Sel 411L - Table 3.24 Extended Security Alpha Plane Switchover Logic Settings

P.3.66
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Differential Elements
➤ In addition, you can use the E87LPS, E87LQS, and E87LGS
SEL
OGIC control equations as listed in Table 3.24 to apply
your own conditions to force the extended security settings.
The exact conditions necessary to force the extended security settings depend
on the assumptions you use when calculating normal security settings. For
rare conditions, where normal security settings you select for sensitivity have
insufficient security margin, you can instead engage extended security settings
with enough margin by stating the appropriate conditions when you design the
E87LPS, E87LQS, and E87LGS SEL
OGIC control equations. In this approach,
the E87LPS, E87LQS, and E87LGS SEL
OGIC control equations define
exceptions from normal prevailing conditions and call for the application of
more secure settings, instead of making the application less sensitive under all
conditions.
For security, the logic of Figure 3.38 checks whether the logic has applied the
extended security settings for at least one power cycle. If so, the logic adds an
intentional dropout delay of two cycles when it switches from extended
security settings back to normal security settings.
Table 3.24 lists the extended security Alpha Plane switchover logic settings.
Table 3.24 Extended Security Alpha Plane Switchover Logic Settings
Setting Description Range Default
E87LPS Enable extended security 87LP Alpha
Plane settings
SELOGIC control
equation
NA
E87LQS Enable extended security 87LQ Alpha
Plane settings
SEL
OGIC control
equation
NA
E87LGS Enable extended security 87LG Alpha
Plane settings
SEL
OGIC control
equation
NA