Date Code 20011026 Applications 5-1
SEL-321/321-1 Instruction Manual
SECTION 5: APPLICATIONS
A 230 KV APPLICATION EXAMPLE FOR POTT SCHEME WITH TIME-STEPPED
BACKUP
Purpose
The following is an example of a possible SEL-321 Relay installation. The example shown is for
a 5 A nominal relay.
This example shows the steps for setting the relay at Breaker 3 to protect Line 2 in Figure 5.1
between Buses B and C. The basic criteria for protecting this line appear below:
• The communications scheme is Permissive Overreaching Transfer Trip.
• Zone 2 serves as time-step backup.
• Current reversals may occur at the Breaker 3 location.
• The maximum expected load is less than 450 A.
Figure 5.1: 230 kV Setting Example System Single-Line Diagram
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