Application Note
Distance protection with transformer in protected area with RelaySimTest Author Ana García |
[email protected] Date Mar 23, 2015 Related OMICRON Product CMC, RelaySimTest Application Area Distance protection Keywords RelaySimTest, Distance protection, Transformer, System Testing Version v1.0 Document ID ANS_15008_ENU
Abstract This application note describes how to test directional distance protection when it is used as a backup protection for a power transformer. This test can be carried out in an easy and comfortable way using the corresponding OMICRON RelaySimTest test template. RelaySimTest offers simulation based system testing methods. To perform a test, a fault scenario is calculated based on the simulation of the power system network. The voltages and currents for the relay location can be used to test the correct behavior of the distance protection when the fault is located before or after the power transformer.
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General information OMICRON electronics GmbH including all international branch offices is henceforth referred to as OMICRON. The product information, specifications, and technical data embodied in this application note represent the technical status at the time of writing and are subject to change without prior notice. We have done our best to ensure that the information given in this application note is useful, accurate and entirely reliable. However, OMICRON does not assume responsibility for any inaccuracies which may be present. OMICRON translates this application note from the source language English into a number of other languages. Any translation of this document is done for local requirements, and in the event of a dispute between the English and a non-English version, the English version of this note shall govern. All rights including translation reserved. Reproduction of any kind, for example, photocopying, microfilming, optical character recognition and/or storage in electronic data processing systems, requires the explicit consent of OMICRON. Reprinting, wholly or partly, is not permitted. © OMICRON 2015. All rights reserved. This application note is a publication of OMICRON.
© OMICRON 2015
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Content 1
2
3
4
Safety instructions ................................................................................................................................4 1.1
Requirements to use this Application Note.....................................................................................4
1.2
Special Safety Instructions for the Application Note .......................................................................5
About this Application Note .................................................................................................................6 2.1
General Requirements....................................................................................................................6
2.2
What this Application Note Describes ............................................................................................6
2.3
Distance function as power transformer backup protection ...........................................................6
System under test .................................................................................................................................8 3.1
Application example – protected area and time grading ................................................................8
3.2
Settings of the system under test in RelaySimTest ........................................................................9
Test cases ........................................................................................................................................... 11 4.1
Application example: Grid topology ............................................................................................. 11
4.2
Suitable test cases ....................................................................................................................... 12 4.2.1
Test Case 1: Fault before transformer ........................................................................................... 13
4.2.2
Test Case 2: Fault after transformer .............................................................................................. 13
5
Measurement and assessment ......................................................................................................... 14
6
Test Set Configuration ....................................................................................................................... 15
7
Visualizing the diagrams with TransView ........................................................................................ 17
8
Performing the test ............................................................................................................................. 20
9
List of Literature ................................................................................................................................. 21
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1
Safety instructions
1.1 Requirements to use this Application Note This application note may only be used in combination with the relevant product manuals which contain all safety instructions. The user is fully responsibility for any application that makes use of OMICRON products. Instructions are always characterized by a symbol even if they are included to a safety instruction. DANGER Death or severe injury caused by high voltage or current if the respective protective measures are not complied. Carefully read and understand the content of this application note as well as the manuals of the involved systems before starting its practical application. Please contact OMICRON before you continue the process if you do not understand the safety instructions, operating instructions, or parts of it. Follow each instruction mentioned there especially the safety instructions since this is the only way to avoid danger that can occur when working at high voltage or high current systems. Furthermore, only use the involved equipment according to its intended purpose to guarantee a safe operation. Existing national safety standards for accident prevention and environmental protection may supplement the equipment’s manual.
Only experienced and competent professionals that are trained for working in high voltage or high current environments may perform this application note. Additional the following qualifications are required: •
Authorized to work in environments of energy generation, transmission or distribution and familiar with the approved operating practices in such environments.
•
Familiar with the five safety rules.
•
Good knowledge of the OMICRON CMC test sets and RelaySimTest.
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1.2 Special Safety Instructions for the Application Note The OMICRON RelaySimTest software controls electrical equipment that can output life-hazardous voltages and currents. DANGER Death or severe injury caused by high voltage or current. Carefully read the Safety Instructions section in the relevant manual provided with the equipment before operating any such electrical equipment. Do not use (or even turn on) any electrical equipment without understanding the information in its manual. Only trained personal may operate RelaySimTest. Always turn off each system involved to the test process before wiring up or rewiring the equipment.
NOTICE Equipment damage or loss of data possible. Do not use (or even turn on) any electrical equipment without understanding the information in its manual. Always turn off each system involved to the test process before wiring up or rewiring the equipment. General Requirements To use this application note it is necessary to read the “Getting started” manual [1] of RelaySimTest before and it is essential to have a good knowledge about the CMC test system.
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About this Application Note
2.1 General Requirements Before you get started with this application note, read the “Getting started” manual [1] of RelaySimTest. Please make sure that you also have a good knowledge about the CMC test system.
2.2 What this Application Note Describes The application note describes how to test a distance relay when it is back up protection for a power transformer using a RelaySimTest template. Therefore it shows the following content: 1. Distance function as power transformer backup protection (general information) 2. Defining the System under Test 3. Defining Test cases 4. Defining Test sets configuration The application note doesn’t describe a classical test of the distance protection itself, when it is performed a detailed test of the distance characteristic zones and a check of the distance parameters like reach and trip delay time. To test the protection thoroughly, such tests are also recommended.
2.3 Distance function as power transformer backup protection Distance protection is a universal short-circuit protection. Its mode of operation is based on the measurement and evaluation of the short-circuit impedance, which is usually proportional to the distance to the fault. The distance function acts as main protection for overhead lines and cables and in addition it works as backup protection for other parts of the network, such as power transformers. Directional distance relaying can be used for transformer backup protection when the setting or coordination of the overcurrent relays is a problem. Besides, overcurrent is more sensitive than distance to the different short-circuit levels that can be found in the network. The directional distance relays operate when the fault current flows toward the protected transformer and adjacent lines. For distance measurements with transformers in the protected area, the next aspects must be taken into account:
Impedance is transformed with the square of the power transformer’s voltage ratio. On star/delta transformers there is a phase rotation corresponding to the power transformer’s vector group. The fault current distribution changes from one side of the transformer to the other. For instance, a two-phase short circuit on one side may appears as a three-phase fault with asymmetric current distribution on the other side.
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Figure 1: Two phase short-circuit
The zero-sequence system cannot be converted by a start/delta transformer. That means that earthfaults are not measured correctly by the distance relay through a star/delta transformer. In isolated or compensated systems, this is usually not a problem. Depending on the system characteristics, a separate earth-fault protection may be required.
Usually in the distance scheme, Zone 1 doesn’t protect the complete line adjacent to the power transformer. The instantaneous tripping is only possible for around 80% to 90% of the line. Zone 2 reaches into, but not beyond the transformer and Zone 3 protects the cable connected to the secondary side of the transformer. Z3 Z2 Z1
D1
Figure 2: Graded distance zones
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System under test
3.1 Application example – protected area and time grading The following figure shows the distance scheme proposed in the previous section: Zone 1 protects up to 80% of the overhead line. Zone 2 protects up to 80 % of the power transformer. Zone 3 protects all three equipment including the cable connected to the second side of the power transformer.
Cable Data 50 Hz 10 kV 2500 A 0,5 km R1‘ = 23 mOhm/km X1‘ = 48 mOhm/km R0‘ = 261,93 mOhm/km X0‘ = 84,5 mOhm/km C1‘= 1,206 µF/km C0‘= 1,206 µF/km
Overhead Line Data 50 Hz 110 kV 200 A 10 km R1‘ = 136,81 mOhm/km X1‘ = 375,88 mOhm/km R0‘ = 410,42 mOhm/km X0‘ = 1,1276 Ohm/km
A
80% transf.
