IG-267-EN versión 01; 07/04/2017
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General Instructions
ekor.rpa
Protection functions
4.4.2. Functionality
The thermal image unit starts up (with an alarm signal) if the
thermal capacity value exceeds the alarm level setting (%),
tripping whenever the trip level setting is exceeded (%).
Once the unit has tripped, this will reset when the thermal
capacity value drops below the trip reset level setting (%).
The settings for the thermal image unit are:
• Enabling the unit: Enable/disable the unit (ON/OFF).
• Temperature rise constant: Temperature rise constant
(from 3 min to 60 min).
• Cooling constant: Cooling constant (from 3 min to
180 min).
• Alarm level: Alarm threshold percentage. The thermal
capacity percentage from which an alarm situation is
considered (from 80 % to 100 %).
• Trip level: Trip threshold percentage. The thermal
capacity percentage from which a thermal overload is
tripped (from 100 % to 200 %).
• Trip reset level: Reset threshold. The thermal capacity
percentage below which the unit is reset (from 50 % to
99 %).
• Rated current: Rated current of the element to be
protected. Variable ranges in accordance with current
transformers used.
The time taken to reach tripping, based on a thermal
capacity equal to zero, given by the following formula:
Where:
t: Tripping time
τ
c
: Temperature rise constant
I
n
: Adjusted rated current
I
therm
: The estimated mean thermal current based on the phase
currents
The trip times for different temperature rise constants are
shown graphically below:
Figure 4.7. Trip time
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