Substation Communication Network Testing: FAT and SAT

Why test the network

In a substation with IEC 61850, the communication network carries GOOSE trips, interlocks, controls, measurements, time synchronization and, in a digital substation, the currents and voltages themselves as sampled values. A badly configured network does not always fail right away: it can work under normal conditions and fail when a link is cut, when a burst of events arrives during a fault or when a bay is added.

That is why the network is tested as one more device of the protection and control system, with its own acceptance criteria defined in the project specification. The substation network engineering guideline IEC TR 61850-90-4 devotes a chapter to these tests.

FAT and SAT

At the factory (FAT). The system is tested assembled at the factory or in the integrator’s lab: panels, IEDs, switches, clock and local SCADA. This is the time to find configuration errors, because fixing them costs less than on site. IEC 61850-4, the part on system and project management, covers quality and testing within the project life cycle.

On site (SAT). What was installed is tested: the real fiber, the switches in their panels, the clock with its antenna, the link to the control center and coexistence with the existing equipment. It repeats the essentials of the FAT and adds what only exists in the substation.

The general standards framework is summarized in standards for commissioning, FAT and SAT.

What is checked

The items are described in general terms; the acceptance values come from the project specification.

1. Inventory and documentation. Each device, with its name, firmware and configuration, matches the drawings and the SCD. The ports in use are the documented ones and unused ports are disabled.
2. Physical medium. Loss of each fiber link within the optical budget, and clean connectors.
3. VLANs, priority and filtering. Each GOOSE and each sampled value stream reaches only the ports that need it, with its VLAN and priority. No IED receives traffic it should not.
4. Redundancy. Links are cut and switches powered down one at a time. With PRP or HSR no message may be lost; with RSTP or MRP the reconvergence and its effect are measured.
5. Time synchronization. All IEDs share the same reference with the required accuracy, and loss of the main clock or its antenna produces the expected alarms and switchover.
6. Load and timing. With the network loaded (for example, simulating a burst of events), trip GOOSE messages still meet their transfer time and no sampled values are lost.
7. Basic security. Default credentials changed, individual user accounts, unnecessary services disabled, firewall rules as designed and security logs working.
8. GOOSE and MMS interoperability. Each GOOSE subscription works between IEDs from different manufacturers, with the right reaction to loss of the message; MMS reports reach the local SCADA and controls are executed.
9. Points to the control center. Each point arrives with the right address, type, quality and time stamp, and controls are executed from the control center.

Tools

The tests use traffic analyzers that decode GOOSE, MMS, sampled values and PTP, relay test sets with an IEC 61850 interface to publish and subscribe messages, MMS client and control center simulators, and optical power meters or OTDRs for the fiber. To review the addresses and subscriptions of the SCD before going to site you can use our free IEC 61850 SCL viewer.

Errors that show up in testing

• GOOSE messages reaching every IED because of missing VLANs or filtering, the origin of a traffic storm.
• Redundancy that works with one outage but not with another, because of a badly closed ring or a wrong bridge priority.
• An IED that does not take time from the clock everyone thinks it does, or uses a different time format.
• GOOSE subscriptions that fail because of configuration revision differences between the SCD and the IED, a case of GOOSE that does not arrive or arrives late.
• Points to the control center with the wrong address or scaling.
• Switch configurations that differ from the documented ones, because of changes made on site and not recorded.

After the tests

When the SAT closes, there is a record of each test with its result, the final SCD and a backup of the configuration of each switch, clock and firewall. That baseline is what makes it possible, years later, to know whether something changed and to repeat the tests when the substation is extended. In an extension it is not enough to test the new bay: the redundancy, load and timing tests of the whole network are repeated, because the new devices change the traffic and topology that all bays share.

We help with your tests

At Tiza Group we carry out FAT and SAT of protection, control and communication systems in medium, high and extra-high voltage substations and in industrial plants, in Colombia or elsewhere on request, including network, redundancy, timing and control center tests, and end-to-end tests. The network design and its test plan are part of our communications engineering service, done remotely. Contact us.

Related guides

• Substation communication network
• Standards for commissioning, FAT and SAT
• Substation Ethernet switch
• IEC 61850 station bus
• Time synchronization in substations
• IEC 61850 GOOSE
• Substation IP addressing and VLAN plan
• IEC 61850 traffic in Wireshark: what a capture reveals
• IEC 61850-3 and IEEE 1613: environmental and EMC requirements
• Substation network redundancy: RSTP, PRP, HSR or MRP
• Substation communications by voltage level

References

• IEC TR 61850-90-4:2020, Network engineering guidelines.
• IEC 61850-4, edition 2.1 (2020), System and project management.
• IEC 61850-10, Conformance testing.
• IEC 61850-5, Communication requirements for functions and device models.
• IEC 62439-3, Parallel Redundancy Protocol (PRP) and High-availability Seamless Redundancy (HSR).

Frequently asked questions