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Medium-voltage distribution systems are used in the following:
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Industrial Applications… Mining & Refining, Petroleum & Chemical, Pulp & Paper, and Primary
& Secondary Manufacturing.
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Commercial Buildings
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Residential Installations
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Transportation Applications
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Submarine Cable Systems
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Mining & Refining
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A large electric shovel in an open-pit mine. Its copper, portable
power cable reels and dereels as the shovel moves.
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Electrical cables have played a critical role in the evolution
of mining practices, leading to widespread use of electricity
for powered equipment, lighting, ventilation and so forth. Over
the years, improved insulating and jacketing materials have been
developed to resist the severe physical conditions to which mining
cables are exposed, and provide maximum protection for the conductors.
Mining cables must be tough, withstand severe handling, have good
resistance to oils, grease, moisture and other contaminants, and
for use in underground mines must meet an appropriate flame test.
Mining cables may be divided into two groups. The first is fixed
mining cables, used for the vertical shafts of bore holes, and
for the permanent power distribution underground. The second group
is the portable mining cables, used for the semi-permanent and
temporary power distribution, and the trailing cables supplying
mobile equipment, such as drag-lines, shuttle cars and drilling
machines.
The fixed shaft and bore hole cables are often 5 kV or 15 kV,
depending on the present and future requirements of the mine.
A number of types of cable may be used for this application, including
Teck Cable designed for vertical applications or steel wire armoured
mineshaft cable.
Above-ground open-pit mining involves heavy mobile equipment,
such as shovels, cranes and drag lines, which receive their power
through trailing cables. The cables are subject to severe service
conditions, continuously being reeled and dereeled, and subject
to heat and severe cold. A typical installation, the Athabasca
Tar Sands in Northern Alberta, employs huge electrically-powered
excavation equipment. The units receive power through trailing
cables built to rigid specifications, which must provide a unique
combination of compact size, durability and low-temperature flexibility.
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The reel of copper portable mining cable on the back of the mobile
drilling machine supplies power safely and reliably.
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Petroleum & Chemical
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Copper power distribution cables, 15 kV, in stacked trays at the
Petrosar Refinery, Corunna, Ontario.
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The Petrosar Refinery, a world-scale petrochemical refinery at
Corunna, near Sarnia, Ontario, is an excellent example of the
use of copper cables in this field. Copper conductors were chosen
for this installation because of their reduced size, high resistance
to corrosion and more reliable connections. The main power supply
to the substation is 230 kV, and from there the electrical distribution
is 15 kV to 5 kV to 600/1000 volt. Copper conductor, aluminum-sheathed
cables are used.
The petroleum field includes off-shore oil platforms. They are
veritable power distribution systems within themselves, some of
considerable size with mobile generating units up to 25 kV. Cables
for use in maritime environments frequently are specified to provide
special resistance to the corrosion effects of the saline environment.
Pulp & Paper
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Jacketed Teck Cables are chosen for pulp and paper installations
because of their flexibility and resistance to mechanical damage
and chemical attack.
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The pulp and paper industry makes wide use of Teck Cables. They
are ideal for environments where cables are subject to mechanical
damage and chemical attack. They may be installed in ventilated,
unventilated or ladder-type trays, attached to walls or ceiling
beams, or directly buried, all in dry or wet conditions. Teck
Cables are designed to withstand temperatures down to -40°C (-40°F),
not unusual for pulp and paper sites in Canada, and for maximum
conductor temperatures up to 90°C (195°F).
Non-jacketed Teck Cables are not acceptable for pulp and paper
applications, since a jacket is required for water and corrosion
protection.
Manufacturing
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Teck Cable, 15 kV being pulled into position on overhead cableways,
during a major upgrading of the General Motors electrical distribution
system
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A wide range of primary and secondary manufacturing industries
benefit from the use of electrical power for their facilities
and processes, using many different types of cables. Electricity
is clean, efficient and reliable, and offers control and monitoring
capabilities that are essential for the high technology of modern
production processes.
