4.2 Advanced Differential Example
4.2.9 Testing Harmonic Restraint
This test is designed to determine the ability of the differential protection to block tripping under transformer energizing in-rush conditions or possibly other system conditions. Test currents are injected on the Primary (HV) winding only.
The OMICRON Diff Harmonic Restraint test module has two test methods:
Shot Test A test allowing specific shots in the Ixf/Idiff plane, to verify the tolerances defined by the manufacturer.
Search Test A test for the exact determination of the characteristic shape and its tolerances.
Determine the harmonic restraint threshold of the SEL 587 differential protection 2nd and 5th harmonic settings for a three phase A-B-C (L1-L2-L3) fault type.
The sweep tests should be performed from Idiff= 0.4 I/In to Idiff= 2.9 I/Ini in 6 steps. Customize a report form "Diff_Rest" to display the test module, test settings, and all test results into the test document.
Step 1: Embedding the test module into the test document
1. Position the cursor in the test document after the Diff Trip Time object.
2. Select IN S E R T | TE S T MO D U L E and then "OMICRON Diff Harmonic Restraint", or click the appropriate toolbar icon.
Step 2: Defining the test report
Select PA R A M E T E R S | RE P O R T. A dialog box appears where you can define the scope of the report.
A detailed description about defining test reports can be found in the "Concept"
manual’s section 5.2 ”Test Reports”.
Select VI E W | RE P O R T to display the test report.
107
Step 3: Entering the general test parameters
1. Select the General tab of the OMICRON Diff Harmonic Restraint test module.
2. It is possible to define a postfault time for verification of the trip blocking during testing whereby the super-imposed harmonic is removed and the relay should trip. Make sure the postfault time exceeds the block delay reset time.
Figure 4-36:
General tab of the Diff Harmonic Restraint
module The setting for the postfault timeis used to control
the trigger after the disappearance of the harmonic element.
To use this feature, select "Apply" and enter a postfault time value.
108
Step 4: Entering Search Test parameters
The search function can be used to obtain the exact harmonic value of diff currents with differing sizes. A search is only possible when a vertical intersection point exists.
1. Select the Search Test tab of the OMICRON Diff Harmonic Restraint test module.
2. Define a test line at Idff= 0.4 In in order to find the exact threshold value for the inrush blocking (2nd harmonic). The phase shift of the harmonic from the fundamental should be set to -120°.
3. Select the fault type as A-B-C (L1-L2-L3) and the harmonic as being the 2nd.
Figure 4-37:
Search Test data entry, Diff Harmonic Restraint module.
Define search lines by clicking "Add Sweep..."
4. Start the search harmonic test.
5. Close the test module to return to the OCC.
6. Select the test module and ED I T | CO P Y to copy the test module for the 5th harmonic.
7. On a new line in the test document, select ED I T | PA S T E to insert this copy of the test module.
8. Double-click this copy to start the Diff Harmonic Restraint test module.
9. Clear the results of the last test using TE S T | CL E A R.
10.Select the fault type as A-B-C (L1-L2-L3) and the harmonic as being the 5.
11.Start the search harmonic test.
109 12.Close the test module to return to the OCC.
Figure 4-38:
Search Test mode in the Diff Harmonic Restraint test module.
The marked test line is Idiff= 1 In along with the threshold is searched.
The expected threshold value is 15%.
Results of the search mode.
13.Select the test module and ED I T | CO P Y to copy the test module for a Shot Test.
14.On a new line in the test document, select ED I T | PA S T E to insert this copy of the test module.
15.Double-click this copy to start the Harmonic Restraint test module.
16.Clear the results of the last test using TE S T | CL E A R in order to perform the Shot Test.
110
Step 5: Entering Shot Test parameters
1. Select the Shot tab of the OMICRON Diff Harmonic Restraint test module.
2. Define the first test point at Idiff= 1.0 In and Ixf-Idiff= 14.25%. The phase shift of the harmonic from the fundamental should be set to -120° (negative).
3. Enter the rest of the test points on either side of the vertical line.
Figure 4-39:
Shot Test mode in the Diff Harmonic Restraint test module
4. Start the shot harmonic test.
The tolerance band for the threshold value for the inrush stabilizati.on (2nd harmonic) and for testing of the marked points
111
Figure 4-40:
Results of the Harmonic Restraint Search Test are displayed next to the test points
5. Close the OMICRON Diff Harmonic Restraint test module. This returns you to the OCC and the test document.
112
Figure 4-41:
Report View of the specified test of the Diff Harmonic Restraint module
113
Step 6: Automatic Testing
The test document contains all of the test modules and their associated parameters for performing a test on the differential relay. The entire test procedure can be repeated in whole or in part by using the test features of the OMICRON Control Center.
1. Select VI E W | LI S T VI E W to see all of the modules that are embedded in the test document.
Figure 4-42:
List View of the modules that were embedded in the test document
This view shows an overview of the specified tests. It does not show all of the tests that were defined for the Advanced Differential example.
The status of each test is given as well as the names of the reports used.
2. Before the entire test plan can be executed from the test document, any existing test results in the individual test reports need to be cleared. To do so, use the TE S T | CL E A R AL L pull-down menu item. Moreover, the test equipment can be checked before running the overall test.
114
115
5 Synchronizer
Synchronizing relays are used to assist:
• connecting a generator to the network or power grid
• reestablishing the connection between two parts of the network
• manually closing of breakers and
• performing a synchronism check.
Synchronizing relays are designed to measure two voltages with respect to phase angle, frequency, and magnitude to safeguard against the
interconnection of two unsynchronized systems.
Figure 5-1:
Typical tests for a synchronizing relay
Synchronizing relays are also used in switching operations to link two parts of a system which are already synchronously connected via other paths in the system.
CLOSE ENABLE
116