5.8
SEL-311C Relay Instruction Manual Date Code 20060320
Trip and Target Logic
Switch-Onto-Fault Trip Logic
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 Other Enable Settings on page SET.2).
The open circuit breaker condition is determined by load current (50L) and
either one of:
➤ Circuit breaker status (52A = logical 0)
➤ Positive-sequence voltage (|V1| < 27PO)
Select OPO = 52 if 3PO is determined by circuit breaker status. Select
OPO = 27 if 3PO is determined by positive-sequence voltage.
If OPO = 52, and 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)
If OPO = 27, and |V1| is less than setting 27PO, 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), positive-sequence voltage, or load current level
(50L). When the circuit breaker is closed:
3PO = logical 0 (circuit breaker closed)
Determining Three-Pole Open Condition
Without Circuit Breaker Auxiliary Contact (OPO = 52)
If a circuit breaker auxiliary contact is not connected to the SEL-311C and
OPO = 52, SEL
OGIC control equation setting 52A may be set:
52A = 0 (numeral 0)
With SEL
OGIC control equation setting 52A continually at logical 0, 3PO
logic is controlled solely by load detection element 50L. Phase pickup 50LP is
set below load current levels.
When the circuit breaker is open, Relay Word bit 50L drops out (= logical 0)
and the 3PO condition asserts:
3PO = logical 1 (circuit breaker open)
When the circuit breaker is closed, Relay Word bit 50L picks up (= logical 0;
current above phase pickup 50LP) and the 3PO condition deasserts after the
3POD dropout time:
3PO = logical 0 (circuit breaker closed)
Note that the 3PO condition is also routed to the permissive overreaching
transfer trip (POTT) logic (see Figure 5.6) and the loss-of-potential (LOP)
logic (see Figure 4.1).
Circuit Breaker
Operated Switch-
Onto-Fault Logic
Circuit breaker operated switch-onto-fault logic is enabled by making time
setting 52AEND (52AEND ≠ OFF). Time setting 52AEND qualifies the
three-pole open (3PO) condition and then asserts Relay Word bit SOTFE:
SOTFE = logical 1
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