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Dear All,
I have doubt in Thermal overload (ANSI 49 RMS) Protection in the relay P3U20.
how to calculate trip time ?
- How to calculate "I" Measured RMS phase current whether we need to convert to secondary value.
how to calculate Ip preload current.
Please refer Page no : 162 & 163 in the attached manual.
Regards,
S.Senthil
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Hi @P3U20-ThermalProtection,
the user manual is giving a necessary expression to calculate trip time.
Let me try to elaborate the given equation.
Thermal protection is giving a trip command as temperature rise reaches 100% value. This of course
depends on load current and starting temperature rise. Starting temperature depends on loading history. In the user manual motor loading history is accounted by "preload" current. The prelaod current represents current value that is keeping the motor at given constant temperature rise level. Saying other words, preload current is "a memory" of motor thermal history.
Let me rewrite the equation here and then give an example.
I hope this helps to clarify.
BR
-juha-
Link copied. Please paste this link to share this article on your social media post.
Hi @P3U20-ThermalProtection,
the user manual is giving a necessary expression to calculate trip time.
Let me try to elaborate the given equation.
Thermal protection is giving a trip command as temperature rise reaches 100% value. This of course
depends on load current and starting temperature rise. Starting temperature depends on loading history. In the user manual motor loading history is accounted by "preload" current. The prelaod current represents current value that is keeping the motor at given constant temperature rise level. Saying other words, preload current is "a memory" of motor thermal history.
Let me rewrite the equation here and then give an example.
I hope this helps to clarify.
BR
-juha-
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