Distribution Automation

The power distribution system in the USA, Canada and many other countries of the world (Brazil, Mexico, Australia, South Africa, Korea etc.) is significantly different to the distribution system in Europe. However, there are some European countries with a partly US-style power distribution system, for example Estonia and Latvia.

Both distribution systems include overhead line distribution and underground distribution with cables.

US-style overhead line distribution consists of distribution substations with outdoor equipment and long to very long distribution lines. In some cases, the length of these overhead lines can exceed 150 miles. Consequently, line losses and voltage drop due to line resistance and reactance are serious problems. The average number of supplied customers with these overhead lines is quite high (several thousand). As a consequence, the number of affected customers is high in case of an outage. This causes significant revenue losses for utilities and leads to decreasing customer satisfaction. To overcome the addressed problems, overhead distribution lines are segmented by Reclosers and Sectionalizers, which may be used for feeder reconfiguration in case of disturbances. Other equipment like voltage regulators (regulating transformer and controller), reactive power regulators (capacitor banks and controller), fault indicators and other equipment are used for optimal operation and fault identification and localization.

For a very long time, the abovementioned distribution equipment has been operated locally.

However, with the introduction of microprocessor based Intelligent Electronic Devices (IEDs) and the availability of affordable communication technology, Distribution Automation for fast fault detection, isolation and system reconfiguration is nowadays one of the major Smart Grid components.

With successful distribution automation, utilities have the opportunity to set up new business models for increased customer satisfaction, for example, the availability of highly reliable power supply for critical industry sites.

On the other hand, the power distribution structure with long distribution lines may also create significant problems, even if power is available. In summer, when all customers switch on their air conditioner, the load on distribution lines may reach dangerous dimensions, leading to thermal overload of the line and other components, and causing significant voltage stability and quality problems. In such situations, intelligent load shedding is a much-desired item. The integration of electronic meters with integrated load disconnection capability is a significant move in the right direction. However more customer-friendly solutions will be intelligent home and building focused energy management systems.

The distribution system in (middle) Europe is based on a different concept, compared to the US-style distribution system. The backbone of this structure is the highly meshed 110kV subtransmission system, covering nearly all load areas, and the very high number of distribution substations. As a consequence, distribution lines are quite short (typically 5 to 20 km), and the average number of customers supplied by one single distribution feeder is typically below 1 000. In addition, the connection of loads is done with precise planning and measurement, leading to highly balanced loads of distribution transformers. In contrast, the US-style distribution system is partly highly unbalanced, leading to additional power quality problems and thermal problems for transformers.

In Europe, Distribution Substations are being integrated and automated using microprocessor-based protection relays, bay controllers, remote terminal units etc. to enable remote control and to reduce outage times. However the (quite short) distribution feeder is not segmented, and the low voltage transformer stations are operated manually. Because of the highly advanced structure of the European Distribution System, there is no incentive for utilities for the Automation of Distribution feeders. In case of a disturbance on a distribution feeder, the number of the affected customers is low, and the amount of revenue loss is also low.

However the increasing integration of Decentralized Energy Resources (DERs), for example photovoltaic systems at low-voltage level and wind generators at medium-voltage level cause voltage quality problems. In some of these areas, voltage magnitude is much higher than the acceptable maximum level of nominal voltage plus 10 %. With the integration of these

“Generators”, the distribution system is no longer a radial system, which can be easily

protected by simple non directional Overcurrent protection relays. In future, the application of differential protection systems will be required to meet the requirements of DERs.

In summary, the automation of the European distribution system, including low-voltage transformer houses as well as so-called microgrids, will be strongly influenced by the acceptance and application of DER solutions.

For the automation of distribution systems, tele-control and supervision of secondary substation and transformer houses is crucial. Therefore information exchange between those components and DMS systems shall be based on common protocols and shall be cyber-secure. The communication concepts shall be flexible for the use of different communication media and technologies due to different geographic and infrastructural conditions.

4.3.4.2 Existing Standards Interoperability standards

IEC 60870-5, Telecontrol equipment and systems

IEC 60870-5-101, Telecontrol equipment and systems - Part 5-101: Transmission protocols - Companion standard for basic telecontrol tasks

IEC 60870-5-103, Telecontrol equipment and systems - Part 5-103: Transmission protocols - Companion standard for the informative interface of protection equipment

IEC 60870-5-104, Telecontrol equipment and systems - Part 5-104: Transmission protocols - Network access for IEC 60870-5-101 using standard transport profiles

IEC 61850-7-4, Communication networks and systems for power utility automation - Part 7-4:

Basic communication structure – Compatible logical node classes and data object classes IEC 61850-7-420, Communication networks and systems for power utility automation – Part 7-420: Basic communication structure – Distributed energy resources logical nodes

Time Synchronization

IEC 61850, Communication networks and systems for power utility automation IEC 61850 fulfills the following time synchronization requirements

Time Synchronization for events (SNTP, accuracy 1 ms) Security

IEC 62351, Power systems management and associated information exchange – Data and communications security

IEC 62351-3, Power systems management and associated information exchange – Data and communications security – Part 3: Communication network and system security – Profiles including TCP/IP

IEC 62351-5, Power systems management and associated information exchange – Data and communications security – Part 5: Security for IEC 60870-5 and derivatives (i.e. DNP 3.0) IEC 62351-6, Power systems management and associated information exchange – Data and communications security – Data and communications security – Part 6: Security for IEC 61850

IEC 62351-7, Power systems management and associated information exchange – Data and communications security – Data and communications security – Part 7: Network and system management (NSM) data object models

IEC 62351-8, Power systems management and associated information exchange – Data and communications security - Part 8: Role-based access control

4.3.4.3 Gaps

The existing standards provide a good coverage of substation and feeder equipment of high- and medium-voltage power systems in their semantic data models. Low-voltage equipment so far is rarely considered in IEC 61850.

4.3.4.4 Recommendation Recommendation S-DA-1

The use cases of the different distribution automation concepts need to be considered in the information data models. Therefore the IEC 61850-7-4 data models shall cover all distribution automation objects.

Recommendation S-DA-2

The IEEE has started activities in the field of distribution automation standardization. The IEC should seek cooperation (TC 8 - power system concepts, TC 57 - requirements for information exchange).

Recommendation S-DA-3

For the interconnection and integration of DER and on-line monitoring and controlling of the smart grid, IEC 61580-7-420 is advised in the integration of DER.

Add DER profile to the network models of IEC 61968 correspondingly Recommendation S-DA-4

For the Integration of the DER and energy dispatching management of the smart grid, IEC 61970 should meet the requirement of distribution dispatching management system.

Speed up the development of the IEC 61970 standard for Active Distribution of the Energy Management System.

4.3.5 Smart Substation Automation – Process bus