Power Transmission Distribution Line Supports of Electrical Transmission
Power Transmission & Distribution Line Supports of Electrical Transmission Lecture #04 (Week # 03) Engr. Bilal Ahmad Qurtuba University DIKHAN
LINE SUPPORTS OF ELECTRICAL TRANSMISSION • The different types of structure (poles or towers) used for supporting the overhead lines or wires, such types of structures are called line supports. • The line support plays a major role in power transmission. • It kept the proper spacing between the conductors and maintained the conductor at the required distance from its ground parts. • It also maintained the specified ground clearance. These clearances are decided by the electrical and mechanical considerations.
TYPES OF LINE SUPPORTS • The main requirement of the line supports is low cost, low maintenance expense and long life. • The line supports are made up wood, concrete, steel or aluminum. • It is mainly classified into two types: 1. Electrical Pole a) Wood Poles b) Concrete Poles c) Steel Poles 2. Electrical Tower a) Self- Supporting Towers b) Guyed or Stayed Towers
ELECTRICAL POLE • A pole which is used for supporting the small voltage (not more than 115 k. V) transmission lines, such type of pole is called electrical pole. • It is usually made up of woods, concrete or steel. These poles are mainly classified into three types. • Their types are explained below in details;
WOOD POLES • It is one of the cheapest types of line supports and used for lines where spans are short, and tension is low. • The wood poles have the limitations of height and diameter. • The double pole structure of the A or H types is used where greater strength is required. • The strength of these types of constructions varies from two to four times the strength of the single pole. • H-type of construction is usually employed for four terminal poles or those carrying switchgear and transformers.
WOOD POLES • Wood pole has a natural insulating property, and lesser flashovers are likely to take place due to lightning. • One of the drawbacks of wood poles is that their strength and durability cannot be predicted with certainty.
CONCRETE POLES • Concrete pole gave greater strength and used in place of a wood pole. • It has a longer life than that of a wood pole because of little degradation. • Their maintenance cost is low. • Concrete poles are very heavy and are liable to damage during loading, unloading, transportation & erection due to their brittle nature.
CONCRETE POLES • Handlings and transportation difficulties are overcome by the use of prestressed concrete supports which can be manufactured in pieces and then assembled at the job sites. • The weight of pre-stressed concrete poles is more durable than any other type of pole. • The material used is less, and it is more durable than any other types of poles.
STEEL POLES • For low and medium voltage tubular steel poles or Girder steel supports are used. • Longer spans are possible with steel poles. • The poles need to be galvanized or painted periodically to prevent them from corrosion. • Their maintenance expense is high.
ELECTRICAL TOWERS • The electrical tower is defined as the tower which is used for carrying the high voltage (above 230 k. V) transmission lines. • Such types of towers are made up aluminum or steel which gives them strength for supporting the heavy electrical conductor. • High voltage and extra high voltage lines require large air and ground clearances. • They have large mechanical loading and insulation costs. • Such types of towers used very long spans. The long-span construction cuts the insulation cost considerably as fewer supports are to be provided. • Such types of towers are either made up of steel or aluminum and hence the possibilities of breakdown are reduced.
TYPES OF ELECTRICAL TOWERS a. Self- Supporting Towers 1. Tangent Tower 2. Deviation Tower b. Guyed or Stayed Towers 1. Portal types 2. V-types
A. SELF- SUPPORTING TOWERS • Self-supporting towers are divided into two categories; wide-base and narrow-base towers. • In the wide base tower, lattice (crisscross) with the roasted connection is adopted. Each leg has a separate foundation. • The narrow-base designs used as a lattice (crisscross) construction of angle, channel or tubular steel section with bolted or welded connection. Self-supporting tower is also classified as: 1. Tangent Tower 2. Deviation Tower
TANGENT TOWER • It is used for a straight run of the line. • Suspension insulators are used with these towers.
DEVIATION TOWER • It is used in a line where the transmission line changes direction. • Strain insulators are used with these towers. • They have a broader base, stronger members and are costlier as compared to tangent towers. • The narrow-based design requires less steel or aluminum in comparison with a wide base tower, but its cost of foundation is more. • The selection between the two is based on the costs of material, foundations, and right-of-way requirement.
B. GUYED OR STAYED TOWERS • Such types of towers are either portal types or V-types. • Both of them had two supports connected at the top by a cross arm and provided with four guys. • In portal structure, each supports is resting on its foundation, V-support structure the two supports are resting one another on one thrust footing only heavier of type. whereas in at an angle to which is of
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