TECHNICAL ASPECTS -LT POWER CABLES LT POWER CABLES AS PER IS 1554-PART 1 & IS 7098 PART 1 SBEE SBEE CA CABLES BLES (INDI (INDIA) LIMITE A) LIMITED www.sbeecables.in Presented By: Nagesh The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
NATIONAL OR INTERNATIONAL STANDARDS ALWAYS REFERS TO “MINIMUM REQUIREMENTS” TO BE MET. IT DOES NOT PREVENTS MANAUFACTURERS EITHER TO MAINTAIN OR TO ADHERE BETTER VALUES OVER AND ABOVE SPECIFIED MINIMUM REQUIREMENTS. MOST OF THE CUSTOMERS ARE NOT AWARE OF THIS ASPECT. WITH THIS MANY MANUFACTURERS TAKE UNDUE ADVANTAGE AND IS EVIDENT FROM FOLLOWING SLIDES. The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
FIRST THING THE GOVERNMENT AGENCIES HAVE TO LOOK IN TO THE FOLLOWING POINTS- Be open & take away from your mind the perception of L1. It is simple, You get what you pay for. We all know the money we spent in Government sector is public money & is Tax payers money, which includes your money too. If we do not spend or utilise it for the proper cause, our personal tax liability will go up or barrowing from International debt funds will go up. Draft the Technical specification of Products keeping in mind the better quality of products, better product life ignoring the minimum requirements as given in the standard. If necessary involve experts from cable manufacturing industries & end users in to Technical committee while drafting clear un ambiguous specifications. Based on consensus of committee decide on product specification. The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
FOLLOWING SLIDES SHOWS THE COMPARISION BETWEEN GOOD QUALITY CABLES & SUBSTANDARD QUALITY CABLES. The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
CASE STUDY ALUMINIUM CONDUCTOR USED IN L.T POWER CABLES AS PER IS 1554 PART 1. GRADE “H2” SHALL BE USED FOR CONDUCTOR CROSSSECTION UP TO 10mm² AS PER IS 8130-1984. GRADE “O,H2, or H4” SHALL BE USED FOR CONDUCTOR CROSSSECTION > 10mm² AS PER IS 8130-1984. The specified conductor cross section given in standard is neither the Geometrical cross section nor have the tolerance. The standard specifies only the Maximum D.C Resistance to be maintained. Most of the reputed cable manufacturers uses the above said draw back to be become L1 and produces sub standard products. Following example illustrates the facts : The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
A. Aluminium Conductor of 120mm²Geometrical: 1. Dia of each Aluminium strand in conductor d =2.83mm. 2. No of strands in conductor n=19 3. Geometrical Cross sectional Area A= (π ) x n x d²/4 = 3.142857 x 19 x (2.83 x 2.83) /4 =120mm². 4. The D.C. Resistance for the Geometrical cross section of 120mm² R = ९ l/A = (0.028264/120) x 1000 =0.236 Ω /km. 5. The weight of 120mm² Geometrical cross section= W= A x Density of Aluminium = 120 x 2.72 = 326.40 kg/km D = Diameter of Each Strand, N = No of Strands, A = Area Rho = Specific resistivity of the metal i.e, for Aluminum 0.028264 The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
B. Actual Conductor cross section & respective weight of Aluminium conductors derived from the measured D.C. Resistance of CABLE OF 120mm² as per IS 8130. i. Specified value of D.C Resistance of 120mm² as per IS 8130 =R= 0.253 Ω /km. ii. No of strands = n= 19. iii. Measured Diameter of Aluminium strand used =d= 2.738mm iv. The Cross sectional area of the Aluminium Conductor= A = (π) x n x d²/4 = 3.142857 x 19 x (2.738 x 2.738) /4 =112mm². v. Weight of Aluminium Conductor = A x Density of Aluminium = 112 x 2.72 = 304.64 kg/km Note: Dia is arrived on the basis of practical experience. D = Diameter of Each Strand, N = No of Strands, A = Area The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
A. Copper Conductor of 2.50 mm² Geometrical: 1. Dia of each Copper strand in conductor d =0.674mm. 2. No of strands in conductor n=7 3. Geometrical Cross sectional Area A= (π ) x n x d²/4 = 3.142857 x 7 x (0.674 x 0.674) /4 =2.50 mm². 4. The D.C. Resistance for the Geometrical cross section of 2.50 mm² R = ९ l/A = (17.24 /2.50) =6.90 Ω /km. 5. The weight of 2.50 mm² Geometrical cross section= W= A x Density of Copper = 2.50 x 8.89 = 22.21 kg/km D = Diameter of Each Strand, N = No of Strands, A = Area Rho = Specific resistivity of the metal i.e, for copper 17.24 The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
B. Actual Conductor cross section & respective weight of Copper conductors derived from the measured D.C. Resistance of CABLE OF 2.50 mm² as per IS 8130. i. Specified value of D.C Resistance of 2.50 mm² as per IS 8130 =R= 7.41 Ω /km. ii. No of strands = n= 7 iii. Measured Diameter of Copper strand used = d= 0.651mm iv. The Cross sectional area of the Copper Conductor= A = (π) x n x d²/4 = 3.142857 x 7 x (0.651 x 0.651) /4 =2.33 mm². v. Weight of Copper Conductor = A x Density of Copper = 2.33 x 8.89 = 20.72 kg/km Note: Dia is arrived on the basis of practical experience. D = Diameter of Each Strand, N = No of Strands, A = Area The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
Armour Weight and no of Strip Calculations for 3.5 Core X 120 Sqmm Dia over Inner sheath = 36.9mm (π) X 36.9 / W (4.0mm) To Calculate the no of strips required = = 29.6 x 90% (Coverage) No of Strips required = 26.65 = 27.00 R.O Note :- Dia over inner sheath calculated as per IS 10462 (PI) Fictitious method. 90% coverage is as per amendment number 5 of IS 1554 Part I Strip Dimension = (W) 4.0 X 0.8 mm (TH) ( As per IS) Armour Weight and no of Wire Calculation for 7 Core X 2.50 Sqmm Dia over Inner sheath = 11.6mm (π) X 11.6 / TH (1.4mm) To Calculate the no of Wire required = = 26 x 90% (Coverage) No of Wires required = 23.43 = 24.00 R.O Note :- Dia over inner sheath calculated as per IS 10462 (PI) Fictitious method. 90% coverage is as per amendment number 5 of IS 1554 Part I Wire Dimension = 1.40 mm (Dia TH) The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
Conclusion: With the case study as in case A & B, following are evident facts- I. The conductor cross section used in cable meeting only the resistance is 112mm² as against required Geometrical cross section of 120mm² . This implies the cables as per IS resistance are undersized to cut cost and to become L1. II. Manufacturer calculate the cable pricing based on Geometrical cross section which obviously contains high Aluminium conductor weight. During price negotiation manufacturer will pass on gradually, in steps discount close to the limit of Aluminium conductor he really uses to meet the maximum resistance as indicated in IS 8130. III. The conductor D.C. Resistance in cable as per IS is 0.253 Ω /km (112 Sqmm) as against 0.236 Ω /km (with actual cross section of 120 Sqmm). With this two things can happen- I² R loss is increased for a given voltage & load current. This means the Sub standard cable get heated up sooner or later which may lead to Electrical short circuits. This could results in human injuries, loss of human life and also electrical power shut downs and hence revenue loss to Government. Energy Loss is incurred due to the above to a considerable extent and loss of revenue to Government. The contents of this is presentation is confidential property of SBEE CABLES INDIA LIMITED. It shall not be copied or reproduced in any form without prior written consent.
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