Overcurrent Elements

Transcription

1 Exercise Objectives Hands-On Relay Testing Session Overcurrent Elements After completing this exercise, you should be able to do the following: Identify overcurrent element settings. Determine effective overcurrent protection settings. Validate relay settings. In this exercise, the instructor will introduce the SEL-387A Current Differential and Overcurrent Relay overcurrent elements, determine how to set the elements for transformer backup protection, and demonstrate how to enter the settings. You will then enter the overcurrent settings into ACSELERATOR QuickSet SEL-5030 Software. After sending your settings to the relay, you will validate the settings and verify the protection scheme. SEL-387A Time-Overcurrent Elements The SEL-387A provides numerous overcurrent elements, as many as 11 per winding and 5 per neutral input. Four levels of phase instantaneous or definite-time elements are available for overcurrent protection, breaker failure protection, overcurrent phase selection for targeting, transformer backup protection, and so on. Two levels of negative-sequence and residual instantaneous elements provide protection against unbalanced conditions and ground faults. Phase, negative-sequence, and residual timeovercurrent elements are available for system backup protection. The SEL-387A also has neutral instantaneous or definite-time elements available. For a more detailed description of each of the overcurrent elements, refer to the SEL-387A Instruction Manual (available at Hands-On Activity 1: Enable Overcurrent Elements In this hands-on activity, you will enable the element for a particular winding and enter settings for backup overcurrent protection. Write your answers in the space provided. Transformer Data Rated 50 MVA Rated high side 161 kv (DAB) Rated low side 14.4 kv (wye) High-side bushing current transformer (CT) ratio (wye connected) Low-side bushing CT ratio (wye connected) Neutral bushing CT ratio Overcurrent Elements Page 1 of

2 Step 1 In ACSELERATOR QuickSet, select Group 1 > Set 1 > Winding 1 Elements. Figure 1 Phase Time-Overcurrent Element Settings Determine the Winding 1 Max Phase Time Overcurrent Trip Level setting. 51P1P = The transformer maximum expected load equals MVA 1000 kv 3 Set the 51P1 pickup to 150 percent of expected maximum load. Step 3 Select Group 1 > Set 1 > Neutral 2 Elements. Figure 2 Neutral Instantaneous Overcurrent Element Settings Overcurrent Elements Page 2 of

3 Step 4 Determine the Neutral Inst Overcurrent Trip Level setting. 50NN21P = Set the 50N element to 50 percent of the maximum ground fault current. Obtain the maximum value from a system fault study. For this example, assume a 5,000 A ground fault current. Step 5 Verify that the Neutral Inst Overcurrent Trip Delay (50NN1D) is set at minimum value of Step 6 Select Group 1 > Set 1 > Winding 2 Elements. Figure 3 Phase Time-Overcurrent Element Settings Step 7 Determine the Winding 2 Phase Time Overcurrent Trip Level setting. 51P2P = Set the phase time-overcurrent element to 150 percent of the continuous rated amperes. Step 8 Set the Winding 2 Phase TOC Curve Selection to coordinate with the downstream time-overcurrent protection. 51P2C = Overcurrent Elements Page 3 of

4 Step 9 Set the Winding 2 Phase TOC Time Dial. 51P2TD = For this exercise, set the time dial to 3 to provide time coordination with downstream devices. You can determine the time dial setting based on a fault coordination study. Step 10 Verify that the following settings are at the default values: 51P2RS = Y 51P2TC = 1 Step 11 Save your settings, and then send them to the relay. Hands-On Activity 2: Validate Overcurrent Elements In this hands-on activity, you will validate the phase and neutral instantaneous overcurrent elements and the phase time-overcurrent elements. Validation Functional Description Figure 4 illustrates the location of Fault F1. The relay should operate when the fault magnitude exceeds the overcurrent relay setting and the time-delay elements time out. Figure 4 Overcurrent Validation Fault Location Overcurrent Elements Page 4 of

5 Validation Pickup Test Values The instructor will use the SEL-AMS (Adaptive Multichannel Source) to inject secondary quantities into the relay terminals to simulate faults (as indicated in Table 1). Table 1 Input (Fault Applied at F1 Location) IAW1 IAW2 IAWn (n = 2 in this example) Simulated F1 Values for Element Pickup Test Element 51P1P 51P2P 50NN21P The instructor will apply the test values to the relay using the SEL-5401 Test System Software front-panel function. Apply a value slightly less than the pickup setting, and slowly increase the current magnitude until the applicable Relay Word bit asserts. Fault Step 1 Reset relay targets by pushing the {TARGET RESET} pushbutton located on the relay front panel. Clear the Sequential Events Recorder (SER) entries. You can perform this task by using either the SER C serial port command or the ACSELERATOR QuickSet human-machine interface (HMI). The instructor will apply the fault current. Step 3 Use the TARn serial port command (n = the Relay Word bit for the element under test) or the ACSELERATOR QuickSet HMI to verify the overcurrent element pickup. Step 4 Verify the following ACSELERATOR QuickSet HMI user-defined target light-emitting diode (LED) indicators: Phase time-overcurrent element 51P1P asserts. Phase time-overcurrent element 51P2P asserts. Neutral instantaneous overcurrent element 50NN21P asserts. Record the element in the Fault column of Table 1. Overcurrent Elements Page 5 of

6 Hands-On Activity 3: Validate Time-Overcurrent Element In this hands-on activity, you will validate the Winding 2 time-overcurrent element. Validate Time-Overcurrent Test Values The instructor will use the SEL-AMS to inject secondary quantities into the relay terminals to simulate faults (as indicated in Table 1). Step 1 Calculate the expected operate time using the equations from Figure 5, and record your answers in Table 2. Figure 5 Time-Overcurrent Operation Equations Element Name 51P1T 51P2T 50NN2T Table 2 Simulated F1 Values for Element Pickup Test Calculated Operate Time at Three Times Pickup Test Time Percentage Difference Clear the SER entries. You can perform this task by using either the SER C serial port command or the ACSELERATOR QuickSet HMI. Overcurrent Elements Page 6 of

7 Winding 2 Time-Overcurrent Timing Test The instructor will apply the test values to the relay at three times the element pickup. Step 1 Reset relay targets by pushing the {TARGET RESET} pushbutton located on the relay front panel. Clear the SER entries. You can perform this task by using either the SER C serial port command or the ACSELERATOR QuickSet HMI. Step 3 After the instructor applies the fault current, use the TARn serial port command (n = the Relay Word bit for the element under test) or the ACSELERATOR QuickSet HMI to verify the overcurrent element pickup. Step 4 Verify that the relay indicator for the Winding 2 phase time-overcurrent element 51P2T asserts at the calculated test time. Step 5 Calculate the error percentage using the following formula: % error = (recorded calculated)/calculated Step 6 Ensure the error percentage is within ±5 percent for this timing test. Overcurrent Elements Page 7 of