Metering in digital substations

Aleksey Anoshin, Aleksandr Golovin (www.digitalsubstation.ru)

Engineers have been putting together the puzzle of digital substation for years. They have utilized IEDs supporting IEC 61850-8-1 [1]; they are also gaining some experience in using non-conventional instrument transformers (NCITs) with IEC 61850-9-2LE interface and stand-alone merging units (SAMUs) in conjunction with protection IEDs supporting IEC 61850-9-2LE. Some of these solutions are already in use; other (and this is more about NCITs or SAMUs and protection IEDs with IEC 61850-9-2LE interface applications) - are being tested in different facilities. Though in some places these novel solutions have already been approved.

But there is one piece of the digital substation puzzle that puts obstacles in putting whole thing together and this is revenue metering. Measurement accuracy of NCITs and SAMUs with IEC 61850-9-2LE interface cannot be proven today because there is no accepted accuracy testing procedure. Though it is worth mentioning that in Russian Federation specific research and development work has been started (Development and production of metrology basis and devices for accuracy testing of measurement equipment with IEC 61850-9-2LE interface). The same work has been established in several other countries.

The second part of this digital revenue metering problem is availability of meters with IEC 61850-9-2LE interface. Digital substation journal editorial staff knows about two such devices: ZMQ802C (Landis+Gyr) and ARIS EM302 (Prosoft-Systems). According to declarations the second device has more rich functionality: it supports MMS server, is capable of receiving several IEC 61850-9-2LE streams (including 256 samples/cycle). And we had a chance to test it.

Given that our journal is not a testing laboratory we gained some support from TEKVEL interoperability testing laboratory. We used specific tools to perform the range of tests which are not covered by any lab in Russia. At least for today. And this is going to be our evaluation of the product.

FIRST SIGHT, FIRST PROJECTIt happened in 2012 when we first had a chance to see ARIS EM meter: they brought it to

test with Profotech fiber optic current and voltage transformers. Testing was a success - meter successfully accepted and processed data from Profotech merging unit (80 samples/cycle) [3]. Measurements, displayed at ARIS EM display, corresponded to those generated by merging unit, there were no errors. Such testing scenarios are common thing in IEC 61850-9-2LE interoperability testing scenarios [4].

Year later First Interoperability Session has been organized in Moscow Power Engineering Institute at Protective Relaying and Automation Department. Then, besides recurring testing with Profotech merging unit [5], interoperability with Energoservice stand-alone merging unit has been proved [6]. Results have been witnessed by independent experts from such companies as Analitic-TS, NPK Optolink, Novintech and RusHydro.

Then there was a real project - Digital revenue metering system - at 220 kV Magistralnaya substation of Grid Company (Republic of Tatarstan). Three-phase set of fiber optic current and voltage transformers has been installed there (Figure 1) in 110 kV overhead line together with ARIS EM meter (Figure 2). Measurements has been transmitted to ARIS EM meter using IEC 61850-9-2LE. This scheme has been implemented in parallel to conventional with the aim to analyze and compare measurements made in two distinct ways. The system has been commissioned but the results are not there yet.

Figure 1. Three-phase set of fiber-optic current and voltage transformers at 220 kV Magistralnaya substation.

Figure 2. ARIS EM302 with IEC 61850-9-2LE interface.

In each and every case we didn’t have a chance to get to know ARIS EM302 better: we didn’t have a chance to configure it and test it according to various scenarios. Finally we got the chance to do it.

HARDWARE AND CONFIGURATION UTILITYARIS EM302 looks very much alike as ARIS C303 bay controller [7] - another product by

Prosoft Systems. These devices are based on the same hardware platform. The only difference is in the dimensions. Everything looks the same way: display, menu structure. ARIS EM302, as ARIS C303, has modular design.

The device that we had has been equipped with power supply module (PS220) and with two processing modules (MBSO, MBSL). MBSL module is responsible for processing of IEC

61850-9-2LE streams: thanks to this module, ARIS EM is capable of receiving and processing of up to 4 IEC 61850-9-2LE streams (either 80 or 250 samples/cycle; or in a combined mode). MBSO module is responsible for metering and power quality parameters calculation functions. Identical to ARIS C303, MBSO processing module is also responsible for time synchronization (options are: integrated GPS/GLONASS module; NTP/PTP protocols; external time synchronization module, connected via RS-485 port).

