendues dans une atmosphère explosive peut être à un niveau bas acceptable.

Distribution automation using distribution line carrier systems - Part 1: General considerations - Section 1: Distribution automation system architecture

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Status
Published
Publication Date
19-Aug-2013
Current Stage
PPUB - Publication issued
Start Date
20-Aug-2013
Completion Date
20-Aug-2013

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IEC TS 60079-32-1
Edition 1.0 2013-03
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
Explosive atmospheres –
Part 32-1: Electrostatic hazards, guidance
Atmosphères explosives –
Partie 32-1: Dangers électrostatiques – Recommandations
IEC TS 60079-32-1:2013-03(en-fr)
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
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---------------------- Page: 2 ----------------------
IEC TS 60079-32-1
Edition 1.0 2013-03
TECHNICAL
SPECIFICATION
SPECIFICATION
TECHNIQUE
Explosive atmospheres –
Part 32-1: Electrostatic hazards, guidance
Atmosphères explosives –
Partie 32-1: Dangers électrostatiques – Recommandations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-6241-2

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
---------------------- Page: 3 ----------------------
– 2 – IEC TS 60079-32-1:2013 © IEC 2013
CONTENTS

FOREWORD ......................................................................................................................... 10

INTRODUCTION ................................................................................................................... 12

1 Scope ............................................................................................................................ 13

2 Normative references .................................................................................................... 13

3 Terms and definitions .................................................................................................... 16

4 Nomenclature ................................................................................................................ 19

5 General ......................................................................................................................... 20

6 Static electricity in solid materials .................................................................................. 21

6.1 General considerations .................................................................................... 21

6.2 The use of conductive or dissipative materials in place of insulating ones ........ 23

6.2.1 General considerations ................................................................... 23

6.2.2 Dissipative solid materials .............................................................. 23

6.2.3 Earthing of conductive and dissipative items ................................... 24

6.3 Precautions required when using insulating solid materials .............................. 25

6.3.1 General .......................................................................................... 25

6.3.2 Restrictions on the size of chargeable insulating surfaces .............. 26

6.3.3 Earthed metal meshes .................................................................... 27

6.3.4 Insulating coatings on earthed conductive surfaces ........................ 27

6.3.5 Conductive or dissipative coatings on insulating materials .............. 28

6.3.6 Static dissipative agents ................................................................. 29

6.3.7 Humidification ................................................................................. 29

6.3.8 Ionisation / Charge Neutralisation ................................................... 29

6.3.9 Methods to determine the incendivity of discharges ........................ 30

6.4 Conveyor belts and transmission belts ............................................................. 31

6.4.1 General .......................................................................................... 31

6.4.2 Conveyor belts ............................................................................... 31

6.4.3 Transmission belts .......................................................................... 32

7 Static electricity in liquids .............................................................................................. 33

7.1 General considerations .................................................................................... 33

7.1.1 Occurrence of flammable atmospheres ........................................... 33

7.1.2 Ignition sensitivity and limitations to the scope of advice................. 34

7.1.3 Charging mechanisms .................................................................... 35

7.1.4 Charge accumulation and conductivity classifications ..................... 35

7.1.5 Incendive discharges produced during liquid handling

operations ...................................................................................... 36

7.2 Summary of precautions against ignition hazards during liquid handling

operations ........................................................................................................ 37

7.2.1 Earthing and avoidance of isolated conductors ............................... 37

7.2.2 Restricting charge generation ......................................................... 37

7.2.3 Avoidance of a flammable atmosphere ........................................... 38

7.2.4 Promoting charge dissipation .......................................................... 38

7.3 Tanks and Containers ...................................................................................... 38

7.3.1 General .......................................................................................... 38

7.3.2 Conductive tanks and containers .................................................... 39

7.3.3 Tanks and containers made entirely of dissipative material ............. 52

7.3.4 Tanks and containers with insulating surfaces ................................ 52

7.3.5 Use of liners in containers .............................................................. 56

---------------------- Page: 4 ----------------------
IEC TS 60079-32-1:2013 © IEC 2013 – 3 –