80% line
Z3
B
Z2
Z1 CT A 200 A / 1 A
1
Y 2 Relay A
VT A 110 kV / 100 V
d5 S= 40 MVA Xcc= 12 % Rcc= 0,5%
Figure 3: Distance scheme in the example
Figure 4 presents the time grading of the distance protection. Relay A has three forward zones. The first zone is instantaneous which means the nominal trip time is 0 seconds. The second zone’s nominal trip time is 400 ms and the third zone trips with an 800 ms delay.
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Z3
0.8 s
Z2
0.4 s 0s
Z1 A
B
Figure 4: Time grading for relay A
3.2 Settings of the system under test in RelaySimTest The parameters of the substation, the bay and relay can be set in the System under Test according to the example in the previous section. Note that the colored numbers in Figure 3 and in Figure 5 are related. Comments: 1. Bay A1: This menu contains the trip and close time of the circuit breaker (CB). With this information the binary outputs of the CMC could simulate the behavior of the CB. However the test template doesn’t use this feature. Furthermore, the Bay menu item contains the sub menu Instrument transformers that includes the CT and VT data (Figure 6). 2. Relay A1: This menu item contains the test current limits and the relay inputs and outputs (Figure 7).
Figure 5: System under test menu
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Figure 6: Instrument transformers
Figure 7: Relay input/outputs
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Test cases Figure 8 shows the Test cases menu. It contains the grid topology (1), the test scenarios (2), the test steps (3) and the test properties (4). The next sections describe this menus referring to the test template of the application note.
Figure 8: Test cases Menu
4.1 Application example: Grid topology The grid topology used in this application example is presented in Figure 9.
Figure 9: Grid topology
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4.2 Suitable test cases This section describes the tests defined in the corresponding RelaySimTest template. To keep the template simple, it uses only the following Fault types:
L1-N L2-L3 L1-L2-L3
Depending on the relay under test, on the relay’s parameters and on the grid where the protection system is used, it may be necessary to add more fault types. The Initial state of a fault is inactive to get transients when the fault is applied. To get particularly high fault currents with DC components the fault inception angle is set to 0°.
Figure 10: Fault with initial state "Inactive"
The RelaySimTest template includes two test cases. One simulates faults before the transformer, in the overhead line, and the second simulates faults after the transformer, in the cable connected to the transformer low-voltage side. In the isolated system at the low-voltage side of the transformer, single L-N faults do not characterize shortcircuits. Therefore they are not added as Test steps. The nominal trip time of the protection is between 0 and 0,8 s, therefore the simulation time after a fault or switching event is at least 1,2 s. Hence the protection system has enough time to show its reaction on the event. The following sections describe in detail the template test cases.
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4.2.1 Test Case 1: Fault before transformer This test case should show that a fault on the first 80% of the overhead line leads to an instantaneous trip of distance protection relay. From the 80% to the 100% of the line the relay has to trip with a 400 ms delay.
Fault locations: 0%, and 100% of the overhead line.
Figure 11: Test Case 1
4.2.2 Test Case 2: Fault after transformer This test case should show that a fault on the low-voltage side of the transformer leads to a trip with 800 ms delay.
Fault locations: 0%, 50% and 100% of the cable length.
Figure 12: Test Case 2
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Measurement and assessment The Define measurements menu of the Test steps tab (see Figure 8 number 3) defines the start and stop event for the trip time measurements.
The “start measuring event” is the beginning of the corresponding fault, if the fault leads to a trip. The “start measuring event” is the beginning of the simulation (0s) or the beginning of the corresponding fault for tests where the relay is not allowed to trip. In both cases the trip command is observed. Therefore the trip signal activation is the “stop measuring event”.
Figure 13: Measurement
The Set assessment condition menu (next to the Define measurements menu) defines the assessment of the test steps. For test points where the relay has to trip, the min/max values have to be entered (option “Custom min/max values”, see Figure 14). For those test points where the relay is not allowed to trip, the option “No stop event occurs” is the required assessment condition.
