IEC 61850 has transformed how substations communicate. In the past, everything depended on copper wiring, physical contacts, and slow serial links. Today, digital substations use Ethernet-based messages that move information instantly between IEDs.
Two of the fastest and most important IEC 61850 services are:
GOOSE – fast event messages used for protection and control
Sampled Values (SV) – high-speed streams of digitized current and voltage
Even though both use Ethernet multicast, they serve completely different purposes. GOOSE carries decisions and status information, while SV carries raw measurement data from CTs and VTs. Understanding the difference is essential when designing safe and reliable substations.
This article explains both technologies in simple language and shows exactly how they compare.ther.
Table of Contents
What Is GOOSE?
GOOSE, as defined in IEC 61850-8-1, is a fast way to send binary or low-frequency information between IEDs, and it can do this in just a few milliseconds. It is commonly used to communicate trip signals, breaker positions, protection pickups, blocking signals, interlocking permissives, and various automation commands.
What makes GOOSE special is that it is event-driven. As soon as a value changes inside the IED, a GOOSE message is published immediately, and the device then retransmits the message several times to guarantee that subscribers receive it. These messages use Ethernet Layer 2 multicast with EtherType 0x88B8. In practice, GOOSE is used instead of traditional wired binary inputs and outputs.
Before IEC 61850, exchanging these signals required long copper cables, physical binary I/O, and complex panel wiring. Every signal had to be wired point-to-point, which was costly, slow, and difficult to modify. With GOOSE, the entire process becomes software-defined. Signals that previously required hardwiring can now be exchanged instantly over Ethernet, making substation automation faster, simpler, and far more flexible.
What Are Sampled Values (SV)
Sampled Values, defined in IEC 61850-9-2, are used to carry digitized versions of analog signals such as current and voltage from CTs and VTs. Instead of sending analog signals through long copper cables, a Merging Unit (MU) or a protection relay converts these analog waveforms into digital samples and sends them across the network using Ethernet.
Unlike GOOSE, which is event-driven, SV messages are continuous. They stream data all the time, whether the values are changing or not. This is because protection relays need a constant flow of samples to calculate electrical quantities accurately. Typical sampling rates are 80 samples per cycle for most digital substations and 256 samples per cycle for advanced or high-performance protection schemes.
Using SV means the traditional analog wiring from instrument transformers to relays is replaced by digital communication. This approach reduces signal distortion, improves accuracy, and allows the same measurement data to be shared with multiple IEDs at once. However, because SV streams never stop, they require very high bandwidth and extremely precise timing, usually synchronized using GPS or PTP (IEEE 1588).
Why GOOSE Exists
Before IEC 61850, protection and control signals were exchanged through physical wiring and relay contacts. These traditional systems worked, but they were slow to update, costly to expand, and difficult to modify during upgrades or testing.
GOOSE removes these limitations by sending protection and control signals over Ethernet instead of copper wiring. It delivers updates in under 3 milliseconds, automatically retransmits frames for reliability, and allows multiple IEDs to receive the same message at the same time through multicast. Because everything is configured in software, engineering becomes faster and more flexible.
Thanks to these benefits, GOOSE is now the standard method for fast functions such as trip commands, blocking, supervision, interlocking, and protection coordination in digital substations.
Why Sampled Values Exist
Sampled Values (SV) were created to replace the traditional copper wiring used for CT and VT signals. In older substations, analog currents and voltages were carried through long copper cables from the switchyard to the protection relays. These cables often introduced problems such as signal distortion, interference, high cost, and safety risks during maintenance. They also made it difficult to duplicate signals for multiple devices.
With SV, this entire process becomes digital. A merging unit (MU) installed near the switchyard converts the analog CT/VT signals into digital samples. These samples are then sent over fiber or Ethernet to all protection relays that need them. The result is accurate, time-synchronized measurements that can be shared easily across many IEDs.
This digital approach enables modern process-bus architectures, improves accuracy, supports better redundancy, and allows multiple relays to receive identical measurement data.
In simple terms: GOOSE replaces binary wiring, and SV replaces CT/VT analog wiring.
IEC 61850 Communication Stack: Where GOOSE and SV Fit
Before comparing GOOSE and Sampled Values (SV), it helps to understand where each service sits in the IEC 61850 communication architecture. The diagram below shows how MMS, GOOSE, SV, and Time Sync map to different network layers.
GOOSE and SV both operate at Ethernet Layer 2, while MMS uses TCP/IP.
This difference explains why they achieve very fast performance and are used for protection-related functions.
GOOSE and SV share some similarities because they use multicast Ethernet and VLAN priority tagging, but their roles are very different:
- GOOSE = fast event messaging (trips, interlocking, blockings)
- SV = high-speed measurement streaming (CT/VT samples)
Understanding their position in the communication stack is the foundation for understanding why they behave differently in timing, bandwidth, and application.
