Job Title : Senior Engineer/supervisor/surveyor – Transmission line projects Projects

Req Id 24345 – Posted 01/22/2019 – KEC –

KEC – Transmission and Distribution – Itanagar

Sr. Field Engineer required with minimum

8 Years of experience

 

interview question –

what are PRELIMINARY WORKS for Transmission line projects –

1. PRELIMINARY WORKS
   A.Selection of Route
   B.Reconnaissance Survey
   C.Preliminary Survey
   D. Approvals & Clearances for the Line Route

 

HOW THE ROUTE OF TRANSMISSION LINE PROJECTS IS SELECTED ?

 

1.0 CRITERIA FOR ROUTE SELECTION:

1.1 The route of a transmission line is decided from the following main considerations.
a) Shortest length, hence least capital cost.
b) Ease during construction and ease in maintenance of the line (route near roads for
easy approach & accessibility).
c) Requirement of future loads (sub stations) near the proposed route so that the line can
be easily connected.
d) Required separation distance from parallel communication lines (P&T, Railways,
etc.) for meeting the conditions of induced voltage for obtaining PTCC approval.
e) Avoiding of forest areas as well as wild life sanctuaries.
f) Cost of securing and clearing right of way (ROW).
g) Maintaining statutory distances from Airports / Helipads.

 

WHATS are the points to  be avoided as far as possible while selecting the route of the line?

1.2 The following areas are to be avoided as far as possible while selecting the route of the line.
a) Tough inaccessible areas where approach is difficult.
b) Towns and villages, leaving sufficient margin for their growth.
c) Areas subject to floods, gushing nalas during rainy seasons, tanks, ponds, lakes, etc.
and natural hazards.
d) Wooded areas with high trees or fruit bearing trees involving payment of heavy
compensations for cutting of the trees.
e) Swamps and shallow lands subject to flood, marshy areas, low lying lands, river beds,
and earth slip zones, etc. involving risk to stability to foundations.
f) High hillocks / hilly areas / sand dunes and areas involving abrupt changes in levels
and requiring too many long spans.
g) Series of irrigation wells.
h) Rifle shooting areas and other protected areas such as army / defence installations and
ammunition depots.
i) Areas which involve risk to human life, damage to public & private properties,
religious places, cremation grounds, quarry sites and underground mines, gardens,
orchards and plantations.
j) Areas which will create problems of right of way and way leaves.
k) Buildings / Storage areas for explosives or inflammable materials, bulk oil storage
tanks, oil or gas pipelines, etc.

WHAT IS Reconnaissance Survey?

Reconnaissance survey of the transmission line route is to be carried out for deciding upon the most economical line route and the most economical location of towers in view of the high cost per location.

reconnaissance survey is essential for the purpose of establishing control points
and collection of first hand information of various important field data required for
transmission line works. These are as below:
a) Crossing points of major EHV lines (66 kV and above) & details of the lines.
b) Crossing points of Railway Tracks & details of such points.
c) Crossing points of major rivers & details of such points.
d) Type of terrain and nature of soil strata along the line route.
e) Names of major towns.
f) Important villages or towns coming enroute.

how to MEASURE EARTH RESISTIVITY ?

2.1 Measurements of earth resistivity shall be made at every 2 to 3 km along the tentative route of
the transmission line. In case soil characteristics change within 2 to 3 km, the earth resistivity
shall also be measured at intermediate locations wherever such characteristics change. The
megger reading and soil characteristics shall also be indicated in the earth resistivity results.
2.2 Earth resistivity along the route alignment shall be measured in dry weather by the four
electrode method keeping inter – electrode spacing of 50 metres.

what is RIGHT OF WAY:

Electricity Act, 2003 (earlier, Indian Electricity Act, 1910). The powers are the same as
conferred on the Telegraph Authority under Section 10 of The Indian Telegraph Act, 1885.
Generally, Right of Way is not purchased. As per sub – section 10 (b) of The Indian
Telegraph Act, 1885, RVPN does not acquire any right other than that of user only in the
property under, over, along, across, in or upon which any line or tower is placed for
construction, operation & maintenance of the line while the owner retains the ownership and
use of the land. These powers shall not be exercised in respect of property vested in or under
the control or management of any local authority without the permission of that authority.

what is PRELIMINARY SURVEY ?

