Introduction
Figure 1. Tower Tower components Transmission Transmission towers support the high-voltage conductors of ov erhead power lines, from the generating station switchyard right up to the source substations and satellite substations located near populated areas. Their shape, height and sturdiness (mechanical strength) depend on the stresses to which they are exposed. Towers do not transmit electricity themselves unless lightning stries the ground wire strung along the top of the structure. This cable is designed to protect conductors by allowing lightning discharges to reach the ground through the tower.
Types Waist-type Waist-type tower
Figure !. "aist-type tower
Figure #. "aist-type tower
This is the most common type of transmission tower. $t%s used for voltages ranging from 11& to '# . *ecause they%re easily assembled, these towers are suitable for power lines that cross very uneven terrain.
Double-circuit tower
Figure +. ouble-circuit tower
Figure . ouble-circuit tower
This small-footprint tower is used for voltages ranging from 11& to #1 . $ts height ranges from ! to & metres.
Guyed-V tower
Figure . uyed- tower
Figure '. uyed- tower
This tower is designed for voltages ranging from !#& to '# . $t%s used mainly for power lines leaving the /a rande and 0anic-utardes hydroelectric complexes. The guyed- tower is more economical than the double-circuit and waist-type towers.
Tublar steel pole
Figure 2. Tublar steel pole
Figure 3. Tublar steel pole
Featuring a streamlined, aesthetic shape, this structure is less massive than other towers, allowing it to blend easily into the environment. For this reason, it%s being used more and more in urban centres. 0easuring between !' and + metres in height, it%s suitable for voltages ranging from 11& to #1 .
Guyed cross-rope suspension tower
Figure 1&. uyed cross-rope suspension tower Figure 11. uyed cross-rope suspension tower "ith its simple design, this tower is easy to assemble. $t%s used on some sections of power lines leaving the /a rande complex and supports '#- conductors. This type of structure re4uires less galvani5ed steel than the guyed- tower, maing it lighter and less costly.
Crossings
Figure 1!. 6rossings
Figure 1#. 6rossings
7n overhead line crossing is the crossing of an obstacle8such as a traffic route, a river, a valley or a strait8by an overhead power line. The style of crossing depends on the local conditions and regulations at the time the power line is constructed. verhead line crossings can sometimes re4uire extensive construction and can also h ave operational issues. $n such cases, those in charge of construction should consider whether a crossing of the obstacle would be better accomplished by an underground or submarine cable.
Conductors 6onductors transmit electric power. 9sually conductors are made of aluminum with a steel core that gives the cable its re4uired strength. 6uriously, these conductors are bare: the air around them provides insulation. ;ach conductor is stranded, meaning it consists of several wires twisted together. This maes a conductor more flexible and more exposed to air, a feature that helps coo l the conductor and therefore increase its conductivity. ;lectricity meets resistance when passing through hot metal, a phenomenon that transforms part of the electrical energy into thermal energy, a type of energy loss. 7 conductor bundle is a series of two, three or four conductors always e pt apart by spacers.
ust as effective as?and much lighter than?one single conductor with a +-cm diameter. round wires protect the line against lightning. uy wires are anchor cables which ensure the mechanical strength of the support structure. 1
The corona effect, intensifies when impurities fall on the wires and when the air is very humid. The cracling sound is loudest when it snows or rains. ;lectrons moving between the wires and the air cause the corona effect. This bac-and-forth movement creates a multitude of tiny electrical discharges, which we perceive as a cracling soun d. The higher the voltage, the greater the chance this phenomenon will occur.
