4-6
Protection and Control
BE1-951
L o a d C u r r e n t
a s % o f S 0 - 5 1 < p i c k u p >
0
9 0
8 0
7 0
6 0
5 0
4 0
3 0
2 0
1 0
1 0 0
4 0
3 0
2 0
1 0
1 0 0
9 0
8 0
7 0
6 0
5 0
1 2 0
1 1 0
1 4 0
1 3 0
1 5 0
T I M E
( M I N U T E S )
3 0
5
2 0
5
S P - G R O U P 3 = 5 , 9 0 , 5 , 7 5 , 5 1 P
S P - G R O U P 2 = 3 0 , 7 5 , 2 0 , 7 0 , 5 1 P
S G 3
S G 2
S G 1
S G 0
S G C
D2837-23.vsd
01-07-99
Figure 4-3. Automatic Operation Based on Load Change
55, setting group two timer times out but no setting group change occurs because a higher setting group
takes precedence. The faint dashed line for SG2, between time = 55 and 75 shows that setting group two
would be active except for setting group three. Current decreases to 75 percent at time = 70, and setting
group three return timer begins timing. Current varies but stays below 75 percent for 5 minutes and at time
= 75, setting group two becomes active and the setting change output pulses. After 20 minutes, setting group
zero becomes active and the setting change output pulses.
This function can also be used to automatically change the active setting group for cold load pickup
conditions. If the switch to threshold for a group is set to 0%, the function will switch to that group when there
is no current flow for the time delay period indicating that the breaker is open or the circuit source is out of
service. The threshold for this is 10% nominal rating of the relay current input.
Not the difference in operation when a switch-to threshold of 0% is used. For this setting the group is
switched to when current falls below 0.5A / 0.1A (5A / 1A nominal), but when any other switch level is used,
the switch occurs when current rises above the switch level.
Figure 4-4 shows how the active setting group follows the load current and time delay settings for setting
group 1. Note that the AUTO input must be at a TRUE (1) logic state in order to allow the automatic logic
to operate. When the breaker opens, the load current falls to zero at time = 15 minutes. After 10 minutes,
setting group one becomes active and the setting group change output pulses TRUE. When the breaker
is closed at time = 40 minutes, load current increases to approximately 90 percent of pickup. As the load
current decreases to 50 percent of pickup, the setting group one return timer begins timing. After ten
minutes, setting group one output goes FALSE, the setting group returns to setting group zero, and the
setting group change output pulses TRUE.
