Impedance characteristic test of relay protection tester
The main function of this test module of the relay protection tester is to analyze the action characteristics of distance protection and determine its impedance action boundary. It can detect the impedance action boundaries of various characteristics such as circular, polygonal, arc-shaped, and straight line. This test module offers two different search methods: “one-way search” and “two-way search”.
Searchable circles, polygons, and other impedance characteristic graphs
By following the instructions to set the parameters, the software can draw a rough graph, which is helpful for comparing with the searched graph.
Test interface description: List of test items
For each test, only one of the following options can be selected for the experiment: “Impedance Boundary Search”, “Z(Ⅰ) Characteristic Curve”, or “Z(V) Characteristic Curve”.
Fault types: Various fault types are provided for testing various types of distance protection. For ground-type distance relays, a single-phase ground fault should be selected; for inter-phase distance protection, an inter-phase fault should be chosen.
The calculation model has two types: “constant current” and “constant voltage”. When choosing “constant current”, the short-circuit current can be set in the box below, and the software will calculate the corresponding short-circuit voltage based on the short-circuit current and short-circuit impedance. When choosing “constant voltage”, the short-circuit voltage can be set in the box below, and the software will calculate the corresponding short-circuit current based on the short-circuit voltage and short-circuit impedance.
The search methods include “single-phase search” and “bidirectional search”. For detailed information, please refer to the relevant explanations in the “Differential Protection” section of the relay protection tester. “Resolution” is only applicable to the bidirectional search method and it determines the test accuracy of the bidirectional search method.
The fault triggering method: In the “time control” triggering mode, the software conducts cyclic tests in the following sequence: “fault pre-delay” – “large fault duration” – “test interruption time”. For detailed explanations, please refer to the relevant instructions in the “Line Protection” section of the Relay Protection Tester.
The minimum action confirmation time is within the “large fault time” and it ensures the protection of multiple possible actions. If the protection action time is shorter than the “minimum action confirmation time”, even if it is a protection action signal, the software will not recognize it because it might be an action from another section. This time is specifically used to avoid a certain section’s impedance action in the “bidirectional search” mode. For example, when searching for the boundary of section II impedance, in the “bidirectional search” mode, the scanning points will definitely enter the impedance range of section I, while the action time of section I is shorter than that of section II, thus causing section I protection to act prematurely.
The fault direction is set according to the protection setting menu and is applicable to directional impedance protection.
Zero-sequence compensation coefficient. When conducting tests for grounding distance relays, it is necessary to correctly set the zero-sequence compensation coefficient. Please refer to the relevant instructions in the “Line Protection” section of the relay protection tester.
Automatically set the parameters of the search line. There is a button for this on the “Set Parameters” page. After clicking this button, the software will automatically calculate the length of the search line and the search center based on the set setting impedance. You can view it on the “Search Impedance Boundary*” page.
Search impedance boundary
When selecting the “Search Resistance Boundary” test item, a radial scanning line needs to be set. The setting of the scanning line should follow the following method:
The scanning center should be set as close as possible to the center of the theoretical impedance characteristic diagram for protection. The scanning center can be directly input with data or selected by clicking with the mouse. After modifying the scanning center, the coordinate axes of the coordinate system will automatically adjust to ensure that the scanning circle is always at the center of the graph, that is, the scanning center is at the center of the graph.
Scan radius: The scan radius should be greater than half of the set value of the protection impedance to ensure that the scan circle covers all the action boundaries of the protection. The search starts from the non-action area (the points outside the scan line). During the test of the relay protection tester, if it is found that when scanning the outer starting point of a certain search line, the protection acts, it indicates that this scan line does not cross the actual impedance boundary. That is, the entire search line is within the action area, which does not comply with the principle that “each search line should have part within the action area and part outside the action area”. At this time, please appropriately increase the “scan radius”.
The scanning step size is only applicable to the “one-way search” method and directly affects the test accuracy when using this method.
The scanning range, by default, is set to 100% of the total range. By setting an appropriate scanning range, it is often possible to avoid false activations of other segment impedance protection. For instance, setting the scanning range to 80%.
Search angle: The series of search lines can be set by specifying the starting angle, ending angle, and angle step size. If the angle step size is set very small, although a large number of points are found, which is beneficial for improving the accuracy of boundary search, it will also significantly increase the test time. During actual testing, please choose an appropriate angle step size.
Automatically set the scanning parameters. On the calibration parameter page, after setting the calibration impedance value, the software will automatically calculate the empirical values for the scanning center position and scanning radius based on the calibration impedance value. If these values are still not satisfactory, adjustments can be made on this basis.
Post time: Apr-21-2026