IEC 60870-5-103 requires each device to publish an interoperability list with the physical layer, the link, the signals and the functions it uses. Comparing the relay list with the master list, box by box, avoids finding out on site that a signal or a function does not exist.
Short answer
The interoperability list is the table that the IEC 60870-5-103 standard requires each device to fill in to declare which options it implements. Before integrating, the relay list is placed next to the master list and compared box by box. Only what both tick works.
Why it exists
IEC 60870-5-103 is a standard of options. It does not oblige a relay to have all signals or all functions. That is why a relay and a master can both be compliant with the standard and still not exchange a specific signal.
The list solves that problem. Each manufacturer ticks what its device supports. The integrator compares the two lists and knows, before arriving on site, what will be visible in the SCADA and what will not.
The four parts of the list
Physical layer
It declares how the devices are connected:
- Electrical interface: RS-485, with the number of unit loads per line the device allows, or RS-232. The EIA RS-485 standard defines unit loads so that up to 32 can operate on one line.
- Optical interface: glass or plastic fiber, with F-SMA or BFOC/2.5 connector.
- Transmission speed: 9,600 or 19,200 bit/s.
A relay with a plastic optical output does not connect to a master that only declares glass fiber without a converter. This is the first cross-check of the comparison.
Link layer
In IEC 103 this part has no options: the list says so. It can be checked in one line and you move on.
Application layer
Most of the differences are here:
- Transmission mode for application data: the standard uses a single mode, with the least significant octet first.
- Common address of ASDU: the device declares whether it handles a single address, equal to the station address, or more than one.
- Selection of information numbers in monitor direction: system functions, status indications, supervision indications, earth fault indications, fault indications, auto-reclosure indications, measurands and generic functions. Each with the information numbers the device actually delivers.
- Selection of information numbers in control direction: system functions, general commands and generic functions.
- Basic application functions: test mode, blocking of monitor direction, disturbance data, generic services and private data.
- Miscellaneous: how measurands are transmitted and with what margin relative to the rated value.
Basic functions
These are the ones that surprise most. Ticking “disturbance data” in the relay is not enough: the master must declare it too. The same goes for blocking of monitor direction, useful during testing, and for test mode.
How to compare them
The comparison is a cross-check of two tables. An orderly procedure is this:
- Gather the two lists. One from the relay and one from the master, in their current version
- Cross-check the physical layer. Medium, connector, speed and number of loads
- Cross-check the common address. A single address or several
- Cross-check the information numbers. Those the relay delivers against those the master expects
- Cross-check the optional functions. Disturbance, generic and private data
- Document the difference. What is lost, what is solved in the gateway and what is accepted
Each difference is recorded with one of three decisions: fixed with additional equipment, solved in a gateway, or accepted as a limitation.
Reading example
The table shows how a line is read with two imaginary lists. The data is illustrative.
| Parameter | Relay | Master | Result |
|---|---|---|---|
| Medium | Plastic fiber, F-SMA connector | Glass fiber, BFOC/2.5 connector | Converter required |
| Speed | 9,600 and 19,200 bit/s | 19,200 bit/s | 19,200 bit/s is used |
| Common address | Single | Single | Compatible |
| Earth fault, phase L1 | Delivers | Does not declare it | The signal is lost or rebuilt |
| Disturbance data | Delivers | Does not declare it | No download over this link |
Every row with a result other than “compatible” is a pending project decision.
Boxes that are often missing
- Measurands in a format the master does not use. The list says whether measurands travel in one message type or the other.
- Information numbers for earth fault or auto-reclosing. A distribution feeder relay may not have them.
- Generic services. They are optional and many masters ignore them.
- Private data. They belong to the manufacturer and are rarely understood by another master. If the project depends on them, see functions and information numbers and check the scope with the manufacturer.
What to do about the differences
Not every difference forces a device change. The options, from lowest to highest cost, are:
- Remove the signal from the scope, with the owner’s approval.
- Rebuild it in the gateway or in the SCADA from other signals.
- Change the relay or its communication module.
The decision must be written down. For the migration to IEC 61850, the same list is the starting point of the signal mapping.
The disturbance data box is explained in disturbance records and commands in IEC 103, and the time box in time synchronization in IEC 103. Signal numbering is detailed in FUN and INF in IEC 103.
Frequent mistakes
- Asking for the list after buying the equipment.
- Comparing only speed and connector, without checking the optional functions.
- Using the list of a similar model instead of the installed one.
- Not storing the list with the firmware version: an update can change it.
How we can help
A comparison done in time avoids surprises on commissioning day. At Tiza Group we cross-check the lists, define the signal list and test the communication end to end. See our SCADA and gateway integration or write to us to quote it.
Related guides
- IEC 60870-5-103: protection relay protocol and the move to 61850
- IEC 104 interoperability: how to read the list
- FUN and INF in IEC 103: how each signal is identified
- Time synchronization in IEC 60870-5-103 and its limits
- Migrating from 103, 101 or Modbus to IEC 61850: how it is planned
References
- IEC 60870-5-103, Companion standard for the informative interface of protection equipment: interoperability list (physical layer, link layer, application layer, basic application functions and miscellaneous).
- EIA RS-485, unit loads per line.
Frequently asked questions
Do two devices that comply with IEC 60870-5-103 always understand each other?
No. The standard offers options, and each manufacturer ticks the ones it implements. They understand each other only in the boxes both tick. What one sends and the other does not recognize is lost, and what one expects and the other does not offer never arrives.
Which part of the list fails most often?
The selection of information numbers and the optional functions: disturbance data, generic services and private data. Private data, moreover, only has meaning for the manufacturer that defines it.
Who must fill in the list?
Each manufacturer fills in its own, one for the relay and another for the master. The integrator compares them and leaves the result in the project engineering document.