G-10 Setting SELOGIC
®
Control Equations Date Code 20001006
SEL-351 Instruction Manual
The individual SELOGIC Control Equation settings explanations (referenced in Settings Sheets 11
through 15 at the end of Section 9: Setting the Relay) discuss whether it makes logical sense to
set the given SELOGIC 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-351 Relay 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) in Section 10: Serial Port Communications and Commands.
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 in Section 3: Overcurrent, Voltage, Synchronism
Check, Frequency, and Power Elements 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 SELOGIC Control Equation operators listed in Table G.1. If this limit
must be exceeded, use a SELOGIC Control Equation variable (SELOGIC Control Equation settings
SV1 through SV12) as an intermediate setting step.
For example, assume that the trip equation (SELOGIC 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 SELOGIC Control Equation setting SV1. Next use the
resultant SELOGIC Control Equation variable output (Relay Word bit SV1) in the SELOGIC
Control Equation trip setting TR.
Note in Table G.3 that the SELOGIC Control Equation variables (SELOGIC Control Equation
settings SV1 through SV16) are processed after the trip equation (SELOGIC 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 SELOGIC Control Equation settings as a whole in a particular setting group have the following
limitations, according to model number (see Table 1.2):
Courtesy of NationalSwitchgear.com
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