G.10
SEL-351A Relay Instruction Manual Date Code 20080213
Setting SELOGIC Control Equations
SEL
OGIC Control Equations
The individual SELOGIC control equation settings explanations (referenced in
SEL
OGIC Control Equation Settings (Serial Port Command SET L) on
page SET.15) discuss whether it makes logical sense to set the given SEL
OGIC
control equation setting to 0 or 1 for certain criteria.
Set SELOGIC Control Equations Directly to 1 or 0—Example
Of special concern are the SELOGIC control equation torque control settings
67P1TC through 51QTC for the overcurrent elements. In the factory settings
the SEL-351A ships with in a standard relay shipment, these are all set
directly to logical 1. See these factory settings in SHO Command (Show/View
Settings) on page 10.25.
If one of these torque control settings is set directly to logical 1, e.g.,
51PTC = 1 (set directly to logical 1)
then the corresponding overcurrent element (e.g., phase time-overcurrent
element 51PT) is subject only to the directional control. See Figure 3.14 for
phase time-overcurrent element 51PT logic.
If the directional control enable setting E32 = N (and 51PTC = 1), then time-
overcurrent element 51PT is enabled (assuming pickup setting 51PP is made)
and nondirectional.
SELOGIC Control
Equation Limitations
Any single SELOGIC control equation setting is limited to 15 Relay Word bits
that can be combined together with the SEL
OGIC control equation operators
listed in Table G.1. If this limit must be exceeded, use a SEL
OGIC control
equation variable (SEL
OGIC control equation settings SV1–SV16) as an
intermediate setting step.
For example, assume that the trip equation (SEL
OGIC control equation trip
setting TR) needs more than 15 Relay Word bits in its equation setting. Instead
of placing all Relay Word bits into TR, program some of them into the
SEL
OGIC control equation setting SV1. Next use the resultant SELOGIC
control equation variable output (Relay Word bit SV1) in the SEL
OGIC control
equation trip setting TR.
Note in Table G.3 that the SEL
OGIC control equation variables (SELOGIC
control equation settings SV1–SV16) are processed after the trip equation
(SEL
OGIC control equation trip setting TR). Thus, any tripping via Relay
Word bits SV1 through SV16 can be delayed as much as 1/4 cycle. For most
applications, this is probably of no consequence.
The SEL
OGIC control equation settings as a whole in a particular setting group
have the limitations, shown in Table G.2.
SEL
OGIC control equation settings that are set directly to 1 (logical 1) or 0
(logical 0) also have to be included in these limitations. Each such setting
counts as one Relay Word bit.
Ta b le G . 2 S E L OGIC Control Equation Settings Limitations
Relay
SELOGIC Control Equation Settings
Limitations per Setting Group
SEL-351A Total number of elements ≤ 486
Total number of rising-edge
or falling-edge operators ≤ 54
Courtesy of NationalSwitchgear.com
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