11KV/415V Overhead Line Specification(REC)


11KV/415V over Head Line’s Specification and Installation (REC):

 11KV LIGHTNING ARRESTER (IS: 3070 (Pt-II)).

Voltage Rating for LA:

  • The rated voltage of lightning arresters shall be 9 KV (rms).
  • This will be applicable to the effectively earthed 11 KV systems co-efficient of earth not exceeding 80 percent as per IS: 4004 with all the transformer neutrals directly earthed.

Normal Discharge Current Rating for LA:

  • The nominal discharge current rating of the lightning arresters shall be 5 KA.

Tests for LA:

  • The following routine and type tests as laid down in IS : 3070 (Part-I) shall be carried out.
  • Routine Test: Dry Power frequency spark over test.
  • Type Tests (Confirmation) :
  1. Voltage withstand tests of arrester insulation.
  2. Power frequency spark over test
  3. Hundred percent 1.2/550 microsecond impulse spark over test
  4. Front-of-wave impulse spark over test.
  5. Residual voltage test.
  6. Impulse current withstand test.
  7. Operating duty test.
  8. Temperature cycle test on porcelain housing.
  9. Porosity test on porcelain components.
  10. Galvanizing test on metal parts.

11 KV DROP-OUT FUSE CUTOUTS: (IS: 9385 (part-I to III).)

  • The distribution fuse cutouts shall be outdoor, open, drop-out expulsion type fuse cutouts suitable for installation in 50 Hz, 11 KV distribution system.
  • The rated voltage shall be 12 KV.
  • The rated current shall be 100 A.

Rated Lighting Impulse withstands Voltage for Fuse:

  • To earth and between poles 75 KV (Peak)
  • Across the isolating distance of fuse base 86 KV (Peak)

Rated One Minute Power Frequency Withstand Voltage (Wet & Dry) for Fuse:

  • To earth and between poles 28 KV (rms)
  • Across the isolating distance 32 KV (rms)

Temperature Rise Limit for Fuse:

  • Copper contacts silver faced 650C
  • Terminals 500C
  • Metal parts acting as spring The temperature shall not reach such a value that Elasticity of the metal is changed

Rated Breaking Capacity for Fuse:

  • The rated breaking capacity shall be 8 KA (Asymmetrical).

Construction Details for Fuse:

  • The cutouts shall be of single vent type (downward) having a front connected fuse carrier suitable for angle mounting.
  • All ferrous parts shall be hot dip galvanized in accordance with the latest version of IS : 2632. Nuts and bolts shall conform to IS : 1364. Spring washers shall be electro-galvanized.

Fuse Base Top Assembly:

  • The top current carrying parts shall be made of a highly conductive copper alloy and the contact portion shall be silver plated for corrosion resistance and efficient current flow.
  • The contact shall have a socket cavity for latching and holding firmly the fuse carrier until the fault interruption is completed within the fuse.
  • The top assembly shall have an aluminum alloy terminal connector. The top assembly shall be robust enough to absorb bulk of the forces during the fuse carrier closing and opening operations and shall not over-stress the spring contact. It shall also prohibit accidental opening of the fuse carrier due to vibrations or impact.

Fuse Base Bottom Assembly:

  • The conducting parts shall be made of high strength highly conductive copper alloy and the contact portion shall be silver plated for corrosion resistance and shall provide a low resistance current path from the bottom fuse carrier contacts to the bottom terminal connector.

Fuse Carrier Top Assembly:

  • The fuse carrier top contact shall have a solid replaceable cap made from highly conductive, anticorrosive copper alloy and the contact portion shall be silver plated to provide a low resistance current path from the Fuse Base Top Contact to the Fuse Link.
  • It shall make a firm contact with the button head of the fuse link and shall provide a protective enclosure to the fuse link to check spreading of arc during fault interruptions.
  • The fuse carrier shall be provided with a cast bronze opening eye (pull ring) suitable for operation with a hook stick from the ground level to pull-out or close-in the fuse carrier by manual operation.

Fuse Carrier Bottom Assembly:

  • The fuse carrier bottom assembly shall be made of bronze castings with silver plating at the contact points to efficiently transfer current to fuse base.
  • It shall make smooth contact with the fuse base bottom assembly during closing operation. The bottom assembly shall have a lifting eye for the hook stick for removing or replacing the fuse carrier.

Fuse Base (Porcelain):

  • The fuse base shall be a bird-proof, single unit porcelain insulator with a creepage distance (to earth) not less than 320 mm. The top and bottom assemblies as also the middle clamping hardware shall be either embedded in the porcelain insulator with sulphur cement or suitably clamped in position.
  • For embedded components, the pull out strength should be such as to result in breaking of the porcelain before pull out occurs in a test. For porcelain insulators, the beam strength shall not be less than 1000 kg.

Fuse Tube:

  • The fuse tube shall be made of fiber glass coated with ultraviolet inhibitor on the outer surface and having arc quenching bone fire liner inside.
  • The tube shall have high bursting strength to sustain high pressure of the gases during fault interruption.
  • The inside diameter of the fuse tube shall be 17.5 mm. The solid cap of the fuse carrier shall clamp the button head of the fuse link, closing the top end of the fuse and allowing only the downward venting during fault interruption.

Type Tests (IS: 9385 Part I & II) for Fuse:

  • Dielectric tests
  • Temperature rise test

Mounting Arrangement for Fuse:

  • The cutouts shall be provided with a suitable arrangement for mounting these on 74 X 40 mm or 100 X 50 mm channel cross arm in such a way that the center line of the base is at an angle of 15 to 20 deg from the vertical and shall provide the necessary clearances from the support.
  • Mounting arrangement shall be made of high strength galvanized steel flat and shall be robust enough to sustain the various stresses encountered during all operating conditions of the cutout.

11 KV PORCELAIN INSULATORS: (IS: 731 and IS: 3188):

  • The porcelain shall be sound, free form defects, through verified and smoothly glazed. Unless otherwise specified, the glaze shall be brown color.
  • The glaze shall cover all the porcelain parts of insulators except those areas which serve as support during firing are left unglazed for the purpose of assembly.
  • The design of insulators shall be such that stresses due to expansion and contraction in any part of the insulator shall not lead to deterioration.
  • The porcelain shall not engage directly with hard metal. Cement used in construction of insulators shall not cause fracture by expansion or loosening by contraction and proper care shall be taken to locate the individual parts correctly during cementing.
  • The cement shall not give rise to chemical reaction with metal fittings and its thickness shall be as uniform as possible.
  • The insulators should preferably be manufactured in automatic temperature controlled kilns to obtain uniform baking for better electrical and mechanical properties.
  • Both pin and strain insulators shall conform to Type B of IS : 731. The strain insulators shall be of Tongue and Clevis type.

 Test Voltage for Insulator:

  • Highest System Voltage : 12 KV (rms)
  • Visible Discharge Test: 9 KV (rms)
  • Wet Power Frequency Withstand Test 35 KV (rms)
  • Power Frequency Puncture Withstand Test (Pin Insulator) : 105 KV (rms)
  • Power Frequency Puncture Withstand Test (Strain Insulator):1.3 times the actual dry flashover voltage of the insulator.
  • Impulse Voltage Withstand Test : 75 KV (rms)

Failing Load for Insulator:

  • Mechanical Failing Load (For Pin Insulators only) : The insulators shall be suitable for a minimum failing load of 10 KN applied in transverse director.
  • Electro-Mechanical Failing Load (For Strain Insulators) : The insulators shall be suitable for a minimum failing load of 70 KN applied axially.

Creepage Distance for Insulator:

  • Highest System Voltage: 12KV
  • Heavily Polluted Atmosphere Pin Insulator: 320mm
  • Heavily Polluted Atmosphere Strain Insulator: 400mm

Tests: (As per IS: 731 ) for Insulator.

  1. Visual examination
  2. Verification of dimensions
  3. Visible discharge test
  4. Impulse Voltage withstand Test
  5. Wet Power Frequency Voltage withstand Test
  6. Temperature Cycle Test
  7. Mechanical Failing Load Test
  8. 24 hour Mechanical Strength Test for Strain Insulators
  9. Puncture Test
  10. Porosity Test
  11. Galvanizing Test
  12. Electro-Mechanical Failing Load Test

Routine Tests for Insulator

  1. Virtual examination
  2. Mechanical routine test
  3. Electrical routine test

Acceptance Test for Insulator

  1. Verification of Dimensions
  2. Temperature Cycle Test
  3. Electro-Mechanical Failing Load Test
  4. Puncture Test
  5. Porosity Test
  6. Galvanizing Test

Marking for Insulator:

  • Name or trademark of manufacturer
  • Month and year of manufacture
  • Minimum failing load in KN
  • ISI certificate mark, if any
  • Markings on porcelain shall be printed and shall be supplied before firing.