7.4 High viscosity liquids ........................................................................................ 57

7.5 High charging equipment ................................................................................. 57

7.5.1 Filters, water separators and strainers ............................................ 57

7.5.2 Pumps and other equipment ........................................................... 58

7.6 Gauging and sampling in tanks ........................................................................ 59

7.6.1 General .......................................................................................... 59

7.6.2 Precautions during gauging and sampling ....................................... 59

7.7 Pipes and hose assemblies for liquids .............................................................. 60

7.7.1 General .......................................................................................... 60

7.7.2 Pipes .............................................................................................. 60

7.7.3 Hoses and hose assemblies ........................................................... 63

7.8 Special filling procedures ................................................................................. 69

7.8.1 Aircraft fuelling ............................................................................... 69

7.8.2 Road tanker deliveries .................................................................... 70

7.8.3 Retail filling stations ....................................................................... 71

7.8.4 Mobile or temporary liquid handling equipment ............................... 75

7.9 Plant processes (blending, stirring, mixing, crystallisation and stirred

reactors) .......................................................................................................... 75

7.9.1 General .......................................................................................... 75

7.9.2 Earthing .......................................................................................... 75

7.9.3 In-line blending ............................................................................... 75

7.9.4 Blending in vessels or tanks ........................................................... 76

7.9.5 Jet mixing ....................................................................................... 76

7.9.6 High speed mixing .......................................................................... 77

7.10 Spraying liquids and tank cleaning ................................................................... 77

7.10.1 General .......................................................................................... 77

7.10.2 Tank cleaning with low or medium pressure water jets (up to

about 12 bar) .................................................................................. 77

7.10.3 Tank cleaning with low conductivity liquids ..................................... 78

7.10.4 Tank cleaning with high pressure water or solvent jets (above

12 bar) ............................................................................................ 78

7.10.5 Steam cleaning tanks ..................................................................... 78

7.10.6 Water deluge systems .................................................................... 79

7.11 Glass systems ................................................................................................. 79

7.11.1 General .......................................................................................... 79

7.11.2 Precautions to be taken for low conductivity liquids ........................ 79

8 Static electricity in gases ............................................................................................... 80

8.1 General ............................................................................................................ 80

8.2 Grit blasting ..................................................................................................... 80

8.3 Fire extinguishers ............................................................................................ 81

8.4 Inerting ............................................................................................................ 81

8.5 Steam cleaning ................................................................................................ 81

8.6 Accidental leakage of compressed gas ............................................................ 81

8.7 Spraying of flammable paints and powders ...................................................... 82

8.7.1 General .......................................................................................... 82

8.7.2 Earthing .......................................................................................... 82

8.7.3 Plastic spray cabinets ..................................................................... 82

---------------------- Page: 5 ----------------------
– 4 – IEC TS 60079-32-1:2013 © IEC 2013

8.8 Vacuum cleaners, fixed and mobile .................................................................. 82

8.8.1 General .......................................................................................... 82

8.8.2 Fixed systems................................................................................. 82

8.8.3 Portable systems ............................................................................ 83

8.8.4 Vacuum trucks ................................................................................ 83

9 Static electricity in powders ........................................................................................... 83

9.1 General ............................................................................................................ 83

9.2 Discharges, occurrence and incendivity ........................................................... 84

9.3 Procedural measures ....................................................................................... 85

9.3.1 General .......................................................................................... 85

9.3.2 Humidification ................................................................................. 85

9.3.3 Hoses for pneumatic transfer .......................................................... 85

9.3.4 Ionisation ........................................................................................ 85

9.4 Bulk materials in the absence of flammable gases and vapours ....................... 86

9.4.1 General .......................................................................................... 86

9.4.2 Equipment and objects made of conductive or dissipative

materials......................................................................................... 86

9.4.3 Equipment and objects made of insulating materials ....................... 86

9.4.4 Dust separators .............................................................................. 87

9.4.5 Silos and Containers....................................................................... 87

9.5 Additional requirements for bulk material in the presence of flammable

gases and vapours ........................................................................................... 93

9.5.1 General .......................................................................................... 93

9.5.2 Measures for resistivity greater equal 100 MΩ m ............................ 93

9.5.3 Measures for resistivity less than 100 MΩ m ................................... 93

9.5.4 Filling of bulk material into a container ............................................ 94

9.6 Flexible intermediate bulk containers (FIBC) .................................................... 95

9.6.1 General .......................................................................................... 95

9.6.2 Additional precautions when using FIBC ......................................... 97

10 Static electricity when handling explosives and electro-explosive devices ...................... 98

10.1 Explosives manufacture, handling and storage ................................................. 98

10.1.1 General .......................................................................................... 98

10.1.2 First degree protection .................................................................... 98

10.1.3 Intermediate protection ................................................................... 98

10.1.4 Second degree protection ............................................................... 98

10.2 Handling of electro-explosive devices .............................................................. 99

10.2.1 General .......................................................................................... 99

10.2.2 Earthing .......................................................................................... 99

10.2.3 Precautions during storage and issue ........................................... 100

10.2.4 Precautions during preparation for use ......................................... 100

11 Static electricity on people ........................................................................................... 100