ARIS EM302 configuration web-interface is also identical to the one implemented in ARIS C303. Once you got the chance to operate ARIS C303, it would be easy for you to configure ARUS EM meter. Thanks to unification.

ARIS EM302 that has been tested didn’t have analog current and voltage interfaces. So as to speak, meter has become a very intelligent calculator.

TEST SCENARIOSWe will test ARIS EM302 meter according to the following two scenarios:

1. Reception and processing of IEC 61850-9-2LE streams (80 and 256 samples/cycle). Sampled value streams will be generated by VOLCANO simulator (TEKVEL). In this test we will check that the values of currents and voltages generated by the simulator correspond to those displayed at ARIS EM302 display.

2. Basic IEC 61850 conformance procedures (as ARIS EM302 supports IEC 61850-8-1 server functionality). In this case we will use specific tool - iTest (TEKVEL).

We will also evaluate usability of configuration interface.

PROCESSING OF IEC 61850-9-2LE STREAMSIt is not big deal to configure ARIS EM302 meter to receive specific IEC 61850-9-2LE

stream. For this user has to access meter’s web-interface, choose Data exchange - Data reception menu item and then to add IEC 61850-9-2LE stream reception module (Figure 3).

Figure 3. List of ARIS EM302 modules.

Then it is required to proceed to System - Modules configuration menu item (Figure 4) and to choose IEC 61850-9-2LE reception module. Then the window will be shown where user can initiate IEC 61850-9-2LE streams search procedure. As a result of this, user gets the list of streams available in the network. In other devices that we tested we had to set IEC 61850-9-2LE parameters manually. In this case it is a lot more convenient: choose the specific stream from the list, apply its parameters and that’s it.

Figure 4. Applying specific IEC 61850-9-2LE stream parameters.

As it has already been mentioned during the test we generated IEC 61850-9-2LE streams using VOLCANO simulator. It is capable of generating both 80 and 256 samples/cycle streams. Both sampling rates are supported by ARIS EM302.

Figure 5. VOLCANO simulator main window.

Figure 6. Currents/voltages RMS value configuration window.

SvID and MAC-destination address values have been set according to Figure 5. Prior to network scanning, sampled value streams generation procedure has been started (with values according to Figure 6).

First time, VOLCANO simulator has been launched on PC under Windows OS - time interval between packets varied. And measurements displayed at meter’s display were different from those generated. It turned out that when calculating RMS values ARIS EM302 relies on internal timer and not on smpCnt parameter which is there in every single IEC 61850-9-2LE packet. We considered this not to be a very good decision because if merging unit is operating correctly and without any jitter then timing errors in meter could lead to measurement errors. If meter relied on smpCnt this would not be the case. In the meantime OMICRON SVScout that we used for cross check showed appropriate values.

Then we launched VOLCANO on Mac. Packets were generated in a very stable manner. Generated values corresponded to those displayed at meter’s display (for both 80 and 256 samples/cycle). Measurements made by ARIS EM302 and OMICRON SVScout corresponded to each other.

IEC 61850 CONFORMANCE TESTINGIn this section we will overview the results of ARIS EM302 conformance testing results.

During the tests we used software package which has been used during the first conformance tests at Research and Development Center at Federal Grid Company of Unified Energy System [8] - iTest. This software package performs testing according to scenarios, described in Conformance Test Procedures for Server Devices with IEC 61850-8-1 interface [9]. These test procedures are implemented by all laboratories which have UCA accreditation (TUV SUD, KEMA, etc.).

Conformance test procedures are distributed over 19 blocks. We will cover the first one - Basic Exchange. This block allows to identify the correctness of implementation of basic communication services (Associate, Abort, Release, GetServerDirectory, GetLogicalDevice Directory, GetLogicalNodeDirectory, GetDataValues, GetDataDirectory, GetDataDefinition).

Prior to conformance testing, it is required to create IEC 61850 server by choosing Data exchange - Data exchange menu item and adding IEC 61850 server (Figure 7).

Figure 7. Creation of IEC 61850-8-1 server.

Then it is required to choose server and to add new logical nodes with specific data objects and bind these data objects to ARIS EM302 internal signals (Figure 8). Everything is straightforward.

Figure 8. Creation of logical nodes.

