ABB REF601 - Thermal Overload Protection; Functionality; Principle of Operation

Section 4 1MDU07212-YN Rev. C
Protection and Control Function
26 REF601 / REJ601
Application Manual
4.9 Thermal overload protection
4.9.1 Functionality
The thermal overload protection protects the apparatus from overheating, which
causes the premature insulation failures. The protection function has two modes of
operation, one for static apparatus like cables, feeders and transformers (REF601
and REJ601) and an additional mode for motor / rotating machines (only available
in REM601). The function models the thermal behavior of apparatus on the basis
of the measured load current and disconnects the apparatus when stored thermal
energy has reached the level of set value.
The maximum permanently stored energy at maximum load current is defined as
100%.
Additional the user can set an alarm level ϑ
alm
to indicate the potential risk.
4.9.2 Principle of operation
The function use for the calculation of the function the highest load current of the
three phases.
Thermal model:
The thermal model can be divided into three conditions:
1. warming of apparatus – (diabatic behavior or adiabatic behavior),
2. no change in thermal image
3. Cooling of the apparatus.
1. Warming of the protected object:
Warming of the protected object can be segregated into two types, diabatic and
adiabatic behavior. In diabatic behavior, the protected object have a heat
dissipation with the environment during warming itself due to the load current.
For current greater than twice the base current I
b
(also known as rated current or
full load current) the behavior is classified as adiabatic, this means, that the heat
exchange with the environment during warming is considerable small related to the
heating.
Warming is defined as:


< 󰇡



󰇢∗100
[
%
]
ϑ
0
= present value of thermal image
I = maximum value of measured phase currents
I
b
= base current (rated current/full load current defined by setting).