Task
A tester has the task of performing both an automatic characteristic test and a search test for a voltage-controlled overcurrent starting function with the test module VI Starting.
The relay under test is a 7SA5 type device from SIEMENS and the test set used is a CMC 156.
8.3.1 Setting Up the Test Object
A detailed description of Test Object and the closely related subject "XRIO" can be found in section 3 ”Setting up the Test Object” of the "Concept" manual, or in the online help under the --- Test Object --- entry of the table of contents.
The relay setting program is used to find the parameters of the characteristic to be tested. Since the 7SA5 is from the SPIROTEC 3 series, the DIGSI 3 program is used. The item to look up is the Fault Detection Program for the distance protection. In this example, the U/I fault detection is set to use L-N voltages for the L-N faults and L-L voltages for the L-L faults. Then the fault detection parameters must be looked up. These are the parameters to be transferred into the test object settings of the VI Starting test module.
Figure 8-3:
Settings for the VI Starting function in the DIGSI 3 relay setting program.
189 The correspondence between the parameters in the relay setting program and the parameters in the VI Starting test object settings is clear. Other relays providing this function use similar names for the parameters, so it should be just as simple to find the values for the test object settings. In this example, the values can be taken directly from the relay setting program without further calculations.
Figure 8-4:
VI Starting parameters in the test object.
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8.3.2 Preparing the Hardware
A detailed description of the Hardware Configuration can be found in the
"Concept" manual’s section 4 ”Setting Up the Test Hardware”, or in the online help under the --- Hardware Configuration --- entry of the table of contents.
The test module VI Starting needs three analog voltages and three analog currents to produce the test quantities and one binary input for the feedback of the starting signal.
Since the CMC 156’s default hardware settings are correct, no additional setting for the used generator groups or analog output assignments in the hardware configuration (HCC) need to be made.
The start contact is connected to binary input number one, which is also the default, so no binary input settings are necessary.
For more details about the settings in the HCC, e.g., for using other test sets such as the CMC 156 or for making connections that differ from the defaults, refer to the HCC settings in the examples for other modules, e.g., State Sequencer.
8.3.3 Automatic Testing of the Characteristic
A characteristic test verifies the given characteristic as specified in the test object settings. This is done in the Verify Characteristics test mode. Testing is done with the fault type A-N, so the L-N characteristics are taken as a reference and the fault type is shown accordingly in the characteristic diagram. By using the Quick test function, four essential test points are automatically added to the test point table. In most cases, these four test points are sufficient for an assessment of the proper operation of the VI Starting function. If required, more test points could be added easily by using other methods provided for adding test points. Refer to the online help for details about adding and removing test points.
After these settings are finished, the automatic test can be started.
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Figure 8-5:
Test View after a characteristic test.
The progress of the test is displayed in the characterictic diagram by the light blue test line with the bullet on it, which represents the actual V-I quantities emitted during testing. The vector diagram indicates the relationship of the voltages and the currents to each other and the value table in the Vector View displays the exact numeric values of test quantities.
The assessment refers to the pick-up values only, since specifications are generally only available for the pick-up characteristic.
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8.3.4 A Search Test
The search test finds an unknown VI starting characteristic. In fact, it finds both the pick-up and the drop-off characteristic. This is done in the Search
Characteristic test mode. No characteristic settings have to be made in the test object in order to use this mode. There is no option to specify test points in this mode as the test module automatically measures four essential points, which are sufficient to determine the characteristics. These are the same test points used in the Quick test. In this test, the fault type B-C is used to search for the L-L characteristics.
Figure 8-6:
Test View after a search test.
The progress of the test is displayed by the test line and the moving bullet. As soon as the values become available, the calculated characteristics are updated, according to the data available at this moment. In the table, the parameters of the pick-up and the drop-off characteristic are displayed. For more details about the search procedure, refer to the online help.
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