Ge 489 User Manual download pdf (Page 123)

GE Multilin 489 Generator Management Relay 4-73

4 SETPOINTS 4.11 S10 MONITORING

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 4.37)

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 4.38)

where: N = programmed Demand Period in minutes,

n = time in minutes

Figure 4–21: ROLLING DEMAND (15 MINUTE WINDOW)

Generator FLA

Generator Rated MVA

3 Generator Rated Phase-Phase Voltage×

----------------------------------------------------------------------------------------------------------------------=

Demand

----

Average

n 1=

∑

808717A1.CDR

TIME

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

1 2 ... 118 119 120 121 122 123 124 125 126 127 128 ... 258 259

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Ge 489 User Manual Page 123