9328900990 Rev L BE1-951 Protection and Control 4-5
D2647-21
08-21-98
D3
D2
D1
D0
AUTO
SG3
SG2
SG1
SG0
SGC
Figure 4-4. Input Control Mode 2
Automatic Setting Group Control
The relay has built in schemes that may be used to automatically change setting groups. One scheme is
based on the history of the current in the relay. Another scheme is based upon the status of the reclose
function (79). To enable automatic change of setting groups, setting group control must be enabled and
the <autologic> bit of SL-GROUP command must be a 1 and can be set as follows:
SL-GROUP = /0,,,,,/0.
When automatic control is enabled it holds precedence over all manual logic control.
The automatic setting group control may be used to force the relay to change to settings that will
automatically compensate for cold load pickup conditions. For instance, if the relay senses current drop
below a very small amount for a period of time, indicating an open breaker, then the relay may move to
an alternate setting group that will allow for the large inrush of current the next time the load is energized.
After current had returned to measurable levels for some period of time, the relay returns to the normal
settings. Another application is to prevent the relay from seeing an overload condition as a fault. If the
relay sees sustained high level phase or unbalance currents that are encroaching on normal trip levels
(indicative of an overload or load imbalance rather than a fault), the relay may move to an alternate
setting group that may accommodate the condition. The relay can be set to alarm for this condition using
the programmable logic alarms.
The relay has the logic to automatically change setting groups based upon the status of the reclose
function (79). This scheme allows the relay to have fast and slow curves, for instance, when the user is
applying automatic reclosing into a fault. On the first trip of a fault the relay may use a setting group with a
fast overcurrent curve and/or a low set instantaneous setting, with the intent of tripping faster than
downstream fuses. On subsequent trips, by monitoring the reclose step, the relay would be in an
alternate setting group with a slower overcurrent response and/or a higher or no instantaneous trip, with
the intent of operating slower than downstream fuses.
The user should also be aware that the 79 function "Sequence Control Block" (79SCB) provides an
alternate method to control relay operation based on the reclose status. See the 79 function description
later in this section for additional details.
Automatic Control by Monitoring Line Current
The Setting Group 1, 2, and 3 switch to and return settings determine how the function selects the active
setting group when automatic selection is enabled.
Automatic control of the active setting group allows the relay to automatically change configuration for
optimum protection based on the current system conditions. For example, in locations where seasonal
variations can cause large variations in loading, the overcurrent protection can be set with sensitive
settings during the majority of the time and switch to a setting group with lower sensitivity (higher pickups)
during the few days of the year when the loading is at peak.
The relay will switch to a setting group when current rises above the "switch-to threshold" for the "switch-
to time," and will return from the setting group when current falls below the "return threshold" for the
"return time.” However, if the "switch-to" threshold is 0 and a non-zero switch-to time is entered, then the
relay changes to the indicated setting group and falls below 10% of nominal (0.5 A / 0.1 A for 5 A / 1 A
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