11.1 General considerations .................................................................................. 100

11.2 Static dissipative floors .................................................................................. 101

11.3 Dissipative and conductive footwear .............................................................. 101

11.4 Supplementary devices for earthing of people ................................................ 102

11.5 Clothing ......................................................................................................... 102

11.6 Gloves ........................................................................................................... 104

11.7 Other Items .................................................................................................... 104

---------------------- Page: 6 ----------------------
IEC TS 60079-32-1:2013 © IEC 2013 – 5 –

12 Electrostatic shock ...................................................................................................... 104

12.1 Introduction .................................................................................................... 104

12.2 Discharges relevant to electrostatic shocks .................................................... 105

12.3 Sources of electrostatic shock........................................................................ 105

12.4 Precautions to avoid electrostatic shocks ....................................................... 106

12.4.1 Sources of electrostatic shocks..................................................... 106

12.4.2 Reported shocks from equipment or processes ............................. 106

12.4.3 Shocks as a result of people being charged .................................. 106

12.5 Precautions in special cases .......................................................................... 107

12.5.1 Pneumatic conveying .................................................................... 107

12.5.2 Vacuum cleaners .......................................................................... 107

12.5.3 Reels of charged film or sheet ...................................................... 107

12.5.4 Fire extinguishers ......................................................................... 108

13 Earthing and bonding................................................................................................... 108

13.1 General .......................................................................................................... 108

13.2 Criteria for the dissipation of static electricity from a conductor ...................... 109

13.2.1 Basic considerations ..................................................................... 109

13.2.2 Practical criteria ............................................................................ 109

13.3 Earthing requirements in practical systems .................................................... 111

13.3.1 All-metal systems ......................................................................... 111

13.3.2 Metal plant with insulating parts .................................................... 112

13.3.3 Insulating materials ...................................................................... 113

13.3.4 Conductive and dissipative materials ............................................ 114

13.3.5 Earthing via intrinsic safety circuits ............................................... 114

13.3.6 Earthing of ships ........................................................................... 114

13.4 The establishment and monitoring of earthing systems .................................. 114

13.4.1 Design .......................................................................................... 114

13.4.2 Monitoring .................................................................................... 115

Annex A (informative) Fundamentals of static electricity .................................................... 116

A.1 Electrostatic charging .................................................................................... 116

A.1.1 Introduction .................................................................................. 116

A.1.2 Contact charging .......................................................................... 116

A.1.3 Contact charging of liquids ........................................................... 116

A.1.4 Charge generation on liquids flowing in pipes ............................... 117

A.1.5 Charge generation in filters ........................................................... 120

A.1.6 Charge generation during stirring and mixing of liquids ................. 120

A.1.7 Settling potentials ......................................................................... 120

A.1.8 Breakup of liquid jets .................................................................... 120

A.1.9 Contact charging of powders ........................................................ 120

A.1.10 Charging by induction ................................................................... 121

A.1.11 Charge transfer by conduction ...................................................... 121

A.1.12 Charging by corona discharge ...................................................... 121

A.2 Accumulation of electrostatic charge .............................................................. 121

A.2.1 General ........................................................................................ 121

A.2.2 Charge accumulation on liquids .................................................... 122

A.2.3 Charge accumulation on powders ................................................. 123

A.3 Electrostatic discharges ................................................................................. 124

A.3.1 Introduction .................................................................................. 124

A.3.2 Sparks .......................................................................................... 124

---------------------- Page: 7 ----------------------
– 6 – IEC TS 60079-32-1:2013 © IEC 2013

A.3.3 Corona ......................................................................................... 125

A.3.4 Brush discharges .......................................................................... 125

A.3.5 Propagating brush discharges....................................................... 126

A.3.6 Lightning like discharges .............................................................. 126

A.3.7 Cone discharges ........................................................................... 127

A.4 Measurements for risk assessment ................................................................ 127

Annex B (informative) Electrostatic discharges in specific situations .................................. 129

