CENTRAL POWER DISTRIBUTION COMPANY OF AP LIMITED

COPORATE OFFICE : : HYDERABAD

Construction standards for CPDCL

I. Erection of 33/11 KV substation

1. The switchyard must be 300 mm (one foot) high over the highest level of the
adjacent area.
2. Substation steel structures:
152 X 152 mm H type beams / 9.1 m PSCC poles.
Concreting of structure poles shall be of size 0.6x0.6x1.5 mts.
All members shall be with Galvanised M.S. Channel of size 100 X 50 mm. All
M.S. parts to be hot dip galvanized after fabrication.
a) 33 KV Bay width shall be : 4.5 m

b) 11 KV Bay width shall be : 3.5 m

c) Minimum height of over head line take off 6.4 mts (19 feet)
d) 33 KV LA`s : Stn type (for common bus).
e) 33 KV and 11 KV bus conductor shall be of 200 sq mm AAA
Conductor (panther)
f) Erection of breakers with CTs shall be on plinth.
g) Erection of PTR in rails shall be grouted in the plinth.
3. i) 3 nos single phase PT`s to be erected on 33 KV bus on the structures.
ii) 1 no 3-Ph PT to be erected on the structures in 11 KV Bus.
4. 33 KV HG fuse set to be erected on independent structure. Arcing horns shall
be 25 X 6 mm Tinned coated copper flat. Bimetallic connectors to be
provided for giving connection to conductor at both ends. Horn gap shall be 15
inches.
5. Galvanized step Bolts to be provided for the foundation supports of VCB.
6. Station DTR with AB switch and H.G fuse set to be erected on structure.
7. Bolts & Nuts shall be hot dip galvanized.
8. 33 KV 800 A AB switches double break on 33 KV side shall be erected.
9. 11 KV side: 11 KV 400 A AB switch double break shall be erected (Bus side).
10. 11 KV 400 A AB switches for feeders shall be erected.
11. 11 KV line type LA`s to be erected 3 nos to each feeder.
12. Earthing:

i. Every equipment structure shall be independent double earthed with

50 x 6 mm GI flat.
ii. PTR neutral shall be double earthed .One to separate earth pit and
other to earth grid with flexible jumper at neutral of PTR.

iii. AB switch handle shall be earthed through No.8 G I wire closely

wound in the spring shape.
iv. The metallic fencing shall be connected to the earth grid.

v. The perimeter of the earth grid will extend for 1 m more out side
metallic fencing.

vi. The metallic fencing should be connected to the earth grid at each
corner and at points not exceeding 5o meters.
vii. Body, OLTC and tank of PTR shall be earthed.

viii. Star point of the LA`s shall be independent double earthed. Star point

of the capacitor bank shall be independent double earthed.

ix. Minimum 14 nos earth pits shall be provided.

13. a) Earth Electrode : 100 mm dia (inner dia) 10 mm thick and 2.75m long CI
pipe with flange at the top

b) Earth grid connections between electrodes with 75 x 8 mm M.S flat. All joints
shall be of but jointing.

c) Connections between earth grid and equipment (Top connections) with

50 x 6 mm GI flat

d) Back filling with Bentonite soil of 300 mm dia metre around the earth

electrode. (Coke and salt shall not be used as they are corrosive)

e) All junctions and raisers in the grid shall be painted with bitumen paint and
then covered with Hessain tape to avoid rusting.

f) All earth pits shall be provided with CC collars and top covers / brick masonry

14. The combined earth grid resistance shall be less than 1 ohm.

15. Sufficient lighting shall be provided in switch yard and in control room.
16. Fire fighting equipment:

i) 2 Nos. trolly type 6.8 Kgs Co2 fire extinguishers shall be provided at
switch yard.

ii) 2 nos. 2 Kgs Co2 fire extinguishers at control room.

iii) Fire bucket stand with 6 nos. (8-10 Kgs) buckets in SS yard

17. VHF communication system as per requirement.

18. Erection of LT AC panel and DC annunciation panels (as per specification /

requirement). Separate earth pit shall be provided for control panels. Battery
charger shall be erected.

