Demand Metering - GE TRANSFORMER MANAGEMENT RELAY 745 Instruction Manual

5.4 S2 SYSTEM SETUP
PATH: SETPOINTS S2 SYSTEM SETUP

DEMAND METERING

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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:
where d = demand after applying input for time t (in minutes)
D = input quantity (constant)
------------------------------------------------------------------------------ -
k =
5
Thermal 90% Response Time
Select "Block Interval" to calculate a linear average of the current over the programmed demand
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
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
"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
"Rolling Demand". Enter the time period over which the current demand calculation is performed.
5-36
Courtesy of NationalSwitchgear.com
DEMAND METERING
ð
CURRENT DEMAND METER
ENTER
TYPE: Thermal
ESCAPE
THERMAL 90% RESPONSE
ESCAPE
TIME: 15 min.
MESSAGE
TIME INTERVAL:
ESCAPE
20 min.
MESSAGE
d t ( ) (
D 1 e
= –
2.3
100
80
60
40
20
0
0 3 6 9 12
Time (min)
745 Transformer Management Relay
Range: Thermal, Block Interval, Rolling Demand
Range: 5, 10, 15, 20, 25, 30, 60 min.
Range: 5, 10, 15, 20, 25, 30, 60 min.
kt
–
)
15 18 21 24 27 30
CURRENT DEMAND METER TYPE
CURRENT DEMAND METER TYPE
5 SETPOINTS
5.4.10 DEMAND METERING
(EQ 5.3)
, start-
TIME INTERVAL
(in
TIME INTERVAL
is set for
is set for "Block Interval" or
GE Multilin