Mobo Aroroy

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A CONCEPTUAL DESIGN OF A

TRANSIMISSION LINE SITUATED

IN THE ISLAND OF MASBATE

Proposed Old

Masbate-Aror

oy

Transmission

LineDesign 1 ELEN 3254

Submitted By:

Moris I. Mascarias, BSEE V-1

Submitted To:

Engr. Jesus Bien


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SUMMARY

This document specifies the requirements for the construction of overhead transmission line

connecting the Old Masbate Diesel Power Plant and a proposed load end station situated at the

municipality of Aroroy in Masbate Province.

DISCLAIMER

This entire documentation is primarily intended for academic presentation. Calculations

presented herewith are based on data gathered as general facts in relation to the subject of its

study. Surveys that may be presented on foregoing parts of this document are mainly gathered

via research in various websites and in no way intended to be presented as absolute facts. -

Hence, the researcher is open to the possibility of conflict between the data to be presented and

the actual status of the case being posed in this study.


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Documentation of the Proposed

Old Masbate- Aroroy Overhead Transmission Line

CONTENTS

SCOPE ................................................................................................. 1

INTRODUCTION .................................................................................. 1

REFERENCES ....................................................................................... 2

DEFINITIONS ...................................................................................... 3

ROUTE SELECTION ............................................................................. 5

EASEMENTS .......................................................................................... 8

STRUCTURES ........................................................................................ 9

CONDUCTORS ..................................................................................... 16

STRUCTURE SPOTTING ...................................................................... 17

CORONA .............................................................................................. 22

EMF ....................................................................................................... 2


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SCOPE

For the construction of the proposed Old Masbate- Aroroy transmission line to be designed

having a 220 KV operating voltage, this document intends to make use of standard parameters

under the guidance of various accredited references and manuals to come up with an

appropriate and credible construct calculated for its specification. Whenever non-standard

parameters may be presented on the concluding parts, those are not contended as a certain

specification and its modification may be regarded appropriate.

INTRODUCTION

The project documented in this report is the Masbates220 kV Transmission Line that starts from

the Masbate Diesel Power Plant located at Barangay Tugbo in the municipality of Mobo, Masbate

and ends at municipality of Aroroy. The line traverses several barangays along the municipalities

of Mobo, Masbate City, Baleno, and Aroroy. The project would be consisted of five phases. The

phase I connects the line from Masbate Diesel Power Plant, the source of power, and Phase Vjoins to the load-end at its farthest point in Aroroy Town. The Transmission Line construction of

Phases II-IV would be consisted of segments of line of transmission poles situated in various

locations. The construction shall conform to the standards of the criteria as required by the listed

references. Drawings and supporting documents are provided as part of the Design Information.


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REFERENCES

The following documents are used to meet the standard criteria for the proposed construction of

the project featured in this study. These documents are presumed to be the latest guidelines

governing the codes and considerations in transmission line construction.

ENA EG-0 Power System Earthing Guide Part 1: Management Principles ENA

EG1 Substation Earthing Guide Energized Line Working with Polymer

Insulators for Voltages 60kV and AboveIEEE ESMOL

HB 102 Co-ordination of power HB 331 HandbookOverhead Line DesignIEEE Std 987 IEEE Guide for Application Of Composite Insulators

NS 167 Pole PositioningNS220 Guide for Overhead Transmission

ASCE Guidelines for Electrical Transmission Line Structural Loading (Manual No. 74)

1724E-204 Guide Specifications for Steel Single Pole and H-Frame Structures

McGrawHill, Steel Poles and Towers

1724E-214 Guide Specification for Standard Class Steel Transmission Poles

1724E-206 Guide Specification for Spun, Prestressed Concrete Poles and Concrete

Pole Structures

1724E-216 Guide Specification for Standard Class Spun, Prestressed Concrete

Transmission Poles

CL&Ps Transmission line route / configuration alternatives

McGrawHill The Linemans and Cable mansHandbook,

REA Design Manual for High Voltage Transmission Lines (REA

Bulletin 621)

BULLETIN 1724E-200 Designmanual for high voltage transmission lines


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DEFINITIONS

ACSR- Aluminum conductor steel-reinforced (ACSR) is a specific type of high-capacity,high-strength stranded conductor typically used in overhead power lines. The outer strands arehigh-purity 1350 or 1370 aluminum alloy, chosen for its excellent conductivity, low weight andlow cost.

