Thermal Overload Protection Implementation - GE Agile P50 Series Technical Manual

P50 Agile P153
Θi+1 = (Irms /k*IFLA) ² · [1 – exp (-t/Te)] + Θi · exp (-t/Te)
Figure 5: Thermal Overload curve
2.5.1

Thermal Overload Protection Implementation

The device incorporates a current-based thermal characteristic, using fundamental load current to
model heating and cooling of the protected plant. The element can be set with both alarm and trip
stages.
Thermal Overload protection is implemented in the THERMAL OVERLOAD column of the relevant
settings group. The magnitudes of the three phase input currents are compared and the largest
magnitude is taken as the input to the thermal overload function.
Thermal over load function supports setting for alarm and trip stages. If the thermal overload function
is enabled and thermal state of the protected equipment exceeds the alarm threshold setting, the
alarm is issued and indicated by illuminated START LED on the relay front panel.
If the thermal overload function is enabled and thermal state of the protected equipment exceeds the
Trip threshold setting, a trip command is issued resulting in operation of output contacts. Trip condition
is indicated by illuminated TRIP LED.
P153/EN M/B
TRIPPING CURVE FUNCTION OF THE PREFAULT LOAD (K = 1.1 & Te = 10 Mins)
10000.00
1000.00
100.00
10.00
1.00
0.10
MULTIPLES OF THERMAL THRESHOLD SETTINGS Iθ>
1
A: No. of prefault load, thermal state = 0%
B: Thermal state = 30%
C: Thermal state = 50%
D: Thermal state = 70%
E: Thermal state = 90%
6 Protection Functions
10
P5005ENa
6-11