GE M60 Instruction Manual page 295

CHAPTER 5: SETTINGS
TCU = thermal capacity used
TCU = TCU value caused by overload condition
start
TCU = TCU value dictated by the hot/cold curve ratio when the motor is running. This value is 0 when the motor is
end
stopped)
t = time in minutes
τ
= cool time constant (running or stopped per current motor status and corresponding
COOL TIME CONSTANT STOPPED
I = equivalent motor heating current
eq
overload_pickup = overload pickup setpoint as a multiple of FLA
hot / cold = hot/cold curve ratio
100
75
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
50
Ieq/Overload Pickup= 80%
25
0
0 30
100
75
Cool Time Constant= 30 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Motor Stopped after running Rated Load
50
TCused_end= 0%
25
0
0 30
MOTOR STOPPED
— The motor manufacturer sometimes provides thermal limit information for a hot/cold motor.
HOT/COLD SAFE STALL RATIO
The M60 algorithm uses this data if this setting is programmed. The value entered for this setting dictates the level at which
thermal capacity used settles for current that is below the motor service factor times FLA. When the motor is running at a
level that is below this limit, thermal capacity used rises or falls to a value based on I
and the selected setting. Thermal capacity used either rises at the fixed rate of 5% per minute or falls as dictated by the
running cool time constant.
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
settings)
Figure 5-80: Thermal model cooling
60 90 120 150 180
Time in Minutes
80% LOAD
60 90 120 150 180
Time in Minutes


TCU = I 1
–

end eq
COOL TIME CONSTANT RUNNING
100
75
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
50
Ieq/Overload Pickup= 100%
25
0
30 60 90
0
Time in Minutes
100% LOAD
100
75
Cool Time Constant= 30 min
TCused_start= 100%
Hot/Cold Ratio= 80%
Motor Overload
50
TCused_end= 0%
25
0
0 30 60 90
Time in Minutes
MOTOR TRIPPED
equivalent
hot

-------- - 
100%

cold
GROUPED ELEMENTS
and
120 150 180
120 150 180
808705A2.CDR
(average three phase RMS
Eq. 5-16
5-167
5