Figure 14: Custom min/max values
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Test Set Configuration The proposed distance test requires one CMC and one PC with RelaySimTest. To perform a test, RelaySimTest calculates a fault scenario based on the simulation of the power system network. It calculates the voltages and currents.
Figure 15: Scheme
This section assumes that the setup in the scheme above is complete:
The PC is running RelaySimTest. The wiring between the CMC and the relay is ready. The CMC and the PC are connected using the USB port. (Connection by Ethernet is also possible).
The Test sets configuration menu defines the CMC and the configuration used for the tests. The test template includes a general CMC as shown in Figure 16.
Figure 16: Test sets configurations
After a click on the “Choose test set” button on the right side of the CMC icon, a new window opens and offers the CMC that is connected to the PC. A click on the CMC selects it.
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Figure 17: CMC is selected
The Getting Started manual of RelaySimTest [1] describes how the wiring between the CMCs and the relays can be configured in the Test sets configuration menu. To perform the tests of this application note the following signals have to be configured: Three test voltages Three test currents Start and trip signals
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Visualizing the diagrams with TransView The Synchronize to TransView option will help you to analyze the Test steps results. To get the distance zones displayed in the TransView Circle Diagrams, save the relay under test RIO file as: %TEMP%\SIMULATIONTEST.RIO Note that the %temp% command allows access to the Windows temporary files (AppData\Local\Temp) where the Synchronize to TransView option saves the COMTRADE file displayed by TransView. The RIO file can be exported from the Test Universe Test Object as follows: 1. Select File in the Test Object main menu. 2. Select Export … in the submenu. 3. Select RIO file type and enter %TEMP%\SIMULATIONTEST.RIO as file name. The RIO file will be saved in the correct location. 4. Save the file.
Figure 18: Export RIO file
The zones in the TransView Circle Diagrams are displayed in the next four figures.
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Figure 19: Synchronize to TransView feature
When a Test Step is executed, the fault trajectories are visible in the TransView Circle Diagrams and it allows to double check that the relay trips in the correct zone. The next examples can be found in the RelaySimTest sample: L1-N fault before transformer: fault location 25% of overhead line The Trip A1 occurs at 19.8 ms. According to the zones time grading this means Zone 1. On the right hand side, the phase 1 fault trajectory ends in Zone 1 in the LE Circle Diagram. Note that you may have to zoom on the Zone 1 because it is very small compared with the other zones.
Figure 20: L1-N fault before transformer: 25% of overhead line © OMICRON 2015
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L1-L2-L3 fault before transformer: fault location 100% of overhead line The Trip A1 occurs at 446.4 ms. According to the zones time grading this means Zone 2. On the right hand side, the three phases fault trajectories end in Zone 2 in the LL Circle Diagram.
Figure 21: L1-L2-L3 fault before transformer: 100% of overhead line
L2-L3 fault after transformer: fault location 50 % of cable The Trip A1 occurs at 837.9 ms. According to the zones time grading this means Zone 3. On the right hand side, the phase 2- phase 3 fault trajectory ends in Zone 3 in the LL Circle Diagram.
Figure 22: L2-L3 fault after transformer: 50% of cable © OMICRON 2015
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Performing the test Before starting the test, it is strongly recommended to perform a wiring check. The execute buttons start the tests. There are different execute buttons - “Execute all” and “Execute selected”. What they mean depends on how the test is performed:
If a test case is open a click on the “Execute selected” button executes only the selected test step. A click on the “Execute all” button runs all test steps of the test case sequentially.
Figure 23: "Execute selected" and "Execute all" in a test case
However, in the Test Manager menu the “Execute selected” button runs all selected test cases, while “Execute all” runs all test cases.
Figure 24: "Execute selected" and "Execute all" in Test Manager
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List of Literature [1] Getting started with RelaySimTest; OMICRON electronics GmbH; 2014 [2] “Numerical Distance Protection: Principles and Applications”; 4th edition; Gerhard Ziegler; PUBLICIS; 2011 [3] “SIPROTEC Distance Protection 7SA6 V4.70 Manual”, SIEMENS
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