 Pin Insulators:

  • The pins shall of single piece obtained preferably by the process of forging.
  • They shall not be made by joining, welding, shrink fitting or any other process using more than one piece material. The pins shall be of good finish, free from flaws and other defects.
  • The finish of the collar shall be such that sharp angle between the collar and the shank is avoided. Aluminum ferrous pins, nuts and washers, except those made of stainless steel, shall be galvanized. The threads of nuts and taped hole when cut after galvanizing shall be well oiled or greased.

Dimensions  for Pin Insulators:

  • Pins shall be of small steel head type S 165 P as per IS : 2486 (Part-II) having stalk length of 165 mm and shank length of 150 mm with minimum failing load of 10 KN.

Tests: (IS: 2486 (Part-I)) for Pin Insulators

  • Checking of threads on heads
  • Galvanizing test
  • Visual examination test
  • Mechanical test
  • Galvanizing test
  • Mechanical test
  • Visual examination test

Helically Formed Pin Insulator Ties:

  • Helically formed ties used for holding the conductor on the pin insulator shall be made of aluminum alloy or aluminized steel or aluminum clad steel wires and shall conform to the requirements of IS : 12048. The ties shall be suitable for pin insulator dimensions of Pt.- I and conductor sizes specified.
  • Elastomer pad for insulator shall be used with the ties to avoid abrasion of the conductor coming into direct contact with the insulator.

Cross arm strap conforming to IS: 2486 (Pt. – II).

  • Aluminum alloy die cast thimble-clevis for attaching to the tongue of strain, insulator on one end and for accommodating the loop of the helically formed dead-end fitting at the other end in its smooth internal contour.
  •  The thimble shall be suitable for all sizes of ACSR conductors as specified. The thimble clevis shall be attached to the insulator by a steel cutting pin used with a non-ferrous split pin of brass or stainless steel.
  • The thimble shall have clevis dimensions as per IS: 2486 (Pt – II).
  • Helically formed dead end grip having a prefabricated loop to fit into the grooved contour of the thimble on one end and for application over the conductor at the other end.
  • The formed fitting shall conform to the requirement of IS : 12048.

Fittings for strain Insulators of Ball & Socket Type:

  • Cross arm strap conforming to IS: 2486 (Pt-II).
  • Forged steel ball eye for attaching the socket end of the strain insulator to the cross arm strap.
  • Forgings shall be made of steel as per IS: 2004. Aluminum alloy thimble-socket made out of permanent mould cast, high strength aluminum alloy for attaching to the strain insulator on one end and for accommodating the loop of the helically formed dead-end fittings at the other end in its smooth internal contour.
  • The thimble socket shall be attached to the strain insulator with the help of locking pin as per the dimensions given in IS : 2486 (Pt-II).

Tests

  • The helically formed fittings for strain insulators shall be subjected to tests as per IS : 12048.
  • The other hardware fittings shall be tested as per IS: 2486 (Part-I).

Fittings for strain Insulators with Helically Formed Conductors Dead-End Grips:

Fittings for Strain Insulators of Tongue & Clevis Type

  • The fittings shall consist of the following components:
  1. Cross arm strap conforming to IS:2486 (Pt.II)-1989.
  2. Aluminum alloy die cast thimble-clevis for attaching to the tongue of strain insulator on one end and for accommodating the loop of the helically formed dead-end fitting at the other end in its smooth internal contour. The thimble shall be suitable for all sizes of conductors ranging from 7/2.11mm to 7/3.35mm ACSR. The thimble clevis shall be attached tothe insulator by a steel cutter pin used with a non-ferrous split pin of brass or stainless steel. The thimble shall have clevis dimensions as per IS:2486 (Pt.II)-1989.
  3.    Helically formed dead-end grip having a pre-fabricated loop to fit into the grooved contour of the thimble on one end and for application over the conductor at the other end. The formed fitting shall conform to the requirement ofIS:12048-1987.
  • Note: As the helically formed fittings are made to suit specific sizes of conductors, the purchase should clearly specify the number of fittings required for each size of conductor

Fittings for strain Insulators with  Conventional Dead end Clamps Alternative to Fitting Covered:

  • Fittings for strain insulators with conventional dead-end clamps for use with tongue & clevis or ball & socket type insulators shall consist of the following components :
  1. Cross arms strap conforming to IS:2486 (Pt.II)-1989
  2.  Dead-end clamp made of aluminum alloy to suit ACSR conductors from 7/2.11mm to 7/3.35mm. The ultimate strength of the clamp shall not be less than 3000 Kg. The shape and major dimensions of clamps suitable for B&S and T&C insulators are shown in figures 7 & 8 respectively.

GUY STRAIN INSULATORS: (IS: 5300)

  • The porcelain insulator shall be sound, free from defects, thoroughly verified and smoothly glazed.
  •  The design of the insulator shall be such that the stresses to expansion and contraction in any part of the insulator shall not lead to its deterioration.
  • The glaze, unless otherwise specified, shall be brown in color.
  • The glaze shall cover the entire porcelain surface parts except those areas that serve as supports during firing.

Type for Guy Insulators:

  • The standard guy strain insulators shall be designations ‘A’ and ‘C’ as per IS: 5300.
  • The recommended type of guy strain insulators for use on guy wires of overhead lines of different voltage levels are as follows:
  • Power Line Voltage :11KV
  • Designation of Insulators: C
  • Dry one minute Power Frequency withstand Voltage: 27 KV (rms)
  • Wet one minute Power Frequency withstand Voltage: 13 KV (rms)
  • Minimum Failing Load: 88(KN)

 Tests: (IS: 5300) for Guy Insulators.

  1. Visual examination
  2. Verification of dimensions
  3. Temperature cycle test
  4. Dry one-minute power frequency voltage withstand test
  5. Wet one-minute power frequency voltage withstand test
  6. Mechanical strength test
  7. Porosity test
  8. Acceptance Tests : (to be conducted in the following order)
  9. Verification of dimensions
  10. Temperature cycle test
  11. Mechanical strength test
  12. Porosity test

Marking for Guy Insulators:

  • Name or trademark of the manufacturer.
  • Year of manufacture.
  • ISI certificate mark, if any
  • Marking on porcelain shall be applied before firing.

Type of Insulators for Guy Insulators:

  • The standard guy strain insulators shall be of designations ‘A‘ and ‘C‘ as per IS:5300.
  • The recommended type of guy strain insulators for use on guy wires of overhead lines of different voltage levels are as follows :
Line Voltage Designation of Insulator
415/240Volt A Type
11KV C Type
33KV C Type (2 No’s of Strings in Series).

Basic Insulator Level for Guy Insulators:

Designation of Insulator Dry one min power frequency withstand Wet one min power frequency withstand
A Type 18 KV (rms) 8 KV (rms)
C Type 27 KV (rms) 13 KV (rms)

 Mechanical Strength for Guy Insulators:

The insulators shall be suitable for the minimum failing loads specified as under:

Designation of Insulator Minimum Failing Load
A Type 44 KN
C Type 88 KN

Routine Test as per Tests (IS: 5300) for Guy Insulators:

  1. Visual examination
  2. Verification of dimensions
  3. Temperature cycle test
  4. Dry one-minute power-frequency voltage withstand test
  5. Wet one-minute power frequency voltage withstand test
  6. Mechanical strength test
  7. Porosity test

Acceptance Tests (to be conducted in the following order):

  1. Verification of dimensions
  2. Temperature cycle test
  3. Mechanical strength test
  4. Porosity test

DANGER NOTICE PLATES:

  • As per provisions of IE Rules 1956, Danger Notice Plates in Hindi or English and, in addition, in the local language with the sign of skull and bones are required to be provided on power line supports and other installations.
  • It is further stipulated in the I.E. Rules that such Notice Plates are not required to be provided on supports like PCC, tubular, wood, steel rails, etc. which cannot be climbed easily without the aid of ladder or special appliances.
  • To adopt a uniform pattern and for helping easy procurement, a specification on Danger Notice Plates has been drawn up.

Standards of Danger Plate

  • The Danger Notice Plates shall comply with IS:2551-1982.

Dimensions of Danger Plate

  • Two sizes of Danger Notice Plates as follows are recommended:
  1. For display at 415 V installations – 200x150mm
  2. For display at 11 KV (or higher voltages) installations – 250x200mm
  • The corners of the plate shall be rounded off.
  • The location of fixing holes as shown in Figs. 1 to 4 is provisional and can be modified to suit the requirements of the purchaser.

