py_iec61850_cdc 0.1.3

A package for Pythonic IEC 61850-7-3 common data classes.

py-iec61850-cdc

This library provides IEC 61850 common data classes conforming to the requirements of IEC 61850-7-3 Ed. 2.1 2020-02 as Python objects for use in Python code. It also provides serialization to JSON for the objects.

IEC 61850-7-2 object / type support is limited to only those types required to support IEC 61850-7-3 objects. This may be extended in the future.

The intended purpose is to extend PNNL's Volttron (https://volttron.org/) platform to allow IEC 61850-style data on the message bus, historians, etc. Many utility-class SCADA platforms already do this inherently (and also support 61850 protocols). This is an attempt to align with that level of SCADA quality.

Usage

The intended usage is to invoke objects in Pythonic servers, such as:

• Modbus (https://github.com/pymodbus-dev/pymodbus),
• Modbus TK (https://github.com/ljean/modbus-tk),
• DNP3 (https://github.com/ChargePoint/pydnp3), or
• IEC 61850 (https://github.com/arthurzas/py61850).

Following polling, objects can be created in the IEC types and distributed using JSON over a message bus, via an API, etc., while still retaining their IEC member structure.

This can also be used to provide commands via RPC. Upon receipt of a py_iec61850_cdc type, a service (e.g. Volttron Agent), can determine if that point exists and then modify it.

This makes for a much easier approach to constructing and sending point commands. The server is the only party that really needs to understand the internal implementation of the point name and the callers don't care about the server-specific implementation. They need only "change this point" by sending one of the command points to the server.

The library will also provide a factory function to take JSON and properly deliver back an appropriate type from the library. This allows servers to receive a message and act very simply.

from py_iec61850_cdc import INS

Searching for Objects / Attributes

Objects are sorted within the library based on logical usage, and annotated with IEC standard and clause numbers, to allow them to be found by users.

For platforms with grep:

grep <IEC clause #> src/py_iec61850_cdc/*
grep '6.2.4.2' src/py_iec61850_cdc/*

grep <IEC class name> src/py_iec61850_cdc/*
grep 'APC' src/py_iec61850_cdc/*

Caution should be used by users to go and read the object definition before using objects. This library replaces CamelCase attribute names with underscored_naming as per PEP8.

Some attribute names had to be changed due to conflict with Python internal naming, such as 'maximum' to 'maximum_value'.

'range' is changed to 'range_v' wherever it is used.

# Can't do this.  'range' is a protected name in Python.
MV.range
# Use this instead:
MV.range_v

'min' and 'max' are changed to 'minimum' and 'maximum' wherever they are used.

# Can't do this:
SV.min
SV.max
# Use this instead:
SV.minimum
SV.maximum

Usage of Pydantic

Pydantic forms a foundation for this library, as IEC 61850-7-3 is a typed dataset. Python is great because there is no typing. However, it's also awful because there is no typing. There is risk of interaction with implementations where these datatypes get misused without obeying the constraints expressed in the IEC standards. As a result, py_iec61850_cdc enforces the typing, sizes, etc. using Pydantic.

Catching validation errors in Python code using this library should follow Pydantic rules, such as:

try:
    some_code()
except ValidationError as exc:
    print(repr(exc.errors()[0]['type']))

Some behaviors to be implemented later using Pydantic "after" model validation, include:

• appropriately updating point quality in response to exceeding configured ranges,
• appropriately updating timestamps, or
• appropriately updating mag based on instmag and db.

For model export, aliases are defined using the CamelCase approach of IEC 61850, to allow it to interact with conformant services that are expecting the naming contained in IEC 61850.

Optional fields are utilized to address the optional versus mandatory behavior in the IEC standards. Use the exclude_none=True parameter when dumping json for transport to lower network content.

Example of dumping an object to JSON:

import json
from py_iec61850_cdc import HMV

my_HMV_object = HMV()

json_message = my_HMV_object.model_dump_json(exclude_none=True)
json_loaded = json.loads(json_message)
print(json.dumps(json_loaded, indent=4))

Example of loading an object from JSON:

import json
from py_iec61850_cdc import factory, HMV

json_message = '''
    {
        "cdcName" : "HMV"
    }
'''

my_HMV_object = factory.factory_json(json_message)

print(my_HMV_object)

cdcName / dataNS - Not Really Optional

For the best function of this library, the cdcName and dataNS have not been made optional (which does not strictly comply with the standard). The reason is simple: when objects are serialized to a text-based format, cdcName gives a method of addressing which object is being inspected. This is useful for APIs, which is a big part of the intent of this library.

Because the intent is to allow Volttron's VIP message bus (or any other API) to exchange these objects as JSON, a way to de-serialize is necessary - cdcName is thus critical. dataNS is provided because it is essentially the basis of the standard already (i.e. the library is based on a specific version of IEC 61850).

To Do List

Project progress is tracked here: To Do

Developers

This library is set up to use the Hatch build tool. It also uses the ruff linter (preferred by Hatch) and pytest.

hatch fmt        # runs ruff linter
hatch test --all # runs all the version tests

Add a git pre-commit hook that runs hatch test --all