B.1 Incendive discharges involving insulating solid materials ............................... 129

B.1.1 General ........................................................................................ 129

B.1.2 Sparks from isolated conductors ................................................... 129

B.1.3 Brush discharges from insulating solid materials ........................... 129

B.1.4 Propagating brush discharges from insulating solid materials ....... 129

B.2 Incendive discharges produced during liquid handling .................................... 130

B.2.1 General ........................................................................................ 130

B.2.2 Calculated maximum safe flow velocities for filling medium-

sized vertical axis storage tanks ................................................... 130

B.3 Incendive discharges produced during powder handling and storage ............. 132

B.3.1 General ........................................................................................ 132

B.3.2 Discharges from bulk powder ........................................................ 132

B.3.3 Discharges from powder clouds .................................................... 132

B.3.4 Discharges involving insulating containers and people .................. 132

B.3.5 The use of liners in powder processes .......................................... 132

B.3.6 Spark discharges in powder processes ......................................... 133

B.3.7 Brush discharges in powder processes ......................................... 133

B.3.8 Corona discharges in powder processes ....................................... 133

B.3.9 Propagating brush discharges in powder processes ...................... 133

Annex C (informative) Flammability properties of substances ............................................. 135

C.1 General .......................................................................................................... 135

C.2 Effect of oxygen concentration and ambient conditions .................................. 135

C.3 Explosive limits for gases
...

SLOVENSKI STANDARD
SIST IEC/TR 61334-1-1:1997
01-avgust-1997

Distribution automation using distribution line carrier systems - Part 1: General

considerations - Section 1: Distribution automation system architecture

Distribution automation using distribution line carrier systems - Part 1: General

considerations - Section 1: Distribution automation system architecture

Automatisation de la distribution à l'aide de systèmes de communication à courants

porteurs - Partie 1: Considérations générales - Section 1: Architecture des systèmes

d'automatisation de la distribution
Ta slovenski standard je istoveten z: IEC/TR 61334-1-1
ICS:
29.240.20 Daljnovodi Power transmission and
distribution lines
33.040.40 Podatkovna komunikacijska Data communication
omrežja networks
33.200 Daljinsko krmiljenje, daljinske Telecontrol. Telemetering
meritve (telemetrija)
SIST IEC/TR 61334-1-1:1997 en

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

---------------------- Page: 1 ----------------------
SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
---------------------- Page: 2 ----------------------
SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
RAPPORT C E1
IEC
TECHNIQUE - TYPE 3
1334-1-1
TECHNICAL
Première
TYPE
REPORT 3 First edition
1995-11
Automatisation de la distribution
à l'aide de systèmes de communication
à courants porteurs —
Partie 1:
Considérations générales —
Section 1: Architecture des systèmes
d'automatisation de la distribution
Distribution automation using
distribution line carrier systems —
Part 1:
General considerations
1: Distribution automation system
Section
architecture
réservés — Copyright — all rights reserved
© CEI 1995 Droits de reproduction
No pa of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut être reproduite ni rt
any form or by any means, electronic or mechanical,
utilisée sous quelque forme que ce soit et par aucun pro-
including photocopying and microfilm, without permission
cédé, électronique ou mécanique, y compris la photocopie et
in writing from the publisher.
les microfilms, sans l'accord écrit de l'éditeur.
rnationale 3, rue de Varembé Genève, Suisse
Bureau Central de la Commission Electrotechnique Inte
Commission Electrotechnique Internationale
CODE PRIX
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PRICE CODE U
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Pour prix, voir catalogue en vigueur •
For price, see current catalogue
---------------------- Page: 3 ----------------------
SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 ©
IEC:1995 - 3 -
CONTENTS
Page
FOREWORD 5
INTRODUCTION 9
Clause
1 Scope 13
2 Reference documents 13
3 Structure of a distribution power network 13
3.1 MV power network 13
3.2 LV power network 15
4 Distribution automation system architecture 17
4.1 Structure 17
4.2 Identification of interfaces 19
5 Interaction between network structure and automation system 19
5.1 Signal injection 19
5.2 Message routing 21
6 Data communication 23
6.1 Layered structure of communication functions 23
Tables 25
Figures 29
Annexes
A Example of network automation: Fault detection and automatic procedures
for sectionalizing the faulty section 43

B List of publications concerning distribution automation using distribution line

carrier systems 53
---------------------- Page: 4 ----------------------
SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 ©IEC:1995 - 5 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
DISTRIBUTION AUTOMATION USING
DISTRIBUTION LINE CARRIER SYSTEMS -
Part 1: General considerations -
Section 1: Distribution automation system architecture
FOREWORD

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IEC 1334-1-1, which is a technical report of type 3, has been prepared by IEC technical

committee 57: Power system control and associated communications.
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The text of this technical report is based on the following documents:
Repo rt on voting
Committee draft
57(SEC)196 57/240/RVC

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

voting indicated in the above table.

