Figure 17: Thermal Overload Protection Logic Diagram; Figure 18: Cooling Time Constant - GE P24DM Technical Manual

P24xM
The DDB signal Thermal Trip indicates tripping of the element . A further DDB signal Thermal Alarm is generated
from the thermal alarm stage. The state of the DDB signal can be programmed to be viewed in the Monitor Bit x
cells of the COMMISSION TESTS column in the relay.

Figure 17: Thermal overload protection logic diagram

Thermal lockout
This function compares the thermal capacity available with the lockout setting immediately after a trip, for
example when the interrupting device is open. If the thermal capacity available is insufficient to allow restart, an
output contact programmed for the lockout function (Thermal Lockout) is energized, which inhibits a restart.
When the motor has cooled down, this function resets the lockout output contact.
The thermal lockout drops off at 97% of the thermal lockout threshold.
The estimated time to next start is the time to reach the thermal lockout threshold. This is in the MEASUREMENTS 3
menu and is given by the following formula:
T = T * Ln (q /q )
r 1 2
Where:
T = cooling time constant,
r
q
= initial thermal state,
1
q
= final thermal state = 97% of thermal lockout threshold.
2
100 %
80 %
20 %
E00777

Figure 18: Cooling time constant

P24xM-TM-EN-2.1
E00776
Thermal State
T1
Chapter 6 - Current Protection Functions
Thermal Alarm
Thermal Trip
T2 T3
Gen
Gen
P1629ENd
Time
P0658ENa
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