VAMP VAMP 59, Инструкции по установке, эксплуатации и настройке

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Technical description 2 Protection functions 2.10 Thermal overload protection
T> (49)
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2.10. Thermal overload protection T> (49)
The thermal overload function protects cables in the feeder
mode against excessive heating.
Thermal model
The temperature is calculated using rms values of phase
currents and a thermal model according IEC 60255-8. The rms
values are calculated using harmonic components up to the
15
th
.
Trip time:
2 2
2
2
ln
a I
I I
t
P


 

Alarm: alarm I k k a
Mode
   

(Alarm 60% = 0.6)
Trip:
Mode
I k k a
  

Release time:
2 2
2
ln
I a
I
C t
P

  


Trip release:
MODE
I k a
  
95 . 0
Start release:
alarm I k a
MODE
   
95 . 0
(Alarm 60% = 0.6)
T = Operation time
 = Thermal time constant tau (Setting value)
ln = Natural logarithm function
I = Measured rms phase current (the max. value of
three phase currents)
Ip = Preload current,
N P
I k I
  

(If temperature rise
is 120%

2 . 1


). This parameter is the memory of
the algorithm and corresponds to the actual
temperature rise.
k = Overload factor (Maximum continuous current), i.e.
service factor. (Setting value)
k  = Ambient temperature factor (Permitted current due
to tamb) Figure 2-9.
I
MODE
= The rated current (I
N
or I
MOT
)

C
= Relay cooling time constant (Setting value)
Time constant for cooling situation
If the motor's fan is stopped, the cooling will be slower than
with an active fan. Therefore there is a coefficient c

for
thermal constant available to be used as cooling time constant,
when current is less than 0.3xI
MOT
.