G.2
SEL-351A Relay Instruction Manual Date Code 20080213
Setting SELOGIC Control Equations
Relay Word Bits
Relay Word Bits
Most of the protection and control element logic outputs shown in the various
figures in Section 3: Overcurrent, Voltage, Synchronism Check, and
Frequency Elements through Section 8: Breaker Monitor and Metering are
Relay Word bits (labeled as such in the figures). Each Relay Word bit has a
label name and can be in either of the following states:
➤ 1 (logical 1) or
➤ 0 (logical 0)
Logical 1 represents an element being picked up, timed out, or otherwise
asserted.
Logical 0 represents an element being dropped out or otherwise deasserted.
See Tab le 9.6 for a complete listing of Relay Word bits and their descriptions.
Relay Word Bit
Operation Example—
Phase Time-
Overcurrent Element
51PT
The following example uses a phase time-overcurrent element to illustrate
protection element operation via the logic output of Relay Word bits. Refer to
phase time-overcurrent element 51PT in Figure 3.14. Read the text that
accompanies Figure 3.14 (Table 3.3 and following text). The following Relay
Word bits are the logic outputs of the phase time-overcurrent element:
Phase Time-Overcurrent Element 51PT Pickup Indication
If the maximum phase current is at or below the level of the phase time-
overcurrent pickup setting 51PP, Relay Word bit 51P is in the following state:
51P = 0 (logical 0)
If the maximum phase current is above the level of the phase time-overcurrent
pickup setting 51PP, Relay Word bit 51P is in the following state:
51P = 1 (logical 1)
If the maximum phase current is above the level of the phase time-overcurrent
pickup setting 51PP, phase time-overcurrent element 51PT is either timing on
its curve or is already timed out.
Phase Time-Overcurrent Element 51PT Time-Out Indication
If phase time-overcurrent element 51PT is not timed out on its curve, Relay
Word bit 51PT is in the following state:
51PT = 0 (logical 0)
Relay Word
Bit
Description
51P indication that the maximum phase current magnitude is
above the level of the phase time-overcurrent pickup setting 51PP
51PT indication that the
phase time-overcurrent element has timed out on its curve
51PR indication that the phase time-overcurrent element is fully reset
Courtesy of NationalSwitchgear.com
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