Date Code 20080110 Control Logic 4-7
SEL-387E Instruction Manual
than TGR during this process, or it may produce multiple group changes before it finally gets to
position 5.
The settings in
Table 4.3 are made in the Global settings area.
CHSG Relay Word Bit Asserts During Setting Group Changes
The Relay Word bit CHSG is asserted whenever a setting group change is in process. It is
defined in
Table 4.9 and Table 4.10 as “Timing to change setting groups.” When group changes
are initiated through one of the SSn SEL
OGIC
control equation settings, CHSG is asserted as
soon as the new SSn bit is asserted and the relay has made the decision to change groups. It
deasserts when the SGn bit for the new group agrees with the SSn bit, indicating that the relay
has changed to the newly requested group number. For example, assume the relay is in Group 1.
The active group bit SG1 equals one, while other SGn bits are zero. All of the SSn bits are also
zero. SS4 is asserted, requesting a change to Group 4. Because SS1 (same group as the active
group) is not asserted, the group change process is initiated, and CHSG is asserted at the same
time as SS4. After the group change is made, SG1 will deassert and SG4 will assert, indicating
the relay is now in Group 4. When this agreement of SS4 and SG4 occurs, CHSG will deassert
to indicate the relay is no longer in the process of changing groups.
When the active group bit SGn and its associated SSn bit are both asserted, for example SG1 and
SS1, the relay does not respond to the assertion of a new SSn bit, such as SS3, and no group
change will occur. Similarly, the CHSG bit will not assert along with SS3, since the SG1 and
SS1 bits are in agreement. This agreement acts like a continuous “reset” applied to the CHSG
bit.
In applications where a system-related condition requires that a change of setting groups must be
done quickly and automatically, this would likely be accomplished via a contact input to the
relay, which would assert an SSn bit. In such cases, you may want to immediately block some
relay elements as soon as the change is needed to prevent misoperation. This could easily be
done via the CHSG bit. CHSG could be used, for example, to supervise the tripping variable for
differential trips. The default TR4 setting is TR4 = 87R + 87U; this could be changed to TR4 =
87R*!CHSG + 87U*!CHSG. CHSG optimizes (in this case minimizes) the amount of time to
block TR4, since CHSG asserts exactly when the change of groups is needed, and deasserts
exactly when the change has taken place.
For setting group changes that do not make use of the SSn bits, namely those using the GRO n
serial port command or the GROUP front-panel pushbutton, CHSG asserts about two cycles
after the change command is received and deasserts shortly after the group change is made. For
these cases, CHSG does not overlap the desired time period quite as precisely as when the SSn
bits are used, but group changes initiated manually through the serial port or front panel are
inherently not as time critical, so a few cycles difference is not likely to matter as much, if at all.
Active Setting Group Retained for Power Loss, Settings Change
The active setting group is retained if power to the relay is lost and then restored. If a particular
setting group is active (e.g., Setting Group 5) when power is lost, it comes back with the same
setting group active when power is restored.
To Next Page
Loading...