19. Sub-station name board, danger boards and feeder name boards are to be
provided.

20. Single line diagram of substation on wooden board shall be provided in

control room.

21. Office furniture such as table, chairs, wall clock, tool box with tools shall be
provided in the control room along with 2 sets of 3 nos. each set. Earth rods of
15 feet long, 2 pairs of gantlets, 1 set of gum boot, rain coat and a helmet.

22. Watering arrangements shall be provided to the earth pits by laying of 12 mm dia G.I.

pipe.

23. Power and control cables shall be run in separate trenches.

24. Switch yard is to be spread with 20 mm size machine crushed, blue granite metal

(HBG) to a thickness 75 mm, after consolidating the earth mat with roller.

25. Cable trench cover plates shall have two hooks

II. Erection of 33KV, 11 KV and LT over head lines:

1) Survey for erection of over head lines; the following points shall be kept in
view.
a) Shortest route
b) As nearer to the road as possible.
c) No. of angle points shall be minimum
d) Future load growth.

2) Tree clearance shall be made in the route.

3) 33 KV, 11KV and LT lines shall be erected in a proper alignment.

 4) 33 KV and 11 KV lines shall be provided with DP structures at all tension
points, at angle points where deviation is more 10 0 and straight runs
tension points are to be provided at intervals of 1 KM.

5) Locations to be concreted at
i) All angle locations
ii) All tension locations
iii) All tapping poles
iv) Locations in the valley where up lift is anticipated
v) All fully submerged locations.
vi) Every 3rd dry location in a 33 KV line.
vii) Every 5th dry location in a 11 KV line.

6) Size of concrete shall be as below:

S.No. Support Size of concrete

1. 8.0 / 9.1 mts. PSCC pole or RS joist / Rail pole 0.6 x 0.6 x 1.5 mts.
2. 9.5 mts. PSCC / RS joist pole / Rail pole 0.6 x 0.6 x 1.8 mts.
0.75 x 0.75 x 2.0
3. 11.0 mts. spun pole
mts.
0.45 x 0.45 x 1.265
4. Stay set
mts.

Note: Coping shall be provided for RS Joist / Rail pole

7) Planting depth of pole shall be 1/6th of the total length.

8) The stays / struts shall be at the following location

i) Angle locations
ii) Dead end locations
iii) T off points
iv) Steep gradient locations to avoid uplift on the poles.

9) The anchor plate of stay shall be of size 450 x 450 x 75 mm made of RCC
with 1:2:4 ratio and using 20mm granite metal.

10) Suitable guy insulator shall be provided to a stay.

11) Guy insulator to the stay shall be located at 3.5 mt. (vertical distance) from
the ground.

12) 2 nos. guy insulators are to be provided for 33 KV line stay.

13) Size of stay wire shall be as below:

S.No. Voltage Size of wire Safe working load

1. LT 7/2.5 or 7/12 920 Kgs.
2. 11 KV 7/3.15 or 7/10 1450 Kgs
3. 33 KV 7/4 or 7/8 2340 Kgs

14) All the pole fittings are to be fabricated with the approved quality steel and
shall be painted with two coats of standard red oxide paint.

15) All bolts, nuts and washers to be used shall be hot dip galvanized.

16) ‘V’ cross arm for 11 KV lines – 65 x 65 x 6 mm MS angle of 10.5 kgs.

17) ‘V’ cross arm for 33 KV lines – 100 x 5 0mm MS channel of 22 kgs.

18) LT cross arm 65 x 65 x 6 mm MS angle 3-Phase 6 kgs.

1-Phase 3 kgs.
19) Size of flat for clamps

LT - 50 x 6 mm
11 KV - 50 x 8 mm
33 KV - 75 x 8 mm

20) Pins for insulators shall be fixed in the holes provided in the cross arms
and pole top brackets fixed with bottom nuts. Disc insulators are to be
used for 11 KV and 33 KV lines and shackle insulators for LT lines at all
tension points.

21) Stringing, tension and sagging shall be done as per standards.

22) Jumpering shall be done at the tension points with the same line conductor
neatly.