it include

1.0 FIXING OF ROUTE ALIGNMENT:
1.1 The alignment of the line route is carried out by survey using a theodolite.
1.2 The following positions are fixed during this survey.
a) Fixing of angle tower positions.
b) Finalizing of crossing points of major EHV lines (66 kV and above) & details of the
lines.
c) Finalizing of crossing points of Railway Tracks & details of such points.
d) Finalizing of crossing points of major rivers & details of such points.
1.3 Measurements of the angles of deviation at all angle / section points are made. Resurvey of
parts of the line route is done wherever it is possible to reduce the number of angle points and
/ or the magnitude of the angles of deviation.
1.4 For the purpose of guidance, the angles of deviation of the different types of towers are as
below:
Tower type Used as Angle of deviation
‘A’ Suspension tower upto 2 degrees
‘B’ Small angle tower upto 15 degrees
‘C’ Medium angle tower upto 30 degrees
‘D’ Large angle & dead end tower upto 60 degrees & dead end
1.5 The length of the line route is also measured. This is done with the use of survey chains or
with the theodolite.
1.6 When using survey chains for measuring the length of the line route, the chain should be kept
horizontal in uneven or undulating land so that horizontal distances are measured and not the
distances along the contours of the land.
1.7 A span is the part of the line between any two adjacent towers. A section is the portion of the
line route with a single span or with a number of consecutive spans between two tension
points with “B”, “C”, or “D” type towers, as applicable.
1.8 The number of consecutive spans between two angle / section points shall not exceed 15
(fifteen) in plain terrain and 10 (ten) spans in hilly terrain.
1.9 The length of any section of the line, i.e., between two angle / section points, shall not exceed
5 km in plain terrain and 3 km in hilly terrain. In case longer sections are available, then cut
points / section points shall be provided by using “B” type tower.
1.10 If the terrain & line route permit, attempts can be made so that the section lengths are, as far
as possible, in multiples of the basic span of the towers for the relevant voltage class.
1.11 The basic spans, which are the design spans for towers, as adopted for the various voltage
levels are as below:
Voltage Level Basic Span
400 kV 400 metres
220 kV 350 metres
132 kV 335 metres
14 Construction Manual for Transmission Lines
2.0 CROSSING OF POWER LINES:
2.1 The crossing of existing power lines shall be at an angle as close to 90 degrees as possible.
2.2 The crossing of the new line over an existing power line is preferably done in the middle of
the span between towers of existing power line where there is maximum sag of the conductor.
When the line to be constructed is crossing another important EHV line for which shutdown
may be difficult, suspension towers in combination with angle / dead end towers, with
extensions as required, may be used.
2.3 The crossing of the new line below an existing power line shall be done at locations where
adequate ground clearance for the new line and the specified clearance from the existing
power line are available. Such crossing shall preferably be in the mid span between towers /
structures of the new power line, where there is maximum sag of the conductor, and near one
of the towers of the crossing span of the existing line for taking advantage of the higher height
of the conductors. These measures reduce the requirement of increasing the height of the
existing line for obtaining the requisite clearance.
3.0 CROSSING OF THE TELECOMMUNICATION LINES:
3.1 The crossing of such lines should preferably be at 90 degrees, but an angle less than 60
degrees is not permissible.
4.0 CROSSING OF RAILWAY TRACKS:
4.1 The angle of crossing should preferably be 90 degrees, but an angle of upto 60 degrees may
be permitted in special cases.
4.2 The crossing span shall be restricted to 300 metres or to 80% of the basic span of the towers
of the relevant voltage class, whichever is less. Angle towers are to be provided on both sides.
4.3 The minimum distance of the towers of the crossing span from the center of the nearest
railway track shall be equal to the height of the tower in metres above normal ground level
plus 6 metres.
4.4 The crossing span over already electrified railway track shall be located at the middle of
overhead equipment span supported by two adjacent traction masts / structures. The distance
between any of the crossing conductors of the line and the nearest traction mast or structure
under the most adverse conditions shall not be less than 6 metres.
4.5 As far as possible, higher levels of land on both sides of the railway track are preferred at
crossings so that there is minimum requirement for increase in the height of the towers. One
tower of the crossing span is located nearer to the Railway track for taking advantage of the
higher height of the conductor on the tower.
4.6 The above paras give only the salient requirements prescribed in the Regulations for Power
Line Crossings of Railway Tracks issued by the Railway Board. The latest issue of the above
Regulations may be referred to for further details.

