LT POWER CABLES AS PER IS 1554-PART 1 & IS 7098 PART 1 SBEE - - PowerPoint PPT Presentation

SBEE SBEE CA CABLES BLES (INDI (INDIA) LIMITE A) LIMITED www.sbeecables.in Presented By: Nagesh

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TECHNICAL ASPECTS -LT POWER CABLES LT POWER CABLES AS PER IS 1554-PART 1 & IS 7098 PART 1

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• 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.

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• 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

• n consensus of committee decide on product specification.

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• FOLLOWING SLIDES SHOWS THE COMPARISION BETWEEN GOOD QUALITY

CABLES & SUBSTANDARD QUALITY CABLES.

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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:

CASE STUDY

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• 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

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• 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= 0.253Ω/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

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• 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

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• 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= 7.41Ω/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

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Armour Weight and no of Strip Calculations for 3.5 Core X 120 Sqmm Dia over Inner sheath = 36.9mm To Calculate the no of strips required = (π) X 36.9 / W (4.0mm) = 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 To Calculate the no of Wire required = (π) X 11.6 / TH (1.4mm) = 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)

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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

• bviously 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 0.253Ω/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.

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• C. Economics on Energy Loss due to the use of Sub standard cable.

KF* Value is given in BICC Handbook

Note:

• In the above table the Values Rated current and A.C Resistances are given by reputed manufacturers of

Aluminium conductor & XLPE insulated cables.

• Kf. Constant is calculated based on –
• Cable is charged at the rate current.
• Cable length of 1KM.
• In actual condition the length and the load current varies and hence corresponding values of Kf is to be

calculated as below. For Example :- load current is 160 Amp and Cable length is 0.5KM, supply Voltage is 415 V A.C. 50Hz

• Value of Kf for Given use condition = ≺² x Kf Standard x Route length in KM.
• Now calculating the Energy loss incurred by Customer due to his decision of buying Sub standard cable,

calculated on the basis of 20 Hours of use, 160 Amp Load, 30 days use in a month-

• ≺= Actual Load current/Rated full load current.
• ≺ for 120mm²= 160/241 = 0.664
• ≺ for 112mm²= 160/225 = 0.711

Energy Consumption with 120mm² cable= ≺² x Kf x 0.5 = 0.664 x 0.664 x 264.42 x 0.5= Rs.58.29/Hour. Energy Consumption with 112mm² cable= ≺² x Kf x 0.5 = 0.711 x 0.711x 244.80 x 0.5= Rs.61.87/Hour. cont……

CABLE

A.C. RESITANCE CURRENT RATING CALCULATED

Kf*

@ 90⁰C, Ω/KM IN GROUND IN AMPS Rs/KM/Hr 3.5 Core 120mm² 0.348 241 264.42 3.5 Core 112mm² 0.325 225 246.80

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NOW- a. Consider the price of 120mm² XLPE Aluminium LT cable =Rs309 per Mtr x 500 Mtr = Rs154500 b. Consider the price of 112mm² XLPE Aluminium LT cable =Rs282 per Mtr x 500 Mtr = Rs141000. c. Total amount saved by Customer due to his decision of buying Sub standard cable of 112mm² =154500-141000= Rs 13500 i. Energy Loss in 120mm² cable/Annum= Rs58.27 x 20 Hrs x 30 Days x 12 Months= Rs419544 ii. Energy Loss in 112mm² cable /Annum= Rs61.87 x 20 Hrs x 30 Days x 12 Months= Rs445464 iii. The Loss of Energy due to use of Sub standard cable for 500 Mtr Length per Annum=(i)-(ii) = Rs419544- Rs445464= -Rs25920 !!!!. iv The net Loss to customer per annum due to use of 500 Mtr of Substandard cable

taking in to consideration of saving he made in buying Sub standard cable= (iii)-(C ) = Rs25920-Rs13500 = Rs12420 !!!!!!!!!!!!!! Who is responsible for the National Waste ??-

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• D. INTANGIBLE LOSSES TO CUSTOMER DUE TO USE OF INFERIOR QUALITY OF

INSULATING AND SHEATHING MATERIAL IN SUB STANDARD CABLES. The National or International cable standards does not specify Density & Shore A hardness of Plastics those used in cable, viz PVC Cables etc. Following are the typical values Shore A Hardness & Density of-

INSULATING PVC TYPE A FR: SHORE HARDNESS=88 +/-1, DENSITY=1.41 TO 1.43gm/cc INSULATING PVC TYPE C : SHORE HARDNESS=88 +/-1, DENSITY=1.35 TO 1.36gm/cc. SHEATHING PVC ST1 FR: SHORE HARDNESS=89 +/-1, DENSITY=1.48 TO 1.49gm/cc. SHEATHING PVC ST2: SHORE HARDNESS=89 +/-1 DENSITY=1.49 TO 1.50gm/cc.

The major contributor to arrive at the above values OF Shore A hardness & Density are based on content & grade of PVC resin, Plasticizers & Fillers in any plastic compounds. The cables those manufactured using above Shore A hardness & Density will serve longer!!!!!. Generally in a substandard cables you can find the above values of shore A hardness & Density are higher than those indicated above. This will result in limited life of Insulating properties, both Electrical, Mechanical & Thermal over the period of time. Hence guarantee given for the substandard cable is limited to 1 year or 1 ½ year.

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• E. DIMENSIONAL MEASUREMENT TECHNIQUES FOR INSULATION & SHEATHING

T T T T T

SHEATH ON UN ARMOURED CABLE SHEATH ON ARMOUED CABLE INSULATION ON SHAPED CORE

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• The best method to measure the Insulation & Sheathing thickness of plastic

is by using optic Instrument like Profile Projector and not Micro meter or Vernier calliper where in dimensional accuracies depends on person who measures, measurements varies depends on person and pressure exerted during measurements.

• Thin Slices of Insulation or Sheathing is used to measure the Nominal, One point

Minimum thickness using Profile projector. The cross sectional views are shown in Previous slide.

• In case of Insulation, Nominal and One point minimum thickness measurements,

Take 6 measurements at an interval of 60⁰. Take average of 6 Measurements. The calculated average value shall not be less than the specified Nominal thickness T.

• The one point Minimum Insulation thickness t, measured value shall not fall below

(0.1mm+0.1T).

• Similarly in case of Nominal thickness of Sheath, 6 measurements are taken at an

interval of 60 ⁰. The calculated average thickness shall not be less than specified nominal thickness T.

• The one point Minimum Sheath thickness t, measured value shall not fall below

(0.2mm+0.2T).

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Keeping in mind all the facts which we discussed and presented today it would be advisable –

• Carry out joint inspection after delivery of the cable to the site by withdrawing

random samples supplied at site.

• Customer can send the samples for testing to any recognised laboratories as

per his wish & discretion.

• Cost of testing may be at supplier’s cost or Customer’s cost which shall be

mutually agreed upon. With the above the manufacturer can not undercut the quality of cable he manufacture since he is afraid of rejection at customer site.

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Some of the Photographs of UV effect on XLPE Insulated Cables are given below. (Photographs are taken from actual installations in various sites)

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.

Some of the Photographs of UV effect on XLPE Insulated Cables are given below. (Photographs are taken from actual installations in various sites)

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.

Some of the Photographs of UV effect on XLPE Insulated Cables are given below. (Photographs are taken from actual installations in various sites)

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.

Some of the Photographs of UV effect on PVC Insulated Cables are given below. (Photographs are taken from actual installations in various sites)

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.