IEC 61850 Sampled Values protocol

IEC 61850 (IEC 61850 – Communication Networks and Systems in Substations) standard defines Sampled Values (SV) protocol as a publisher/subscriber type communication. This protocol is used for information exchange between Merging Units and IEDs (IED – Intelligent Electronic Device) in a Substation over the Ethernet.

The "Implementation Guidance for Digital Interface to Instrument Transformers Using IEC 61850-9-2", or IEC 61850-9-2LE (LE - Light Edition), guide is used as a reference in the implementation of the SV protocol. The guide can be found on this link IEC 61850-9-2LE.

The concept of SV communication is that the publisher periodically sends messages with exactly defined time intervals. The time interval depends on two factors: measured signal frequency and Samples Per Periode (SPP). IEC 61850-9-2LE defines two SPP values of 80 and 256. So, for example, if the measured signal frequency is 50 Hz and SPP is 80, the sending time interval will be 1/50/80, or 250 µs.

All messages are published under a topic. The subscriber receives all messages from the system, but filters and parses only the messages sent with the subscribed topic.

Since the SV protocol is publisher/subscriber based, communication is possible only inside the local network (LAN).

The protocol defines the SV message as shown on Figure 2. The field definition is presented in Table 1.

The APDU field contains the payload of the SV messages. Every APDU contains up to 8 ASDU (Application Specific Data Unit), where each ASDU contains one three phase current and voltage measurements and each ASDU has a unique SV identification value. The content of an APDU can be found on Figure 3.

The guide also defines the scaling factors for current and voltage measurements. Current measurements should be scaled with the factor of 1000 and the voltage with the factor of 100 and written in integer format.

Sampled Values protocol in Typhoon HIL toolchain

As mentioned, SV protocol is implemented using IEC 6180-9-2LE guide. Whole SV protocol is defined by using following components from Schematic library: SV Setup, SV Publisher and SV Subscriber.

SV Setup

SV Setup component window is shown in Table 2.

SV Setup component is used to define SV parameters per HIL device. If SV protocol is used in the model, exactly one SV Setup component must exist on the schematic. The component is shown on Table 2.

Table 2. SV Setup component

Component	Component dialog window	Component properties
SV Setup		HIL device ID Override HIL device ID for MAC address Source device MAC address Signal frequency Samples per periode Enable message quick parse

SV Publisher

SV Publisher component is used for specifying parameters for one ASDU field inside the APDU (Figure 3). With each SV Publisher component, user can specify if the component creates new SV message or will it add an ASDU in an existing SV message. If the component creates new SV message, the user can specify destination address, user priority, VLAN ID and APP ID values.

Table 4. SV Publisher componet

Component	Component dialog window	Component properties
SV Publisher		General: Create Destination MAC address User priority VLAN ID APP ID ASDU index ASDU: svID confRev Synchronization I scaling factor I type V scaling factor V type Signal Quality Generate quality Current signal quality Voltage signal quality Va quality Vb quality Vc quality Vn quality

The example of using SV Publisher components is illustrated on Figure 5. Only one SV Publisher component exists in the model with the parametes defined as on the right picture. The component creates new SV message with one ASDU entry where the values are not scaled and are written in real format. The signal quality is fixed and predefined.

All input signal to SV Publisher component must be vectors of length 4. The vector should be encoded as [Ia, Ib, Ic, In], [IQa, IQb, IQc, IQn], [Va, Vb, Vc, Vn] and [VQa, VQb, VQc, VQn]

The Figure 6 illustrates the message captured with the network sniffing tool.

To add an extra ASDU in the existing SV message, just add another SV Publisher component and choose Create: Sequence ASDU option. This is illustrated on Figure 7. The SV Publisher component is the same as in the example above and creates a new SV message. The SV Publisher1 component is defined to add an ASDU to the message with APP ID 0x4000 as shown on the right picture.

The capture of the new created message is illustrated on Figure 8.

SV Subscriber

SV Subscriber component is used for subscribing to a certain ASDU field from a certain SV message on the network. To subscribe to an SV message, user must specify the APP ID and SV ID for message filtering. APP ID value is used to filter the SV message from the network, and SV ID is used to extract the corresponding ASDU from the message.

All output terminals of SV Subscriber component are vectors of length 4. The vectors are encoded as [Ia, Ib, Ic, In], [IQa, IQb, IQc, IQn], [Va, Vb, Vc, Vn] and [VQa, VQb, VQc, VQn].

Table 6. SV Subscriber component

Component	Component dialog window	Component properties
SV Subscriber		APP ID SV ID I scaling factor I out type V scaling factor V out type

Virtual HIL support

Virtual HIL currently does not support this protocol. When using a Virtual HIL environment (e.g. when running the model on a local computer), inputs to this component will be discarded and outputs from this component will be zeroed.