RIGHT OF WAY:
6.1 The width of the right of way should be kept as per the provisions of the applicable part /
section of the Indian Standard Code of Practice for Design, Installation and Maintenance of
Overhead Power Lines (IS: 5613).
6.2 For lines upto 220 kV, IS 5613 (Part 2 / Sec 2) recommends the following right of way widths
taking into consideration the theoretical requirement of right of way and transport
requirements of maintenance:
Transmission Voltage Recommended Width of Right of Way
132 kV 27 metres
220 kV 35 metres
6.3 For 400 kV lines, the following right of way width, as per RVPN practice, shall be maintained
taking into consideration the theoretical requirement of right of way and transport
requirements of maintenance:
Transmission Voltage Recommended Width of Right of Way
400 kV 52 metres

pit marking drawing ?

what are the CLASSIFICATION OF SOIL:
2.1 The different types of soils are generally classified as under.
2.2 Normal Dry Soil:
Normal dry cohesive soils of any colour, viz., loose murram / sand, etc. which is readily
removable with ordinary spades, pick axes and shovels.
2.3 Hard soil / Hard murram / Dense soil:
Generally any soil such as stiff clay, gravel, cobble stone and black cotton soil which
requires the close application of pick axes or jumpers or scrifiers to loosen it.
2.4 Soft / disintegrated / fissured rock:
Soil consisting of decomposed or fissured rock, hard gravel, kankar, lime stone, laterite or
any other soil of similar nature.
2.5 Hard rock:
Soil in which chiselling, drilling or blasting is required for excavation.
2.6 Sandy soil:
Soil with negligible cohesion which is prone to collapsing when excavated.

what are the  CLASSIFICATION OF SOIL:
2.1 The different types of soils are generally classified as under.
2.2 Normal Dry Soil:
Normal dry cohesive soils of any colour, viz., loose murram / sand, etc. which is readily
removable with ordinary spades, pick axes and shovels.
2.3 Hard soil / Hard murram / Dense soil:
Generally any soil such as stiff clay, gravel, cobble stone and black cotton soil which
requires the close application of pick axes or jumpers or scrifiers to loosen it.
2.4 Soft / disintegrated / fissured rock:
Soil consisting of decomposed or fissured rock, hard gravel, kankar, lime stone, laterite or
any other soil of similar nature.
2.5 Hard rock:
Soil in which chiselling, drilling or blasting is required for excavation.
2.6 Sandy soil:
Soil with negligible cohesion which is prone to collapsing when excavated.
3.0 CLASSIFICATION OF FOUNDATIONS:
3.1 The type of the foundation to be casted at any location depends upon the type of soil, sub –
soil water level and the presence of surface water. While classifying foundations, the worst
conditions are to be considered and not necessarily the conditions prevailing at the time of
inspection. For example, there may be areas where sub – soil water rises when canal water
is let out in the fields raising the sub – soil water level to a considerable degree. Similarly,
the effect of monsoon or when nearby reservoirs are full is also to be considered and not the
conditions prevailing in open season or summer when work is normally carried out. The
classification of foundation is done as given hereunder.
3.2 Normal Dry Foundation:
This is used at locations where normal dry cohesive soils are met and where sub – soil
water is met below the foundation base level.
3.3 Wet Foundation:
This is used at following kind of locations:
a) Where sub – soil water is met at 1.5 metres or more below the ground level.
b) Which are in surface water for long periods with water penetration not exceeding one
metre below the ground level, e.g., paddy fields or sugar cane fields.
70 Construction Manual for Transmission Lines
3.4 Partially Submerged Foundation:
This is used at locations where sub – soil water table is met between 0.75 metre and 1.50
metre below the ground level.
3.5 Fully Submerged Foundation:
This is used at locations where sub – soil water table is met within 0.75 metre below the
ground level.
3.6 Black Cotton Soil Foundation:
This is used at locations where soil is clayey / expansive type, not necessarily black in
colour, extending to the required depth of excavation of the pit, which shrinks when dry &
swells when wet resulting in differential movement of the soil.
3.7 Soft Rock or Fissured Rock Foundation:
This is used at locations where decomposed or fissured rock gravel, kankar, limestone,
laterite or any other soil of similar nature is met. Wet fissured rock foundation is adopted in
case of fissured rock locations where water table is met at 1.5 metre or more below ground
level. A separate foundation design shall be used if water level is encountered at less than
1.5 metre below ground level.
3.8 Hard Rock Foundation:
This is used at locations where chiselling, drilling and blasting is required for excavation of
hard rock type foundations. Rock anchoring is to be provided to resist uplift forces for these
locations.
3.9 Sandy Soil Foundation:
This is used where soil with negligible cohesion is met.

 

so if you read all care fully then you will be crack interview .

some more technical question

What are the step of excavation of pits in foundation and template setting.

What are the calculation for form box for transmission line foundation projects .

 

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Job Title : Senior Engineer/supervisor/surveyor – Transmission line projects Projects

 

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