Digital Interface for Switchgear (IEC 62271-3)

Short answer

IEC 62271-3, 2015 edition, is the product standard for high-voltage switchgear above 1 kV with digital communication according to the IEC 61850 series. It replaces metallic parallel wiring with a serial link, either built into the switchgear or as external equipment that adapts existing switchgear. The standard defines which information model it supports, which communication services it must implement and how the operating time is measured when the command arrives over the network.

Scope

Clause 1 clarifies what it covers. The standard applies to switchgear and its assemblies for all rated voltages above 1 kV. It specifies the digital communication equipment with the rest of the substation automation and its effect on testing. Specifically, it defines:

• a selection of the information models of the IEC 61850 series that the switchgear supports;
• conformance classes for the set of communication services;
• the modifications and additions to the type and routine tests because of the serial interface.

A note states its intent: to promote interoperability of the communication interfaces. Interchangeability is outside its scope, as in the IEC 61850 series. Sampled values are also outside it: the standard deals with GOOSE messages and the client-server model, not the process bus.

Process-level logical nodes

Clause 5.1 requires the interface to be modeled with logical nodes of IEC 61850-7-4, according to the functions the switchgear has. If the function exists and has a serial interface, the node is mandatory:

An example from the standard: the controller of a smart circuit-breaker implements XCBR, and if it also includes synchronism check, it adds RSYN. For the additional data on insulation, arcs and partial discharges, the SIMG, SARC and SPDC nodes are extended according to IEC 61850-7-4. See the guide on primary equipment logical nodes.

Service conformance classes

Clause 5.2.1 defines three classes, based on the ACSI conformance statements of IEC 61850-7-2:

For class a, the SendGOOSEMessage service is mandatory. In classes b and c the manufacturer specifies the detail. A controller of a given class is not required to implement a particular logical node.

Times: t1, t2 and t3

The manufacturer must specify the timing performance of the smart switchgear and declare where interface point A is, the connection for the external link. All times refer to that point (clause 5.3.1).

• t1: total processing delay of the communication device (if any) and of the switchgear controller.
• t2: operating time of the switchgear.
• t3: total operating time of the smart switchgear. It includes t1 and t2.

The time is calculated from the reception of the first GOOSE message with the trip command at point A until the switchgear operates. For the overall calculation, the performance of the external IEDs and of the network must be added. If the controller or the communication device is supplied separately, as in a retrofit, the system integrator specifies the total t1.

Opening and closing of the circuit-breaker

Clause 5.3.2 refines the definitions of IEC 62271-100 for smart switchgear:

• Opening time: from the reception of the first message with the trip command, with the breaker closed, until the arcing contacts separate in all poles.
• Closing time: from the reception of the first message with the close command, with the breaker open, until the contacts touch in all poles.

In the measurements, the consistency between the position indication that comes out of the serial interface and the actual position is verified. The guide on circuit-breaker operating time testing explains the classic measurement with contacts.

Reliability, availability and maintenance

For switchgear with a digital interface, clause 5.6 takes IEC 61850-3 and adds these preferences:

• reliability class R3 of IEC 60870-4;
• maintainability class M3 of IEC 60870-4;
• every controller must have self-supervision and error detection functions for the switchgear it controls.

In addition, the failure of a controller or of a communication device must not cause loss of functions other than those for which it is directly needed, and must not affect functions elsewhere. If the circuit-breaker has several trip coils, clause 6.1.3 requires redundancy in communication and controllers: both must be duplicated to match the trip scheme. For the network design, see SAS reliability and availability in IEC 61850-3.

Physical interface

The serial link that connects the switchgear to the substation automation system uses optical fiber or a copper-based medium (clause 6.2.1). The interface point is a connector, optical or electrical, on the controller or on the communication device, and it preferably marks the split of responsibilities between the switchgear manufacturer and the integrator. The minimum degrees of protection of the connectors are IP44 outdoors, IP41 indoors and IP20 inside a suitable cabinet (clause 6.3.3). Termination boxes outside the enclosure have at least IP44 indoors and IP65 outdoors.

Tests

• Interface conformance (clause 7.2). Applies clause 6 of IEC 61850-10. It can be done on the controller alone, if the manufacturer provides a way to simulate the switchgear, or together with it. See IEC 61850-10 conformance testing.
• Timing measurement, type test (clause 7.3). Demonstrates that the opening and closing times are within the rated limits. There are two configurations: with the command sent directly to the switchgear controller and with the communication equipment as part of what is tested. Each test is repeated at least five times, because the measured time depends on the data load on the network. Network load is the volume of data transmitted, not the electrical load of the system.
• Routine test (clause 8.2). Clause 7.3 is applied with one measurement for opening and one for closing in each configuration.

The GOOSE messages that carry trips are explained in IEC 61850 GOOSE. The immunity of the auxiliary and control circuits is covered in electromagnetic compatibility of switchgear. To review the configuration file you can use the IEC 61850 SCL viewer.

The other parts of IEC 62271 are arranged in the standards for primary equipment testing.

What the manufacturer must report in a bid

Clause 9 asks for these communication interface data, in addition to what the switchgear standards require:

• conformance class according to 5.2.1;
• PICS, MICS, TICS and PIXIT of IEC 61850-10;
• number of redundant communication links;
• timing performance according to 7.3;
• availability class;
• maximum number of protection IEDs the controller can subscribe to, with a minimum of two.

For inquiries, the standard recommends including at least the same information.

When to call us

If your switchgear receives the trip by GOOSE, at Tiza Group we remotely review the SCD and the publisher and subscriber configuration of the IEDs of the main brands, and we check the total operating time with you, worldwide. See remote relay configuration and our IEC 61850 engineering. Write to us and we will send you a quote.

Related guides

• Electromagnetic compatibility of switchgear
• IEC 61850 GOOSE: how it works, stNum, sqNum and testing
• GOOSE that does not arrive or arrives late: causes and diagnosis
• IEC 61850 primary equipment logical nodes: XCBR, XSWI, TCTR
• Circuit-breaker operating time testing: what it measures

References

• IEC 62271-3, High-voltage switchgear and controlgear - Part 3: Digital interfaces based on IEC 61850, 2015 edition, clauses 1, 5.1, 5.2.1, 5.3, 5.6, 6.1.3, 6.2, 6.3.3, 7.2, 7.3, 8.2 and clause 9.

Frequently asked questions