Demand - GE 750 Instruction Manual

S6 Monitoring

Demand

DEMAND
NOTE
GE Multilin
a) Main Menu
PATH: SETPOINTS S6 MONITORING
[ ]
MESSAGE
MESSAGE
MESSAGE
Current demand is measured on each phase, and on three phases for real, reactive,
and apparent power. Setpoints allow the user to emulate some common electrical
utility demand measuring techniques for statistical or control purposes.
The relay is not approved as or intended to be a revenue metering instrument. If
used in a peak load control system, the user must consider the accuracy rating and
method of measurement employed, and the source VTs and CTs, in comparison with
the electrical utility revenue metering system.
The relay can be set to calculate demand by any of three methods.
• Thermal Exponential: This selection emulates the action of an analog peak
recording thermal demand meter. The relay measures the quantity (RMS
current, real power, reactive power, or apparent power) 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:
where d = demand value after applying input quantity for time t (in minutes),
D = input quantity (constant), k = 2.3 / thermal 90% response time.
100
80
60
40
20
0
0 3
FIGURE 5–40: Thermal Demand Characteristic (15 minute response)
The 90% thermal response time characteristic defaults to 15 minutes. A
setpoint establishes the time to reach 90% of a steady-state value, just as the
response time of an analog instrument. A steady state value applied for twice
the response time will indicate 99% of the value.
• Block Interval: This selection calculates a linear average of the quantity (RMS
current, real power, reactive power, or apparent power) over the programmed
demand time interval, starting daily at 00:00:00 (i.e. 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.
The Block Interval with Start Demand Interval Logic Input calculates a linear
average of the quantity (RMS current, real power, reactive power, or apparent
power) over the interval between successive Start Demand Interval logic input
pulses. Each new value of demand becomes available at the end of each pulse.
The
S3 LOGIC INPUTS
programs the input for the new demand interval pulses.
http://www.GEmultilin.com
DEMAND
CURRENT [ ]
See page 5–80.
REAL POWER [ ]
See page 5–81.
REACTIVE POWER [ ]
See page 5–82.
APPARENT POWER [ ]
See page 5–83.
kt
d t ( ) D 1 e ( – )
= –
6 9 12 15 18 21
Time (min)
MISC FUNCTIONS START DMND INTERVAL
750/760
Feeder Management Relay
(EQ 5.20)
24 27 30
setpoint
5–79