Thermal Time Constant - ABB DCS 500B Description

Functional Software description
Thermal time
constant
72
Alarm and tripping limits can be selected by means of four pa-
rameters
MODEL1.ALARM L (1407)
MODEL1.TRIP L (1408)
MODEL2.ALARM L (1506)
MODEL2.TRIP L (1507)
Initial values are selected so that the overloadability is quite high.
For example, the current must continuously be √120 * 100 = 109.5
% before alarm is given and for trippings the current must be √130 *
100 = 114 %.
Recommended value for alarm is 90...100% and for tripping
106...110%.
MODELx.ALARM L (xxxx) = (alarm % 2 /100)
MODELx.TRIP L (xxxx)
Example. The tripping limit is 106% --> MODELx.TRIP L (xxxx) =
112
Time constants for thermal models are given by two parameters
MODEL1.TC (1409)
MODEL2.TC (1608)
It has to be noted that the thermal time constant cannot be used di-
rectly when calculating the tripping time. Often the motor manufac-
turer presents a curve that defines how long the motor can be
overloaded with a certain overload factor. Parameters MODEL1.TC
(1409) and MODEL2.TC (1608) can be selected by means of figure
on the next page.
= (trip % 2 /100)
DCS 500 Software Description