Sampled Values, usually written SV, is the IEC 61850 mechanism for streaming digitized instantaneous current and voltage measurements across a substation process bus. Instead of running copper cables carrying analog secondary currents from a current transformer straight into a relay, a device near the primary equipment samples those signals thousands of times a second and multicasts the numbers as Ethernet frames. The profile most vendors implement is the 9-2LE Light Edition guideline, later formalized in IEC 61869-9. Any protection or metering device on the bus can subscribe to the same stream, so one measurement point can feed many functions.
IEC 61850 Sampled Values in one line: IEC 61850 Sampled Values (SV, or 9-2) is a protocol for publishing digitized instantaneous current and voltage samples as multicast Ethernet frames on a substation process bus. It replaces the copper analog wiring between instrument transformers and relays, letting multiple subscribers consume the same synchronized measurement stream.
In a conventional substation, each current transformer and voltage transformer sends a low-level analog secondary signal - typically 1 A or 5 A for current and 100 V to 120 V for voltage - along dedicated copper conductors into every relay, meter, and recorder that needs it. Those runs are heavy, must be tested end to end, and create safety hazards such as an open CT secondary developing dangerous voltage. Sampled Values removes that copper. A device close to the primary plant digitizes the instantaneous waveform and publishes the numeric samples onto the station Ethernet.
Each SV frame carries a block of samples, a sample count that increments and wraps once per cycle, a quality flag for every measured quantity, and an identifier that tells subscribers which stream this is. Because the frames are multicast at Layer 2 rather than routed, publishing is effectively a broadcast that any subscriber on the same VLAN can pick up without a point-to-point connection. This is what lets a single measurement location serve line differential, distance, metering, and disturbance recording at once.
The two common sample rates reflect two uses. Protection typically runs at 80 samples per cycle - 4000 samples per second on a 50 Hz system, 4800 on 60 Hz - which is enough bandwidth for the phasor and transient content that relays act on. Power quality and high-fidelity metering use a higher rate, commonly 256 samples per cycle, to capture harmonics and fast transients. The publisher and every subscriber must agree on the rate for the numbers to line up.
A relay that subscribes to two or three SV streams - for example three phase currents and three phase voltages from different publishers - has to combine samples that were taken at the same instant. If one publisher's clock drifts relative to another's, the relay ends up comparing a current sample from one moment against a voltage sample from a slightly later moment, which corrupts every phasor, power, and impedance calculation it makes. Accurate time alignment across all publishers is therefore not a nice-to-have; it is the condition for the whole scheme to work.
The mechanism that provides this alignment is Precision Time Protocol, specifically the power utility profile of IEEE 1588 known as IEC 61850-9-3. A grandmaster clock, usually disciplined by GPS, distributes time across the process bus so that publishers timestamp their samples to well under a microsecond of each other. Each SV frame carries a flag indicating whether its samples are synchronized and to which time source, so a subscriber can decide whether the data is trustworthy or should be treated as degraded.
This dependency reshapes how engineers think about substation reliability. In the copper world, a single relay's failure affected only that relay. On a process bus, the timing infrastructure and the network itself become shared assets whose health matters to every protection function subscribing to the affected streams. Redundant clocks, redundant network paths using protocols such as PRP or HSR, and careful VLAN and bandwidth planning are all part of engineering an SV process bus that is at least as dependable as the wiring it replaces.
It is important to be precise about where Sampled Values live and where they do not. SV is a fast, high-volume, real-time stream engineered for protection devices sitting on the same local process bus. It is not a wide-area telemetry protocol and it is never carried up to a control center or a cloud platform. The raw sample stream stays inside the substation, between the merging units and the intelligent electronic devices, or IEDs, that subscribe to it.
What a cloud SCADA layer such as Merobix consumes is the output of those IEDs, not the SV bus. A relay processes the sampled current and voltage into meaningful quantities - RMS currents and voltages, real and reactive power, frequency, phasors, and status such as trip, alarm, and breaker position - and reports those over an outbound protocol like IEC 60870-5-104, DNP3, or MQTT. The cloud sees engineering-unit measurements and events at telemetry rates, cleanly separated from the microsecond-critical sampling underneath.
For an operator monitoring assets across many sites, that separation is a feature. The protection engineering that depends on precise sampling and timing stays local and deterministic, while the cloud platform aggregates the resulting measurements, trends them, alarms on them, and correlates them across sites. Merobix does not need to understand SV framing or PTP to be useful; it needs the IED to have already turned the fast stream into the values and events that field and control-room staff care about, which is exactly the boundary IEC 61850 draws between the process bus and the station layer.
IEC 61850-9-2 defines how Sampled Values are mapped onto Ethernet, and the widely used 9-2LE was a vendor implementation guideline that pinned down concrete choices like sample rates so different devices would interoperate. IEC 61869-9 is the later standard that formalized the digital interface for instrument transformers, aligning and superseding much of what 9-2LE specified. In practice engineers still say 9-2, but new equipment is designed to the IEC 61869-9 profile.
Two rates are common. Protection applications typically use 80 samples per cycle, which is 4000 samples per second at 50 Hz and 4800 at 60 Hz. Power quality and high-accuracy metering use a higher rate around 256 samples per cycle to capture harmonics and fast transients. The publisher and every subscriber must be configured for the same rate.
No. SV is a high-bandwidth, latency-critical stream meant to stay on the local substation process bus between merging units and relays. Control centers and cloud SCADA platforms receive the processed measurements and events that the relays and metering IEDs produce, transported over telemetry protocols such as IEC 60870-5-104, DNP3, or MQTT, not the raw sample stream itself.
Primary references from the standards bodies and regulators that define this topic:
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