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Exercise Objectives
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
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 time-
overcurrent 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 http://www.selinc.com).
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
Hands-On Relay Testing Session
Overcurrent Elements
SEL
AC
ERATOR
Page 1 of 7
®
QuickSet
SEL-5030 Software. After
20120723
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Related Manuals for Sel SEL-387A
Summary of Contents for Sel SEL-387A
- Page 1 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.
- Page 2 Step 1 QuickSet, select Group 1 > Set 1 > Winding 1 Elements. ERATOR Figure 1 Phase Time-Overcurrent Element Settings Step 2 Determine the Winding 1 Max Phase Time Overcurrent Trip Level setting. 51P1P = ________________ MVA •1000 The transformer maximum expected load equals kV •...
- Page 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 0.50.
- Page 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...
- Page 5 IAWn (n = 2 in this example) 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.
- Page 6 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.
- Page 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. Step 2 Clear the SER entries.
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