AC Cable Design Calculations
Cable Calculation
AS per SEC(Saudi Electricity Company) standard
Design Basis Standards and its Specifications for cables :
1- Cables are sized based on SEC Standard TES-P-119.29 (LV Cable Sizing & Selection).
2- Formula used within sheet are that provided by SEC Standard TES-P-119.29.
3- As per 01-TMSS-01 , Ambient Temperature of 40ยฐC is considered for Cable Sizing.
4- For Main Incomer , The short circuit withstand for CU. Conductors , XLPE insulated is given by the formula :-
ISC = 0.143 S / โt
Where:
Isc : Short Time Rating Current in KA.
S : Conductor Cross Section Area in mm2.
t : Current Duration in Seconds.
For 1C x 630 mm2 Cable , for 3 Second S/C :-
Isc = (0.143 x 630) / โ3 = 52.015 KA
The secondary side neutral cable size will be the same size of phase cable (1C x 630 mm2) only one run and it will withstand the S.C rating of 25KA.
Thus , The given cable can withstand the system fault level (25KA)
5- Cable Sizes given are subject to change as per load updates.
6- Indicated Lengths are approximate , The actual route length may increase / decrease as per actual site conditions.
7-As per Sec Standard No. (TES-P-119.29) , Clause (7.1.9) , Page 11 , Voltage drops (Regulation in%) shall be limited as :
a) Total Voltage Drop from Station Transformer to loads not exceed 5%.
b) Station Transformer to Main Distribution Board (MDB) not exceed 0.8%.
c) Main Distribution Board (MDB) to Various loads not exceed 4.2%.
8- As per Sec Standard No. (TES-P-119.29) , Clause (7.2) , Page 10 , Grouping Factor as below :-
a) Cables from Station Transformer to Main Distribution Board (MDB).
– 0.87 For Single Core Cable with Trefoil Touching Configuration.
b) Cables from Main Distribution Board (MDB) to Various loads
– 0.45 For Cable up to 16mm2.
– 0.7 For Cable up to 16mm2.
when
1- Derating current is greater than load current.
2- Voltage drop within range.
3- Short circuit current is equal or greater than BB Short circuit current (25KA )
