Thermal Elements - GE 489 Instruction Manual

4.10 S9 THERMAL MODEL
It should be noted that the RTD bias feature alone cannot create a trip. If the RTD bias feature forces the thermal capacity
used to 100%, the machine current must be above the over-load pickup before an overload trip occurs. Presumably, the
machine would trip on stator RTD temperature at that time.
4
SETPOINTS S9 THERMAL MODEL

THERMAL ELEMENTS

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Once the thermal model is setup, an alarm and/or trip element can be enabled. If the generator has been offline for a long
period of time, it will be at ambient temperature and thermal capacity used should be zero. If the generator is in overload,
once the thermal capacity used reaches 100%, a trip will occur. The thermal model trip will remain active until a lockout time
has expired. The lockout time will be based on the reduction of thermal capacity from 100% used to 15% used. This reduc-
tion will occur at a rate defined by the stopped cooling time constant. The thermal capacity used alarm may be used as a
warning indication of an impending overload trip.
4-68
100
Hot/Cold = 0.85
80
Rated Temperature=130°C
Insulation Rating=155°C
60
40
20
RTD Bias Minimum
0
–50 0 50
Maximum Stator RTD Temperature
Figure 4–18: RTD BIAS CURVE
THERMAL ELEMENTS
ð
THERMAL MODEL
ENTER
ð
ALARM: Off
ESCAPE
ASSIGN ALARM
ESCAPE
RELAYS (2-5): ---5
MESSAGE
THERMAL ALARM
ESCAPE
LEVEL: 75% Used
MESSAGE
THERMAL MODEL
ESCAPE
ALARM EVENTS: Off
MESSAGE
THERMAL MODEL
ESCAPE
TRIP: Off
MESSAGE
ASSIGN TRIP
ESCAPE
RELAYS (1-4): 1---
MESSAGE
489 Generator Management Relay
RTD Bias Maximum
RTD Bias Center Point
100 150 200 250
808721A1.CDR
4.10.3 THERMAL ELEMENTS
Range: Off, Latched, Unlatched
Range: Any combination of Relays 2 to 5
Range: 10 to 100% Used in steps of 1
Range: On, Off
Range: Off, Latched, Unlatched
Range: Any combination of Relays 1 to 4
4 SETPOINTS
GE Multilin