SCADA

SCADA — Supervisory Control and Data Acquisition — is the umbrella term for the control-centre systems that observe and command remote field equipment. In a power-utility context, the SCADA front-end polls RTUs at substations across the WAN, aggregates telemetry into the operator HMI, and dispatches control commands (open/close breakers, change tap positions, raise alarms).

Where it sits

A typical control-centre stack:

SCADA front-end ↔ RTU Data Concentrator ↔ RTUs at substations ↔ IEDs

The SCADA layer sits below the analytical applications — EMS for transmission, ADMS for distribution — and feeds them the real-time data they reason on. The line between SCADA and EMS/ADMS is fuzzy: in modern platforms (GE PowerOn Advantage, Hitachi Energy Network Manager, Siemens Spectrum Power) SCADA is integrated with the management functions rather than a separate product.

Protocols

The northbound application protocols crossing the WAN are typically:

• DNP3 — common in the UK distribution estate and across North America.
• IEC 60870-5-104 — common in European transmission.

Both were originally specified without authentication or encryption. End-to-end protection is provided by IEC 62351 (DNP3 Secure Authentication, IEC 60870-5-104 over TLS) where deployed, or by network-layer mechanisms (IPsec, MACsec, MPLS isolation) where not.

Cadence

SCADA telemetry runs at human timescales — poll cycles of seconds to tens of seconds, event-driven exceptions in between. This is several orders of magnitude slower than the substation-internal traffic (Sampled Values at 4 kHz, trip GOOSE at sub-millisecond latencies), and fundamentally different in failure mode: a SCADA outage means operators run blind for a few minutes; a process-bus outage means the protection scheme fails to trip.