Telecontrol and substation protocols: IEC 60870-5-104, DNP3, IEC 61850

Where they appear

Water, oil & gas, district heating and electrical substations use telecontrol protocols to connect remote stations (RTUs) to a control centre (SCADA) over long, slow or unreliable links. Plant engineers meet them at the interface to a grid operator or when integrating switchgear.

IEC 60870-5-101 / 104

• 101 = serial, 104 = over TCP/IP, port 2404.
• Data is addressed by common address of ASDU (station) and information object address (IOA).
• Type identifications describe the data: single-point and double-point information, measured values (normalized, scaled, floating), counters, commands — each optionally with a time tag.
• Spontaneous transmission on change plus general interrogation; time synchronization by command.

DNP3

• Common in North America and in water/utility SCADA; serial or TCP/UDP 20000.
• Master ↔ outstation; data points grouped into object groups (binary inputs, analog inputs, counters, binary outputs) and event classes 1–3 plus static class 0.
• Supports unsolicited reporting, time-stamped events and secure authentication.

IEC 61850

The substation automation standard defines an object model, not just a protocol:

• Logical nodes with standard names: XCBR (circuit breaker), PTOC (overcurrent protection), MMXU (measurements)…
• MMS over TCP/IP for client/server (SCADA ↔ IED),
• GOOSE — fast multicast Ethernet messages between protection devices (interlocking, tripping),
• Sampled Values — digitized current/voltage samples from merging units.
• Configuration in SCL files: ICD/CID (device), SCD (substation).

Practical notes

Map points by address and type, not by name; agree time zones and time synchronization (events are useless without correct timestamps); define behaviour on communication loss for commands; and keep these links behind proper network segmentation.