GE 469 Manual

GE Power Management 469 Motor Management Relay 4-43
4 SETPOINT PROGRAMMING 4.6 S5 THERMAL MODEL
4
4.6.5 MOTOR COOLING
The thermal capacity used value decreases exponentially when the motor current is below the
OVERLOAD
PICKUP
setpoint. This reduction simulates motor cooling. The motor cooling time constants should be entered
for both stopped and running cases. Since the cooling is exponential, the time constants are one-fifth of the
total time to go from 100% thermal capacity used to 0%. A stopped motor normally cools significantly slower
than a running motor. Motor cooling is calculated as follows:
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 curve 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
overload_pickup= overload pickup setpoint as a multiple of FLA
hot / cold = hot/cold curve ratio
Figure 4–17: THERMAL MODEL COOLING
TC
used
TC
used_start
TC
used_end
–
()
e
t
τ⁄
–
()
TC
used_end
+=
TC
used_end
I
eq
overload_pickup
-------------------------------------------


1
hot
cold
-----------
–


100%
×
=
0
25
50
75
100
0 30 60 90 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Ieq/Overload Pickup= 80%
0
25
50
75
100
0 30 60 90 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant= 15 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Ieq/Overload Pickup= 100%
0
25
50
75
100
0 30 60 90 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant= 30 min
TCused_start= 85%
Hot/Cold Ratio= 80%
Motor Stopped after running Rated Load
TCused_end= 0%
0
25
50
75
100
0 30 60 90 120 150 180
Time in Minutes
Thermal Capacity Used
Cool Time Constant= 30 min
TCused_start= 100%
Hot/Cold Ratio= 80%
Motor Stopped after Overload Trip
TCused_end= 0%
Thermal Model Cooling, 80% Load
Thermal Model Cooling, Motor Stopped
Thermal Model Cooling, 100% Load
Thermal Model Cooling, Motor Tripped

GE 469 Specifications

General

Model	GE 469
Category	Relays
Frequency	50/60 Hz
Protection Functions	Overcurrent
Communication Protocols	Modbus, DNP3, IEC 61850
Display	LCD
Mounting	Panel