15.3 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-block (BRCB) - internal events (caused by trigger options data-change, quality-change, and data-update) issue immediate sending of reports or buffer the events (to some practical limit) for transmission, such that values of data object are not lost due to transport flow control constraints or loss of connection. BRCB provides the sequence-of-events (SOE) functionality;
unbuffered-report-control-block (URCB) - internal events (caused by trigger options data-change, quality-change, and data-update) issue immediate sending of reports on a best efforts basis. If no association exists, or if the transport data flow is not fast enough to support it, events may be lost.
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
IEC 61850 Client supported data attributes:
|Common Data Class||Function Constraint||Data attributes|
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.
IEC 61580 has a distinct number_type field when compared to other protocols.
|OCTET STRING 6|
|OCTET STRING 8|
|OCTET STRING 64|
|VISIBLE STRING 32|
|VISIBLE STRING 64|
|VISIBLE STRING 65|
|VISIBLE STRING 129|
|UNICODE STRING 255|
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:
- Case 1: Direct control with normal security (direct-operate);
- Case 2: SBO control with normal security (operate-once or operate-many);
- Case 3: Direct control with enhanced security (direct-operate);
- Case 4: SBO control with enhanced security (operate-once or operate-many).
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.
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
(when not specified)
|string||User-friendly name for a device||Yes|
|description||string||Description of a device||No|
|device_alias||string||Alphanumeric string to identify a device||Yes|
|enable||boolean||Enabling/disabling of a device||No||1||0||1|
|protocol||string||Protocol to be used||Yes||IEC 61850 Client|
|tls||string||Selecting if TLS should be used||No||
|ip||string (IP address format)||
IP address of server device
TCP communication port
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|
|password||string||Authorization password for server device||No|
Origin identificator for device
Table IEC 61850 Client parameters for Signals tab
(when not specified)
|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||No||1||0||1|
|log||boolean||Allow signal to be logged. If log is 0 signal will not be logged. If log is more than 0 signal will be logged||No||0|
|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||SPS, DPS, INS, ENS, ACT, ACD, MV, CMV, SAV, SPC, DPC, INC, ENC, BSC, ISC, APC, BAC|
|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||ST,MX, CO, SP|
Model of output control
Full object reference of a dataset
Full object reference of a report control block
Integrity period in milliseconds
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
-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.