IEC 61850

Introduction

IEC 61850 is an international standard defining communication protocols for intelligent electronic devices at electrical substations. It is a part of the International Electrotechnical Commission’s (IEC) Technical Committee 57 reference architecture for electric power systems. The abstract data models defined in IEC 61850 can be mapped to a number of protocols. Possible mappings in the standard can be MMS (Manufacturing Message Specification), GOOSE (Generic Object Oriented Substation Event), SMV (Sampled Measured Values). These protocols can run over TCP/IP networks or substation LANs using high speed switched Ethernet to obtain the necessary response times below four milliseconds for protective relaying.

As of version v1.5.0, WCC Lite supports MMS type messaging. Logging and groups setting services are not supported.

IEC 61850 Server

WCC Lite can act as a IEC 61850 server to serve data to remote SCADA systems. For example, WCC Lite can be used to acquire data from various protocols (Modbus, IEC 60870-5-103, etc.), this data can be redirected and propagated further to a single or multiple IEC 61850 clients. IEC 61850 Server supports TCP and TLS connection types. TCP connection can be secured with password authentication.

Commands

WCC Lite IEC 61850 Server implementation defines four command types which are described by their control model:

Normal security commands are considered for execution if the command signal is found in Excel configuration. There aren’t any additional checks in command execution in any master protocol.

Enhanced security commands need feedback from master protocol to either to succeed or fail. If feedback is not received within command_ack_timeout_ms timeframe, the command is considered as failed.

Command value attributes (e.g. stVal) must be updated separately (if they need to be updated).

When using SBO commands, select is not routed to master protocol and select logic is performed only in IEC 61850 Server protocol.

Configuring datapoints

To use IEC 61850 Server in WCC Lite, it has to be configured via an Excel configuration and data model must be uploaded. This configuration contains two Excel sheets where parameters have to befilled in - Devices  and Signals.

IEC 61850 Server parameters for Devices tab:

Parameter Type Description Mandatory

name

string User-friendly name for a device No
description string Description of a device No
device_alias string Alphanumeric string to identify a device Yes
enable boolean Enabling/disabling of a device Yes
protocol string Protocol to be used (”IEC 61850 Server”) Yes
tls string Selecting if TLS should be used No
bind_address string (IP address format) IP address of and interface to use with server (0.0.0.0 for any interface) Yes
host string (IP address format)

IP address list of allowed IPs (separated with spaces)

Yes
port integer

TCP communication port

Yes
tls_local_certificate string

Local certificate for TLS connection

Yes (for TLS)
tls_peer_certificate string Certificate authority file for TLS connection Yes (for TLS)
tls_private_key string File consisting of private key for TLS connection Yes (for TLS)
event_history_size integer Event log size No
ied_name string Name of an Intelligent Electronic Device Yes
authorization string Authorization type (”password”) No
password string Authorization password for server device No
model_filename string Filename of data model uploaded to WCC (with or without file extension) Yes
edition string

Which IEC61850 edition to use: ”1”, ”2”, ”2.1”

(Default: 2)

No

command_ack_timeout_ms

integer

Timeframe (ms) in which enhanced-security commands must be acknowledged

(Default: 3000)

No
report_buffered_size integer

Report control blocks buffer size in bytes

(Default: 65536)

No
report_unbuffered_size integer

Unbuffered report control blocks buffer size in bytes (Default: 65513)

No

IEC 61850 Server parameters for Signals tab:

Parameter Type Description Mandatory
signal_name string User-friendly signal name Yes
device_alias string Device alias from a Devices tab Yes
signal_alias string Unique alphanumeric name of the signal to be used Yes
enable boolean Enabling/disabling of an individual signal Yes
number_type string Number format type  Yes
ld_instance string Instance of a logical device Yes
ln_class string Logical node class type Yes
ln_instance integer Instance of a logical node  No
ln_prefix string Prefix of logical node string No
cdc string Common Data Class (CDC) name Yes
data_object string Name of data object in dataset Yes
da_value string Name of a data attribute value node Yes
da_time string Name of a data attribute time node No
da_quality string Name of a data attribute quality node No
da_fc string Functional constrain for data object Yes
control_model

string

Model of output control

Yes

(for commands)

Converting and uploading data model

To use IEC61850 Server protocol in WCC Lite, user must upload a data model in specific format (file extension .cfg). These data models can be converted from SCL files (.icd or .cid files). To convert a data model, the user must use WCC Excel Utility. There’s a separate tab for this operation as shown in picture below.

image-1601465307717.png

Converted file can be uploaded in WCC Lite web interface, Protocol Hub section. Current model can be also downloaded in the same page as shown in picture below.

image-1601465353342.png

Debugging a IEC 61850 server application

If configuration for IEC 61850 Server is set up, handler for protocol will start automatically. If configuration is missing or contains errors, protocol will not start. It is done intentionally to decrease unnecessary memory usage.