This series of IEC 1334, listed in annex B, concerns distribution automation systems supported

by two-way communication channels using medium- and low-voltage distribution power mains

as data transmission media.

Such communication channels will be referred to as "DLC", which stands for distribution line

carrier.

Distribution automation systems are intended to provide a large amount of facilities related to

two main applications, concerning network automation and customer service automation.

Table 1 summarizes the most important options concerning the above-mentioned applications.

Requirements concerning these options will be included in the future IEC 1334-1-2.

As medium-voltage and low-voltage power mains have been designed for electric energy

supply and, consequently, can only offer poor performances for data transmission, stringent

requirements are necessary in order to ensure data integrity and transmission efficiency

suitable to the application needs.

The aim of these publications is to provide adequate information for correct design and reliable

operation of distribution automation systems using DLC.
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INTRODUCTION

Distribution networks, in spite of being difficult channels for data communication because of

signal attenuation, noise level and the fact that coupling side impedance can vary unpredictably

with time, have always been considered by the electric utilities as the most attractive resource

for supporting the introduction of automation techniques aimed at reducing operating cost and

capital expenditure.

Compared to other communication media, distribution networks are owned by the electric

utilities. This allows the creation of new services without requiring additional communication

carrier costs or significant operational increase of costs.

Moreover, electric utilities can keep direct control over the transmission equipment, thus

avoiding reliance on a third party.

For these reasons, a number of communication systems using distribution networks as a

transmission medium have been already developed at industrial levels.

The first systems, due to the limited possibilities offered by technology, could only offer a one-

way link from control centres towards the remote equipment to be controlled.

However, they opened the way to the implementation of distribution automation techniques

suitable to satisfactorily respond to certain important needs, mainly related to the field of

customer service automation, as for example:
– introduction of advanced tariff system (indirect load management);
– direct management of customer load.

In more recent years, due to the progress of electronics, two-way communication systems

providing low data transmission speed (not more than a few bits/s) have been installed. They

have been utilized to support network automation techniques requiring the acknowledgement of

commands sent towards line switches, as for example:
– automatic sectionalizing of feeders affected by fault;
remote operation of capacitor banks.

At present industrial development of very effective two-way communication systems can be

envisaged. Their main feature is the ability to provide higher data transmission speed (from

tens to hundreds of bits/s), so that a single channel can support most applications of

distribution automation, thus allowing favourable cost/benefits evaluation.

In this way, a large number of facilities related to both network and customer service

automation seems to be able to find a very comprehensive solution within the framework of

integrated distribution automation systems.
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It should be noticed that, even though the technique for transmitting communication signals on

a distribution network is quite similar to that already well developed for high-voltage lines,

stringent constraint for identifying cost-effective solutions is to be considered as a mandatory

requirement.

Experience with high-voltage line carrier systems may not be directly applicable to distribution

network line-carrier systems due to factors including cost considerations. Therefore, line carrier

communication systems on distribution networks should be treated as a completely new

application area in relation to what is already known for high-voltage networks.
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DISTRIBUTION AUTOMATION USING
DISTRIBUTION LINE CARRIER SYSTEMS -
Part 1: General considerations -
Section 1: Distribution automation system architecture
1 Scope

This technical report of type 3, after a short description of the structure of distribution networks

for both medium- and low-voltage levels, presents the architecture of a distribution automation

system (DAS) using distribution line carrier systems.

It outlines and discusses the interaction between the distribution network structure and the

configuration of the distribution automation system.

It provides an overview of the functional elements which constitute the basic structure and it

deals with the main options concerning the coupling methods for the transmission signal

injection.

It also identifies the ISO-OSI levels involved in the functional architecture of distribution

automation systems.
2 Reference documents
IEC 38: 1983, IEC standard voltages

ISO 7498: 1984, Information processing systems - Open Systems Interconnection - Basic

reference model
3 Structure of a distribution power network

A distribution power network includes two main power networks referred to as MV (medium-

voltage) and LV (low-voltage).