Conductivity- Measure of a material's ability to conduct an electric current.

Corona- An electrical discharge brought on by the ionization of a fluid surrounding a conductorthat is electrically energized. The discharge will occur when the strength (potential gradient) ofthe electric field around the conductor is high enough to form a conductive region, but not highenough to cause electrical breakdown or arcing to nearby objects.

Easements- An easement is a non-possessory right of use or enters onto the real property ofanother without possessing it.

Efficiency - The useful power output divided by the total electrical power consumed a fractionalexpression

NESCNational Electrical Safety Code,published exclusively by IEEE, the NESC sets theground rules for practical safeguarding of persons during the installation, operation, ormaintenance of electric supply & communication lines & associated equipment. It contains thebasic provisions that are considered necessary for the safety of employees & the public under thespecified conditions.

Right of Way- Describes the legal right, established by usage or grant, to pass along a specificroute through grounds or property belonging to another, or a path or thoroughfare subject tosuch a right.

SagAn act of drooping as an effect of elevation.

Truss- A structure that "consists of two-force members only, where the members are organizedso that the assemblage as a whole behaves as a single object.

Mechanical Load -The force exerted on a body on surface while the force is a vector quantitythat possesses magnitude.

Tension- Describes the pulling force exerted by each end of a string, cable, chain, or similarone-dimensional continuous object, or by each end of a rod, truss member, or similar threedimensional objects.

Wind Loading- Analyzes effects of wind in the natural and the built environment and studiesthe possible damage, inconvenience or benefits which may result from wind.

ClearanceOpen space between two elements of a structure to aid in proper placement, tocompensate for minor inaccuracies in modification, or to allow unobstructed movement betweenparts.

ToleranceStructures potential to cope with changes in the following elements of its

surroundings such as a physical dimension, a measured value or physical property of a material,such as temperature, humidity, etc., and remain functioning.


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DESIGN BRIEF

A design brief is prepared to outline each section of the transmission line construction. It includes

the following information.

Project scope and description

Proposed route or end points

System loading requirements

Operating voltage

Line capacity (or in some cases, conductor size and material type for phase conductors)

Maximum design operating temperature of the conductors

Maximum design temperature under wind loading conditions

Minimum design operating temperature of the conductors

Permissible tower material, (e.g. concrete, wood, steel)

Permissible construction type, (e.g. H-pole, standoff insulators, etc.)

Allowance for additional circuits, if applicable

Conductor size and material type for overhead earth wire, where require whether the

overhead earth wire is not required for the full length of line whether an OPGW (optical

pilot ground wire) is required

Required Earthing of structures including maximum pole earth resistance and allowable

Earthing construction (for contestable projects the Client is generally responsible for the

Earthing study)

Protection requirements, where relevant to the scope of works

Any special conditions or arrangements already made for easements, right-of-way and

access to private land

Any special conditions or arrangements already made with the local council or roads

authority for lines on public roads.


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ROUTE SELECTION

In The process of analysis of the routing selection of the 69 KV transmission line from Mobo,Masbate up to its load end station at Aroroy Town, Several objectives are listed which areprimary considerations that advise the erection of the structure. These are;

Cost effectiveness and reliable system of transmission that interconnects to specified

substations and switching stations.

Maximization of the efficiency of the project

Minimization of adverse effects to sensitive environmental resources

Minimization of adverse effects to significant cultural resources

Minimization of adverse effects on designated scenic resources and heritage sites.

