GE 745 Instruction Manual page 138

S2 SYSTEM SETUP
Note
NOTE
5–42
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:
where d = demand after applying input for time t (in minutes)
D = input quantity (constant)
k = ------------------------------------------------------------------------ -
Thermal 90% Response Time
100
80
60
40
20
0
0
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
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
DEMAND METER TYPE
current to indicate 90% of actual value.
• TIME INTERVAL: This message is displayed only when the
is set for "Block Interval" or "Rolling Demand". Enter the time period over which
TYPE
the current demand calculation is performed.
The TIME INTERVAL is only displayed when "Block Interval" or "Rolling Demand" is selected
for the CURRENT DEMAND METER
kt
–
d t ( ) D 1 e ( )
= –
2.3
3 6 9 12 15 18
Time (min)
FIGURE 5–6: Thermal demand time
(in the same way as Block Interval above). The value is updated
is set for "Thermal". Enter the time required for a steady-state
TYPE.
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
21 24 27 30
CURRENT
CURRENT DEMAND METER
(EQ 5.3)