5-8 Trip and Target Logic Date Code 20001006
SEL-351 Instruction Manual
Figure 5.3: Three-Pole Open Logic (Top) and Switch-Onto-Fault Logic (Bottom)
Three-Pole Open Logic
Three-pole open (3PO) logic is the top half of Figure 5.3. It is not affected by enable setting
ESOTF (see Settings Sheet 1 of 18 in Section 9: Setting the Relay).
The open circuit breaker condition is determined from the combination of:
• Circuit breaker status (52A)
• Load current condition (50L)
If the circuit breaker is open (52A = logical 0) and current is below phase pickup 50LP
(50L = logical 0), then the three-pole open (3PO) condition is true:
3PO = logical 1 (circuit breaker open)
The 3POD dropout time qualifies circuit breaker closure, whether detected by circuit breaker
status (52A) or load current level (50L). When the circuit breaker is closed:
3PO = logical 0 (circuit breaker closed)
Courtesy of NationalSwitchgear.com
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