Section 4
1MAC050144-MB C
Protection functions
306
615 series ANSI
Technical Manual
4.5.3.2
Function block
Figure 145:
Function block
4.5.3.3
Functionality
The motor thermal overload protection function 49M protects the electric motors from
overheating. 49M models the thermal behavior of motor on the basis of the measured load
current and disconnects the motor when the thermal content reaches 100 percent. The
thermal overload conditions are the most often encountered abnormal conditions in
industrial motor applications. The thermal overload conditions are typically the result of
an abnormal rise in the motor running current, which produces an increase in the thermal
dissipation of the motor and temperature or reduces cooling. 49M prevents an electric
motor from drawing excessive current and overheating, which causes the premature
insulation failures of the windings and, in worst cases, burning out of the motors.
4.5.3.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are Enable and Disable.
The operation of the motor thermal overload protection function can be described using a
module diagram. All the modules in the diagram are explained in the next sections.
Figure 146:
Functional module diagram
Max current selector
The max current selector selects the highest phase current and reports it to the thermal level
calculator.
49M
I_A
I_B
TRIP
I_C
I
2
BLOCK
BLK_RESTART
ALARM
START_EMERG
AMB_TEMP
ALARM
BLK_RESTART
Max
current
selector
I_A
Thermal
level
calculator
Internal
FLC
calculator
Alarm and
tripping
logic
START_EMERG
BLOCK
TRIP
I_B
I_C
I
2
AMB_TEMP
Содержание 615 Series ANSI
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Страница 707: ...Section 15 1MAC050144 MB C Applicable standards and regulations 700 615 series ANSI Technical Manual ...
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