23) Stiffner piece shall be used for binding at all 33 KV / 11 KV pin insulators

24) All the holes required for MS parts shall be drilled suitably (punching / gas
cutting shall be avoided).
 25) Clearances:

1. Clearances along / across the road and cross country (Refer I.E. Rule No.77)

Clearance other than

along the road or across
Voltage Across Along the road
If bare If insulated
Conductor conductor
1. Low Medium Voltage 19 ft. 18 ft. 15 ft. 13 ft.
(5.791 m) (5.486 m) (4.572) (3.963)
2. High Voltage upto 11 20 ft. 19 ft. 15 ft. 3 ft.
KV (6.096 m) (5.791 m) (4.572 m) (3.963)
3. High Voltage above 20 ft. 19 ft.
11 KV upto 33 KV (6.096 m) (5.791 m)

2. Clearance from building (Refer I.E. Rule No. 79)

Vertical Horizontal
Voltage
Clearance Clearance
1. Low medium voltage and 8’ (2.439 m) 4’ (12.218 m)
service line
2. a. For high voltage lines 12’ (3.658 m) 4’ (1.218 m)
upto and including 11000
volts
b. For high voltage lines 12’ (3.658 m) 6’ (1.829 m)
above 33000 volts
3. For extra high voltage 1’ (0.305 m) 1’ (0.305 m)
line
*(For every additional
33000 volts or part thereof)

3. Clearance over the River.

Minimum 10’(3.048 m) over highest flood level for rivers which are not
navigable. For navigable rivers, clearance to be fixed in relation to the tallest
mass, in consultation with the concerned navigation authorities.

4. Tree Clearance

i) For EHVT Lines all tall trees with 40’ (12.19 m) on either side of the
line and all trees which are falling or would fall to be cut.

ii) All bush growth 20’ (6.096 m) on either side to be completely cleared.
Grafted fruit trees which will not grow tall may be left out.
 iii) All branches or leaves which are with 3’ (0.914 m) from the
conductors/ neutral, neutral and earth wires in case of LT Line shall be
cut.

5. Clearance from supporting structure of another line

i) Low or Medium voltage lines 4’ (1.210 m)
ii) High Voltage lines 6’ (1.829 m)
iii) Extra High Voltage lines 9’ (2.744 m)

26) Earthing:
i) For PSCC / RCC poles, the metal cross arms and insulator pins shall be
bonded and earthed at every pole with earthing.

ii) All special supports on which AB Switches etc. are mounted shall be
earthed.

iii) Supports on either side of the road, railway track or river crossing shall
be provided with pipe earthing.

iv) Bentonite soil shall be used for refilling the earth pit. (Charcoal and
salt shall not be used as they are corrosive).

v) The earth resistance shall be less than 2 ohms.

27). Guardings shall be erected at all road crossing locations, communication line
crossings as per standards. All the guardings are to be provided with pipe
earthing.
Miscellaneous items:

a. Location numbers for each pole shall be painted on the pole with
black enamel paint on white enamel painted base. Two coats of paint to be
provided.

b. Pole schedules are to be prepared. All approach roads available

and power line crossing locations shall be marked in the drawings.

c. Anti-climbing devices and enamel danger boards are to be

provided at all railway crossings, road crossings and DP structures.
III. Erection of Distribution Transformer

1) The SP structure pole shall be concreted for a size of 0.6 x 0.6 x 1.5m for
8m / 9.1m PSCC pole
2) AB switch shall be erected with struts for single pole structure.

3) AB switch shall be earthed on the structure and at the handle.

4) 1-Phase DTR shall be earthed with 50 mm dia., 10 mm thick and 2.5 mts.
long 1 no. CI pipe with 25 x 4 mm GI flat.

5) Channel cross arm with insulator shall be fixed between AB switch and
HG fuse set on SP structure (for vertical AB switch) for jumbering
support.

6) HG fuse horn gap shall be 8 inches.

7) LT Cable shall be run on M.S. angle cross arms on the structure pole with
wooden / PVC cleats.

8) Distribution box shall be minimum thickness of 2mm for load bearing

members and 3.15 mm for base channel.

