5-36
745 Transformer Management Relay
GE Multilin
5.4 S2 SYSTEM SETUP
5 SETPOINTS
5
5.4.10 DEMAND METERING
PATH: SETPOINTS
ÖØ
S2 SYSTEM SETUP
ÖØ
DEMAND METERING
This section assigns the demand setpoints for monitoring current demand on all three phases of each windings. Current
demand on the 745 is performed one of three ways: Thermal, Rolling Demand or Block Interval.
•
CURRENT DEMAND METER TYPE
: Select the method to be used for the current demand metering.
Select “Thermal” to emulate the action of an analog peak-recording thermal demand meter. The 745 measures the cur-
rent 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” based on the following equation:
(EQ 5.3)
where
d
= demand after applying input for time t (in minutes)
D
= input quantity (constant)
k =
Select "Block Interval" to calculate a linear average of the current over the programmed demand
TIME INTERVAL
, start-
ing 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 pro-
grammed 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.
DEMAND METERING
[ENTER] for more
CURRENT DEMAND METER
TYPE: Thermal
Range: Thermal, Block Interval, Rolling Demand
THERMAL 90% RESPONSE
TIME: 15 min.
Range: 5, 10, 15, 20, 25, 30, 60 min.
TIME INTERVAL:
20 min.
Range: 5, 10, 15, 20, 25, 30, 60 min.
ENTER
ESCAPE
ð
ð
MESSAGE
ESCAPE
MESSAGE
ESCAPE
d t
( )
D
1
e
kt
–
–
(
)
=
2.3
Thermal 90% Response Time
-------------------------------------------------------------------------------
Time (min)
0
20
40
60
80
100
0
3
6
9
12
15
18
21
24
27
30
Demand
(%)