Lettering of Danger Plate

  • All letterings shall be centrally spaced. The dimensions of the letters, figures and their respective position shall be as shown in figs.
  • The size of letters in the words in each language and spacing between them shall be so chosen that these are uniformly written in the space earmarked for them.

Languages of Danger Plate

  • Under Rule No. 35 of Indian Electricity Rules, 1956, the owner of every medium, high and extra high voltage installation is required to affix permanently in a conspicuous position a danger notice in Hindi or English and, in addition, in the local language, with the sign of skull and bones.
  • The type and size of lettering to be done in Hindi is indicated in the specimen danger notice plates shown in Fig. 2 and 4 and those in English are shown in Figs.
  • Adequate space has been provided in the specimen danger notice plates for having the letterings in local language for the equivalent of’ Danger’,’ 415′ ‘11000’ and ‘Volts’.

Material & Finishing of Danger Plate:

  • The plate shall be made from mild steel sheet of at least 1.6mm thick and vitreous enameled white, with letters, figures and the conventional skull and cross-bones in signal red color (refer IS:5-1978) on the front side. The rear side of the plate shall also be enameled.

Tests of Danger Plate:

  • The following tests shall be carried out :
  1. Visual examination as per IS:2551-1982
  2. Dimensional check as per IS:2551-1982
  3. Test for weather proofness as per IS:8709-1977 (or its latest version)

ACSR and AAC over head conductors:

  • A Conference on Standardization of Specifications and Construction Practices in Rural Electrification was held on 4th and 5th January, 1971 in New Delhi. Besides the Rural Electrification Corporation, representatives of various State Electricity Boards, the Indian Standards Institution (BIS), Central Water & Power Commission (CEA),Central Board of Irrigation and Power and many other organizations participated in the discussions.
  • Based on the consensus arrived at the Conference, REC Specification No. 1/1971 covering 7/2.21 mm (25 mm2 aluminum area) and 7/3.10mm (50mm2 aluminum area) AAC for use on LT lines and 7/2.59 mm (30mm2 aluminum area) and 7/3.35mm (50mm2 aluminum area) ACSR for use on 11 KV and LT lines was issued.
  • Subsequently, the Specification was revised to incorporate an additional size of ACSR viz 7/2.11mm (20mm2 aluminum area) for use on 11 KV and LT lines and then again to incorporate three more sizes of ACSR viz. 7/3.35mm (50mm2 aluminum area), 7/4.09mm (80mm2 aluminum area) and 6/4.72mm + 7/1.57 mm (100mm2 aluminum area) for use on 33 KV lines.
  • The sizes of conductors standardized for lines of different voltages are indicated below :

ACSR Conductor for 33KV Lines :

  1. ACSR 7/3.35mm (50mm2 aluminum area)
  2. ACSR 7/4.09 mm (80mm2 aluminum area)
  3. ACSR 6/4.72 mm + 7/1.57 mm (100mm2 aluminum area)

ACSR Conductor for11 KV Lines

  1. ACSR 7/2.11 mm (20mm2 aluminum area)
  2. ACSR 7/2.59 mm (30mm2 aluminum area)
  3.  ACSR 7/3.35 mm (50mm2 aluminum area)

ACSR Conductor for LT Lines

  1. ACSR 7/2.11 mm (20mm2 aluminum area)
  2.  ACSR 7/2.59 mm (30mm2 aluminum area)
  3. ACSR 7/3.35 mm (50mm2 aluminum area)
  4.  AAC 7/2.21 mm (25mm2 aluminum area)
  5. AAC 7/3.10 mm (50mm2 aluminums area)

Standards for ACSR Conductor :

  • IS: 398 (Pt.I)-1976 and IS: 398 (Pt.II)-1976.

Joint in Wires & Conductors:

  • All aluminums conductors: No joints shall be permitted in any wire.
  • Aluminum Conductor Steel Reinforced :

Aluminum Wires for ACSR Conductor:

  • No two joints shall occur in the aluminums wires closer together than 15 meters.

Steel Wires for ACSR Conductor :

  • No joints shall be permitted in steel wires used for ACSR of Sizes 20mm2 aluminums area (7/2.11mm), 30mm2 aluminums area (7/2.59mm), 50mm2 aluminums area (7/3.35mm) and 80mm2 aluminums area (7/4.09 mm).
  • In the case of ACSR of 100mm2 aluminums area (6/4.72mm + 7/1.57 mm) having seven galvanized steel wires, joints, in individual wires shall be permitted but no two such joints shall be less than 15 meters apart in the complete steel core.

Tests for ACSR Conductor:

  • The samples of individual wires for the tests shall normally be taken before stranding. The manufacturer shall carry out test on samples taken out at least from 10% of aluminums wire spools and 10% of steel wire coils. However, when desired by the purchaser, the test sample may be taken from the stranded wires.
  • The wires used for all aluminums conductors shall comply with the following tests as per IS:398(Pt.I)-1976.
  1.  Breaking load test
  2.  Wrapping test
  3.  Resistance test
  • The wires used for aluminums conductors, steel reinforced shall comply with the following tests as per IS:398
  1. Breaking load test
  2. Ductility test
  3. Wrapping test
  4. Resistance test
  5. Galvanizing test

Packing & Marking :(IS: 1778-1980)

  • The gross mass for various conductors shall not exceed by more than 10% of the values given in the following

Conductor Size Gross Mass for ACSR Conductor

(1) AAC

  • 25mm2 Al. area (7/2.21 mm) 500 Kg.
  • 50mm2 Al. area (7/3.10 mm) 500 Kg.

(2)ACSR

  • 20mm2 Al. area (7/2.11 mm) 1000 Kg.
  • 30mm2 Al. area (7/2.59 mm) 1000 Kg.
  • 50mm2 Al. area (7/3.35 mm) 1500 Kg.
  • 80mm2 Al. area (7/4.09 mm) 1500 Kg.
  • 100mm2 Al. area (6/4.72mm + 7/1.57mm) 2000 Kg.

Conductor Size Normal conductor length for ACSR Conductor

  1.  AAC

  • 25mm2 Al. area (7/2.21mm) 1.0 Km.
  • 50mm2 Al. area (7/3.10mm) 1.0 Km.
  1. ACSR

  • 20mm2 Al. area (7/2.11 mm) 2.0 Km.
  • 30mm2 Al. area (7/2.59 mm) 2.0 Km.
  • 50mm2 Al. area (7/3.35 mm) 2.0 Km.
  • 80mm2 Al. area (7/4.09 mm) 1.5 Km.
  • 100mm2 Al. area (6/4.72mm + 7/1.57mm) 2.0 Km.
  • Longer lengths shall be acceptable.
  • Short lengths, not less than 50% of the standard lengths, shall be acceptable to the maximum extent of 10% of the quantity ordered.

Marking for ACSR Conductor:

  • The following information shall be marked on each package:
  1. Manufacturers’ name
  2. Trade mark, if any
  3. Drum or identification number
  4. Size of conductor
  5. Number and lengths of conductor
  6. Gross mass of the package
  7. Net mass of conductor
  8. I.S.I certification mark, if any

Pre stressed Cement Concrete Poles(FOS 2.5) For 11KV & LT Lines:

  •  A research project for evolving economical designs of cement concrete poles for use on 11 KV and LT Lines was entrusted to the Cement Research Institute (CRI) of India.
  • The basic design parameters for these poles as given in Clause 6 of this Specification were approved by the Fifth Conference on standardization of Specifications and Construction Practices in Rural Electrification held in May, 1974.
  • Some of these design parameters which were based on certain foreign codes/practices and certain other provisions of this Specification, although at variance with the stipulations of IS:1678 – 1960, had been adopted to achieve economy in the designs. However, these modifications have since been incorporated in the revised IS:1678 – 1978.
  • This Specification covers PCC poles with an overall length of 7.5 M, 8.0 M and 9.0 M suitable for use in overhead 11 KV and L.T. power lines and double pole structures for 11/0.4 KV substations.

Application Standard for PCC Pole:

  • IS: 1678-1978, Specification for pre stressed concrete poles for overhead power, traction and telecommunication lines.
  • IS: 2905-1966. Methods of test for concrete poles for over-head power and telecommunication lines.
  • IS: 7321-1974. Code of practice for selection, handling and erection of concrete poles for over-head power and telecommunication lines.

Average Permanent Load for PCC Pole:

  • That fraction of the working load which may be considered of long duration over a period of one year.

Load Factor for PCC Pole:

  • The ratio of ultimate transverse load to the transverse load at first crack.

Transverse for PCC Pole:

  • The direction of the line bisecting the angle contained by the conductor at the pole. In the case of a straight run, this will be normal to the run of the line.

