G.3
Date Code 20080213 Instruction Manual SEL-351A Relay
Setting SELOGIC Control Equations
Relay Word Bits
If phase time-overcurrent element 51PT is timed out on its curve, Relay Word
bit 51PT is in the following state:
51PT = 1 (logical 1)
Phase Time-Overcurrent Element 51PT Reset Indication
If phase time-overcurrent element 51PT is not fully reset, Relay Word bit
51PR is in the following state:
51PR = 0 (logical 0)
If phase time-overcurrent element 51PT is fully reset, Relay Word bit 51PR is
in the following state:
51PR = 1 (logical 1)
If phase time-overcurrent element 51PT is not fully reset, the element is either:
➤ Timing on its curve
➤ Already timed out
➤ Is timing to reset (one-cycle reset or electromechanical
emulation—see setting 51PRS)
Relay Word Bit Application Examples—Phase Time-Overcurrent Element
51PT
Common uses for Relay Word bits 51P, 51PT, and 51PR:
Other Relay Word Bits
The preceding example was for a phase time-overcurrent element,
demonstrating Relay Word bit operation for pickup, time-out, and reset
conditions. Other Relay Word bits (e.g., those for definite-time overcurrent
elements, voltage elements, frequency elements) behave similarly in their
assertion or deassertion to logical 1 or logical 0, respectively. The time-
overcurrent elements (like the preceding phase time-overcurrent element
example) are rather unique because they have a Relay Word bit (e.g., 51PR)
that asserts for the reset state of the element.
Relay Word bits are used in SEL
OGIC control equations, which are explained
in the following subsection.
Relay Word Bit Common Use
51P testing (e.g., assign to an output contact for pickup testing)
trip unlatch logic (see SEL
OGIC control equation
unlatch trip setting ULTR example later in this section)
51PT trip logic (see SEL
OGIC control equation
trip setting TR example later in this section)
51PR used in testing (e.g., assign to an output contact for reset indication)
Courtesy of NationalSwitchgear.com
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