Cooling Time Thermal Replica
The thermal replica starts to cool down as soon as the negative-sequence current I
2
is lower than Max.
continuously perm. I2. The thermal replica decreases according to the parameter Cooling time
therm.replica. The parameter Cooling time therm.replica is the time required by the thermal
replica to cool down from 100 % to 0 %. If the parameter Cooling time therm.replica is set to 0, the
thermal replica is reset immediately.
The parameter Cooling time therm.replica depends on the construction type of the machine, espe-
cially of the damper winding. Preloading is considered when unbalanced loading occurs again during the
cooling time. The protection device thus operates in a shorter time.
Functional Measured Values
The following formula is used to calculate the functional measured value ΘI2/Θop:
[forunbl2-030812-02.tif, 1, en_US]
With
ΘI2/Θop Functional measured value indicating the thermal replica of the unbalanced
load
Integrating method of measurement of the thermal replica of the negative-
sequence system
K Unbalanced-load factor of the machine (parameter Unbalanced load
factor K)
I
2
/
Irated,machine
Unbalanced-load as a per unit value (negative-sequence current/rated current
of the machine)
If the functional measured value reaches 100 %, the operate of the function is initiated.
Application and Setting Notes
The function is used in the applications of machines. You can get the necessary settings from the technical
data of the synchronous generators and motors. The setting example is applied for a generator application.
Parameter: Max. continuously perm. I2, Warning delay
•
Default setting (_:11011:101) Max. continuously perm. I2 = 10.0 %
•
Default setting (_:11011:104) Warning delay = 15 s
If the negative-sequence current I
2
exceeds Max. continuously perm. I2 , the stage picks up and a
warning indication is given after the set time delay Warning delay .
The parameter Max. continuously perm. I2 is given in percentage of the rated current of the
protected object.
The setting value of the parameter Max. continuously perm. I2 depends on following parts:
•
Design of the machine (salient pole or non-salient pole rotor synchronous machine)
•
Cooling system (directly or indirectly cooled)
•
Size of the machine
Depending on the standards IEEE C50.12 and IEC 60034-1, the parameter is given in the range between 5 %
and 12 %. To set the parameter Max. continuously perm. I2 , technical data of the machine is
6.22.4
Protection and Automation Functions
6.22 Unbalanced-Load Protection
SIPROTEC 5, Overcurrent Protection, Manual 689
C53000-G5040-C017-8, Edition 07.2017
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