Minimization off conflicts with local and national land resource policies Minimization of the need to acquire property by eminent domain

Maintenance of public health and safety

In compliance with the aforesaid criteria, the project route is decided to be as shown below.

Line Route


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Proposed Project Area

The route is identified by avoiding, to such extent possible and applicable, areas where a

transmission line could create significant impacts such as:

Existing high-density residential areas.

Agricultural areas where center pivot irrigation systems are used.

Areas where horizontal clearances are limited because of trees or nearby structures.

Environmentally sensitive sites such as areas with threatened or endangered species of

Animals

Areas of Cultural Significance

Line Route


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The proposed project area is the most reasonable option concluded by the following

considerations.

Public and Social considerations

Distance of transmission centerline to homes and businesses

Distance and impact to public facilities, parks, and trails

Extent of tree and vegetation removal which should be minimized

Distance and to historical sites in the area

Environmental/Cultural considerations

Adherence to national and local regulations

Adherence to sound environmental principles

Avoidance of areas such as burial sites, wildlife protected areas, protected wetlands, andscientific research areas of threatened and endangered species of animals.

Engineering/Construction considerations

Adherence to sound engineering/construction principles

Safety

Reliability

Accessibility

Engineering Considerations

Suitable soil conditions

Required angle structures

Structure size

Span lengths

Potential total line length due to the proposed location

Special construction requirements

Cost effectiveness


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EASEMENTS

Pole positioning and location shall be in accordance with the regulation of Electric Power

research Institute. In this documentation, citation in Ausgrids NS 167, Pole Positioningalso

serves as a basis. Where possible, line routes shall follow existing roads, and be contained within

the reserved area for pole erection.

In the case of the proposed location, savings or other advantages due to reduction of distances

may be obtained by traversing private property or other land not dedicated as public roads. In

this case, negotiations with property owner shall be coordinated.

Several routes where vehicle access is not appropriate to conduct maintenance and repairs shall

be established a right of way.

Re-routing of small segments may be applied in instances of impossibility to establish a

right-of-way due to the unsatisfiable demands of the property owner.

Below are lists of easements permits and authorizations that are meant to be secured;

Private properties Easement from owner and permission to cutdanger trees and for traversing the respectiveproperties

Highways Permit or Agreement with National and localGovernment for the utilization of CentralNautical Highway

Other public bodies Authorization for each respective concerns

City and National Government Building Permits

Instances of joint and common use of poles ofother organizations

Permit or agreement

Wire crossing Permission of utility


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STRUCTURES

Cited references for the contents of the structure analysis are the ASCE Guidelines for Electrical

Transmission Line Structural Loading (Manual No. 74) and the 1724E-204, Guide Specifications

for Steel Single Pole and H-Frame Structures. The aforesaid manuals provide the major criteria

for the design consideration employed in this documentation.

In economic considerations for transmission lines 230 KV and below, wood structures is

apprehended as a more economic choice. However in the case of the Mobo-Aroroy project, in

which longer spans between pole structures should be employed from which heavier loading

situation would occur, steel structures may be considered more economical considering the long

term maintenance cost associated with wood structures.

Economic studies are conducted to determine by comparison, the structure configuration that

may be best employed. - Or materials to be used such as base pole class of wood, steel or

prestressed concrete. Similarly, such studies are also employed to determine efficiency in terms

of material costs, cost of foundations and erection and different structural heights that defines

the structures reliability.

Factors that define the structure reliability are defined as follows:

Strength: Horizontal spans are limited by cross brace, poles, etc. Vertical spans are

limited by cross arms structure strength. For H-frame structures, horizontal and vertical

spans are also limited by pullout resistance for H-frame structures.

Conductor Separation: Conductor separation is intended to provide adequate space

for line crew personnel on poles, prevention of contact and flashover between

conductors.

Clearances-to-Ground: Limits on spans are directly related to height of structures.

Insulator Swing: The ratio of horizontal to vertical span will be limited by insulator

swing and clearance to structure.


