ABB Relion 620 Series - Page 364

the ambient temperature of a motor exceeds or remains below 40°C. A motor
operating at a higher temperature, even if at or below rated load, can subject the
motor windings to excessive temperature similar to that resulting from overload
operation at normal ambient temperature. The motor rating has to be appropriately
reduced for operation in such high ambient temperatures. Similarly, when the
ambient temperature is considerably lower than the nominal 40°C, the motor can be
slightly overloaded. For calculating thermal level it is better that the FLC values are
scaled for different temperatures. The scaled currents are known as internal FLC.
An internal FLC is calculated based on the ambient temperature shown in the table.
The Env temperature mode setting defines whether the thermal level calculations
are based on FLC or internal FLC.
When the value of the Env temperature mode setting is set to the "FLC Only"
mode, no internal FLC is calculated. Instead, the FLC given in the data sheet of
the manufacturer is used. When the value of the Env temperature mode setting is
set to "Set Amb Temp" mode, the internal FLC is calculated based on the ambient
temperature taken as an input through the Env temperature Set setting. When the
Env temperature mode setting is on "Use input" mode, the internal FLC is calculated
from temperature data available through resistance temperature detectors ( RTDs)
using the AMB_TEMP input.
Table 364: Modification of internal FLC
Ambient Temperature T
amb
Internal FLC
<20°C FLC x 1.09
20 to <40°C FLC x (1.18 - T
amb
x 0.09/20)
40°C FLC
>40 to 65°C FLC x (1 –[(T
amb
-40)/100])
>65°C FLC x 0.75
The ambient temperature is used for calculating thermal level and it is available in
the monitored data view from the TEMP_AMB output. The activation of the BLOCK
input does not affect the TEMP_AMB output.
The Env temperature Set setting is used:
• If the ambient temperature measurement value is not connected to the
AMB_TEMP input in ACT.
• When the ambient temperature measurement connected to 49M is set to "Not in
use" in the RTD function.
• In case of any errors or malfunctioning in the RTD output.
Thermal level calculator
The module calculates the thermal load considering the TRMS and negative-
sequence currents. The heating up of the motor is determined by the square value
of the load current.
However, in case of unbalanced phase currents, the negative-sequence current
also causes additional heating. By deploying a protection based on both current
components, abnormal heating of the motor is avoided.
The thermal load is calculated based on different situations or operations and
it also depends on the phase current level. The equations used for the heating
calculations are:
Protection functions
1MRS757644 H
364 620 series
Technical Manual