ABB RELION REX640 Technical Manual page 395

1MRS759142 C
REX640
Technical Manual
Max current selector
Max current selector selects the highest measured TRMS phase current and reports it
to Thermal level calculator.
Internal FLC calculator
Full load current (FLC) of the motor is defined by the manufacturer at an ambient
temperature of 40°C. Special considerations are required with an application where
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 441: Modification of internal FLC
Ambient Temperature T
amb
<20°C
20 to <40°C
40°C
>40 to 65°C
>65°C
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:
Protection functions
Internal FLC
FLC x 1.09
FLC x (1.18 - T x 0.09/20)
amb
FLC
FLC x (1 –[(T -40)/100])
amb
FLC x 0.75
Section 4
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