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For the purpose of the design featured in this study, which are subjected into various

parameters, primarily defined by the climate condition of the proposed location of the structure,

as well as the environmental concerns posed by the regulating bodies of forest preservation, the

use of steel structures shall be employed.

DESIGN CALCULATIONS:

For a 69 KV, steel transmission tower, the following preliminary values are assumed by

considering NESC heavy loading standards.

DESIGN OF STEEL TOWER

Conductor: ACSR galvanized stranded-steel ground wire. Three no. 1, hard-drawn strandedcopper, 120,000 volts.

Span = 400 ft.Nor. sag = 9 ft. 0 in. Nor. tension (60F.) = 570 lb.Max. Sag = 10 ft. 6 in. Max. Tension (0F., %-in. ice, 8 lb. Wind) =1960 lb.

Elastic limit, No. 1 wire = 2180 lb.


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Wind pressure on wires (%-in. ice, 8 lb. per square foot wind):

%-in. ground wire = 0.917 X 400 = 367 lb.No. 1 conductor = 0.885 X 400 = 354 lb.Wind on pole = 13 lb. per square foot X 1 times exposed area of windward side = 20 lb. perlineal foot.

With the above transverse loading and no broken wires, the compressive stress in the leg abovethe foundation is obtained by taking moments of the forces about the panel point 2 ft. 1 in. abovethe foundation.

Ground wire 367 lb. X 42.4 = 15,560 ft.-lb.Power wires 354 lb. X 39.9 = 14,120 ft.-lb.Power wires 354 lb. X 2 X 37.4 = 26,480 ft.-lb.

Wind on pole = 20 lb. X = 17,980 ft.-lb.

Total bending moment =15,560 ft.-lb. + 14,120 ft.-lb. + 26,480 ft.-lb. + 17,980 ft.-lb.= 74,140 ft.-lb.

Since the lever arm of the resisting forces = 1.9 ft.:

7 4,140 ft.-lb. (1.9 ft. X 2 legs) = 19,500 lb.

Vertical load-steel = 1700 lb.

Vertical load-wires and insulators = 1500 lb.

3200 lb. 4 legs = 800 lb.

Total compressive stress in each leg = 19,500 lb. + 800 lb. = 20,300 lb.

Since 1 L 3 X 3 X M = 1.44 sq. in,

Maximum unit stress in each leg = 20,300 1.44 = 14,100 lb. per square inch.

The transmission tower is to be designed with identical faces on its sides. - Hence, the leg is

restrained from buckling in one direction by the intersecting diagonals, so the maximum l/r will

be computed as follows;

l r = 44in. 0.92 = 48 or;

l r = 22in 0.59 = 37

The ultimate strength of the angle based on the greater value of l/r in the curve in Fig. 33 of

422

2


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McGrawHill, Steel Poles and Towersis 14,100 lb. per square foot; therefore;

Safety Factor = 35,000 14100 = 2.5

STRESS IN DIAGONALS

Assumptions are;

Ground wire = 367 lb. X 1 = 367

Conductors = 354 lb. X 3 = 1062

Wind on pole = 201b. X 6 = 120

Total = 1549 lb.

By web systems of two faces of McGraw Hills transmission poles and towers, the configurationof the tower design, will yield a shear stress of 775 lb. per face. The stress in the diagonal just

below the arm is to equal the shear multiplied by the secant of the slope.

Assuming a 45 slope for the diagonals;

Stress = 775 lb. X (1 cos 45) =1100 lb.

STRESS IN CROSSARMS

The cross arms should be designed for maximum wind loads on both spans or for the maximum

ice and wind loads on one span combined with a longitudinal load due to the breaking of the wire

in the other span. Ice loads are of minimal effect on the project location.- However, still included

in the calculation as set by standards.

CONDITION No. 1

Vertical load (%-in. ice on wires) - 0.770 lb. per foot X 400 ft. = 308 lb.

Insulator and pin = 25 lb. 333 lb.

= 333 lb.

