Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
Thermal Overload Protection
0,1
1,0
10,0
100,0
1000,0
1234567891
I/IB
Time in s
0
Time Constant 146s, 0% Time Constant 146s, 100%
Figure 8: Tripping characteristic for thermal protection at τ = 146sec or t
6IB
= 5sec
If in contrary the blocking time in warm condition is stated, so the equation 11.2
should be applied:
s830
21,136
136
ln
s5
=
⎟
⎠
⎞
⎜
⎝
⎛
−
−
=
τ
(16.)
The time constant can be, due to the applied thermal replica, very strong divergent
from the first one. In this case after 5s only 21% of the thermal capacity is filled. So
the time constant is around 6 times higher than the first one.
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 25 / 66
Valid from Version V4D02
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