Figure 9. Binding of data objects to internal ARIS EM302 signals.

Having done this, we can proceed to testing. It is required to start iTest, load device model and choose Basic Exchange conformance testing block. We performed the test and the results are presented in Table 1.

Table 1. IEC 61850 conformance tests results (Basic Exchange block).

Test case Short description Result

Ass1 Associate and release a TPAA association

Failed (socket is closed prior to ACSE session).

Ass2 Associate and client-abort association

Passed

Ass3 Associate with maximum number of clients simultaneously

Failed (due to Ass1 failure)

AssN2 Associate with incorrect association parameters

Failed (due to Ass1 failure)

AssN3 Associate with maximum+1 number of clients simultaneously

Passed

AssN4 Detection of lost link Failed (due to Ass1 failure)

AssN5 Power supply interruption Passed

Srv1 GetServerDirectory (LOGICAL-DEVICE)

Passed

Srv2 GetLogicalDeviceDirectory Passed

Srv3 GetLogicalNodeDirectory (DATA) Passed

Srv4 GetDataDirectory, GetDataDefinition and GetDataValues

Passed

Srv5 GetDataValues with multiple data and data hierarchy

Passed

SrvN1abcd LD/LN/Data services with incorrect parameters

Failed (there is no correct response - access object-non-existent).

SrvN4 SetDataValues of read-only data objects

Failed (Data Write Success response is generated instead of object-access-denied response).

6 out of 14 tests have been failed. In 4 cases it happened because of the same error: server could not release the connection in appropriate way. This may endanger interoperability and client logs may include errors. Other two errors are more serious. In first case ARIS EM302 generates incorrect response at incorrect client request and this may endanger data exchange process. In second case server generates positive response on data write request for read-only attribute.

CONCLUSIONSARIS EM302 meter has rich functionality. And it is not only about performing its

main functions, but is also about IEC 61850: it supports both IEC 61850-8-1 (GOOSE, MMS) and IEC 61850-9-2LE. And this makes this product unique on the market. But our tests showed some drawbacks in IEC 61850 implementation. We can note though that presence of errors in this part is a regular thing for products of many Russian manufacturers. Important thing here is to admit these errors and make appropriate corrections. Then device will become both unique and quality product – both for domestic and foreign markets.

Prosoft-Systems comments: Our company’s motto is 100% successful integration of our products at customers’ facilities. We always care about discovered errors, which may lead to potential problems. We are constantly improving our firmware. The problems discovered during the testing have already been corrected and new firmware version is verified (at the moment this publication is issued – ed. notes).

REFERENCES1. IEC 61850-7-2. Edition 2.0. Communication networks and systems for power utility automation

– Part 7-2: Basic information and communication structure – Abstract communication service interface (ACSI).

2. Implementation Guideline For Digital Interface To Instrument Transformers Using IEC 61850-9-2. UCA International Users Group. Modification index R2-1, 2004.

3. IEC 61850-9-2LE interoperability testing report. Revenue metering device ARIS EM (Prosoft Systems) – Merging Unit (Profotech). Fryazino, 2012. http://equipment.digitalsubstation.ru/components/com_mk61850/assets/pdf/prototests/iec-a31645894.pdf.

4. 2013 IEC 61850 Interoperability test (Munich, Germany; October 27 - November 1, 2013). Final report.

5. IEC 61850-9-2LE interoperability testing report. Revenue metering device ARIS EM (Prosoft Systems) – Merging Unit (Profotech). Moscow, 2013. http://equipment.digitalsubstation.ru/components/com_mk61850/assets/pdf/prototests/iec-cbe94f74d.pdf.

6. IEC 61850-9-2LE interoperability testing report. Revenue metering device ARIS EM (Prosoft Systems) – Stand-Alone Merging Unit (Energoservice). http :// equipment . digitalsubstation . ru / components / com _ mk 61850/ assets / pdf / prototests / iec - 21289267 b . pdf .

7. ARIS C303 Test drive. Digital substation (online version), 2013. http://digitalsubstation.ru/blog/2014/05/21/test-drajjv-aris-c303/.

8. NTC FGC UES conducted first IEC 61850 conformance tests in Russia. Digital substation, April 2014, p. 3.

9. Conformance Test Procedures for Server Devices with IEC 61850-8-1 interface. UCA International Users Group.