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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
3.0
NOTES ON MAIN LVAC CABLE SIZING CALCULATION:(FROM FEEDER PILLER TO LVACDB) LVACDB)
3.1
Considerations made on Main LVAC Cable Sizing Calculation
a.
Cable Parameters Parameters are are based based on M/s M/s Oman Cable Company Company Catalogue Catalogue (Relevant (Relevant sheets sheets are attached attached))
b.
LV Main Main cables cables are of 1.1kV 1.1kV grade cables cables with Copper Copper Conducto Conductor, r, XLPE insulated, insulated, PVC Sheathed Sheathed,, armoured type. (Ref.table
#59
of Oman Cable Copmany catalogue Sheet. No.69)
c.
All Voltage Voltage drops drops are are checked checked with with permissi permissible ble limits limits of of 2.5% as per per Distributi Distribution on company company standard standard
3.0
Derating Factors for the LVAC Cable Sizing from the Transformer feeder piller to the 415V ACDB Main Incomer cables from 1000 kVA F.P to MDB panel is proposed is as mentioned below: 2R x 1C x 630 Sq. mm Cu. XLPE insulated armoured cables for Phases and 1R x 1C x 630 Sq. mm Cu. XLPE insulated armoured cables for Neutral.
4.1
i
Temperature factor
Cables Cables (or (or part part of route) route) runnin running g in enclosed enclosed trenches trenches entering entering control control buildi building: ng: Table no. 67 of Oman Cable catalogues is referred Similar to above philosophy, in this part of the cable laying, the overall temperature derating fa ctor is 0.9
4.2
Group Rating factor
Group rating factors are applicable for more than one trefoils or more than 3 cable together. Table no. 66 of Oman Cable catalogues is referred. Hence, in this this case, for entire entire route length length of the cable group rating factor is is
4.3
=
1
Thermal Resitivity factor
This factor is applicable in case of cables directly buried While in this case of cable, the same is not applicable as cables are placed in trench (air with restricted circulation. Hence, the same is taken as
=
1
=
0.952
Table no. 75 of Oman Cable catalogues is referred.
4.4
Depth of laying
This factor is applicable in case of cables directly buried or placed in duct bank. Table no. 69 of Oman Cable catalogues is referred.
4.5
Overall Derating Factor
Considering the above, overall derating factor
=
Temperature Derating Factor x Group Derat ing Factor x Termal Resistivity Derating Factor x Derating Factor due to depth of Laying
=
3
0.8568
MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
5.0
Sample calculation
5.1
Cable sizing calculation for incomer cable of Main DB incomer
a
Ampacity calculation :
Maximum demand load (Maximum con.load) Hence, FLC for this load b
= = =
709 kVA (Actual load 567.5 KW pf-0.8) 709/(1.732*0.433) 945.8888 Amp
Group derating factor (as explained in 4.2 above)
=
1
Temp derating factor (as explained in 4.1 above)
=
0.9
Thermal resistivity factor (as explained above)
=
1
And, depth of laying factor
=
0.952
Hence, overall derating factor is
=
0.8568
Uprated current
=
FLC/Overall derating factor
=
945.888825477761/0.8568
=
1103.979 A
Cable size selected
=
4C x 240 sqmm
Ampacity rating
=
380
Hence, required number of runs
=
Upreated current / Ampacity of each cable
=
1104/380
=
2.90521
Ampacity calculation :
(from table-59 for armoured cable)
Hence,1 run of 4C x 240 sqmm XLPE/Cu Cable per phase is selected.
c
Voltage drop calculation :
√ 3 x I x ( R cos Ø + X sin
Ø)
/N
Vdrop
=
Where,
I
=
Load current for each cable (A)
L
=
Total Length of cable (M)
=
300
m
r
=
Cable Resistance at 90°C
=
0.0989
Ω /km
(From cable catalogue)
R
=
r.L
=
0.0989*300/10^3
=
0.02967
x
=
Cable Reactance
=
0.0710
Ω /km
(From cable catalogue)
X
=
x.L
=
0.071*300/10^3
=
0.0213
cos
Ø
=
0.8
sin
Ø
=
0.6
=
8
N
Number of runs
Values of r and x are taken from cable catalogue attached with this document. And 'L' is taken as 250 m for cable length in trench from TX-1 to Main ACDB.
Hence,
Vdrop1
=
1.732 x 945.9 x [( 0.0989 x (300/1000) x 0.8 + 0.071 x (300/1000) x 0.6)] / 2
=
7.478
And hence, cumulative %ge voltage drop
……………….….Voltage drop
Volts
=
100 * 16.141 / 433
=
1.73
%
Since voltage drop is within the limits of 2.5%, the cable size of 2 run per phase of 4Cx240 sq.mm and 1 run of 1Cx630 sq.mm for neutral selected is adequate.
4
MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
Reference Documents
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION
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MAIN PUMPING STATION - LV POWER CABLE SIZING CALCULATION