This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
XXXXXXX
XXXXXXX
HT CABLE SIZING CALULATION
Change Number: ChangeNoAuthor: Selvan SakthiveluDesign Office:Reason for new revision:(see last page for modification record)
CLASS II (GE INTERNAL NON-CRITICAL)Ref : ReferenceRevision : A0Date : 05 Jun 12Page : 2/5
1.0 OBJECTIVE:
The objective of this document is for calculation of HT power cables.
2.0 REFERENCES:
The following references are used for this calculation:
2.1. Gloster cable catalogue.
2.2. Fault current considered as 26.2 kA for 0.16 second(Operating time for VCB and Numerical Relay)
Operating time for VCB = 65 ms = 0.065 s ; Numerical Relay = 40 ms = 0.040 s,
Total time = 0.065+ 0.040 =0.105 s
Fault duration considered = 0.16 s
2.3. Derating factor = Temperature factor x grouping factor
Temperature factor = 1.0 for 40 deg C ambient
Grouping factor = 0.68 for 6 layers of cable trays with 6 cables in each tray touching each other
Therefore, Derating factor = 1.0 x 0.68 = 0.68
3.0 DESIGN CRITERIA:
The cable selected shall fulfill the following criteria:
3.1. To be able to withstand the short circuit current.
3.2. To be able to carry full load current after considering appropriate derating factor for ambient temperaturevariation, method of laying (in air and in trays in our case).
3.3. Voltage drop limited to 1% for cables to switchgear and transformers feeders and 3% for cables to motorfeeders .
4.0 INCOMING CABLE FOR 33 kV SWITCHGEAR
4.1 SHORT CIRCUIT WITHSTAND CAPABILITY OF CONDUCTOR
Fault current is taken as 26.2 kA for 0.16 second
Minimum cross section required = Fault current x √Emek
k = 0.094 (constant for Aluminium)
Minimum cross section required = 26.2 x √0.16 0.094