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Instruction manual
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AQ G3x7 Generator protection IED
82 (211
)
Figure 3-47 The function block of the negative sequence overcurrent protection function
3.2.11
T
HERMAL OVERLOAD
T>
(49)
The line thermal protection measures basically the three sampled phase currents. TRMS
values of each phase currents are calculated including harmonic components up to 10
th
harmonic, and the temperature calculation is based on the highest TRMS value of the
compared three phase currents.
The basis of the temperature calculation is the step-by-step solution of the thermal differential
equation. This method provides “overtemperature”, i.e. the temperature above the ambient
temperature. Accordingly the final temperature of the protected object is the sum of the
calculated “overtemperature” and the ambient
temperature.
The ambient temperature can be set manually. If the calculated temperature (calculated
“overtempeambient temperature) is above the threshold values, status signals
are
generated: Alarm temperature, Trip temperature and Unlock/restart inhibit temperature.
Figure 3-48: The principal structure of the thermal overload function.