If the thermal overload function is enabled and thermal state of the protected equipment exceeds the
Trip threshold setting, a trip command is issued resulting in operation of output contacts .Trip condition
is indicated by illuminated TRIP LED.
General trip will reset if Thermal state reduces to 100% or current is less than 10% of the rated
current. If the Thermal Lockout setting is disabled, then Thermal trip will reset when Thermal state
reduces below 100%. If the Thermal lockout setting is enabled, Thermal trip will reset when Thermal
state reduces below Lockout Thresh. setting.
The thermal state measurement is made available in the MEASUREMENTS 2 menu.
The thermal state can be reset from the HMI panel by enabling the Thermal Reset setting to ‘Yes’
under RECORD CONTROL menu.
Note: When resetting the thermal state any associated inhibits also reset (for example start inhibit threshold).
Figure 7: Thermal Overload protection logic diagram
2.3.4 Thermal Lockout
The function compares the thermal capacity available with the lockout setting immediately after a trip,
for example when the interrupting device is open. If the thermal capacity is insufficient to allow restart,
an output contact programmed for the lockout is energised, which inhibits a restart. When the motor
has cooled down, this function resets the lockout output contact.
The Thermal lockout is activated if the following conditions are met:
• Motor shutdown (i.e. the interrupting device is open) and
• Thermal state value θ higher than the lockout thresh setting.
The estimated time to next start is the time to reach the thermal lockout threshold. This is displayed in
the MEASUREMENT 2 menu.
2.3.5 Inhibit Thermal Trip During Motor Start-up (Inh Trip dur st)
Some motors have extreme starting conditions such as a very long start time or a very high start
current value. During start-up of these motors the thermal curve is inhibited to avoid false trips.
The Inh Trip dur st function once Enabled inhibits thermal tripping during the start-up of motor. This
inhibition is activated as soon as the motor start is detected. On expiry of the time allowed for starting,
this inhibition is deactivated.
Note: When the thermal state of the motor reaches 90%, this value is retained at 90% during the remaining
period of the Prol.Start Time.
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