Transverse Load at First Crack for PCC Pole:

  • For design, the transverse load at first crack shall be taken as not less than the value of the working load.

Working load for PCC Pole:

  • The maximum load in the transverse direction, that is ever likely to occur, including the wind pressure on the pole.
  • This load is assumed to act at a point 600 mm below the top with the butt end of the pole planted to the required depth as intended in the design.

Ultimate Failure for PCC Pole:

  • The conditions existing when the pole ceases to sustain a load increment owing to either crushing of concrete, or snapping of the pre stressing tend on or permanent stretching of the steel in any part of the pole.

Ultimate Transverse Load for PCC Pole:

  • The load at which failure occurs, when it is applied at a point 600 mm below the top and perpendicular to the axis of the pole along the transverse direction with the butt end of the pole planted to the required depth as intended in the design.

Application for PCC Pole:

 7.5 M and 8.0 M Poles

  • These poles shall be used at tangent locations for 11KV and L.T. lines in wind pressure zones of 50 kg/M2, 75 Kg/M2 and 100 Kg/M2 in accordance with REC Construction Standards referred to in the following:

Pole length: 7.5M

  • 11KV lines without earth wire L.T. lines, horizontal formation.
  • Reference to REC Construction Standards: A-4, B-5

Pole length: 8M

  • 11KV lines with earth wire L.T. lines, vertical formation.
  • Reference to REC Construction Standards: A-5, B-6

9.0 M Poles

  • These poles shall be used for double pole structures of distribution transformer centers as per REC Construction Standards F-1 to F-4 and for special locations in 11 KV and L.T. Lines, such as road crossings etc.

Materials for PCC Pole::

(1) Cement

  • The cement used in the manufacture of pre stressed concrete poles shall be ordinary or rapid hardening port land cement conforming to IS: 269 – 1976 (Specification for ordinary and low heat port land cement) or IS: 8041 E-1978 (Specification for rapid hardening port land cement).

(2) Aggregates

  • Aggregates used for the manufacture of pre-stressed concrete poles shall conform to IS : 383 – 1970 (Specification for coarse and fine aggregates from natural sources for concrete). The nominal maximum size of aggregates shall in no case exceed 12mm.

(3) Water

  • Water should be free from chlorides, sulphates, other salts and organic matter. Potable water will be generally suitable.

(4) Admixtures

  • Admixtures should not contain Calcium Chloride or other chlorides and salts which are likely to promote corrosion of pre-stressing steel.

(5) Pre-stressing Steel

  • The pre-stressing steel wires, including those used as un tensioned wires  should conform to IS : 1785 (Part-I) – 1966 (Specification for plain hard drawn steel wire for pre stressed concrete. Part-I cold drawn stress relieved wire), IS: 1785 (Part-II) – 1967 (Specification for plain hard-drawn steel wire)., or IS : 6003 – 1970 (Specification for indented wire for pre-stressed concrete).
  • The type designs given in Annexure-I are for plain wires of 4 mm diameter with a guaranteed ultimate strength of 175 Kg/mm2.

(6) The concrete mix:

  • Itshall be designed to the requirements laid down for controlled concrete (also called design mix concrete) in IS : 1343 – 1980 (Code of practice for pre stressed concrete) and IS : 456 – 1978 (Code of practice for plain and reinforced concrete), subject to the following special conditions;
  1.  Minimum works cube strength at 28 days should be at least 420 Kg/cm2.
  2. The concrete strength at transfer should be at least 210Kg/cm2.
  3. The mix should contain at least 380 Kg. of cement per cubic meter of concrete.
  4. The mix should contain as low a water content as is consistent with adequate workability. If it becomes necessary to add water to increase the workability, the cement content also should be raised in such a way that the original value of water cement ratio is maintained.

Design Requirements for PCC Pole::

  • The poles shall be planted directly in the ground with a planting depth of 1.5 meters.
  • The working load on the poles should correspond to those that are likely to come on the pole during their service life. Designs given in Annexure-I are for 140 Kg. and 200 Kg. Applied at 0.6 M from top.
  • The factor of safety for all these poles shall not be less than 2.5.
  • The average permanent load should be 40% of the working load.
  • The F.O.S. against first crack load shall be 1.0.
  • At average permanent load, permissible tensile stress in concrete shall be 30 Kg/cm2.
  • At the design value of first crack load, the modulus of rupture shall not exceed 55.2 kg/cm2 for M-420 concrete.
  • The ultimate moment capacity in the longitudinal direction should be at least one fourth of that in the transverse direction.
  • The maximum compressive stress in concrete at the time of transfer of pre stress should not exceed 0.8 times the cube strength.
  • The concrete strength at transfer shall not be less than half the 28 days strength ensured in the design, i.e. 420 x 0.5= 210 Kg/cm2.
  • For model check calculations on the design of poles, referred to in Annexure-I, a reference may be made to the REC “Manual on Manufacturing of solid PCC

Dimensions and Reinforcements for PCC Pole:

  • The cross-sectional dimensions and the details of pre stressing wire should conform to the particulars given in Annexure-I.
  • The provisions of holes for fixing cross-arms and other fixtures should conform to the REC standards referred to in clause 4 of this specification and in accordance with the construction practices adopted by the State Electricity Boards.

Manufacture for PCC Pole::

  • All pre stressing wires and reinforcements shall be accurately fixed as shown in the drawings and maintained in position during manufacture. The un tensioned reinforcement, as indicated in the drawings, should be held in position by the use of stirrups which should go round all the wires.
  • All wires shall be accurately stretched with uniform pre stress in each wire.
  • Each wire or group of wires shall be anchored positively during casting. Care shall be taken to see that the anchorages do not yield before the concrete attains the necessary strength.

Cover for PCC Pole:

  • The cover of concrete measured from the outside of the pre stressing tendon shall be normally 20 mm.

Welding & Lapping of Steel for PCC Pole:

  • The high tensile steel wire shall be continuous over the entire length of the tendon.
  • Welding shall not be allowed in any case. However, jointing or coupling may be permitted provided the strength of the joint or coupling is not less than the strength of each individual wire.

Compacting for PCC Pole:

  • Concrete shall be compacted by spinning, vibrating, shocking or other suitable mechanical means. Hand compaction shall not be permitted.

Curing for PCC Pole:

  • The concrete shall be covered with a layer of sacking, canvas, hessian or similar absorbent material and kept constantly wet up to the time when the strength of concrete is at least equal to the minimum strength of concrete at transfer of pre stress. Thereafter, the pole may be removed from the mould and watered at intervals to prevent surface cracking of the unit, the interval should depend on the atmospheric humidity and temperature.

The pre stressing wires for PCC Pole:

  • Itshall be de tensioned only after the concrete has attained the specified strength at transfer (i.e. 210 Kg/cm2). The cubes cast for the purpose of determining the strength at transfer should be cured, as far as possible, under conditions similar to those under which the poles are cured.
  • The transfer stage shall be determined based on the daily tests carried out on concrete cubes till the specified strength indicated above is reached. Thereafter the test on concrete shall be carried out as detailed in IS: 1343 – 1960 (Code of practice for pre stressed concrete).
  • The manufacturer shall supply when required by the purchaser or his representative, result of compressive test conducted in accordance with IS : 456 -1964 (Code of practice for plain and reinforced concrete) on concrete cubes made from the concrete used for the poles.
  •  If the purchaser so desires, the manufacturer shall supply cubes for test purposes and such cubes shall be tested in accordance with IS: 456 – 1964 (Code of practice for plain and reinforced concrete).
  • The de tensioning shall be done by slowly releasing the wires, without imparting shock or sudden load to the poles. The rate of de tensioning may be controlled by any suitable means either mechanical (screw type) or hydraulic.
  • The poles shall not be de tensioned or released by cutting the pre stressing wires using flames or bar croppers while the wires are still under tension.

Separate eye-hooks or holes for PCC Pole:

  • It shall be provided for handling and transport, one each at a distance of 0.15 times the overall length, from either end of the pole.
  • Eye-hooks, if provided, should be properly anchored and should be on the face that has the shorter dimension of the cross-section. Holes, if provided for lifting purposes, should be perpendicular to the broad face of the pole.
  • Stacking should be done in such a manner that the broad side of the pole is vertical. Each tier in the stack should be supported on timber sleepers located at 0.15 times the overall length, measured from the end. The timber supports in the stack should be aligned in a vertical line.
  • Poles should be transported with their broad faces placed vertically and in such a manner that shocks are avoided. Supports should be so arranged that they are located approx. at a distance equal to 0.15 times the overall length from the ends.
  • The erection of the pole should be carried out in such a way that the erection loads are applied so as to cause moment with respect to the major axis. i.e. the rope used for hoisting the pole should be parallel to the broader face of the pole.