333 lb. X 35 in = 11,660 in.-lb.

Weight of arm = 15 lb. per foot X X 12 = 860 in.-lb.

312

2


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Horizontal load (8 lb. per square foot wind on wire 0.885 lb. per foot X 400 ft.)

= 354 lb. X 12 in = 4,250 in.-lb.

Total bending moment = 16,770 in.-lb.

3in. X 3 in. X 5/16in. X i/c = 2 X 0.95 = 1.90.

Max. Unit stress in cross arm = 16,770 1.90 =8800 lb. per square inch.

CONDITION No. 2

Vertical load (3-in. ice on wires) - 0.770 lb. per foot X 200 ft. = 154 lb.

Insulator and pin = 25 lb.

179 lb.

179 lb. X 35 in =6270 in.-lb.

Weight of arm = 15 lb. per foot X X 12 =860 in.-lb.

Horizontal load (8 lb. per square foot wind on wire -0.885 lb. per foot X 200 ft.) =

177 lb. X 12 in =2120 in.-lb.

Total Bending Moment = 9250 in.-lb.

9250 1.90 = 4900 lb. per square inch,

Longitudinal load:

1960 lb. X X 1.50 = 3720 lb.

3720 1.94 = 1900 lb. per square inch,

3.1

2

2.85

1.50


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Maximum unit stress in cross arm = 4900 + 1900 = 6800 lb. per square inch.

The four legged Pratt Braced towers, designed for a 220 KV transmission line tower will be

employed in this in this project.

TOWER HEIGHT

For Minimum Permissible Ground Clearance (h1) for 220kV;

h1 = 7.01m

Maximum Sag (h2):

For the sag tension calculation for the conductor and earth wire, citation will be made with

provisions of IS: 5613:1985For the following combinations;

-100% design wind pressure after accounting for drag coefficient and gust response factor

at every day temperature

-36% design wind pressure after accounting for drag coefficient and gust response factor

at minimum temperature.


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For the conductors with higher aluminum content normally used for 220kV lines, increased sag

of 2 to 4% of the maximum sag value is allowed.

T22 [T2 + A E (t2- t1) - t1] =

From the above equation, we get sag tension of the conductor (T2).

Sag =

The following combinations of factors will be considered:No Wind, t2 = 00 C

No Wind, t2 = 750 C

No Wind, t2 = 320 C

Full Wind, t2 = 320 C

75% Full Wind, t2 = 320 C

Sag value for different temperatures and for different wind conditions are calculated and the

maximum value of the above combinations + 4% extra will gives the h2 of the conductor.

Vertical Clearance between Ground Wire and Top Conductor (h4): The same procedure isrepeated as done in finding sag of the conductor (h2) but only difference is instead of conductorproperties substitute earth wire properties.

H = h1 + h2 + h3 +h4 = 33.52 m.

FOUNDATION DESIGN

Tower foundations shall be capable of withstanding loadsspecified strength limit state and

serviceability limit state conditions. Pole embedment depths shall be is indicated in NS220,

Ausgrids Overhead Design Manual, and Sections 6.2 Foundations as cited.

AL P E

24T

AL P E

24T

PL

8T


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CONDUCTORS

Conductor materials which used for Mobo-Aroroy overhead transmission lines shall have the

following electrical and physical properties.

The conductor shall have a high conductivity for minimal losses

It should have tensile strength.

It should have a high melting point and thermal stability.

It should be flexible to permit us to handle easily and to transport to the site easily.

It should be corrosion resistance.

As cited in ACSR Manual, Aluminum Wires and Cables, conductor data sheet shall be the

following;

ACSR Code Name Zebra

No. of Conductor/Phase One

Stranding/ Wire Diameter 54/3.18mm AL + 7/3.18mm steel

Total Sectional Area 484.5 mm2

Overall Diameter 28.62 mm

Approximate Weight 1621 Kg/ Km

Calculated D.C Resistance at 20 0C 0.06915 ohm/Km

Minimum Ultimate Tensile Strength 130.32 KN

Modulus of Elasticity 7034 Kg/mm2

Coefficient of Linear Expansion 19.30 x 10-6/ 0C

Max. Allowable Temperature 750C

EARTHWIRE

By NESC Standard for Transmission Conductors, earth wires to be employed as lightning and

high voltage surge arresters for 220 KV line transmission towers shall have the properties as

summarized below.

