Testing of IEC 61850 Sampled Value based Devices and Systems

Author:Alexander Apostolov, USA

Sampled Measured Values Test System Components

A test system designed for IEDs or distributed applications based on IEC 61850 9-2 has multiple components that are needed for the testing of the individual devices, as well as a complete application. A simplified block diagram of such a system is shown in Figure 1. The first component of the test system is the test Configuration Tool. It takes advantage of one of the key components of the IEC 61850 standard – the Substation Configuration Language. The Configuration Tool is used to create the files required for configuration of different components of the test system. It imports or exports different configuration files defined by Part 6 of IEC 61850.

The test system Configuration Tool reads the information regarding all IEDs, communication configuration and substation description sections. This information is in a file with .SCD extension (for Substation Configuration Description) and is used to configure the set of tests to be performed. The overall functionality of any IEC 61850 compliant device is available in a file that describes its capabilities. This file has an extension .ICD for IED Capability Description.
The IED configuration tool sends to the IED information on its instantiation within a substation automation system (SAS) project. The communication section of the file contains the current address of the IED. The substation section related to this IED may be present and then shall have name values assigned according to the project specific names. This file has an extension .CID (for Configured IED Description).

The second component of such a system is a Simulation Tool that generates the current and voltage waveforms. The specifics of each simulated test condition are determined by the complete, as well as the configured functionality of the tested device or application.

The simulation tool requirements will also be different depending on the type of function being tested. For example, if the tested function is based on RMS values or phasor measurements, the simulation tool may include a sequence of steps with the analog values in each of the steps defined as phasors with their magnitude and phase angle. Based on these configuration parameters the simulation tool will generate the sine waveforms to be applied as analog signals or in a digital format to the tested components or systems.

If the tested functions are designed to detect transient conditions or operate based on sub-cycle set of samples from the waveform, an electromagnetic transients simulation will be more appropriate. Different network simulation tools allow the user to configure the specifics of the network model, type of fault, fault location, etc. that are then used to calculate the waveforms to be applied to a device or system under test.

The third part of the test system is the Virtual Merging Unit simulator. While under conventional testing the waveforms generated by the simulation tool will be applied to the tested device as current and voltage analog signals, a Virtual Merging Unit will send sampled measured values as defined in IEC 61850 over the Ethernet network used for the testing.

The Virtual Merging Unit simulator supports the defined by IEC 61850 9-2 LE 80 samples/cycle in 80 messages/cycle. Each message contains one sample of the three phase currents and voltages (WYE class).

The fourth component of the test system is the Test Evaluation Tool that includes the monitoring functions used to evaluate the performance of the tested elements within a distributed sampled analog value based system. Such evaluation tool requires multiple evaluation sub-modules that are targeted towards the specifics of the function being tested. They might be based on monitoring the sampled measured values from a tested merging unit, GOOSE messages from a tested IED, as well as reports or waveform records from the tested device.
The fifth component of the test system is the Reporting Tool that will generate the test reports based on a user defined format.

Testing of IEC 61850-9-2 Based Merging Units
Since Merging Units are an essential component of any IEC 61850 process bus based application, they have to be tested to ensure that they provide the required sampled measured values. The currents and voltages applied to the Merging Unit will be based on current and voltage waveforms produced from the network simulator in order to simulate different system conditions, such as high current faults or low current minimum load conditions.

At the same time the Test Evaluation tool will need to receive the sampled analog values from the tested merging unit and compare the individual sampled values from the Merging Unit with the samples coming from the network simulator. The testing of Merging Units will require first of all a very accurate time synchronization of both the test device and the tested MU.

It is necessary to analyze the phase (time) and magnitude differences of the individual samples and compare these to the calibration specifications of the MU. Proper documentation and reporting is required in the same manner as meter testing is performed today (Figure 2). The Merging Unit test module supports the sampling rates defined for protection applications in IEC 61850 9 – 2 LE. The merging unit test evaluation tool is used for receiving, processing, viewing, and saving Sampled Values according to the implementation guideline of the UCA International Users Group. It subscribes to the Sampled Values streams from one or multiple merging units and displays the waveforms of the primary voltages and currents in an oscilloscope view. Individual values on the traces can be looked up and compared with each other (Figure 3).

Testing of a merging unit and in particular it's time synchronization is a challenging task. The test set is time synchronized and generates analog voltages and currents, which are accurately defined in magnitude and phase. The evaluation tool captures the Sampled Values from the merging unit for a detailed assessment of the conversion performance. For a comparison of the generated and measured values, SV Scout can also subscribe to the Sampled Values of the test set and display them as a reference. RMS values and phase angles are calculated from the Sampled Values and displayed in a phasor diagram and a table. The reference for the phase angles is selectable (Figure 5). The Detail View provides additional information about a selected Samples Values stream and its individual channels. This includes the zero crossings of specific channels, values for individual samples, and the decoded quality information.

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