Cable Sizing Calculations front sheet

DIRECTORATE GENERAL FOR JUBAIL PROJECT JUBAIL INDUSTRIAL CITY

ليبجلا عورشمل ةماعلا ةرادلا

ةيعانصلا ليبجلا ةنيدم

JOB No. 202-T06 T06-202 :مقر لمع

DESIGN OF POWER AND TELECOMMUNICATION SYSTEM FOR

STAGE 1 OF JUBAIL 2

FACILITY NO. 1-08-071 071-08-1 : ةأشنملا مقر

CONTRACT NO. 071-C11

C11

-

071

:

دقعلا مقر

SUBSTATION FOR STAGE 1 OF JUBAIL 2

230kV CABLE SIZING CALCULATIONS

SCALE: DOCUMENT No. Revision : 0

None 0 7 1 - 4 1 0 - 2 0 T W - E A - 0 0 8

CONTENTS

6. Results and Conclusions:

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6

i) The proposed cable size of 2000mm2 XLPE copper between GIS and 400MVA

transformers is adequate.

...

6

ii) The proposed cable size of 630mm2 XLPE copper between GIS and 133MVA

This document deals with sizing calculations for the 13.8kV cables proposed between pad transformers to mounted switches and from pad mounted switches to existing substation SS/6F. It may be noted that as per PTS, the CONTRACTOR shall obtain this calculation from the cable manufacturer but now a rough calculation is done for the purpose of selecting the tentative size of the cable.

2. Design Input:

• Design Parameters:

The following design parameters are considered.

Nominal Voltage : 13.8 kV

System short circuit current for 1 sec. : 25 kA

Maximum conductor short circuit temperature : 250°C

Maximum permissible continuous conductor temperature : 90°C

3. Assumptions:

Maximum ambient temperature of 40°C is assumed inside the duct banks

4. Methodology:

This calculation is carried out in line with SEC-EOA standards SES-P-104.03.

5. Calculations:

5.1

Table 03-5(6A) of SES-P-119.03,

5.1.1 Cable Ampacity in Air

Though this is manufacturer specific, a typical value of 1890A is considered from Table 03-5(6A) given in SES-P-104.03. Also though this value pertains to oil filled cable, the same is considered for XLPE cable, which results in safer design, since XLPE insulated cables typically have more ampacity than oil filled cables.

5.1.2 Derating Factors

5.1.2.1 Derating Factor for Variation in Air Temperature (F21)

In our case, the cable is partially laid in Cable Cellar which is partially air conditioned and the other portion is laid in Cable Trench. Since the cable trench is not air conditioned, the ambient temperature is considered as 40°C. But since the air is not circulated, the heat generated by the cables increases the temperature by a few degrees. For safe design, this increase is considered as 10°C and hence derating factor of 0.89 for 50°C air temperature [from Table 03-5(21) of the above SES] is considered.

5.1.2.2 Grays Derating Factor for Cables Installed above Ground (F22)

In each cable trench, three single core cables are laid with a spacing of 400mm. This spacing is more than twice the diameter of the cable and for safer design, this factor is taken as 0.95 from Table 03-5(22) of the above-mentioned SES.

5.1.3 Derated Ampacity

This is the product of Ampacity in air multiplied by Derating factors. In other words,

Derating ampacity = 1890 x F21 x F22

= 1890 x 0.89 x 0.95 = 1598 A

Since this is greater than the 1339A required as per Section 4.03A.1 of PTS-1135, the cable of 2000mm2 _{size selected is adequate.}

5.2 Ampacity Calculations for 630mm2 _{XLPE Copper Cable}

Table 03-5(6A) of SES-P-119.03,

5.2.1 Cable Ampacity in Air

Though this is manufacturer specific, a typical value of 1890A is considered from Table 03-5(6A) given in SES-P-104.03. Also though this value pertains to oil filled cable, the same is considered for XLPE cable, which results in safer design, since XLPE insulated cables typically have more ampacity than oil filled cables.

proposed laying conditions. Since in our case cable is not buried, the following typical derating factors given in Section 4.9.4.3 of the above-mentioned SES are considered.

5.2.2.1 Derating Factor for Variation in Air Temperature (F21)

In our case, the cable is partially laid in Cable Cellar which is partially air conditioned and the other portion is laid in Cable Trench. Since the cable trench is not air conditioned, the ambient temperature is considered as 40°C. But since the air is not circulated, the heat generated by the cables increases the temperature by a few degrees. For safe design, this increase is considered as 10°C and hence derating factor of 0.89 for 50°C air temperature [from Table 03-5(21) of the above SES] is considered.

5.2.2.2 Grays Derating Factor for Cables Installed above Ground (F22)

In each cable trench, three single core cables are laid with a spacing of 400mm. This spacing is more than twice the diameter of the cable and for safer design, this factor is taken as 0.95 from Table 03-5(22) of the above-mentioned SES.

5.2.3 Derated Ampacity

This is the product of Ampacity in air multiplied by Derating factors. In other words,

Derating ampacity = 1890 x F21 x F22

= 1890 x 0.89 x 0.95 = 1598 A

Since this is greater than the 1339A required as per Section 4.03A.1 of PTS-1135, the cable of 2000mm2 _{size selected is adequate.}

5.2.4 Short Circuit Current Rating for Copper Conductor

Nominal conductor area in mm2 _{= 2000 mm}2

for XLPE, copper conductor = Time Area 142 × (from Section 4.9.6 of above SES) = 1 2000 142 × = 284 kA

Since this is higher than the required short circuit of 63kA, the offered conductor size is adequate.

6. Results and Conclusions: 6.1 Results:

i) The proposed cable size of 2000mm2 _{XLPE copper between GIS and}

400MVA transformers is adequate.

ii) The proposed cable size of 630mm2 _{XLPE copper between GIS and 133MVA}

transformers is adequate.

6.2 Conclusions:

Based on the results of the calculations, it is concluded that the proposed conductor sizes for 230kV cables is adequate.

7. References:

SES-P-104.03 – Cable selection

8. Attachments: