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Thermal
Thermal Θ Measurements Menu
displays the heating
percentage of the system being watched in
percentages.
Thermal Θ is evaluated according to the IEC
formulations; the actual formula is given below.
Where,
t trip delay (minutes),
T
e
thermal constant (minutes),
I load current (A),
I
Θ
set current (A),
k trip threshold translation constant (-),
%Θ
P
preheating percentage (%),
%Θ
trip
heating trip percentage (%).
Thermal Θ measurement, alarming and protection are
important functions for machines and systems where
the actual conductor heating cannot be partially or
entirely measured by direct means, or where
overcurrent protection cannot provide the sensitive
protection characteristics needed around lower current
value limits.
Thermal Θ measurement, alarming and protection are
the essential functions of modern electrical protection
systems and have unique functionalities, therefor
cannot be replaced by other functions.
Note that the percentages refer to the allowed
maximum thermal loading, which is determined by the
manufacturer or characteristics of the
machines/conductors being protected. □
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