IEC 60870-5-103 is a protective relay protocol: the master polls the relay and the relay reports states, measurands, events and disturbance records. With the general interrogation the master gets the complete state of the relay, without time tag and with cause of transmission 9, and the relay closes it with a termination message. Events and measurands follow with their own message types.
A protocol designed for relays
IEC 60870-5-103 defines the information interface of protection equipment. A master, usually a gateway or a substation control system, reads the states, measurands, events and disturbance records of a relay. It also sends it a few commands.
The architecture is polling master. The master is the primary station and only it starts transfers. The relay is the secondary station and answers when polled. The data the relay has to send is split into two classes, as in IEC 101: class 1, high priority, and class 2, low priority. By default the master polls class 2 and the relay indicates, in its reply, that it has class 1 data pending.
That is why 103 is a relay protocol. It does not define a power system station model or the aggregation of data of a whole substation. The overview and the comparison with 101 and 104 are in IEC 60870-5-103.
Message types in monitor direction
103 reuses the ASDU idea of the series. The most used types, from the relay to the master, are:
| ASDU | Content |
|---|---|
| 1 | Time-tagged message (event: start, trip, state) |
| 2 | Time-tagged message with relative time (fault events) |
| 3 | Measurands I |
| 4 | Time-tagged measurands with relative time (fault location) |
| 5 | Relay identification |
| 6 | Time synchronization |
| 8 | End of general interrogation |
| 9 | Measurands II |
| 10, 11 | Generic data and generic identification |
| 23, 26 to 31 | List of recorded disturbances and transfer of their data |
In control direction, from the master to the relay, the messages are time synchronization (6), general interrogation (7) and general command (20). There are also generic data and commands and the acknowledgement of the disturbance data transfer.
Each piece of information carries its identification with FUN and INF: one octet for the function type (FUN) and another for the information number (INF). The address of each signal is that pair.
Indications are double-point
In 103 binary states are always double-point information: two bits that distinguish four cases. A protection contact that in 101 would be a single point arrives here as a double point. A SCADA or gateway that maps them to another protocol must convert the double point into the matching single point and define what to do with the intermediate and indeterminate values.
The general interrogation
When the link starts, the master does not know the current state of the signals that do not change. To get it, it sends the general interrogation (ASDU 7). The relay answers as follows:
- The master sends the general interrogation. ASDU 7, with a scan number
- The relay answers with all the selected signals. Current states, no time tag, cause of transmission 9
- The relay sends the end of the interrogation. ASDU 8, which closes the cycle
- Time-tagged events follow. Later changes arrive as time-tagged messages
Three characteristics:
- The signals in the answer carry no time, because they are a snapshot of the state and not an event.
- They are identified by cause of transmission 9, which in 103 means “general interrogation”. The cause is a field of the ASDU, and the list of causes of 103 does not match the one in 101.
- The relay closes with the termination of general interrogation message. If the master does not receive it, it cannot know whether it received the complete state.
Many masters send the general interrogation right after resetting the link with the relay. When the relay restarts, it reports it with the reset or start-up messages, and the master interrogates again.
Events, measurands and commands
Events. State changes and fault events arrive with a time tag, and fault events also with relative time from the start. They include phase starts, general trip, zones, breaker failure and trips by function.
Measurands. They are sent with the measurand types I and II. The value is expressed as a fraction of the rated value, with a maximum of 1.2 or 2.4 times that value, which the relay declares. If the measured value exceeds the range, it saturates and is flagged as overflow. Polling measurands continuously loads the link; it is better to send them only when they change by more than a deadband.
Commands. The master sends general commands: switching the protection, the teleprotection or the auto-recloser on or off, resetting the LEDs and selecting between setting groups. The relay confirms receipt and, when it finishes, reports the result.
Disturbances. The relay can report that it holds a disturbance record, list the records and transfer them by channels. The master acknowledges the transfer. Reading and analyzing the records is covered in Downloading events and oscillography from a relay.
What to check when integrating
- That the master runs the general interrogation on connection and receives the termination message.
- That the SCADA treats answers with cause 9 as state, not as events.
- The conversion of double points to the types of the upper-level protocol.
- The time synchronization of the relay. Without it, events carry a time of little use; the relay clock is set with the synchronization message or with an external source.
- The measurand polling rate and the deadband.
After 103
New relays communicate with IEC 61850 and gateways translate to 104 or DNP3 (IEEE 1815). The migration is covered in IEC 60870-5-103 and Mapping IEC 61850 to IEC 104 and DNP3.
We can help with your relays
At Tiza Group we load relay settings through remote relay configuration, worldwide, and we do the SCADA and gateway integration of IEC 103 relays, with point-to-point tests of signals, measurands and commands. Write to us and we will quote it.
Related guides
- IEC 60870-5-103: protection relay protocol and the move to 61850
- FUN and INF in IEC 103: how each signal is identified
- Disturbance records and commands in IEC 60870-5-103
- Downloading events and oscillography from a relay, by brand
- General and counter interrogation in IEC 101/104
References
- IEC 60870-5-103: companion standard for the informative interface of protection equipment; ASDUs in monitor and control direction, general interrogation, general commands and transfer of disturbance data; interoperability list.
Frequently asked questions
What does the general interrogation do in IEC 103?
It makes the relay send all the selected signals in their current state, without time tag and with cause of transmission 9. When it finishes, the relay sends a termination of general interrogation message. The master uses it when the link starts or reconnects.
Why is IEC 103 not suitable for talking to a control center?
Because it describes the information of a relay: its protection functions, states, measurands and records, with a master that polls it over a serial link. It does not define data exchange between stations of a power system. For a control center, IEC 101, IEC 104 or DNP3 (IEEE 1815) are used.
How are commands sent to the relay?
With general commands: switching the protection or the auto-recloser on or off, resetting the LEDs or selecting a setting group. The relay confirms that it received the order and, when it finishes, sends the activation termination, positive or negative.