First American IEC 61850 based system debuts in Peru

Since control and protection were automated in the 1990s, serial communication has been the dominant technique for data exchange between devices in substations. The resulting technological advances have, however, given rise to many incompatible communication protocols, and in fact, some manufacturers have used the difference in protocols to distinguish their equipment from that of other manufacturers. As substations have a service life of around 40 years, longer than that of control and protection devices, the constant changes in technology have also resulted in mismatching of protocols even among devices from the same manufacturer. This has necessitated protocol conversion devices, which are costly, complex and can cause delays in communication. Sometimes, dozens of such converters operate together in a large system and the benefits gained from digital communication cannot then be fully gained.

Adoption of an internationally accepted standard has helped rectify this situation. By putting the communications concerned into a standardised framework, the IEC 61850 protocol has made it possible for control and protection relays from different manufacturers to function together without the use of protocol converters. Its ingredients are the modern high-performing 100Mbit/s industrial Ethernet and the advanced configuration/engineering methods based on the computer language XML – the prerequisite for faster information exchange between manufacturers and hence smoother project execution and commissioning.

The distribution system

Luz del Sur is a privately owned electric power distribution company that provides service to more than 723 000 customers in the south east of Peru's capital city Lima. Luz del Sur covers an area of 3000 km2, including 30 of the most important districts of Lima, which together have a population of more than 3 million inhabitants.

Stretching along 120 km of the coast, this area is packed with important commercial, service, and tourist activities as well as a significant proportion of the country's manufacturing firms.

Like other privatised utilities, Luz del Sur wanted a power automation system that would provide flexibility and scalability in future extensions, so the standard IEC 61850 was the most obvious choice for substation level communication. The IEC compliant Siemens Sicam PAS controller then became a logical choice for the central control unit of the substations.

In the event the automation system implemented in Bujama substation consisted of Siprotec 4 relays and a Sicam PAS station controller working in accordance with the IEC 61850 protocols. Bujama comprises three voltage levels, namely 60 kV, 22.9 kV and 10 kV, two transformers rated at 12.5 and 25 MVA, and several feeders. An existing RTU and a new RTU send information to the central controller which passes the data over to the regional control centre via the DNP 3.0 protocol.

The system was handed over to the customer in October of 2005 and is the first completed project in the Americas to incorporate the IEC 61850 protocols.

System requirements

Luz del Sur listed the following main requirements for its substation automation system.

• The control and protection functions of its substations should be implemented by combined control-and-protection relays.

• The equipment must be controllable at bay level and station level.

• The automation system should be based on the IEC 61850 international standard to enable inter-operability and hence facilitate the integration of relays from other manufacturers, not at the first stage but in the future.

• The network communication in the substation must be redundant, so that a single fault will not disrupt communication.

• The automatic system must be equipped with a human-machine interface that displays the status of the entire substation and allows the operator to perform switching and view events and alarms. The accuracy of time-stamping of the events should be 1ms.

• The substation controller should collect the information from an existing RTU of the substation.

• DNP 3.0 was to be the communication protocol between the substation and operation/monitoring point at the control centre.

Automation system

Overall system

Siemens played an active role in the establishment, and is involved in the maintenance of, IEC 61850, which gives it something of an advantage in developing compliant products in parallel with IEC activities. Figure 2 shows an overview of the automation system supplied by Siemens for Bujama substation. Sicam PAS provides the overall station control and supervision in a service platform. The protection devices lie on the 100 Mbit/s optical Ethernet ring network with redundancy. The on-site Sicam PAS station is connected in this ring via a switch with high availability. Figure 4 shows the bay and protection devices on the switchgear panels.

Communication methods

IEC 61850 makes available two main types of communication between devices:

• Client-server communication between the station controller and the bay/protection devices

• Generic Object Oriented Substation Event (GOOSE) among the bay and protection devices

Client-server communication is for the transfer of commands and the associated information reports, fault records and so on. These messages are not time-critical. The communication protocols include TCP/IP, which would simplify the data transfers over the corporate network.

GOOSE is a fast communication among bay and protection devices. The messages are exchanged not via traditional hard-wires between devices, but rather over the Ethernet. For Bujama substation, GOOSE is employed in the following two functions:

• The message “busbar earthed“ is logged once at the incoming feeder and distributed to all the Siprotec devices on busbar section concerned by means of GOOSE messages.

• Interlocking between 22.9kv and 60kV levels is done via GOOSE. All the position information from disconnectors and switchgears are reported by the intelligent electronic devices (IEDs), i.e. the protection relays, to the network.

Ethernet

Shown in simplified form in Figure 5, secure optical Ethernet rings with ring management offer the required reliability on the communication bus in the Bujama substation. If a protection relay fails or if the fibre optic between two devices is broken, communications between certain devices would be interrupted. The ring management function would reconfigure the system by means of the rapid-spanning-tree algorithm (RSTP) and divert the data flow to an alternative path in the ring. The Ethernet switches reside inside protection relays and the whole system has been designed in accordance with IEC 61850 for the severe electromagnetic environment of high voltage substations.

Human machine interface

The service platform consists of a monitor and an industrial computer running the process visualisation system Sicam PAS CC. Figure 3 shows the display of the substation layout. Events are logged in resolution of 1ms as they occur in the devices. For each event, information about the cause and the source is also provided.

External connections

SICAM PAS receives the data from various parts of the substation and forwards it to the Luz del Sur control centre via the DNP 3.0 protocol.

Communication with devices that do not follow IEC 61850, for example, the transformer regulator, fan controller and certain transformer meters, was achieved via the protocol DNP 3.0. Through the protocol IEC 60780-5-101, Sicam PAS receives information from a Siemens mini-RTU that collects the data from other non-IEC 61850 devices in the substation. The mini-RTU makes it possible for events based on other messaging systems to be integrated. An existing RTU also provides to the Sicam PAS all information from the old substation equipment via DNP 3.0 protocol (Figure 5).

Site testing

Commissioning of the station level installation began in the first half of September 2005 and was handed over in October 2005. The following tests were carried out on site.

• Test of communications to individual bays, control centre and service platform

• Tests of functions

• Protection checks

• Selected operational tests carried out with Luz del Sur

Outlook

Although a tight completion deadline was imposed on this project by Luz del Sur, IEC 61850 compliance helped project management, installation, system tests and commissioning run more smoothly. The installed Siemens system has been shown to meet the availability, operational safety and future-proof requirements of the utility, while operation to IEC 61850 makes easier the future extension of the substation. The flexibility of Ethernet configuration and the solid basis of this network technology are the key to this, as well as to the effective control and display systems.

Luz del Sur is including IEC 61850 in the specification of the next installation, which is some evidence to support the view that the standard is on its way to becoming the single reference for substation communication.