Material of Earth wire Galvanized steel

No. of Earth Wire One or two *depending on the shielding angle as

required by the location

Stranding/ Wire Diameter 7- 3.15mm

Total Sectional Area 54.55 mm2


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Overall Diameter 9.45 mm

Approximate Weight 428 Kg/ Km

Calculated D.C resistance at 200C 3.375 ohm/Km

Min. Ultimate Tensile Strength 5710 Kg

Modulus of Elasticity 19361 Kg/mm2

STRUCTURE SPOTTING

The specifications of the route alignment of tower structures are profiled through the use of the

Google map imagery of the Masbate province. The output documentation shall be in the form of

digitized route alignment drawing by the utilization of the PLS-CADD, providing the digital

imagery of the terrain modeling along the selected route.

Following considerations are employed in the spotting of locations for the transmission towers

featured in this document;

The alignment of the transmission line shall be economical upon its construction and

access for its maintenance.

Routing of transmission line in protected /reserved forest area should be avoided. In case

that as such is not possible, the cutting down trees shal be kept at minimum.

The number of angle points shall be kept to a minimum.

The distance between the terminal points specified shall be kept shortest possible, and

consistent with the encountered terrain.

Low lying areas, river beds and earth slip zones shall be avoided to minimize risk to the

foundations and towers.

Ground level alignment shall be utilized.

Crossing of communication line shall be minimized and it shall be at right angle. Proximity

and parallel alignment with telecommunication lines shall be eliminated to avoid danger

of induction.

Areas subjected to flooding shall be avoided.

As provided by the REA, Design Manual for High Voltage Transmission Lines, clearances for

220 KV lines shall be of 7 meters at minimum. The ground clearance curve should not touch or

cross the ground line. Besides normal ground clearance, the clearance between power

conductor and objects like other power or telecommunication lines, houses, roads etc., shall also

be checked.


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While crossing over existing power lines, one of the crossing span of the new line is preferably

located near the existing power line, to take advantage of the higher height of the conductors

near the tower. This reduces the necessity of increasing the height of the towers of the new line

for obtaining the requisite clearance. Double suspension tension insulator strings, depending on

the type of the towers shall to be used in the new line on such crossings. Minimum clearances in

meters between lines crossing each other, specified for 220KV shall be 4.58 meters.

A tower schedule is prepared which contains all the information such as location numbers, type

of tower, span length, section length, sum of adjacent spans, weight spans as affected by of one

side as well as both sides under maximum and minimum sag conditions and angle of deviations.

SAG TEMPLATE CALCULATIONS

When calculating maximum sags for new conductors, allowances shall be made for conductorcreep and for minor errors in construction. This additional creep allowance does not have to be

applied to existing conductors which are being diverted or reconstructed.

Conductor: ACSR Zebra (420 mm2)

Construction: 54 Aluminums / 7 Steels / 3.18 mm

PARAMETERS:

Basic Span () : 350 meters

Ultimate Tensile Strength of Conductor (U.T.S.) : 13290 Kg

Overall diameter of the Conductor (d) : 28.62 mm

Weight of the Conductor (w) : 1.621 kg / m

Wind Pressure (P) : 83.38 Kg /m2

Coefficient of linear Expansion () : 19.3 106 per C

Youngs Modulus of elasticity (Final) (Ef) : 0.686 10 6 Kg / cm2

Youngs Modulus of elasticity (Initial) (Ei) : 0.4675 10 6 Kg / cm2

Maximum temperature (Ambient) : 50 C

Maximum temperature (Conductor) : 75 C

Minimum Temperature (Ambient) : (-) 2.5 C

Minimum Temperature (Conductor) : (-) 2.5 C

Normal Temperature : 32.2 C

Area of Cross section of Conductor (A) : 4.845 cm2

Factor of Safety (F.O.S.) (at 32.2 C) : 4

Factor of Safety (F.O.S.) (Otherwise) : 2


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Weight of Conductor per unit area () : = w = 1.621

