GE 489 Instruction Manual page 116

4.10 S9 THERMAL MODEL
e) MACHINE COOLING
The 489 thermal capacity used value is reduced exponentially when the motor current is below the
point. This reduction simulates machine cooling. The cooling time constants should be entered for both stopped and run-
ning cases (the generator is assumed to be running if current is measured or the generator is offline). A machine with a
stopped rotor normally cools significantly slower than one with a turning rotor. Machine cooling is calculated using the fol-
lowing formulae:
where: TC
used
TC
used_start
TC
used_end
t
τ
I
eq
4
overload_pickup = overload pickup setpoint as a multiple of FLA
hot / cold
100
75
50
25
0
0
100
75
50
25
0
0
4-66
(
TC TC TC
= –
used used_start
I
⎛
eq
TC ------------------------------------------ -
=
⎝
used_end
overload_pickup
= thermal capacity used
= TC value caused by overload condition
used
= TC value dictated by the hot/cold curve ratio when the machine is running
used
(= 0 when the machine is stopped)
= time in minutes
= Cool Time Constant (running or stopped)
= equivalent heating current
= hot/cold curve ratio
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Ieq/Overload Pickup= 80%
30 60 90 120 150
Time in Minutes
80% LOAD
Cool Time Constant= 30 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Motor Stopped after running Rated Load
TCused_end= 0%
30 60 90 120 150
Time in Minutes
MOTOR STOPPED
Figure 4–17: THERMAL MODEL COOLING
489 Generator Management Relay
t τ ⁄
–
) e ( )
TC
+
used_end used_end
hot
⎞ 1 ⎛ ⎞
× 100%
---------- -
–
⎠ ⎝ ⎠
cold
100
75
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
50
Ieq/Overload Pickup= 100%
25
0
180
0 30 60
Time in Minutes
100% LOAD
100
75
Cool Time Constant= 30 min
TCused_start= 100%
Hot/Cold Ratio= 80%
Motor Stopped after Overload Trip
50
TCused_end= 0%
25
0
180 0 30 60
Time in Minutes
MOTOR TRIPPED
4 SETPOINTS
OVERLOAD PICKUP
(EQ 4.31)
(EQ 4.32)
90 120 150 180
90 120 150 180
808705A1.CDR
GE Multilin
set-