Table 2 summarizes the values of standard and exceptional voltages of the distribution power

network, according to IEC 38.
3.1 MV power network

MV power networks are supplied through HV/MV transformers, installed in HV/MV substations,

typically as shown in figure 1.

Each HV/MV transformer whose MV winding neutral point can be either isolated or connected

to earth by means of a suitable impedance supplies a section of busbar.
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Each busbar section supplies a number of MV feeders through circuit-breakers with associated

protection and possibly control (auto-reclosing) devices..

MV busbar sections in an HV/MV substation may be interconnected through a circuit-breaker to

allow energizing all the MV feeders from one HV/MV transformer.

For power factor compensation, one switched capacitor bank per busbar section may also be

installed.

MV feeders are an aggregation of several line sections delimited by switches, without any

protection device associated, installed within an MV/LV substation. A typical diagram is shown

in figure 2.

In relation to the operation of line switches, which can be either motorized or not, the resulting

configuration of the MV power network is dynamic.

Each line section can be composed of one or more of the following main types: underground or

overhead insulated cables, overhead lines with bare conductors.

Since most feeders rejoin MV busbar of adjacent HV/MV substations, the MV power network

composed by MV feeders and MV/LV substations is a meshed network. A typical diagram is

shown in figure 3.

In some cases, the MV network supplied by the same HV/MV substations, can include two

different voltage levels, interconnected between themselves by means of suitable MV/MV

transformers.

From the point of view of data transmission and network automation requirements, it is

important to stress that this network can be operated in two different ways:
– radial scheme,
– interconnected scheme.

In the first case, each feeder is energized through a single circuit-breaker connected to a

busbar section of an HV/MV substation, up to the end of the line sections where the final switch

called "border line switch" is open.

In the second case, each feeder is energized by several circuit-breakers, normally belonging to

different substations.
3.2 LV power network

LV power networks are supplied through MV/LV transformers, installed in MV/LV substations.

Each MV/LV transformer, whose LV winding neutral point is generally directly connected to

earth, energizes a busbar section which supplies a number of LV lines through circuit-breakers

with associated overload and overcurrent relays or fuses.
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Since most LV lines coming out from an MV/LV substation rejoin LV busbar of neighbouring

MV/LV substations, the structure of the LV network (whose typical diagram is shown in

figure 4) is similar to that of the MV power network as far as meshing possibilities and radial or

interconnected operation is concerned.

LV lines may also include line sections of different types: underground or overhead insulated

cables, overhead lines with bare conductors. Each LV line is responsible for the supply of

number of LV customers.

Since line switches can be operated for various reasons, the resulting configuration can also

change dynamically.
4 Distribution automation system architecture
4.1 Structure

Figure 5 shows the general architecture of a distribution automation system (DAS), using a

DLC system and providing both the facilities concerning network and customer automation.

This architecture, whose diagram is strictly dependent on the distribution power network

structure, includes the following units:

- central unit (CU) which performs all the functions required by the applications needs. It

may be connected to a number of central medium-voltage units (CMUs), installed in each

HV/MV substation, and/or to a number of central low-voltage units (CLUs) installed in each

MV/LV substation.
- (CMU) which is located in HV/MV substations. It injects the
central medium-voltage unit

transmission signal into the MV power network by means of an appropriate coupling device,

establishing in this way a communication channel with the remote medium-voltage units

(RMUs).

- remote medium-voltage unit (RMU), which is located at any MV distribution installation

(typically an MV/LV substation, an MV customer, etc.). It injects the appropriate trans-

mission signal into the MV power network by means of an appropriate coupling device. The

RMU is connected at:
- each energy delivery point supplying an MV customer, to the corresponding MV
metering unit, performing energy measurement and data consumption processing;

- each MV/LV substation to a central low-voltage unit (CLU) performing the functions

required by network automation (telecontrol) and/or customer service automation;

- typical points of MV networks to intelligent units performing other network automation

applications (e.g. feeder switch selectors, fault detectors, reclosers, etc.);

central low-voltage unit (CLU) which is located in each MV/LV substation. It provides the

signal injection on the LV network in order to carry out a communication link with the remote

low-voltage units (RLUs).

- remote low-voltage unit (RLU) which is typically located at the LV customer premises and

connected to the LV metering unit.

