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120
Thermal phase overload protection
(THOL)
&DOFXODWLRQV
The parameters for the thermal phase overload protection function are set via the local
HMI or PST (Parameter Setting Tool). Refer to the Technical reference manual for set-
ting parameters and path in local HMI.
To make the correct settings, the following data are required for the protected object:
•
Final temperature rise after continuos load with specified load current
Max. permissible continuous temperature and thermal time constant τ of the object
•
•
Max. ambient temperature
•
Max. temperature rise due to radiant power from the sun - if significant
The time constant can be found if a curve is available which shows the temperature rise
as a function of time for a given load current. At load current Iload and final temperature
rise T
the following is valid:
fin
7LPH
1 x τ
7HPSHUDWXUH ULVH LQ
63
RI 7
:
ILQ
If different values of τ are calculated from the curve, select the lowest value of τ to ob-
tain the best protection.
The time to function is calculated from the formula:
2
I
2
---------- - -
p
–
I
base
τ In
⋅
------------------------------------------------------- -
t
=
T
–
2
I
trip
----------- -
–
---------------------------- -
I
T
base
base
Where:
p
is Ip/I
base
Ip
is continuous load current before the current is increased to I
T
is ambient temperature. (T
amb
tion is not used)
2 x τ
86
T
amb
is 20° C as a fixed value if temperature compensa-
amb
3 x τ
4 x τ
95
98
&KDSWHU
&XUUHQW
5 x τ
99
(Equation 57)
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