Functionality; Operation Principle - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.1.11.3
4.1.11.4
346

Functionality

The thermal overload protection for motors function MPTTR protects the electric
motors from overheating. MPTTR 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.
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. MPTTR
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.

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of MPTTR can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
The function uses ambient temperature which can be measured locally or remotely.
Local measurement is done by the protection relay. Remote measurement uses analog
GOOSE to connect AMB_TEMP input.
If the quality of remotely measured temperature is invalid or
communication channel fails the function uses ambient temperature
set in Env temperature Set.
I_A
Max
I_B current
selector
I_C
I
2
Internal
AMB_TEMP FLC
calculator
START_EMERG
BLOCK
GUID-1E5F2337-DA4E-4F5B-8BEB-27353A6734DC V2 EN
Figure 170: Functional module diagram
Max current selector
Max current selector selects the highest measured TRMS phase current and reports it
to Thermal level calculator.
Thermal Alarm and
level tripping
calculator logic
1MRS757644 F
OPERATE
ALARM
BLK_RESTART
620 series
Technical Manual