9) The 3-Phase DTR structure shall have 3 nos. earth electrodes out of which
1 no. shall be CI of 50mm dia, 10 mm thick and 2.5 mt. long and 2 nos. of
40 mm dia, 2 mm thick and 2.5 m long GI pipe.

10) Bentonite soil of 50 kgs shall be filled 300 mm width around the electrode
instead of coke and salt as they are corrosive.

11) The DTR neutral, body shall be earthed with GI flat of size 25x4 mm.

12) Lightning arrestors shall be connected to the DTR and earthed.

13) The stay / struts shall be concreted.

14) LT distribution box shall be fixed at a height of 1.5 mts.(5 feets) from the
ground.

15) Distribution Transformer shall be erected on plinth / structure at a height

of 8 feet above ground level. (HT live part shall have 12’ clearance
from the ground level).

16) All earth pits shall be inter connected and provided with CC collars or
brick masonry.

17) The earth electrode shall be fixed 200 mm (about 8 inches) below ground
level.

18) All MS parts shall be painted with 2 coats of standard red-oxide paint.
 19) All bolts, nuts and washers shall be hot dip galvanization only.

20) Bi-metallic connectors shall be provided at HV and LV side of DTR.

IV Laying of 11 KV / LT UG Cables

1. Laying of 11 KV / LT cable shall be done in a trench.

2. Location of trench shall be in the foot path along the road.

3. The minimum depth of laying of any cable from ground

surface to the top of the cable shall be as follows.
i) LT – 0.7mt. depth x 0.45 mts. width
ii) 11 KV – 0.9 mts depth x 0.45 mt. width
iii) 33 KV – 1.1 mts. depth x 0.45 mt. width

4. The bottom of the trench shall be carefully leveled and kept

free from stones.

5. Cables shall be laid in ground on a 50mm sand bed and

covered on top and sides with sand & earth.

6. Protective shabad stones / RCC slabs painted with

APCPDCL shall be placed over the sand on cables and filled with borrowed
earth to the level.

7. Clearance from communication cables shall be 0.4 mts.

8. During the paving of new cable, cable rollers shall be

provided through out the cable trench (to avoid damage to the cable).

9. The minimum safe bending radius for 11 KV, multi core

XLPE cable shall be taken 12D, where ‘D’ is outer dia metre of cable.

10. Before laying the cables their IR values shall be measured

with the megger as a precautionary check against any probable damage.

11. Cable laid across the streets or under railway tracks shall be
through pipes.

12. Cable end termination / straight through joint both indoor

and out door shall be heat shrinkable or push on type of ISI standard.

13. Cable joints

i) Straight through joint shall be done as per standards
ii) End joints

14. House keeping shall be done at the work spot.

 15. Brick layer shall be provided between two cables, if they
laid in one trench.

16. Cable marker plates shall be tied to the UG cable at an

interval of 100 mts.

17. Cable route markers shall be provided above the ground

level at intervals of 900 mts. along the entire route of the cable, cable joints
and turning points.

18. Danger boards shall be provided at all the cable

terminations, tapping points and at all RMUs.

19. All MS parts shall be painted.

20. Permanent records of all cable installations with drawings

shall be made available along with a floppy for guidance.

21. The 5 way & 3 way RMU shall be erected on a plinth (as
per specification).

22. RMU shall be double earthed with 25 x 4 mm GI flat

23. 2 nos. earth pits shall be provided for each RMU.

V. ( Civil Works)

1. Power Transformer Plinth:

a). Earth work excavation 3.3 x 3.3 x 1.2 = 13.06 m3

b). Footing : 3.0 x 3 .0 x 1.5 = 13.5 m3 – Above ground 0.45 m

Below ground 1.05 m
CC(1:3:6) mix with 12mm to 20 mm HBG metal

c). Bedding: 3.3 x 3.3 x 0.15 =1.63 m3

CC(1:3:6) mix with 40 mm HBG metal
d). Nominal reinforcement : Vertical rods with 8 mm rods at 300 mm c/c
e) Nominal reinforcement : Stirrups with 6mm M S rods at 200 mm c/c.

2. Foundation for structures (Girders/RS Joists):

a). Bed concrete CC (1:3:6) mix with 40 mm HBG metal.