A 4.845

= 0.334571723 Kg /m / cm2

Minimum Ground Clearance : 7.01 meters

CONDITION: I

Temperature = 32.2 CWind = NILFactor of Safety = 4

Working tension; T1 = U.T.S = 13290F.O.S 4

T1 = 3322.5 Kg

Working Stress; f1 = T1 = 3322.50A 4.845

f1 = 685.75851 Kg / cm2

Loading factor; q1 = P2 + w2 =1 (for no wind; P = 0)W

The working stress is determined by the following formula:

f12(f1k) = 22q12Ef24

k = f122q12Ef24 f12

k= 685.75851(350)2 (0.334571723)2 (1)2 (0.686 106)24 (685.75851)2

= 685.75851833.46049

k = (-) 147.70198

CONDITION: II

Temperature = 75 CWind = NILFactor of Safety = 4

Working tension; T1 = U.T.S = 13290F.O.S 4


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T1 = 3322.5 Kg

Working Stress; f1 = T1 = 3322.50A 4.845

f1 = 685.75851 Kg / cm2

Loading factor; q1 = P2 + w2 =1 (for no wind; P = 0)W


f12(f2(k- t Ef) = 22q12Ef24

f22[f2{147.70198(19.3 106) 42.8 (0.686 106)}]

= (350)2 (0.334571723)2 (1)2 (0.686 106)24

f22(f2+ 714.36542) = 3.919470757 108

f22= 555.553321 Kg / cm2

Working tension; T2= f2 A = 555.553321 4.84 = 2691.656 Kg / cm2

Maximum Sag; s = 2 q28 f2

= (350)2 (0.334571723) (1)8 555.553321

= 9.22 meters

CONDITION: III

Temperature = (-) 2.5 CWind = NILLoading factor; q3 = P2 + w2 = 1 (for no wind; P = 0)

W

Difference of temperature; t =2.532.2 =34.7 C


f32[f3(k t E f) = 22q32E f24

f32[f3{147.70198(19.3 10 6) (34.7) (0.686 106)}]


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= (350)2 (0.334571723)2 (1)2 (0.686 106)24

f32(f3+ 311.71908) = 3.919470757 108

f3= 851.8511701 Kg / cm2

Working tension; T3 = f3 A

= 851.8511701 4.845

= 4127.219 Kg / cm2

Factor of Safety = 13290 = 3.22, hence O. K.4127.2

Maximum Sag; s = 2

q38 f3

= (350)2 (0.334571723) (1)8 851.8511701

= 6.01 meters

For Sag calculation at any span, the following formula can be used.

Sag at any Span = Sag at Basic Span (Span Length)

2

(Basic Span) 2


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CORONA

Corona is defined as a self-sustained electric discharge in which the field intensified ionization islocalized only over a portion of the distance between the electrodes.

During unusual situations in the overhead transmission line when the intensity of the electric

field exceeds the dielectric strength of air, the area around the conductor experiences electricdrilling, which causes increased losses and apparent conductivity.

Corona phenomenon initiates as a hissing noise and is heard and ozone gas is formed which canbe detected and characterized by its color.

The object of this documentation was to obtain data for the choice of conductor to be used ona 220-kv. 60- Cycle line. The results show the effect of weathering of conductors, the type ofconductors of two different diameters, the effect of size of conductor strands and the method ofstranding.

