5–94
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
The 489 can measure the demand of the generator for several parameters (current, MW,
Mvar, MVA). The demand values of generators may be of interest for energy management
programs where processes may be altered or scheduled to reduce overall demand on a
feeder. The generator FLA is calculated as:
(EQ 5.40)
Power quantities are programmed as per unit calculated from the rated MVA and rated
power factor.
Demand is calculated in the following manner. Every minute, an average magnitude is
calculated for current, +MW, +Mvar, and MVA based on samples taken every 5 seconds.
These values are stored in a FIFO (First In, First Out buffer).The size of the buffer is dictated
by the period that is selected for the setpoint. The average value of the buffer contents is
calculated and stored as the new demand value every minute. Demand for real and
reactive power is only positive quantities (+MW and +Mvar).
(EQ 5.41)
where:
N
= programmed Demand Period in minutes,
n
= time in minutes
FIGURE 5–27: Rolling Demand (15 Minute Window)
5.11.6 Pulse Output
PATH: SETPOINTS
ZV
S10 MONITORING
ZV
PULSE OUTPUT
MESSAGE
MVA DEMAND
ALARM EVENTS: Off
Range: On, Off
Generator FLA
Generator Rated MVA
3 Generator Rated Phase-Phase Voltage
×
--------------------------------------------------------------------------------------------------------------
=
Demand
1
N
---
Average
N
n
1
=
N
∑
=
808717A1.CDR
TIME
0
20
40
60
80
100
120
140
160
t=0
t+10
t+20
t+30
t+40
t+50
t+60
t+70
t+80
t+90
t+100
MAGNITUDE
PULSE
[
Z
]
POS. kWh PULSE OUT
RELAYS (2-5): ----
Range: Any combination of Relays 2 to
5
MESSAGE
POS. kWh PULSE OUT
INTERVAL: 10 kWh
Range: 1 to 50000 kWh in steps of 1
MESSAGE
POS. kvarh PULSE OUT
RELAYS (2-5): ----
Range: Any combination of Relays 2 to
5
