As can be noted from the results, when the cable has been loaded with stable current for time which is
ve times of the time constant t end temperature of 68.35
̊
C is reached. This represents 71 % of the
thermal capacity used. According to the data sheet with this current temperature should be around 65
̊
C and can be seen that the model is now 3 degrees overprotecting.
Figure. 5.4.21. - 103. Thermal image response with maximum load when the installation is according to the presumptions.
With maximum allowed load the end temperature 89
̊
C has been reached with thermal capacity 99.6%
used. From this result can be noted that the thermal image matches perfectly into the expectations.
Cable alarm from the overheating could be set securely.
When comparing the result to fully tuned model in the application let’s include all of the installation
correction factors to the image.
500 mm
2
cross sectional 66 kV copper cable is installed with no adjacent cables (k=1) into dry gravel
and clay (k=0.85) ground in depth of 1.5 meter (k=0.95). Cable 1s permissible short circuit current is
71.4 kA and its insulation is XLPE. The cables screen circuit is open and the laying of the cable is flat.
Its current carrying capacity is 575A in 65
̊
C and 680A in 90
̊
C. Reference temperature for ground
installation is 15
̊
C. Cable thermal time constant is 183.8 min.
AQ-F255
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
174