Testing of PCC Pole:

Transverse Strength Test

  • Poles made from ordinary Portland cement shall be tested only on the completion of 28 days and poles made from rapid-hardening cement only on the completion of 14 days, after the day of manufacture.
  • The pole may be tested in either horizontal or vertical position. If tested in horizontal position, provisions shall be made to compensate for the overhanging weight of the pole, for this purpose the over-hanging portion of the pole may be supported on a movable trolley or similar device.
  • The pole shall be rigidly supported at the butt end for a distance equal to the agreed depth of planting i.e. 1.5 M.
  • Load shall be applied at a point 600 mm from the top of the pole and shall be steadily and gradually increased to design value of the transverse load at first crack. The deflection at this load shall be measured.
  • A pre stressed concrete pole shall be deemed not to have passed the test if visible cracks appear at a stage prior to the application of the design transverse load for the first crack.
  • The load shall then be reduced to zero and increased gradually to a load equal to the first crack load plus 10% of the minimum ultimate transverse load, and held up for 2 minutes.
  • This procedure shall be repeated until the load reaches the value of 80 per cent of the minimum ultimate transverse load and thereafter increased by 5 per cent of the minimum ultimate transverse load until failure occurs. Each time the load is applied, it shall be held for 2 minutes.
  •  The load applied to pre stressed concrete pole at the point of failure shall be measured to the nearest five Kilograms.
  • The pole shall be deemed not to have passed the test if the observed ultimate transverse load is less than the design ultimate transverse load.

Measurement of Pole Cover for PCC Pole:

  • After completion of the transverse strength test, the sample pole shall be taken and checked for cover.
  • The cover of the pole shall be measured at 3 points, one within 1.8 meters from the butt end of the pole, the second within 0.6 meter from the top and the third at an intermediate point and the mean value compared with the specified value.
  • The mean value of the measured cover should not differ by more than(±)1 mm from the specified cover. The individual values should not differ by more than (±) 3 mm from specified value.
  • If these requirements are not met, the workmanship with reference to aligning of the end plates and pre stressing wires and assembly of moulds should be improved and inspection at pre-production stage tightened suitably.

Marking for PCC Pole:

  • The pole shall be clearly and indelibly marked with the following particulars either during or after manufacture but before testing at a position so as to be easily read after erection in position.
  1. Month and year of manufacture
  2. Transverse strength of pole in Kg.
  3. Maker’s serial No. and mark

Main Points should be look after for Overhead Line Installation:

Overhead lines:

  • The general precautions during storage and handling of shall be taken in accordance with relevant IS code.
  • While laying the conductor shall betaken from top of the drum and the repeated in the direction of arrow on it.. Care shall be taken to avoid contact with steel works, fence, etc by giving soft wood protection, using wooden rollers.
  •  Proper tools shall be used during stringing work. During stringing operation standard sag table or chart shall be followed and care shall be taken to ensure that there are no kinks in the conductor. Joints in conductors shall be staggered. Mid span joints in conductors shall be avoided.
  • After stringing the conductor, it shall be clamped permanently with shackle or strain clamps. An angle or section shall be selected while pulling up conductors.

Jumpers:

  • While stringing, sufficient length shall of conductors be kept at shackle terminations for making jumpers. Jumpers shall be neat and as far as possible symmetrical to run of conductors. These shall be made to prevent occurrence of faults due to wind or birds. PG clamps may be preferred to binding of conductors at jumper location or service taps.

Cross Arms :

  • The cross arms shall be made of MS Structural steel. The length of cross arms shall be suitable for accommodating the number of insulators on them with spacing of conductor. A gap of minimum 50 mm shall be left from the center of pin hole to end of cross arm on either side. The cross arm shall be complete with pole clamp made of MS flat of size not less than 50 x 6 mm with necessary nuts, bolts, washers, etc. The length of cross arm for carrying guard wires shall always run not less than 300 mm beyond outer most bare conductor of configuration.
  • Cross arms shall be properly clamped to the support taking into consideration the orientation of lines.

Porcelain insulators and fittings:

  • The porcelain insulators shall be confirming to IS 731 – 1971 for overhead lines. This shall be glazed, crack / burr free.
  • The insulator shall have adequate mechanical strength, high degree of resistance to electrical puncture and resistance to climatic and atmospheric attack.
  • All iron parts shall be hot dip galvanized & all joints shall be airtight. Pin insulators / shackle  insulators / disc insulators shall be erected on cross arms and ‘D’ iron clamp shall be used or as specified by Engineer-in-charge. Shackle insulators shall be used in conjunction with ‘D’ iron clamps when configuration of conductor is vertical.
  • These shall also be erected on cross arm at intermediate support in case of long lines, deviation from straight lines. Care shall be taken that insulators are not damaged during erection.

Binding material:

  • Binding of conductor with the insulator shall be done with soft aluminum wire / conductor. The binding of conductor to insulator shall be sufficiently firm and tight to ensure that no intermittent contact develops. The end of binding wire shall be tightly twisted in close spaced spiral around the conductor to ensure good electrical contact and strengthen the conductor.

Supports and spacing of poles:

  • Support of overhead line shall be of adequate strength confirming in all respects to rules 76 of Indian electricity rules.
  • Pole spacing and clearance between lowest conductor above the ground level across / along the street shall be in accordance with rule 85 of Indian electricity rules. Suitable foundation shall be provided for erection of poles.
  • The foundation shall include excavation in all types of soil and rocks and back filling, RCC, reinforcement, formwork.
  • Excavation for foundations for poles / stay / strut : After the location of supports / stay are pegged accurately, the excavation work shall be taken up and care should be taken while excavating that pits are not oversized.
  • The pit should be excavated in the direction of the line. The depth and size of pit shall be such that normally 1/6th of the length of pole is buried in the ground and suitable for foundation of support.
  • For stay the position of pit shall normally be such stay makes as large an angle as possible with the support and it shall be in the range of 40 to 60 degrees.
  • The length of stay rod shall project 450 mm above the ground level. The pit for strut shall be located at a distance not less than 1.8M from the pole.
  • The depth of pit shall be such that at least 1.2M of the strut is buried in the ground.

Stay / strut:

  • Stay set shall consist of stay rod, anchor plate, bow tightened / turn buckle, thimbles, stay wire and stain insulators.
  •  The stay rod shall be with stay grip in case of turn buckle is used instead of bow tightened. The entire stay set assembly shall be galvanized. The stay wire shall be either 7/4.0 mm diameter or 7/3.15 mm diameter GI having tensile strength of not less than 70 kgf/sq mm and confirming to IS 2141. T
  • The anchor plate shall be of MS galvanized and not less than 300 mm x 300 mm x 6.4 mm thick. The stay rod / buckle rods shall be minimum 16/19 mm diameter galvanized steel rod having tensile strength not less than 42 kgf/sq mm. Minimum length of stay rod and buckle shall be 1800 mm and 450 mm respectively.

Erection stay sets:

  • The anchor plate shall be galvanized MS plate. The stay rod with anchor plate shall be embedded in cement concrete 1:3:6. A stay shall be provided at all angle and terminal poles. Double stay shall be provided at all dead ends and in such case, these shall be as far as possible to be set parallel to each other.

Cage guard:

  • All metal supports of overhead lines and metallic fitting attached shall be permanently and effectively earthed. Cage guard / cradle guard shall be made of 6 SWG GI wire confirming to IS 2633 including netting, stretching and jointing of cage and lacing by 10/12 SWG GI wire, binding by 14/16 SWG GI wire.

Danger boards:

  • All supports carrying HV lines shall be fitted with danger plates confirming to IS 2551 at height of 3 M from ground indicating the voltage of line. The script shall be both in ‘English/Hindi’.

Anti climbing devices:

  • Necessary arrangement for preventing unauthorized persons from ascending any of the supports and structure carrying HV lines without the aid of ladder or special appliance shall be made.
  •  Unless otherwise specified barbed wire confirming to IS 278 having four points barbed spaced 75 +/- 12 mm apart shall be wrapped helically with a pitch of 75 mm around the limb of support and firmly commencing from the height of 3.5 M and up to 5 or 6 M as directed by the engineer.

Lightning arrestor:

  • Lightning arrestor suitable for HT lines shall be installed one unit per phase at terminations, transformer stations, etc.
  • The devices shall be connected ahead of fuse provided if any. Independent earth electrode shall be provided for LA.
  • The earth lead from earth electrode to LA shall be continuous. The LA shall confirm to IS 3070 and shall be non linear distribution class.
  • The LA shall be non-linear type, distribution class, outdoor type suitable for effectively earthed system. The LA shall consist of line terminal stud, earth terminal stud, number of spark gaps in series with non-linear resistor, the whole assembly housed inside a hermetically sealed porcelain bushing.
  • Neoprene rubber gasket shall be provided between metal caps and porcelain bushing. Non-linear resistor shall be silicon carbide blocks metalized at both ends to ensure good electrical contact between terminals, non-linear resistor & spark gaps.
  • Mounting bracket shall be hot dip galvanized suitable for mounting LA on structure.