Key Difference #1 – Data Type
GOOSE carries events and status values
Examples:
- stVal
- Op.general
- Pos.stVal
- Blk
- q (quality)
- timestamps
These values change occasionally.
SV carries analog samples
Examples:
- Current sample instMag.i
- Voltage sample instMag.v
These values change hundreds or thousands of times per second.
Because of this, SV requires far more bandwidth and stricter timing than GOOSE.
Key Difference #2 – Transmission Behavior
GOOSE
- Event-driven
- Sends instantly when a change happens
- Then retransmits using fast → slow intervals (Tmin → supervision period)
- Low bandwidth
- Must be deterministic
SV
- Periodic streaming
- Sent continuously even if nothing changes
- Very high bandwidth
- Must be precisely synchronized with the sampling clock
Key Difference #3 – Latency Requirements
GOOSE
- Typically 1–4 ms
- Used for trip and interlocking signals
- Requires low latency but not microsecond-level sync
SV
- Requires sub-millisecond timing
- Protection algorithms depend on accurate sample timing
- Often synchronized using IEEE 1588 (PTP) or GPS
This is why SV networks require:
- PRP/HSR redundancy
- Time synchronization
- Strict traffic engineering
Key Difference #4 – Ethernet Transport
Both use Ethernet multicast, but with different identifiers.
GOOSE
- EtherType: 0x88B8
- Multicast MAC: 01-0C-CD-01-00-XX
- Mandatory VLAN + priority
SV
- EtherType: 0x88BA
- Multicast MAC: 01-0C-CD-04-00-XX
- Mandatory VLAN + priority
These MAC addresses ensure switches can forward frames only to interested subscribers.
Key Difference #5 – Use Cases
GOOSE Applications
- Trip signals
- Breaker open/close
- Transfer trip
- Reclosing coordination
- Blocking signals
- Interlocking logic
- Automation events
SV Applications
- Differential protection
- Distance protection
- Busbar protection
- Transformer protection
- Relay measurement inputs
- Digital instrument transformers
- Merging unit output
SV feeds protection relays with real-time waveforms.
GOOSE sends decisions and states between relays.
Network Requirements
GOOSE Network
- Low latency
- Priority traffic
- Separate VLAN
- Supported by PRP/HSR
- Low bandwidth
SV Network
- Very high bandwidth
- Precision timing required
- PRP/HSR mandatory for protection
- Strict switch configuration
- No congestion allowed on the VLAN
Practical Example – Protection Trip
Here is how GOOSE and SV work together in a real fault scenario.
- SV provides CT/VT samples to the protection IED (hundreds of samples per millisecond).
- The protection IED detects a fault based on the samples.
- The IED publishes a GOOSE trip message.
- The breaker IED receives GOOSE and opens the breaker.
- Breaker position changes (Pos.stVal) and is sent back using GOOSE.
In other words:
- SV feeds the IED with measurement data.
- GOOSE shares the decisions and breaker status.
Both are essential.
Summary Table – GOOSE vs SV
| Feature | GOOSE | Sampled Values (SV) |
|---|---|---|
| Purpose | Fast events & status | Analog CT/VT sampling |
| Data | Boolean/status | Continuous samples |
| Trigger | Event-driven | Periodic streaming |
| Speed | ~1–4 ms | Sub-ms |
| Bandwidth | Low | Very high |
| Typical Source | Relay / Bay Controller | Merging Unit / Relay |
| EtherType | 0x88B8 | 0x88BA |
| Use Case | Trip, block, interlock | Protection measurement |
| Network Need | Deterministic | Deterministic + high bandwidth |
| Priority | High | Highest |
FAQ – GOOSE vs SV
Can GOOSE Replace SV?
GOOSE cannot replace SV because GOOSE does not carry high-speed analog samples.
Protection functions such as differential or distance relays must use SV.
Can a Substation Use Only GOOSE Without SV?
Yes — in non-process-bus substations, there are no merging units and no digital CT/VT. Protection IEDs receive analog signals directly through copper wiring.
These substations still use GOOSE for fast signaling but do not use SV at all.
Can a Substation Use Only SV Without GOOSE?
Almost never.
Even in fully digital substations, trip signals still need GOOSE or wired outputs.
Conclusion
GOOSE and Sampled Values are two of the most important technologies in IEC 61850. They are both fast, deterministic, and use Ethernet multicast, but they serve completely different purposes.
- GOOSE replaces binary wiring.
- SV replaces analog CT/VT wiring.
GOOSE is event-driven and sends protection and control signals in milliseconds.
SV streams continuous analog samples to protection relays with extremely high timing accuracy.
Together, they form the foundation of modern digital substations, supporting faster automation, safer operation, and reduced wiring. Understanding the differences between GOOSE and SV is essential for protection engineers, SCADA integrators, and anyone working with IEC 61850 systems.