New IEC 61850 Protocol - Mapping based on XMPP

Henry Dawidczak and Thierry Dufaure, Siemens AG, Energy Management, Germany

While the first edition of the IEC 61850 series, published in 2003, focused on standardizing communication between applications within a Substation Automation Domain, the second edition published in 2010 extends its domain of application up the Power Utility Automation System. The IEC 61850 series specify:

  • An Abstract Communication Service Interface (ACSI)
  • A semantic model based on an object oriented architecture
  • Specific Communication Service Mappings (SCSM)
  • A project engineering workflow including a configuration description language (SCL) based on the XML language

All those aspects allow the engineering and the deployment of interoperable multivendor systems. IEC TC57 standardizes with the IEC 61850-8-2 part a new SCSM of the IEC 61850 using the XMPP communication technology. This new mapping will neither replace nor compete with the existing IEC 61850-8-1 SCSM (Mapping of IEC 61850 to MMS and ISO/IEC 8802-3). The scope of the new SCSM is to address the Smart Grid specific challenges and use cases, which quite deviate from the classical substation automation use cases and environment as illustrated in Table 1.

To begin with, the new SCSM shall continue granting the interoperability of systems. It shall provide a uniform communication solution between different applications.  The standardization effort from the requirement analysis to the solution specification involved the coordination of several working groups within TC57. The use of technologies supported by open source tools and the lack of IP or license restrictions related to the communication technologies are additional criteria that were uncompromisingly considered. Open international standardization projects are the prerequisite of a successful realization and deployment of interoperable Smart Grid projects, for the user as well as for the system integrator as for the manufacturer.

The standardization effort started with the requirement engineering: the identification of the requirements based on the use cases. The results were published in the draft TR IEC 61850-80-3. The requirements were prioritized, and the degree of fulfillment of the candidate technologies assessed. The results are published in the final version of the TR IEC 61850-80-3. The XMPP technology (Extensible Messaging and Presence Protocol) has been elected as the communication solution, as it was identified as the only candidate to offer a 100 % coverage of the high rated cyber security requirements.
The second step has been the development of the specification of the mapping of the IEC 61850-7-2 Abstract Communication Service Interface (ACSI).

XML messaging will be the container for the transmission of the Payload data. Additional required services such as the time synchronization interface will rely on existing and approved technologies. The SCSM is available as a first committee draft CD of the IEC 61850-8-2.

Use Case Microgrid
The basis for all use case descriptions are the Smart Grid Architecture Model (SGAM) (Figure 1), and the traffic light concept. DER-Systems consist of electrical production sites, storages and controllable loads. DER-Systems can contain one or more DER Units, and in a hierarchy one or more DER-Systems. The DER-Units can be of one type (homogeneous system like PV-farms, Wind farms), or of different types (heterogeneous system deploying PVs, wind turbines, electrical storages, etc…). The DER Management System (DER MS) controls the DER-System. It can be located at the Energy Management System of the Prosumer, or at an aggregator level (e.g. at a Virtual Power Plant (VPP), or at a facility operator of a Microgrid (FDEMS). A Microgrid is a special deployment/application of a DER System. It consists in at least a distribution network, several controllable loads (at least partially controllable),  and several DER units. It is characterized by the following properties:

  • A Microgrid can, on demand, follow an islanding mode, e.g. be isolated / disconnected from the distrbution / transport grid its Point of Common Coupling (PCC) is connected to
  • As a direct consequence, a Microgrid shall include a frequency stabilization unit
  • Each DER generator within a Microgrid shall support network protection in case of a fault (fault-ride-through)
  • A Microgrid shall support the black-start capability, i.e. allowing the system restoration in the islanding mode
  • In the islanding mode, a Microgrid shall supervise the balance between the electrical generation and load, i.e. a Microgrid shall include a local balancing authority during both the islanding mode as well as the normal mode
  • A Microgrid Control Center controls all major electrical loads and generators and shall therefore dispose on a secure communication connection with them; a secure communication connection between the DER-MS of the Microgrid and the associated DSO/TSO Control Center shall be availabe at least in normal mode; in islanding mode, the connection to the assoicated DSO/TSO is required for performing the transition to the normal mode (connection to the electrical grid)

 

The two main modes of the Microgrid are therefore:

  • Islanding mode (autonomous)
  • Normal mode (PCC connected to the electrical grid)

The islanding mode is setup by opening the PCC, and therefore the Microgrid has been disconnected from the electrical grid. Mostly, these are unwanted transitions, as an isolated Microgrid has rarely a perfect balance between its generation and all its consuming loads.
While in normal mode, the Microgrid follows the same energy management rules as any other DER Systems; particularly, the DSO/TSO operator is entitled to overrule in an emergency situation, i.e. to reduce the maximal active power feeded at the PCC from the Microgrid (red traffic light).

The Microgrid operator is entitled, as any other DER System, to market its active power surplus.
Nanogrids are very similar to bigger Microgrids. A single facility or smaller industrial plant could deploy its own low-voltage nanogrids, while determining an emergency configuration, following their safety policy, and running it in case of faulty external power supply (to preserve the functionality of essential pumps, control systems).
However emergency configurations should remain weather-independent, i.e. involving diesel generators or batteries. An automation process would start disconnecting the secondary/less important consumers, and would supervise the operation of the remaining ones.

The balance between generation and load should be computed at the project design time and be used as setpoint in the automation system. In all cases, a reliable and secure communication needs to be established between all the major system components.

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