SIST IEC/TR 61334-1-1:1997

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
International Electrotechnical Commission
PRICE CODE U
IEC Me.tptyHapontae 3neurporexmoiecnan HoMr+ecwa
Pour prix, voir catalogue en vigueur •
fa
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
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international co-operation on all questions concerning standardization in the electrical and electronic
fields. To this end and in addition to other activities, the IEC publishes International Standards. Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt
with may participate in this preparatory work. International, governmental and non-governmental organizations
liaising with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
The formal decisions or agreements of the IEC on technical matters, express as nearly as possible, an
2)
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the
s or guides and they are accepted by the National Committees in that
form of standards, technical repo rt
sense.
In order to promote international unification, IEC National Committees undertake to apply IEC International
4)
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
Attention is drawn to the possibility that some of the elements of this International Standard may be the
6)
subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In exceptional
rt of one
circumstances, a technical committee may propose the publication of a technical repo
of the following types:
type 1, when the required support cannot be obtained for the publication of an
•
International Standard, despite repeated efforts;
• type 2, when the subject is still under technical development or where for any other
reason there is the future but not immediate possibility of an agreement on an International
Standard;
type 3, when a technical committee has collected data of a different kind from that which
•
is normally published as an International Standard, for example "state of the art".
Technical reports of types 1 and 2 are subject to review within three years of publication to
decide whether they can be transformed into International Standards. Technical reports of
type 3 do not necessarily have to be reviewed until the data they provide are considered to be
no longer valid or useful.
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.

---------------------- Page: 5 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 - 7 -
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.

---------------------- Page: 6 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 – 9 –
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.

---------------------- Page: 7 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 - 11 -
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.

---------------------- Page: 8 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
- 13-
1334-1-1 © IEC:1995
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.

---------------------- Page: 9 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 – 15–
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.

---------------------- Page: 10 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 ©IEC:1995 - 17-
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.

---------------------- Page: 11 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 – 19 –
(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.

---------------------- Page: 12 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 – 21 –
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.

---------------------- Page: 13 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 ©IEC:1995 - 23 -
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.

---------------------- Page: 14 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 - 25 -
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
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.).

---------------------- Page: 15 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 - 27 -
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

---------------------- Page: 16 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 O lEC:1995 29 - -
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

---------------------- Page: 17 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR 61334-1-1:1997
1334-1-1 © IEC:1995 - 31 -
MV busbars
°Q4
O
O
MV busbars
= Circuit-breaker
0 = Line switch
l EC 974/95
Figure 3 - Typical diagram of an MV power network

---------------------- Page: 18 ----------------------

SIST IEC/TR 61334-1-1:1997SIST IEC/TR
...