by  Stan Thompson, Megger Relay Test Equipment, Dallas

It was developed to control and protect power systems by standardizing the exchange of information between intelligent electronic devices (IED) within an automated substation and a remote control link. Some of the benefits of the IEC 61850 standard are:

The substation high speed per-to-peer messaging is accomplished using what is called the “Goose” (generic object oriented substation event) message. When we speak of peer-to-peer messaging we are talking about the exchange of information between relays and other protective devices in the substation. In the traditional substation, copper wires run from the trip contacts of a relay to the trip coil on a circuit breaker. In an IEC 61850 substation instead of copper wires the trip Goose message will be sent via the Ethernet cable or similar fibre-optic communication cable to trip the circuit breaker.

This message will be used extensively when performing tests. The first step in testing a relay or a protection scheme, which operates using IEC 61850 protocol, is the ability to “read” these messages and respond accordingly at high speed. There are different types of Goose messages that are used. The relay being tested will publish or send a trip Goose to tell the breaker to trip. The test set subscribes to the Goose issued by the relay under test. When the test set reads the trip Goose, it will publish a Goose message telling the relay that the breaker tripped. In a trip and reclose scheme, the relay may publish another Goose telling the breaker to close, the test set will read the close Goose, and then publish a Goose back to the relay saying that the circuit breaker has closed, and so on.

The Megger MPRT range of 3-phase automatic relay test sets offer the option of testing IEC61850 applications, with enhancements to the software and hardware to provide a user-friendly package for testing the protection and control applications in an IEC61850 substation environment, basically operating by changing the analogue outputs of the test set to Goose messages. The user associates a specific Goose from a specific device to a specific binary Input. With the addition of soft binary inputs (SBI) and outputs (SBO) we can now assign a Goose message to multiple soft binary inputs and similarly we can assign a Goose message out to multiple soft binary outputs. While the MPRT has a limited number of binary inputs (10) and outputs (6), we can now assign up to 20 SBI's and 20 SBO's, which provides more testing flexibility and faster response times.

The MPRT must be able to not only read the Goose messages, but it must respond at high speed to those messages. The MPRT firmware provides for the simultaneous capture of multiple Goose messages, and the high speed response time to multiple Goose messages. One of the applications is the use for interoperability tests of multiple relays. Testing two relays by simulating breaker failure is only the beginning. With multiple relays transmitting multiple Goose messages all at the same time, responding at high speed to all of those messages becomes the bigger challenge. The MPRT will capture multiple Goose messages from multiple devices, and respond back at high speed (less than 1 ms).

Field experience in the testing of IEC 61850 relays with the MPRT package has been very positive, and in a recent field test one of the top IEC 61850 experts for CFE (Comisión Federal de Electricidad) used the Goose configurator and MPRT to test both SEL and Areva relays in their IEC 61850 automated substation.

One of the keystone advantages of the IEC 61850 standard is the interoperability between relays from different manufacturers, and one of the key factors that engineers are interested in is the response time of the various IED's on the network. The following example using the dynamic control in the Megger AVTS software, and the Goose configurator software, shows tests conducted using GE UR D60 and SEL 421 relays to simulate a breaker failure scenario, where the MPRT provides the trip currents to both relays and simulates the circuit breakers associated with each relay.

The labels of each trace are as follows:

DI3: GE UR Trip Goose Indication 1 (phase Inst. OC and breaker failure initiate)

DI4: GE UR reclose goose indication 2 (reclose)
DI5: SEL 421 trip goose indication 1 (breaker failure trip)
DO1: MPRT circuit breaker goose indication 1 (breaker A position GE UR)
DO2: MPRT circuit breaker goose indication 2 (breaker B position SEL 421)

Another feature of the MGC is the ability to compare and verify imported Goose from SCL files with captured Goose messages using Merge. When the Merge tab is pressed, a new tab Merged is created. All Goose messages that are similar will contain an “M” icon. Confirmed Goose messages can now be assigned MPRT binary inputs and outputs. Following figure shows the assigned MPRT inputs and outputs associated with each Goose message.

In Fig. 3, all indications of the first Goose have been assigned to binary inputs (subscribed). The second Goose all indications are mapped to binary outputs (published). Now all the user has to do is download the Goose configurations into the MPRT by pressing the DL button, and the unit is ready to test.

The Megger Goose configurator software, MGC for short, is used to configure the MPRT for testing of IEC 61850 devices. The MGC user interface provides a quick and easy to use tool to configure the MPRT test set. As mentioned earlier, each IED has a specific Goose message or messages that it will publish to the network. The MGC program will assist the user in programming the MPRT for these specific Goose messages. A Goose message can be imported directly from an SCL (substation configuration language) file or captured directly by “sniffing” the network. An SCL file contains all the devices that are within that particular substation. Once a message is imported or captured, the user will be able to either subscribe or publish Goose messages for a specific relay or relays.

As a protection communication protocol the IEC61850 is under test at many new substations and it may take some time to prove itself as a 100% safe and reliable system that can completely replace the current system of copper wire based signalling.

During this transition time, most of IEC61850 substations use conventional copper wire as a back up, and it is essential to monitor and analyze the IEC61850 communication speed for various IED's. Fig. 4 describes a recent test set-up in South America using the MPRT with MGC Goose Configurator. The Goose message response time of two different relays versus their contact trip time was measured. One of the relays tested showed the same response time to the Goose message as to the contact trip, while the other relay reacted much quicker to the contact trip than to the Goose message. These are exactly the sorts of things that utilities want ironing out before they “go-live” with IEC61850. The Goose configurator is an extremely useful tool to sniff the network to monitor and analyse Goose messages from various aspects especially during this transition period.

The standard is rapidly gaining acceptance throughout the world, with the electrical industrials being quick to develop products to take advantage of the benefits offered by the standard. Many transmission companies were early adopters of the standard, and in some countries the majority of new substations are IEC61850 compliant. Distribution companies have been slower to adopt due to the legacy issues associated with older distribution substations, however, they are expected to adopt with new installations and upgrades. Indeed a recent Siemens report detailing 97 IEC61850 substations reported that 37 of these were distribution class voltage levels. Protection and control engineers are increasingly being exposed to the need to test the operation of the IEC61850 communications within their substations to ensure combined interoperability of different manufacturers' IEDs, and the MPRT test system provides a user friendly solution to this requirement.

Contact Marius Pitzer, Megger, Tel 011 452-6287,
marius.pitzer@megger.com