Cable Laying Direct in Ground:

  •  The method shall be adopted where the cable route is through open country, along road / lanes, etc and where no frequent excavations are encountered and re excavation is possible without affecting other work.

Width of trenches:

  • The width of trench for laying single cable shall be 35 cm Where more than one cable are to be laid in the same trench in horizontal formation, width of trench shall be increased such that the inter-axial spacing between the cables for 415 volts shall be 20 cm and for 11 shall be 35 cm.

Depth of trenches:

  • Where cables are laid in single formation, the total depth of trench shall not be less than 75 cm for cable up to 1.1 KV grade and shall not be less than 120 cm for cable above 1.1 KV grade. Wherever more than one tier formation is unavoidable and vertical formation is adopted, the depth of trench shall be increased by 30 cm for each additional tier to be formed.

Protective covering:

  • Cable laid in trenches shall have covering of clean dry sand not less than 170 mm above the base cushion of sand before the protective cover is laid.
  • The cables shall be protected by B class/second class brick of not less than 20 cm x 10 cm x 10 cm or protective cover placed on top of the sand and both sides of cable for full length of the cable to the satisfaction of Engineer-in-charge.

Back filling:

  • The trenches shall be back filled wit excavated earth free from stones or other scrap edged debris and shall be rammed and watered, if necessary, in successive layers not exceeding 300 mm unless otherwise specified.

Route marker:

  • Route marker shall be provided along straight runs of cables and at points of change in direction as approved by Engineer-in-charge and in general at intervals not exceeding 100 meters in straight run. Route marker shall be made out of 100 mm x 100 mm x 5 mm GI/Al plate bolted or welded on 35 mm x 35 mm x 6 mm MS angle iron of 600 mm long.
  • Such route markers shall be mounted and grouted parallel to and 0.5 meter away from the side of trench. The work “cable” with voltage grading and size of cable shall be inscribed on the marker.

Advertisements

Tampering Methods of Energy Meter


Tampering Method of Electrical Energy Method:

  • Following Description is only for awareness regarding Electrical Energy Theft. Do not use these techniques otherwise You may be booked under Electrical energy theft act 135.

Sub Station Abstracts


Sub Station Equipments and Safety Clearance

Rating of Lighting Arrestor:

  • Size of L.A = 1.5 X Phase to Earth Voltage    OR   
  • Size of L.A =1.5 X system Voltage/1.732       OR
  • Size of L.A = 0.81 X highest System Voltage

Lighting Arrestor Protection Radius:

  • Protection Radius (Rp) = Sqrt (H X (2D-H)+L(2D+L))
  • H= Actual Height of L.A
  • D= 20 meter, 40 meter or 60 meter
  • L= V X T (T=Discharge Time & V= 1m/ms)

Creepage Distance:

  • 18 mm to 22 mm /KV for Moderate Polluted Air.
  • 25 mm to 33 mm /KV for Heavily Polluted Air.
  • In HVDC System The value is double from above value.

Lighting Arrestor Rating:

Rated Voltage

Highest Voltage

L.A Rating

132kv

145kv

120kv To 132kv

220kv

245kv

198kv To 216kv

400kv

420kv

336kv

Location of Lighting Arrestor:

Rated Voltage

Max Distance from Equipment

132kv

35 meter To 45 meter

220kv

Closed To Transformer

400kv

Closed To Transformer

 Size of Corona Ring:

Rated Voltage

Size of Corona Ring

Less than 170 KV

160mm Ring Put on HV end

170KV To 275KV

350mm Ring Put on HV end

More than 275KV

450mm Ring Put on HV end

More than 275KV

350mm Ring Put on HV end

 Capacity of Sub Station as per GERC:

Size of S/S

Electrical Load

66 KV

80 MVA

132 KV

150 MVA

220 KV

320 MVA

400 KV

1000 MVA

 Breaking / Short Circuit Capacity of Sub Station:

Size of S/S

Short Circuit Current

66 KV

25 KAmp  for 1 or 3 sec

132 KV

31.5 KAmp  for 1 or 3 sec

220 KV

40 KAmp  for 1 or 3 sec

400 KV

40 KAmp  for 1 or 3 sec

 Fault Clear Time:               

                Size of S/S

Fault Clear Time

66 KV

300 mili Sec

132 KV

160 mili Sec

220 KV

120 mili Sec

400 KV

100 mili Sec

 Normal Type of Conductors:

Voltage

Main Bus

Auxiliary Bus

11KV

Twin ACSR Zebra

ACSR Zebra

33KV

ACSR Zebra

ACSR Zebra

132KV

ACSR Zebra

ACSR Panthers

220KV

Twin ACSR Zebra

ACSR Zebra

400KV

1/14.2 mm Dia Alu Pipe

Twin ACSR Moose

 Number of Disc Insulator:

System

Number

Strength (KN)

11KV

4

120KN

33KV

4

120KN

132KV

10

120KN

220KV

14

70KN

220KV (Anti  Fog)

2 X 15

120KN

400KV (Anti  Fog)

2 X 25

120KN

 Minimum Clearance:

Voltage

Phase to Earth Wire

Phase to Phase

Section Clearance

2.2KV

28cm

33cm

27.45cm

33KV

380cm

43cm

27.7cm

132KV

107cm

12cm

25cm

220KV

178cm

20.6cm

42.8cm

400KV

350cm

40cm

65cm

 Ground Clearance:

                Voltage

Meter

33KV

3.7meter

66 KV

6.1meter

132 KV

6.1meter

220 KV

7.0meter

400 KV

8.8meter

 Conductor Spacing:

Voltage

Highest Voltage

Lighting Impulse Level (Kvp)

Min Clearance

Ground Clearance

Safety working Clearance

Phase to Earth

Phase to Phase

11KV

12kv

70

178mm

229mm

3700mm

2600mm

33KV

36kv

170

320mm

320mm

3700mm

2800mm

132 KV

145kv

550

1300mm

1300mm

4600mm

3700mm

220 KV

245kv

950

2100mm

2100mm

5500mm

4300mm

400 KV

420kv

1425

3400mm

4200mm

8000mm

6400mm

  Earthing Resistance Value:

Particular

Max Earthing Resistance

Power Station

0.5Ω

EHT Sub Station

33KV Sub Station

Double Pole Structure

Tower foot Resistance

10Ω

Distribution Transformer

220KV Sub Station

1Ω To 2Ω

400KV Sub Station

0.5Ω

 Losses in 11 kv Transformer at 75c (As per CBIP):

Transformer

No Load Loss(kw)

Load Loss (kw)

% Impedance

3.15MVA

2.9

20

6.25

4MVA

3.2

27

7.15

5.3MVA

3.9

31

7.15

6.3MVA

4.5

37

7.15

 Losses in 66 kv Transformer at 75c (As per CBIP):

Transformer

No Load Loss(kw)

Load Loss (kw)

% Impedance

6.3MVA

6

40

8.35

8MVA

7.1

48

8.35

10MVA

8.4

57

8.35

12.5MVA

9.7

70

8.35

20MVA

13

102

10.0

 Standard Rating of 66KV Transformer (As per CBIP):

Transformer

KV

Type of Cooling

6.3MVA

66KV/11KV

ONAN

8MVA

66KV/11KV

ONAN

10MVA

66KV/11KV

ONAN

12.5MVA

66KV/11KV

ONAN / ONAF

20MVA

66KV/11KV

ONAN / ONAF

 % Impedance for Transformer (As per IS 2026):

33KV Transformer

66KV Transformer

MVA

%Impedance

MVA

%Impedance

1MVA

5%

6.3MVA

8.35%

1.6MVA

6.25%

8MVA

8.35%

3.15MVA

6.25%

10MVA

8.35%

4MVA

7.15%

12.5MVA

8.35%

5MVA

7.15%

20MVA

10%

6.3MVA

7.15%

16MVA

10%

8MVA

8.35%

25MVA

10%

10MVA

8.35%

31.5MVA

12.5%

MVA

%impedance

Less Than 1MVA

5%

1MVA To 2.5MVA

6%

2.5MVA To 5MVA

7%

5MVA To 7MVA

8%

7MVA To 12MVA

9%

12MVA To 30MVA

10%

More Than 30MVA

12.5%

  Bus Bar Materials:

