Substation automation system

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The task of building Substation Automation Systems rests on the strong technological development of large-scale integrated circuits, leading to the present availability of advanced, fast, and powerful microprocessors. The result has been an evolution of substation secondary equipment, from electro-mechanical devices to digital devices. This in turn has provided the possibility of implementing Substation Automation using several intelligent electronic devices (IEDs) to perform the required functions (protection, local and remote monitoring and control, asset management, metering, etc.).

Substation Automation is quite a mature application, which has been performed for many years. Its core functions are:
·     protection;
·     local control and supervision;
·     remote control and supervision;
·     equipment supervision;
·     metering;
·     measuring;
·     online diagnosis.

The functionality of microprocessor-based IEDs includes multiple functions for protection, control and monitoring. This is the basis of Substation Automation systems which have been widely introduced in substations but with proprietary communication solutions. The driving force for a communication standard is interoperability between devices of different suppliers to be independent from one supplier and one generation of IEDs. IED communication is also referred to as “IEC 61850 station-bus application”, which lets IEDs communicate with each other and with a substation controller. An extension to this communication is the so called “IEC 61850 process bus”. This technology (see Figure below) allows signals of a conventional or non-conventional instrument transformer to be sampled and digitally transmitted to one or several protection and measuring devices.

The standards listed below are available on  IEC webstore.

The substation automation component architecture represented in Figure above is mostly made of three zones of components, which may be interconnected through wires or communication.

·     The Process zone includes the primary equipment of the substation mainly switching (i.e. circuit-breakers, switches and disconnectors), power transformer regulator and measuring elements (i.e. current and voltage sensors/transformers) including digital sensors.

·     The Field zone includes equipment to protect, control and monitor the process of the substation, mainly through IEDs, and controllers. IED is a generic representation covering components such as (but not limited to):
–   Protection relays or reclosers;
–   Operation, Revenue and Grid meters;
–   Fault detectors;
–   Bay or switch controller;
–   Generic I/O interface.

·     Field Controller is a generic representation covering components such as (but not limited to):
–   Feeder controller (connecting/disconnecting/reclosing sequences);
–   Voltage Regulator controller;
–   Network Interface Controller (NIC) or Router (remote connection interface sometimes integrated in NIC).

·     The Station zone supports the aggregation level which interfaces with other elements and systems of the electrical network. It mostly supports four main technical functions, which can be grouped or separated in different components:
–   RTU which serves as terminal for remote activities, the Station controller, which is in charge of performing automatic functions;
–   possibly HMI/archiving which offers the local operators capabilities of visualizing and archiving local data;
–   controller such as (but not limited to) a station or feeder controller, or also a capacitor bank controller or a load tap changer controller;
–   communication which can be a Network Interface Controller (NIC) and/or just a Router function.

Communication protocols, as presented in the Figure above, can be used either as in a) or b).

a)  Within the substation, IEC 61850-8-1 (for any kind of data flows except sample values) and IEC 61850-9-2 (for sample values) are used to support the selected set of System Capabilities.
IEC TR 61850-90-4 provides network engineering guidelines for communication inside a substation (automated MV/LV substations are not really covered yet).
IEC 61850 mostly replaces the former IEC 60870-5-103, used for connecting protection relays.
In the specific case of automated MV/LV substations, communications are more commonly based on industrial networks.

b)  Outside the substation, “vertical communications” can rely IEC 60870-5-101 or IEC 60870-5-104, while horizontal communications can rely on IEC TR 61850-90-5 (full mapping over UDP) or IEC TR 61850-90-1 (tunnelling).

Future vertical communication may rely on IEC TR 61850-90-2 (guideline for using IEC 61850 to control centres) and on IEC TR 61850-90-12 (guidelines for using IEC 61850 over WAN) to provide a seamless architecture, based on IEC 61850.

A new mapping of IEC 61850 over the web services technology (IEC 61850-8-2) has been specified, in order to enlarge (in security) the scope of application of IEC 61850 outside the substation, while facilitating its deployment.

The information layer of substation automation, represented in the Figure above, is mostly based on the IEC 61850 information model.

We have indicated that the IEC 61850-7-4 is the core part depicting this model, however other “namespaces” of the IEC 61850 series can be used such as:
·     IEC 61850-7-410: Hydroelectric power plants
·     IEC 61850-7-420: Distributed energy resources (DER) logical nodes
·     IEC 61400-25 series: Wind turbine power plants
·     IEC TR 61850-90-2: Communication to control centres
·     IEC TR 61850-90-3: Condition monitoring
·     IEC TR 61850-90-4: Network engineering guidelines
·     IEC TR 61850-90-5: Synchrophasors
·     IEC TR 61850-90-6; Distribution automation
·     IEC TR 61850-90-7: PV inverters – superseded by IEC 61850-7-420 

For protocols which are not IEC 61850 native such as the IEC 60870-5-101 or IEC 60870-5-104, a mapping of IEC 61850 information model is possible using the IEC TS 61850-80-1, enabling users of these technologies to use the power of data model driven engineering (and then more seamless integration) without changing of communication technologies.