DEMA CPM 310 G User Manual page 77

I > Thermal Overload Protection Menu
Θ
Main Screen » Set » I
Thermal Overload Protection is symbolized as I
IEC Standards, and coded as 49 in IEEE/ANSI
Standards.
I > symbol indicates that the protection function
Θ
measures the phase RMS current and behaves
according to the thermal overload protection formula.
IEC 60255-8 compliant thermal overload formula is
given below.
where
>
Θ
t
T
e
I
I
Θ
k
%Θ
p
%Θ
trip
Thermal overload protection is a unique function of
protection which is usually utilized to provide
overloading protection for power transformers, power
cables, motors and overhead lines at current range of
(1.0- 1.5) I
By combining I
overcurrent protection functions in appropriate
schemes within the boundaries of (1.0- 1.5) I
providing the optimum balance between maximum
supply continuity and accurate protection for electrical
power systems is easier.
Thermal overload protection plays a critical role in
modern systems where transient overcurrent and high-
order harmonics are observed frequently. Thermal
overload protection function provides maximum supply
continuity by giving the system sufficient time to
recover transient overcurrent, which do not perform a
significant stress on components and need not to be
cleared instantaneously; while providing a solid
protection by monitoring "hidden" effects of high-order
harmonics on elements of the system and intervening
when necessary. ↺
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trip time (minutes),
thermal constant (minutes),
RMS load current (A),
set current (A),
trip threshold multiplier (-),
overload pre-heating (%),
overload trip heating (%).
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