Ge 489 User Manual download pdf (Page 110)

4-60 489 Generator Management Relay GE Multilin

4.10 S9 THERMAL MODEL 4 SETPOINTS

b) CUSTOM OVERLOAD CURVE

If the induction generator starting current begins to infringe on the thermal damage curves, it may become necessary to use

a custom curve to tailor generator protection so successful starting may be possible without compromising protection. Fur-

thermore, the characteristics of the starting thermal (locked rotor and acceleration) and the running thermal damage curves

may not fit together very smoothly. In this instance, it may be necessary to use a custom curve to tailor protection to the

thermal limits to allow the generator to be started successfully and utilized to its full potential without compromising protec-

tion. The distinct parts of the thermal limit curves now become more critical. For these conditions, it is recommended that

the 489 custom curve thermal model be used. The custom overload curve allows users to program their own curves by

entering trip times for 30 pre-determined current levels.

The curves below show that if the running overload thermal limit curve were smoothed into one curve with the locked rotor

thermal limit curve, the induction generator could not be started at 80% voltage. A custom curve is required.

Figure 4–12: CUSTOM CURVE EXAMPLE

MULTIPLE OFFULL LOADCURRENTSETPOINT

TIME TO TRIP IN SECONDS

0.1

1.0

100

1000

10000

0.5

100

1000

PROGRAMMED 469 CUSTOM CURVE

RUNNINGSAFETIME(STATOR LIMIT)

ACCELERATION SAFETIME(ROTOR LIMIT)

MACHINE CURRENT @ 100% VOLTAGE

MACHINE CURRENT @ 80% VOLTAGE

489

TYPICAL CUSTOM CURVE

808825A3.CDR

GE Multilin

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Ge 489 User Manual Page 110