GE 469

5–56 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
(EQ 5.5)
(EQ 5.6)
where: TC
used
= thermal capacity used
TC
used_start
= TC
used
value caused by overload condition
TC
used_end
= TC
used
value dictated by the hot/cold safe stall ratio when
the motor is running (= 0 when the motor is stopped)
t = time in minutes
τ = Cool Time Constant (running or stopped)
I
eq
= equivalent motor heating current
ol_pkp = overload pickup settings as a multiple of FLA
hot / cold = hot/cold safe stall ratio
FIGURE 5–15: Thermal Model Cooling
Hot/Cold Safe Stall Ratio
The motor manufacturer may provide thermal limit information for a hot/cold motor. The
469 thermal model adapts for these conditions if the
HOT/COLD SAFE STALL RATIO settings
is programmed. This settings value dictates the level of thermal capacity used the relay will
settle at for current levels below the
OVERLOAD PICKUP LEVEL. When the motor is running
TC
used
TC
used_start
TC
used_end
–()e
t τ⁄–
()TC
used_end
+=
TC
used_end
I
eq
ol_pkp
----------------
⎝⎠
⎛⎞
1
hot
cold
----------–
⎝⎠
⎛⎞
100%×=
808705A2.CDR
0
25
50
75
100
0 30 60 90 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant=15min
TCused_start=85%
Hot/Cold Ratio=80%
Ieq/Overload Pickup= 100%
0
25
50
75
100
0306090 120 150 180
Time in Minutes
Thermal Capacity U sed
Cool Time Constant=15min
TCused_start=85%
Hot/Cold Ratio=80%
Ieq/Overload Pickup=80%
0
25
50
75
100
0306090 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant=30min
TCused_start=85%
Hot/Cold Ratio=80%
Motor Stopped after running Rated Load
TCused_end=0%
0
25
50
75
100
0306090 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant=30min
TCused_start= 100%
Hot/Cold Ratio=80%
Motor Overload
TCused_end=0%
MOTOR TRIPPED
100% LOAD
MOTOR STOPPED
80% LOAD