Schweitzer Engineering Laboratories SEL-321 - Creating Other Tripping Schemes; Direct Transfer Trip Schemes; Direct Underreaching Transfer Trip Schemes; Permissive Underreaching Transfer Trip Schemes

2-12 Specifications Date Code 20011026
SEL-321/321-1 Instruction Manual
Creating Other Tripping Schemes
Permissive Underreaching Transfer Trip Schemes
Use the POTT logic for the echo keying and Weak-Infeed logic. Program an output contact with
Zone 1 distance elements to key permissive trip.
Direct Underreaching Transfer Trip Schemes
Three-Pole Trip Applications. Assign an input to DT (Direct Trip). Program this element in
the unconditional trip variable (MTU) to trip the breaker upon assertion of the DT input.
Program an output contact with Zone 1 distance elements to key the communication equipment
to send the direct trip signal when any Zone 1 element asserts.
Single-Pole Trip Applications. Assign inputs to DTA, DTB, and DTC. Assertion of an input
causes the corresponding trip variable to assert.
Direct Transfer Trip Schemes
Three-Pole Trip Applications. Assign an input to DT (Direct Trip). Program this element in
the unconditional trip variable to trip the breaker upon assertion of the DT input. Program an
output contact with a tripping element to key the communication equipment to send the direct
trip signal when the relay asserts a tripping signal.
Single-Pole Trip Applications. Assign inputs to DTA, DTB, and DTC. Assertion of an input
causes the corresponding trip variable to assert.
Figure 2.1 shows the necessary connections between the SEL-321 Relay and the communication
equipment.
Figure 2.1: Signal Connections Between Relay and Communication Equipment