Description Bus Bar and Jumper Material
400 kV Main Bus 114.2 mm dia. Aluminium pipe
400 kV equipment interconnection 114.2 mm dia. Aluminium pipe
400 kV overhead bus & droppers in all bays. Twin ACSR Moose
220 kV Main Bus Quadruple / Twin ACSR Zebra / Twin AAC Tarantulla
220 kV Auxiliary Bus ACSR Zebra
220 kV equipment interconnection Twin ACSR Zebra / Single ACSR Zebra
220 kV overhead bus & droppers in all bays. Twin ACSR Zebra / Single ACSR Zebra
132 kV Main Bus ACSR Zebra
132 kV Auxiliary Bus ACSR Panther
132 kV equipment interconnection ACSR Zebra / ACSR Panther
132 kV overhead bus & droppers in all bays. ACSR Panther
33 kV Main Bus ACSR Zebra
33 kV Auxiliary Bus ACSR Zebra
33 kV equipment interconnection, overhead bus and droppers:  
(i) Bus coupler & transformer bay ACSR Zebra
(ii) Feeder bay. ACSR Panther
11 kV Main Bus Twin ACSR Zebra
11 kV Auxiliary Bus ACSR Zebra
11 kV equipment interconnection, overhead bus and droppers:  
(i) Transformer bay Twin ACSR Zebra / Single ACSR Zebra
(ii) Bus coupler ACSR Zebra
   

Specification for Rewireable Porcelain Cut Out Fuse Unit


Technical Specification for Rewire able Porcelain Cut Out Fuse Unit

Electrical Characteristics & Performance:

  •  The rated currents of fuse carriers & fuse bases are 16A, 32A, 63A, 100A, 200A, 300A, 400A & 500A.
  • The re- wire able fuses shall comply with IS : 2086 as amended from time to time up to date unless otherwise stated elsewhere in this specification.
  • The rated breaking capacity of the fuses up to 16A rating is 2 KA and for above 16A rating the same shall be 4 KA, at a p.f. not exceeding 0.4 (lag).
  • The fuses wire shall conform to IS: 9962:1981 or latest amendment thereof, if any.
  • The fuses wire shall be surrounded by an asbestos/porcelain tube for tending distribution of temperature symmetrically. However, it may not be necessary for rating up to 100Amps.
  •  The ends of the tubes shall be baffled by the construction of the body & holder so that flame cannot emit.
  • The length of the fuse wire & mass of the terminals shall be so designed to give desired current- time characteristics of the fuse wire.
  • The continuous rating of tinned-copper fuse wire in semi-enclosed fuses shall not be greater than 60% of their minimum fusing current.
  • The fuse shall glow within 30 minutes when carrying 1.9 times its rated current.
  • The fuse shall carry 1.6 times rated current for at least 30 minutes.
  • The fuses unit shall be capable of withstanding the let through fault current corresponding to prospective fault current.
  • The fuse carrier shall be capable to carry following size of fuse wires(tinned Copper Wire):
Rated Current Size of Fuse (mm) Fusing Current
16Amps 0.5 mm 25 Amp
32Amps 0.9 mm 50 Amp
63Amps 1.6 mm 100 Amp
100Amps 2.0 mm 160 Amp
200Amps 2X2.3 mm 300 Amp
300Amps 2X3.2 mm 480 Amp
400Amps 2X3.66 mm 600 Amp
500Amps 2X4.0mm 800 Amp

Technical Specification for L.T Rewire able Porcelain Fuse Unit

Mounting-of Fuse Unit:

  •  The Fuse Unit can be mounted in an enclosed or open state at any angle on a vertical plain without impairing their performance.

Contacts:

  •  The contacts of Fuse Unit shall be robust construction and securely fixed on porcelain fuse base/ carrier and shall conform to the ; provision of IE Rule,1956 with latest amendments.
  • Fixed and Moving Contact materials & other requirements: Annealed Electrolytic Copper duly electroplated with tin or silver to avoid oxidization above 500 C . For fuse up to 100A tin plating shall be used with 8-10 micron thickness of plating.
  • Fixed contacts shall be of spring loaded reversible loop type for base & that for Moving contact (carrier) is knife contact type of ‘U‘SHAPE.
  • The current density of contact material shall not exceed limit as per IS;2086;1993 or other applicable standard .
  • The resistivity of contact material shall be less than0.017 micro ohm/meter.
  • The melting point and specific heat of contact shall be 10800C & 375 J/KGK respectively.
  • The magnitude of temperature rise of contacts at maximum ambient temperature of 400C for fixed & for carrier is 550C.
  • The voltage drop cross contacts with carrier fully engaged with contacts shall not exceed the limit as stated in IS; 2086; 1993 or other applicable standards.
  • The spring material of reversible loop base shall be of phosphor bronze.

Terminal Blocks:

  •  The terminal blocks shall be made of solid brass/solid copper alloy block of adequate mass to keep down the temperature of the fuse unit. The temperature rise of fuse contacts and terminals need be limited to lower values as far as possible up to 100% rated current for continuous operation to keep down the rate of contacts.
  • Terminal blocks shall be of following sectional area and lengths to take cable connections by means of standard terminal screws up to 100A only. Above termination of Incoming/outgoing cables will be made extended copper strips of thickness not below the size specified as follows and also as stated in Annexure.
Rating Min Acceptable Section Area(Including area of Hole) Length (Min) Dia of hole in Terminal Block and in extended Plate Size of Extended Terminal Plate
16 Amps 60 mm2 9 mm. 4.5 mm Nil
32 Amps 80 mm2 9 mm. 5.5 mm Nil
63 Amps 200 mm2 9 mm. 9.5 mm Nil
100Amps 300 mm2 9 mm. 12.6 mm Nil
200 Amps 700 mm2 9 mm. 10 mm (In Ex.Plate) 5 x31 mm2
300 Amps 1000 mm2 9 mm. 12 mm (In Ex.Plate) 6 x41 mm2
400 Amps 1100 mm2 9 mm. 12 mm (In Ex.Plate) 6 x46 mm2
500 Amps 1200 mm2 9 mm. 16 mm (In Ex.Plate) 7 x50 mm2
  •  The hole in the Terminal Block shall be of appropriate diameter to receive Aluminum Conductor of rated current carrying capacity.
  • The brass socket of alum cable should have identical curre4nt carrying capacity of that of the cable. The extended plates should be adequately electro-tinned and provided with hole/brass bolts and nuts/washer for termination of Incoming/outgoing cable.
  • To eliminate hazards of accidentally touching live parts, the extended terminals may be either provided with protective enclosure (for extended pert only)or duly insulated with heat shrinkage PVC Tube.
  • The heat shrinkage PVC covering should be of 1.1 KV Grade.
  • The following are the recommended cable size for different current rating of fuse.
Fuse Rating Size of Aluminum Overall Dia of Conductor
16Amp 1X6 mm2 2.80 mm
16Amp 1X6 mm2 5.10 mm
32Amp 1X35 mm2 7.50 mm
100Amp 1X70 mm2 11.2 mm
200Amp 1X95 mm2 12.50 mm
300Amp 1X120 mm2 (2 No Parallel) 14.5 mm
400Amp 1X185 mm2 (2 No Parallel) 17.5 mm
500Amp 1X300 mm2 (2 No Parallel) 22.5 mm

Withdrawal Force:             

Fuse Rating

Withdrawal Force

16Amp

0.5 To 2.5 Kg

32Amp

1.5 To 5.5 Kg

63Amp

3 To 10 Kg

100Amp

4  To 10 Kg

200Amp

15 To 70 Kg

300Amp

15 To 70 Kg

400Amp

20 To 80 Kg

500Amp

20 To 80 Kg

Insulation Resistance:

  •  The insulation resistance of the fuse carrier & base contacts measured at a voltage of 500V D.C. between the following parts shall be as under;
  • Between live terminals and exposed metal parts-10 Meg.Ohm.
  • Between live terminals and outgoing terminals-10 Meg.Ohm
  • The power frequency withstand value shall be 2 KV r. m. s. for 1 minute for 1-phase 240V, 16A & for all rating of 500A, 3- Ph. ,4- Wire shall be 2.5 KV r. m. s. for 1 minute.

 Constructional Features of the Fuse Unit:

  •  The Fuse unit can be mounted in enclosed or open state at any angle on a vertical plain without comparing their performance.
  • The fuse unit shall be manufactured from the best quality of materials available indigenous.
  • The constructional features of the fuse unit shall be in accordance with the following stipulations in general.
  • One Fuse base made of porcelain containing fixed contact which shall be connected to fixed terminal and shall be so constructed to engage suitably with the carrier contact.
  • The fixed contacts shall be of reverse loop type to prevent any tendency to throughout the fuse carrier under service conditions specified in IS; 2086;1993.
  • The phosphor bronze leaf shall be used to achieve the desired pressure of contacts.
  • One Fuse base made of porcelain containing contacts with fuse element. The carrier contacts shall be suitable for engaging with fixed contact and capable of having a fuse element attached to it.
  • The fuse holder shall be of grip type. The carrier contacts shall be ‘U’ shaped and of knife contact design.