If IEC 61850 Server does not work properly (e.g. no communication between devices, data is corrupted, etc.), a user can launch a debug session from command line interface and find out why link is not functioning properly.

To launch a debugging session, a user should stop iec61850-server process and run iec61850-server command with respective flags as you can see below:

iec61850-server 

-h [--help] Show help message
-c [--config] arg Configuration file location
-V [--version] Show version
-d [--debug] arg Set Debug level
-r [--redis] Show Redis messages
-C [--commands] Show command messages
-R [--readyfile] arg Ready notification file

IEC 61850 Client

WCC Lite can be used as a master station to collect data from IEC 61850 compatible server devices such as protection relays. As relays require fast, secure and responsive interfaces, WCC Lite can be considered as a valid option. For additional security a user can use encrypted transmission (TLS) or set up a password.

As TCP (TLS) connection can encounter issues and break, automatic reconnection is implemented. After every failed reconnection attempt the fallback delay is doubled starting from 1 second up until 32 seconds. After that connection reestablishment will be attempted every 32 seconds until a successful connection.

Acquiring data via report control blocks

As per IEC 61850 standard, the report control block controls the procedures that are required for reporting values of data objects from one or more logical nodes to one client. Automatic reporting enables data servers (slave devices) to only send data on its (or its quality) change, thus saving network bandwith. Instances of report control blocks are configured in the server at configuration time.

Report control blocks send information that is defined in their respective datasets. Dataset is a set of data elements grouped to represent some data group. For example, it is a common practice to group measurements and events into different groups.

A server restricts access to an instance of a report control block to one client at a time. That client exclusively shall own that instance and shall receive reports from that instance of report control blocks. There are two classes of report control blocks defined, each with a slightly different behaviour:

Buffered report control blocks are therefore useful to keep event data, for example, keeping the last known state of a relay switch where a loss of information might lead to a confusion and even financial losses. Unbuffered report control blocks are particularly useful for data which is useful only momentarily, e.g. measurements of voltages, current or power. This information can change frequently and old measurements might not reflect the real state of a substation.

To allow multiple clients to receive the same values of data object, multiple instances of the report control classes shall be made available.

Buffered report control blocks are usually configured to be used by a specific client implementing a well-defined functionality, for example, a SCADA master. The client may know the ObjectReference of the BRCB by configuration or by the use of a naming convention.

Parsing of report control blocks is based on types of Common Data Class (CDC). Some of these types can have more then one data point of interest. Table below shows what data attributes are supported from various Common Data Classes. To select which data attribute should be used a da_value column should be filled with a data attribute name. Common Data Classes consist of data attributes with different Functional Constraints therefore to get the status points of interest correctly the user must fill in a correct value in da_fc column.

IEC 61850 Client supported data attributes:

Common Data Class Function Constraint Data attributes

SPS

DPS

INS

ENS

ST stVal
ACT ST

general

phsA

phsB

phsC

neut

ACD ST

general

dirGeneral

phsA

dirPhsA

phsB

dirPhsB

phsC

dirPhsC

neut

dirNeut

MV MX

instMag

mag

CMV MX

instCVal

cVal

SAV MX instMag

SPC

DPC

INC

ENC

ST stVal

BSC

ISC

ST valWTr

APC

BAC

MX mxVal

Some of data attributes are structures themselves, for example, mag attribute is a struct that can hold integer or float values. To select a fitting attribute the user should extend da_value parameter with additional attributes, for example, if float magnitude value is to be selected from MV Common Data Class, da_value column should be filled with mag.f value; if the user intends cVal magnitude value in float format from CMV Common Data Class, da_value should be filled with cVal.mag.f value. See IEC 61850-7-3 for more information about Common Data Classes.

To ensure the integrity of configuration, WCC Lite has additional checks implemented at configuration time. If report control block (or its dataset) with a predefined ObjectReference doesn’t exist, it is considered that IEC 61850 Client has not been configured properly or configuration has been changed in either of IEC 61850 devices and cannot be matched, therefore should be considered invalid.

Controlling remote equipment via commands

The control model provides a specific way to change the state of internal and external processes by a client. The control model can only be applied to data object instances of a controllable Common Data Class (CDC) and whose ctlModel DataAttribute is not set to status - only. Such data objects can be referred to as control objects. If controls are enabled in a IEC 61850 Server device the user can configure controls by filling control_model column in Excel configuration with a control model (direct-with-normal-security, sbo-with-normal-security, direct-with-enhanced-security, sbo-with-enhanced-security) as well as setting functional constraint in da_fc column to CO.