Size 960 x 960 x 150 mm.

b). Footing CC (1:3:6) mix with 12 mm to 20 mm HBG metal of size 760 x760x
1350mm.
c). Coping 450 x 450 x 300mm with 1:8 slope.
d). Offset bed concrete to footing 100 mm
3. Plinth for Breaker:

a). Bed concrete of size 1800 x 1800 x 150 mm.

CC (1:3:6) mix with 40 mm HBG metal

b). Footing CC (1:3:6) mix with 20 mm HBG metal of size

1.6 x 1.6 x 1.0 m Above ground: 0.3 m
Below ground = 0.7 m
c). Plastering to sides with CM (1:3)

4. Septic Tank: :

a). 2 x 0.9 x 2.3 m (inner dimensions)

b). Bottom sand filling – 150 mm height
c). Over the sand filling 150mm thick cement concrete 1:3:6 mix with 20 mm granite
metal.
d). Brick masonry with CM (1:6) to be constructed on all sides of a tank

e.) Roof slab of 100mm thick RCC (1:2:4) with 12 mm to 20mm HBG metal.
f.) Opening 0.6 x 0.6m, two way reinforcement with 10mm and 8mm at 150mm c/c.
g). AC Ventilating pipe with cowl 4.5m long 100mm dia.
h). Floor inner sides – Top and upto – 600mm below GL plaster with (1:3) CM thickness
of
20mm.

i). The floor of the tank should be sloped at 1 in 30 towards one end to facilitate cleaning
of deposits and the manhole should be above this.

j). 0.6 x 0.6m CI frame and cover for manhole.

k). SWG pipe line with 150 mm dia shall be laid from the toilet to septic tank.

l). The outlet from the septic tank should be standard `T` fitting of glazed earthen wear
pipe.

m). The center of the outlet pipe should be 150mm below the center of the inlet.

5). AC Rain water pipes:

a). 100 mm dia with required specials such as bends, shoes as fixed with clamps on
teakwood gutties with screw etc pipe joints shall be filled with cement paste.

b). All rain water pipes shall be fixed 40mm clear of extreme outer face of walls with
strong galvanized malleable steel holder bats having 125mm long ragged tail and
circled strap in two pieces with galvanized bolted connections.
6. Specification for drilling and installation of Borewells

a). Required total yield is approximately 40 liters/min.

b). Bore of 150 mm dia.

c). Casing pipe of PVC to suit the 150 m dia bore shall be lowered to a depth of 12M.

d). The PVC rigid (HDPE) pipes of 32 mm dia and 25 mm dia of approved IS standard
shall be provided in the borewell to the required deph including assembly of gunmetal
foot valve.

e). A 20mm dia GI pipe shall be supplied and line laid from the borewell and connected
to the PVC water storage tank installed over control building.

f). Two separate 12mm dia GI pipe lines from the water tank shall be laid. One
connection shall lead to the toilet and the other line shall be laid up to switchyard.

g). 3 nos brass taps 12mm dia of ISI standard shall be supplied and fixed.

CONTROL ROOM

Painting:

Outside walls:

2 coats of cement paint snowcem / durocem over a primary coat (Total 3 coats).

Internal walls:-

2 coats of OBD, over one coat of cement prime paint (only ready mixed paints in
sealed containers).

Wood work:- Two coats of synthetic enamel paint of standard make, over one coat of
primary (Total 3 coats).

Steel work:-Two coats of synthetic enamel paint over one coat of red oxide paint.

RCC roof slab:- CC(1:2:4) mix using 12mm to 20 mm size HBG metal

Waterproof cement compound at 1 Kg/bag.

Necessary slopes towards rain water pipes.

 MATERIALS

Quality of materials (General)

1. Sand to be used shall be composed of hard silicon materials. It shall be clear and of a
sharp angular grit type and free from earthy or organic matter and deleterious
materials.

Only river sand free from calcium chloride or other chlorides and salts which are
likely to promote corrosion of steel shall be used.

2. The aggregate shall be of clean broken hard granite. It shall be hard, close grained
quality. It shall also be as far as possible cube like, preferably angular, but not flaky,
perfectly clean and free from earth, organic or other deleterious matter.