Each of the above-mentioned units can be subdivided into a maximum of three functional

components as shown in figure 6 and described below.
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(xxCU) accepts messages with their destination addresses and
– The communication unit

delivers messages with their source addresses. Possible functions performed by the xxCU

are: message routing, error handling, modulation, demodulation, signal injection, etc.

The xxCUs can communicate with each other (via the power mains) and with their
processing units.
(xxPU) processes data in order to allow their transfer between the
– The processing unit
interfaces (to the outside of the DLC system) and the xxCUs.

Possible functions performed by the xxPU are: message interpretation, data compression,

interface serving, etc.
(xxl) towards the outside of the DLC system perform the data transfer
– The interfaces
between the DLC system and the foreign system(s).

It can be stressed that the central unit (GU) does not contain a communication unit because it

does not communicate via the mains. Access to other communication media is provided by a

(Cl).
corresponding interface

The described architecture represents the most general functional model of a DLC system for

distribution automation system applications.

When the aim of the distribution automation system concerns only customer service

automation, it is possible to envisage alternative solutions, whose reference model depends on

the extension of the facilities to be provided.

As an example, figure 7 shows a DLC system directly exchanging data between an HV/MV

substation and the LV consumers supplied by an MV/LV transformer. In this case, it consists

only of one CMU and of a number of RLUs. The function of the RMU and the CLU are
performed by the CMU.

Figure 8 shows another example where a DLC system only allows house meter reading via the

mains from a socket located in the street, to which a hand-held CLU can be connected.

In figure 9 a system is presented which uses DLC only within the LV network(s). The CLUs are

connected to the CU via the public switched telephone network (PSTN).
4.2 Identification of interfaces

Table 3 lists the foreign systems and the DLC subsystems to which the DLC interfaces are

connected. In a real system, some of them may be omitted, some are functionally implemented

and some are physically reachable.
5 Interaction between network structure and automation system
5.1 Signal injection
The injection of the transmission signal into the MV power lines may be:
a) on MV busbar, upstream of the MV feeders' circuit-breakers or switches;
b) on MV lines, downstream of MV feeders' circuit-breakers or switches.
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The first solution is a more cost-effective installation, due to the reduced amount of coupling

devices required, but it can ensure data transmission only for energized feeders.

This solution, even though completely acceptable for customer service automation functions,

could appear as a serious constraint of the communication medium if used for network

automation, as remote control of MV line switches along a feeder, affected by a permanent

fault, would be impossible until the fault is identified and sectionalized.

On the other hand, this limitation can be easily overcome by entrusting to the CLUs installed in

the remote-controlled MV/LV substations the ability of performing autonomous functions aimed

at:
– firstly, the detection of the actual line section affected by the fault;

secondly, to command the opening of the line switch immediately upstream of the above-

mentioned section line.

In the case of a decentralized automation system, two possible procedures are described in

annex A. It is important to stress that both procedures do not involve any increase of CLUs

hardware cost, as they require only a dedicated software.
5.2 Message routing

Taking into account the architecture of the distribution automation system, described in

clause 3, one of the most important functional aspects of the system concerns message

routing.
ant to stress and determine the effect and interference that the dynamic
It is import

configuration of the LV and MV network (the actual status of the circuit-breakers and line

isolators) and the MV power system transmission characteristics will have on the message

routing activity.

Figure 5 shows the messages exchanged between the CU and a prefixed CLU follow a route

which can be subdivided into two sections:
– the first point-to-point section, between CU and CMU;
the second multi-point section, between CMU and RMU to which the prefixed CLU is
connected.

The multi-point characteristic of the second section comes from the fact that the same physical

medium (MV network), which allows an HV/MV substation to supply the group of MV/LV

substations, simultaneously links the CMU to a corresponding group of RMUs.

Therefore, the message routing depends on the MV network real status, whose change, due to

network operation, also involves a change of the HV/MV substation supplying one or more

MV/LV substations. Consequently an RMU may be alternatively connected to different CMUs.

In addition, it may be necessary to use a store-and-forward technique within the RMUs in order

to overcome two obstacles due to the physical medium transmission characteristics and to the

need for an acceptable signal-to-noise ratio.
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Such obstacles are:

- the physical medium attenuation and the transmitted output power limitation due to the

electromagnetic compatibility with other systems;
- the standing waves, due to the line impedance mismatching.