Line installation
obsites by crawler carrier. Then the steel tower parts and hardware are delivered to their sites by the same method. ect according to the specific re4uirements of the engineering team. ect, wor begins on restoring the right-of-way and dismantling temporary access roads. 7 tour of the site with the landowner ensures that the restoration wor meets his expectations. 6ompensation is also provided for any losses incurred.
allo- for "ini"u" clearance ,special to-ers are to e designed.*+e "ini"u" clarance aove ground to otto" "ost conductor s+ould e .% "t /0.! "t for every !!v or part t+ereof y -+ic+ t+e voltage of t+e e1ceeds !!K& .2o-ever "ini"u" clearance of .$ "t to ground is to e "aintained
=ow the electric transmission system wors Typical transmission line structures • How dependable electricity reaches you
Transmission lines are sets of wires, called conductors, that carry electric power from generating plants to the substations that deliver power to customers. 7t a generating plant, electric power is Cstepped upD to several thousand volts by a transformer and delivered to the transmission line. 7t numerous substations on the transmission system, transformers step down the power to a lower voltage and deliver it to distribution lines. istribution lines carry power to farms, homes and businesses. The type of transmission structures used for any pro>ect is determined by the characteristics of the transmission lineEs route, including terrain and e xisting infrastructure. Typical transmission line structures • High-voltage (230-kV, 345-kV, 400-kV (DC), 500-kV (DC):
6urrently in 0innesota, the high-voltage system is generally comprised of !#&-iloolt and #+ systems. There are also two direct current (6) lines, one of +&&- and one at &&-.
11- and 11- systems are responsible for transmitting power from the larger transmission system and generation facility throughout the entire state.
Transmission ominal oltage: !- "## $V HVDC Type: Tower Typical Tower =eight: %"&-%'# (eet Typical Bight-of-"ay "idth: %)#-%'# (eet
Transmission ominal oltage: &## $V Type: Tower Typical Tower =eight: *#-%&# (eet Typical Bight-of-"ay "idth: %)#-+## (eet
Transmission ominal Transmission oltage: ,"& $V ominal oltage: +,# Type: Double C$t ole $V Typical Tower =eight: Type: H-.rame %%&-%&# (eet Typical Tower Typical Bight-of-"ay =eight: "idth: )#-*# (eet %"#-%)# (eet Typical Bight-of-"ay "idth: %##-%)# (eet
Transmission ominal oltage: %)% $V Type: /ingle ole Typical Tower =eight: 0#-*& (eet Typical Bight-of-"ay "idth: %##-%&# (eet
Transmission ominal oltage: %%& $V Type: /ingle ole Typical Tower =eight: &&-'# (eet Typical Bight-of-"ay "idth: *#-%,# (eet
Transmission ominal oltage: )* $V Type: /ingle ole Typical Tower =eight: &#-0# (eet Typical Bight-of-"ay "idth: 0#-%## (eet
=ow dependable electricity reaches you 1W23 /143C2
eneration and transmission cooperatives (GTs), lie reat Biver ;nergy, operate power generating facilities. 7t a steam generating plant, the fuel (coal, nuclear or biomass) heats water to mae steam and drive a turbine. $n a combustion turbine, the fuel (gas or oil) is burned and the hot gas drives a turbine. "ind hydro and solar are other forms of energy producers.
High-5oltage transmission lines
Transformers at the generating plant increase the voltage up to a transmission voltage (3 , 11 , !#& , && , ' ), so it can travel long distances over high-voltage transmission lines. GTs operate these lines, which carry the electric energy from the generating stations to the places where electricity is used.
T367/8I//I17 /49/T6TI17 Transformers reduce the electric energy down to a lower voltage (3 , #+ ) maing it suitable for high-volume delivery over short distances.
L1C6L DI/T3I94TI17 /49/T6TI17 Transformers reduce the electric energy down to a lower voltage (3 , #+ ) maing it suitable for high-volume delivery over short distances.
Distribution lines /ines belonging to local electric co-ops carry electricity Large industrial user to transformers that reduce power levels to 1!&H!+& or 0ost industries need !,+&& to +,1& 1!&H!&2 volts for use in schools, farms, small volts to run heavy machinery. They businesses and homes. usually have their own substation at the facility.