Corona activity on the 220 kV transmission line can generate a small amount of sound energy.Corona also results in a small amount of power loss to the transmission line. The audible noiselevel can increase during foul weather conditions. Water drops may collect on the surface of theconductors and increase corona activity so that a crackling or humming sound may be heardnear a transmission line. Audible noise decreases with distance away from a transmission line.Corona is affected by the voltage of the line, the diameter of the conductor, and thecondition of the conductor and suspension hardware. The electric field gradient is therate at which the electric field changes and is directly related to the line voltage. Theelectric field gradient is greatest at the surface of the conductor. Large-diameterconductors have lower electric field gradients at the conductor surface and, hence,lower corona than smaller conductors, everything else being equal.

In this document the following solutions are proposed to be employed;

Minimize the voltage stress and electric field gradient. This is accomplished bymaximizing the distance between conductors that have large voltagedifferentials, using conductors with large radius, and avoiding parts that havesharp points or sharp edges.

Surface Treatments: Corona inception voltage can sometimes be increased byusing a surface treatment, such as a semiconductor layer, high voltage putty orcorona dope.

Employ proper geometric configuration of the conductors.

Eliminate unwanted voltage transients in the line, which can cause corona tostart.

By increasing the diameter of the conductor: Diameter of the conductor can beincreased to reduce the corona discharge effect.

Using Bundled Conductors, multiple conductors per phase are used in the 220 KV

line. This is a common way of increasing the effective diameter of the conductor,which in turn results in less resistance, which in turn reduces losses.


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MAGNETIC FIELDS

A double circuit 220kV transmission lines crosses several plane land surfaces in Masbateprovince and connects the Aroroy Substation and the Old Masbate diesel power plant inthe province. Each line is on one side of the tower and consist of three phase with eachphase consisting of a bundle of two conductors. The lines also have two conductors onthe top of the towers (called earth wires) that do not carry current but act as to shield

the line from lightning current surges.

Considering the EMF-Effect associated with the proposed design, the followingmeasures are conducted.

- The undergrounding of the power lines with the required transition enclosures: and

- Retaining the power lines above ground mounted on poles, with the slight realignmentof the easement.

Electric fields are created by the electric charges on high voltage equipment. They

diminish rapidly with distance and are shielded by common materials such as trees orbuildings. Electric fields have not been identified as a source of major safety issues.However, they can potentially cause a number of effects such as audible noise, RF noiseinterference and visible spark.Electric field strengths associated with 220 KV transmission lines typically are in therange of 1 - 3 kV/m under the power lines - contact shocks to occur. At the edge of thetransmission line easement, typically 20 to 30 meters from the power line poles, theelectric fields are typically in the range of 0.1 - 1.0 kV/m.

It is also possible for voltages to be induced in long metallic structures that are alignedso that they run parallel to the transmission lines. However, the induction is significantly

small; running through lengthy structures that makes it becomes dissipated andgenerally wontreach the bottom part that would affect the public.

There are a number of ways to reduce EMF effects: F irstly, as the magnitude of the EMFis inversely proportional to the distance from the current carrying elements, one canincrease the distance of the public from the conductors. Hence by increasing the widthof an easement, increasing the height of a transmission line or increasing the distanceto the boundary of the terminal station will reduce the magnetic field strengthmagnitude. Higher transmission poles will produce a lower EMF, so there is a potentialtrade-off between the height of a transmission pole and its effect on visual amenity andthe reduction in EMF. There are practical limits to the physical height of poles and sizeof the easements and substation sites so this solution, whilst generally practical, doesnot suit every situation.

More compact structures have lower EMF as better cancellation of the fields occurs if theconductors are close together but there are engineering limits to how close conductorscan be place to each other.

EMF shielding is possible using materials of high magnetic permeability. However, thissolution is expensive and usually only used to solve specific local problems.

Other solutions, such as current cancellat ion loops may offer alternative, but less provenoptions for addressing magnetic field problems.


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The various solutions are applied during detailed design. Generally speaking physicalseparation will provide appropriate EMF levels and this particularly applies totransmission lines through rural areas where the lines are well away from areas desedwith people.


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