Depending on the application, different behaviours of a control object shall be used. Therefore, different state machines are defined. Four cases are defined:

IEC 61850 standard enables the user to plan command transmission in advance - set the timer when the command should be issued. However, as this possibility is rarely used in practice, it is not implemented as of version v1.5.0. All issued commands are executed immediately.

For more information on control class model, please consult IEC 61850-7-2 standard.

If ctlModel is read-only, messages from internal database will be ignored for this point, otherwise a subscribe callback will be launched to handle commands as soon as they are sent. If CDC of a signal does not have means of control, ctlModel parameter is ignored.

Originator identification can be attached to a station so that replies to command requests could be forwarded to only one device. To use this functionality a user should select an origin identificator by filling value in Excel configuration, originator column. Originator category is always enforced to tell that remote control command is issued.

Configuring datapoints

To use IEC 61850 Client in WCC Lite, it has to be configured via an Excel configuration. This configuration contains two Excel sheets where parameters have to be filled in - Devices  and Signals tables.

Table IEC 61850 Client parameters for Devices tab:

Parameter Type Description Mandatory

name

string User-friendly name for a device No
description string Description of a device No
device_alias string Alphanumeric string to identify a device Yes
enable boolean Enabling/disabling of a device Yes
protocol string Protocol to be used (”IEC 61850 Client”) Yes
tls string Selecting if TLS should be used Yes (for TLS)
host string (IP address format)

IP address of server device

Yes
port integer

TCP communication port

(Default:102)

Yes
tls_local_certificate string

Local certificate for TLS connection

Yes (for TLS)
tls_peer_certificate string Certificate authority file for TLS connection Yes (for TLS)
tls_private_key string File consisting of private key for TLS connection Yes (for TLS)
event_history_size integer Event log size No
ied_name string Name of an Intelligent Electronic Device Yes
authorization string Authorization type (”password”) No
password string Authorization password for server device No
originator string

Origin identificator for device

No

Table IEC 61850 Client parameters for Signals tab:

Parameter Type Description Mandatory
signal_name string User-friendly signal name Yes
device_alias string Device alias from a Devices tab Yes
signal_alias string Unique alphanumeric name of the signal to be used Yes
enable boolean Enabling/disabling of an individual signal Yes
number_type string Number format type  Yes
ld_instance string Instance of a logical device Yes
ln_class string Logical node class type Yes
ln_instance integer Instance of a logical node  No
ln_prefix string Prefix of logical node string No
cdc string Common Data Class (CDC) name Yes
data_object string Name of data object in dataset Yes
da_value string Name of a data attribute value node Yes
da_fc string Functional constrain for data object Yes
control_model

string

Model of output control

No

dataset

string

Full object reference of a dataset

Yes

report_control_block

string

Full object reference of a report control block

Yes

intgPd

integer

Integrity period in milliseconds

No

It should be noted that ACT and ACD messages can only be parsed from report if either only ‘general’ attribute or all attributes attached to all three phases and neutral can be found in report

IEC 61850 Client has an additional signal which can be configured to show communication status. It is used to indicate if the server device has disconnected from client (WCC Lite). To configure such signal, two columns should be filled with particular values. To a newly created additional signal one should make job_todo equal to device_status and tag_job_todo equal to communication_status. Communication error status is set after a disconnection of a server device.

Debugging a IEC 61850 Client application

If configuration for IEC 61850 Client is set up, handler for protocol will start automatically. If configuration is missing or contains errors, protocol will not start. It is done intentionally to decrease unnecessary memory usage.

IEC 61850 Client command line debugging options

iec61850-client

-h [ –help ] Show help message
-c [–config] arg Configuration file location 
-V [–version] Show version
-d [–debug] arg Set debugging level
-r [–redis] Show Redis messages 
-C [–commands] Show command messages 
-D [–datasets] Show dataset messages 
–report Show report messages 
-R [–readyfile] arg Ready notification file

If IEC 61850 Client does not work properly (e.g. no communication between devices, data is corrupted, etc.), a user can launch a debug session from command line interface and find out why link is not functioning properly.

To launch a debugging session, a user should stop iec61850-client process and run iec61850-client command with respective flags as was shown above.


Revision #4
Created 29 September 2020 17:02:03 by Raimundas Slavinskas
Updated 1 October 2020 08:48:01 by Raimundas Slavinskas