In conclusion, it is evident that the CMU will have an autonomous communication channel

towards each set of RMUs installed in the MV/LV substations energized by the same HV/MV

substation.

The same considerations can be made of the LV network where system changes may affect

the message routing between a CLU and its related RLUs.
6 Data communication
6.1 Layered structure of communication functions

In order to provide a flexible and as open as possible a communication system, its

implementation shall be developed, according to ISO 7498 (ITU-T X.200).

The Basic Reference Model of Open Systems Interconnection contains seven logic layers:

- layer 7: application layer (highest layer);
- layer 6: presentation layer;
- layer 5: session layer;
- layer 4: transport layer;
- layer 3: network layer;
- layer 2: data link layer;
- layer 1: physical layer (lowest layer).

The layered modularity of the model makes it possible to omit some layers (i.e. to omit some

logic functions) and/or to integrate some layers (i.e. to integrate some logic functions).

On the basis of requirements for distribution automation system architecture, we have selected

a model featuring the following protocol layers:
- an application layer;
- one or more intermediate layers (options);
- a data link layer;
- a physical layer.

It is considered useful to leave open the possibility to introduce (as an optional way) these

intermediate layers (e.g. a network layer and/or a transport layer). Such a need is justified by

the fact that some devices which are present in the system architecture (e.g. CMU and CLU),

can operate, owing to design choices, as simple transit node, with limited true application

functions.

The reference model and the characteristic of the proposed protocol will be described in the

future IEC 1334-4.
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Table 1 - Facilities offered by distribution automation systems using DLC systems

Network automation Customer service automation

1 Remote operation of distribution feeder switches 1 Indirect load management through multi-rate tariffs

2 On-line updating of the network connection status 2 Remote reading of consumption data

3 Provision of operational data for design planning, 3 Remote modification of contractual parameters

analysis of network pe rformance and scheduling of
4 Reduction of energy consumption to a necessary
maintenance activity
minimum (selective load control)
4 Fault identification and selectionalizing
5 Information about consumption and cost available to
5 "Leakage" detection customers

6 Implementation of enhanced strategies for voltage 6 Monitoring of supply reliability

regulation and loss reduction due to reactive power
7 Tamper detection
7 Selective load shedding under emergency conditions
Direct load management
8 Peak load control (water heaters, space heaters, air
conditioners, etc.)
9 Alarm report and recording (reclosers and intelligent
MV unit)
Table 2 - Values of standard voltages (IEC 38)
Standard reference voltages Exceptional values 2)
Medium voltage kV 10 – 20 – 35 1 ) 6 – 8,4
15-23
11 –22-33
Low voltage V 120/240 127/220
230/400 220/380
277/480 240/415
370/660
400/690
1) Single-phase three-wire system.
2)

Other voltages may exist and may be supported by an IEC Standard in the future (e.g. 30 kV, etc.).

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Table 3 - Interfaces to foreign systems
DLC - interface
Central Central MV Remote Central LV Remove
interface interface MV interface LV
interface interface
CI CMI RMI CLI RLI
I/O I/O
PSTN I/O
I/O I/O
ISDN I/O
I/O I/O
PSN I/O
I/0 I/O I/O
Foreign DOV
I/O I/O
telecom Radio I/O
UO I/O I/O
system Cable
Existing telecommand system
(ripple control, teleswitch, etc.) I/O
Sensors (temperature, voltage,
current, etc.)
Sensors {gas, water, etc.)
O O O O
Actuators (switches, breakers,
Local alarm, etc.)
I/O I/O I/O I/O
foreign Operator via terminal
I/O I/O
system Consumer terminal
Consumer display O O
I/O I/O
Electricity metering unit
I/O
DLC sub- CLU via CLI
system
RMU via RMI I/O
NOTE
PSTN = Public switched telephone network
ISDN = Integrated services digital network
PSN = Packet switched network
DOV = Data over voice
= Input to DLC-interface
O = Output from DLC-interface
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HV busbars
MV busbars
To MV feeders
= Circuit-breaker
= Capacitor bank
IEC 972/95
Figure 1 - Typical diagram of an HV/MV substation
MV busbars
LV busbars
To LV lines
O = Line switch
= Circuit-breaker or fuse
lEC 973(95
Figure 2 - Typical diagram of an MV/LV substation
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MV busbars
°Q4
MV busbars
= Circuit-breaker
0 = Line switch
l EC 974/95
Figure 3 - Typical diagram of an MV power network
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