GE 745 - Page 138

5–42 745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
S2 SYSTEM SETUP CHAPTER 5: SETPOINTS
Select “Thermal” to emulate the action of an analog peak-recording thermal demand
meter. The 745 measures the current on each phase every second, and assumes the circuit
quantity remains at this value until updated by the next measurement. It calculates the
‘thermal demand equivalent’ as follows:
(EQ 5.3)
where d = demand after applying input for time t (in minutes)
D = input quantity (constant)
k =
FIGURE 5–6: Thermal demand time
Select “Block Interval” to calculate a linear average of the current over the programmed
demand TIME INTERVAL, starting daily at 00:00:00 (that is, 12 am). The 1440 minutes per
day is divided into the number of blocks as set by the programmed time interval. Each new
value of demand becomes available at the end of each time interval.
Select “Rolling Demand” to calculate a linear average of the current over the programmed
demand TIME INTERVAL (in the same way as Block Interval above). The value is updated
every minute and indicates the demand over the time interval just preceding the time of
update.
• THERMAL 90% RESPONSE TIME: This message is displayed only when the CURRENT
DEMAND METER TYPE
is set for “Thermal”. Enter the time required for a steady-state
current to indicate 90% of actual value.
• TIME INTERVAL: This message is displayed only when the
CURRENT DEMAND METER
TYPE
is set for “Block Interval” or “Rolling Demand”. Enter the time period over which
the current demand calculation is performed.
NOTE
Note
The TIME INTERVAL is only displayed when “Block Interval” or “Rolling Demand” is selected
for the CURRENT DEMAND METER TYPE.
dt() D 1 e
kt–
–()=
2.3
Thermal 90% Response Time
-------------------------------------------------------------------------
Time (min)
0
20
40
60
80
100
0 3 6 9 1215182124 27 30
Demand (%)