Date Code 20110408 Instruction Manual SEL-551 Relay
Section 3
Relay Elements and Logic
Relay Word Bits and SELOGIC Control Equations
This section describes relay elements and logic with numerous figures and
accompanying text. Details on setting ranges are given in the setting sheets in
Section 4: Setting the Relay. See the SHO Command (Showset) on page 5.16
for a listing of the factory settings shipped with the relay.
Relay Word Bits
The outputs of the logic in most of the figures in this section are labeled Relay
Word bits. Relay Word bits have label names (e.g., 51P1T, TRIP, CLOSE,
etc.). They are logic points that can have a state of:
1 (logical 1) or 0 (logical 0)
depending on the operation of the associated logic. Logical 1 represents an
element being picked up, timed out, or otherwise asserted. Logical 0
represents an element being dropped out or otherwise deasserted. All Relay
Word bits and their descriptions are shown in Table 4.5 and Table 4.6 and are
used in SEL
OGIC
®
control equations.
SELOGIC Control
Equations
SELOGIC control equation settings are the inputs for the logic in many of the
figures in this section. See the SEL
OGIC Control Equation Settings (SET L
Command) on page SET.6 for a listing and short description of each of the
SEL
OGIC control equation settings. See the SHO Command (Showset) for a
listing of the factory SEL
OGIC control equation settings shipped with the relay.
Create traditional or advanced custom schemes with SEL
OGIC control
equations.
SEL
OGIC control equation settings are written in Boolean algebra logic,
combining Relay Word bits together with different operators. Parentheses can
also be used in SEL
OGIC control equation settings. More than one set of
parentheses can be used in a given SEL
OGIC control equations setting, but they
cannot be “nested” (parentheses within parentheses). See Trip Logic on
page 3.17 and Reclosing Relay on page 3.22 for examples of using
parentheses (factory settings for ULTR and 79BRS, respectively). Operators
in a SEL
OGIC control equations setting are processed in the following order:
Table 3.1 Processing Order of SELOGIC Control Equation Operators
Operator Logic Function
/ rising-edge detect
\ falling-edge detect
( ) parentheses
!NOT
* AND
+OR
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