Porcelain:

  •  The fuse and carrier shall be made from good quality porcelain which is made from felspar (It serves as the fluxing or melting constituents), Quarts and chins clay.
  • The thickness of porcelain shall be 15 mm. minimum at fuse base and 20 mm. minimum for the grip of the handle for the fuse carrier.

Thickness of Porcelain:

  •  The fuse base and carrier shall be of robust design so as to impart sufficient mechanical endurance strength and withdrawal force to sustain impact from blown fuse and handling throughout its life.
  • The thickness of porcelain shall be 15 mm. minimum at fuse base and 20 mm. minimum for the grip of the handle for the fuse carrier.

 Marking On Ceramics:

  •  Every fuse carrier shall have marking clearly and indelibly cast, attached or permanently marked in the intended manner outside surface visible to operator.
  • Rated Current.
  • Rated voltage.
  • Size of Fuse Wire.
  • Nature of Supply.
  • Manufacturers Trade/ Brand Name Mark.

 Sealing:

  •  The holes in fuse carriers for fixing contacts shall be filled up with insulating grad ligur/epoxy based compounds to avoid accidental contact with the live parts.
  •  Live parts on the underside of the fuse base shall be either covered by a shield or barrier 3mm. below the surface of the base and covered with a water-proof insulating sealing compound which will not deteriorated or flow at a temperature lower than 1000C.

Low Voltage and High Voltage Cable Testing


Low Voltage and High Voltage Cable Testing

 Low Voltage XLPE Distribution Cables:

Insulation Resistance:

  • Cables shall be tested for insulation resistance with an insulation tester (i.e. Megger) at 1000 Volts for 1 minute.
  • The minimum insulation resistance to earth or between phases shall be 100 meg-ohms.
  • The instrument used for this measurement shall have a minimum resolution of 10 meg-ohms on the 0 to 500 meg-ohm range.
  • At the conclusion of LV insulation resistance testing, the neutrals must be connected to the earth stakes.

Phasing Test:

  • The correct phasing of all LV circuits shall be checked at all positions where the LV cables are terminated into fuse bases and where any LV cable is run from point to point.
  • This test shall be performed with an instrument designed for the purpose. Mains frequency voltage of 240 Volts is not acceptable for this test.
  • The neutral conductor shall be connected to the earth stake for this test.

Continuity Test (resistance of bolted connections):

  • For loop LV systems, a continuity test shall be carried out on each LV circuit to ensure that all bolted connections are complete and adequate. The test shall be carried out as follows:
  • (1)     At the transformer firmly bond all 4 conductors together
  •  (2)   Undertake a continuity test at every point where there is a service provision or open point. In a fused service pillar the bottom row of fuses bases must be the point at which the test is undertaken as that is the furthest extent of the network.
  • The difference between the readings of each phase conductor and the neutral for each individual test shall not be greater than 10% of each other. Any difference greater than this may indicate a loose or dirty connection and will require further investigation.
  • The instrument used for this measurement should have a resolution to the second decimal point in the 0 to 5 ohm range.
  • A typical instrument would be the earth “Megger” type and taking into account the resistance values of the test leads.

Earth Resistance Test:

  • In any overhead or underground network the earth resistance at any point along the length of a LV feeder is to have a maximum resistance of 10 ohms prior to connection to the existing network.
  • In any overhead or underground network the overall resistance to earth Shall be less than 1 ohm prior to connection to the existing network.

 11 KV AND 33 KV XLPE Cables:

Phasing Test

  • The correct phasing of all HV circuits shall be checked at all positions where the HV cables have been terminated.
  • This test shall be performed with an instrument designed for the purpose. 240 Volt mains frequency is not acceptable for the performance of this test. The test may be conducted on either the wire screens or the aluminum conductors.
  • Where the test is performed on the wire screens, they shall be disconnected from earth.

 Outer Sheath Insulation Resistance (Screen wire test)

  • The purpose of the test is to determine soundness of the outer polyethylene sheath against water ingress, mechanical damage and termite attack.
  • Values below 0.5 meg-ohms (500 kΩ) can indicate sheath damage. Values between 1.0 and 10 meg-ohms may not indicate damage in a single location. Fault finding can often be very difficult. In new cables, values of greater than 100 mega ohms are required.
  • The integrity of the outer sheath shall be checked after cables have been buried by an insulation tester (Megger) at 1000 Volts.
  • The test shall be conducted for 1 minute between each wire screen and earth after the cable has been jointed and terminations installed.
  • For cables after repairs, the resistance must not be less than 10 meg-ohms.
  • Where HV cable circuits are cut and joined to new circuits, sheath testing must be carried out on the existing old circuit prior to joining to the new cable.

 HV test on XLPE cables already in service or previously energized

         Except for New Cables, Testing at Voltage greater than 5.0KV is not permitted

  • Studies carried out on DC high voltage testing of XLPE cables now conclude that;
  • DC testing above 5kV of field aged XLPE cables generally increases water tree growth and reduces service life.
  • 5kV is not considered a “High Voltage DC Test”. The test voltages for tests on XLPE cables is now limited to 5kV after in service repairs and 10kV for new installations.
  • A 5kV Megger is suitable for a 5kV test on cables after repairs.
  • The changes to this section will also make it possible for a repaired cable to be tested by repair crews and made available for immediate return to service.

Application

Test Voltage

Criteria

After repairs – Sheath

1kV Megger 1 minute

10 meg-ohms min.

After repairs – Insulation

5kV Megger 1 minute

1000 meg-ohms min.

After repairs – Insulation

5kV DC 1 minute

5.0 μA (micro-amps) max.

 HV test on new XLPE cable:

  •  Prior to the performance of this test, the screen wires must be connected to the permanent earth position.
  • The cable shall be tested at the test voltage and the pass criteria shall be in accordance with the following table:

Application

Test Voltage

Criteria

New cables – Sheath

1kV Megger 1 minute

100 meg-ohms min.

New cables – Insulation

10kV DC 15 minute

1.0 μA (micro-amps) max

New cables – Insulation

10kV DC 15 minute

1000 meg-ohms min.
  • If further repair works are undertaken, and they require additional joints to be installed, the complete HV testing procedure shall be repeated.

Alternative HV Test Requirement on Insulation for 11kV Cables

  • Where it is not practical to conduct a high voltage test, the test requirements for insulation (core to screen wire) may be limited to testing for the condition of “safe to energize”. The following list of circumstances and conditions must be met as a minimum requirement:
  • The cable circuit voltage shall be 11kV,
  • The circuit outage duration shall be not more than 48 hours,
  • The work shall involve extending or repairs to existing circuits,
  • The insulation test shall be applied for 1 minute between each
  • phase core and screen with a 1000 Volt minimum insulation tester (Megger),
  • Typically the test result should be in the order of 1000 meg-ohms.

Paper Insulated Cables:

Tests on LV Cables

  • An insulation resistance test shall be conducted with a 1000 Volt megger. Test results as low as 10 meg-ohms on old cable circuits are common and therefore considered safe to energies.

Test on 11kV and 33kV Cables between Cores and Earth

  • For three core belted cables, the test on any core shall be conducted between the core and lead sheath with the remaining two cores connected to earth.
  • The test voltages and pass criteria shall be in accordance with the table below.

Application

Test Voltage

Criteria

11kV new cables

5kV Megger 1 minute

100 meg-ohms.

11kV after repairs

5kV Megger 1 minute

100 meg-ohms.

33kV – no TF’s connected

5kV Megger 1 minute

1000 meg-ohms.

33kV – with TF’s connected

5kV Megger 1 minute

15 meg-ohms.

66kV XLPE CABLES

Core to Sheath Test after Repairs:

  • After repairs have been carried out, the 66kV XLPE cable shall be energized at power frequency for 24 hours without load. DC testing is not permitted.
  • The cable sheath link box/cross bonding system shall be put into its normal condition.

Outer Sheath Integrity Test:

  • An insulation resistance test between the metallic sheath and earth shall be conducted. The anti-termite barrier must be connected to the metallic sheath and the insulation test performed to earth.
  • The test voltage applied for 1 minute shall be 5kV DC applied with either a high voltage test set or insulation resistance tester (Megger).

References:

  • ETSA TECHNICAL STANDARD
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