Norsk Hydro's magnesium plant is located at Bécancour, about 140
km (84 miles) east of Montreal. The plant supplies magnesium in
various forms (ingots, billets, T bars) to the North American
market. Large amounts of electrical energy are required for the
foundry, electrolysis and dehydration processes.
The plant substation has two 136 MVA transformers, each supplied
by a separate independent 230 kV transmission line. Either of
the transformers is capable of supplying the total power requirements
of the plant.
Originally, power distribution from the substation to the plant
was overhead lines. This system was replaced by directly buried
PILC cables to satisfy requirements of safety to personnel and
reliability of power supply to the plant. At one point, the directly
buried PILC cables were routed underneath an existing building
which added to the unique nature of the project.
Another example is at General Motors of Canada, in Oshawa. When
GM embarked on a major upgrading of its electrical system, they
began by adding a third incoming line transformer of 25/45 MVA
at 44/13.8 kV, to the two existing units. Any two of the three
transformers are capable of carrying the electrical load. To interconnect
and extend cable feeders from the transformer substation to the
various centres of the manufacturing complex, a total of nine
new circuits were installed primarily in overhead trays and short
duct sections. Teck Cables were supplied in continuous lengths
of 244m (800ft), on special reels mounted on reel carriers, from
which they were pulled into position on the overhead cableways.
Copper's excellent fatigue strength and tensile strength are assets
during such installations.
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Twelve underground PILC cables supply power to the Norsk Hydro
magnesium plant at Bécancour, Québec, replacing the overhead lines
shown at the right.
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Commercial Buildings
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Two feeders, each consisting of two, wire-armoured copper cables
in parallel, supply power to the substation on the 68th floor
of the Scotia Plaza, in Toronto.
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Towns and cities rely heavily on electrical power. Medium-voltage
cables supply power to multi-storey office buildings, hotels and
commercial complexes, including stadiums, arenas and airport terminals.
In Canada, a large proportion of the distribution systems are
underground.
An example of a commercial building installation, is the Scotia
Plaza, a 69-storey office tower in Toronto, which has two internal
substations. One is located underground where the incoming power
at 13.8 kV is metered. At the main electrical room, secondary
feeders at 600 and 347 volts convey power to the lower part of
the building. Secondary feeders for the upper storeys originate
from the second substation in the 68th floor of the electrical
room. This substation receives power at 13.8 kV from the main
electrical room below, by means of two feeders each consisting
of two steel wire-armoured cables in parallel. The armouring has
stainless steel bands at regular intervals, to resist displacement
during the pulling operation and to improve vertical support.
An interesting commercial power distribution system is in a recreational
park at Île Ste. Hélène, Montreal. The park was created for the
celebration of the 350th anniversary of the founding of Montreal.
Concentric neutral cable, rated at 28 kV, enters the park from
a substation near the main entrance, and feeds switching stations
located in three of the buildings on the site. From the switching
stations, power is supplied for the lighting and all of the electrically-powered
equipment and facilities in the park. About 13 km (8 miles) of
the copper cable were installed to complete the underground distribution
system.
An example of a more unusual installation is the power distribution
system for the CN Tower. It is in two parts, one handling the
ground level and the other the upper level. The Sky Pod, about
340 m (1,120 ft.) above ground, has a microwave transmission level,
and two levels of observation areas. Another level is a two-tier
revolving dining room seating 400 people, and there are two levels
for TV and FM facilities. Level No. 7 is the mechanical floor
containing the electrical system. Copper single-conductor, aluminum-sheathed
cable is used for the main distribution on both the ground and
upper levels. Copper conductors were chosen for space conservation
and terminating reasons.
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Copper single-conductor cables on overhead racks in the tunnel
from the main electrical room to the lower core of the CN Tower.
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Residential Installations
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The main circuits for residential areas are often buried copper
concentric neutral cables, because of the major advantages of
underground systems.
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The main power distribution systems for multi-storey apartment
buildings and condominiums, are similar to those for office towers
and hotels, depending on the size of the structure and the electrical
load. The medium-voltage cable enters the property or building,
and connects to the transformer facilities.
The distribution systems supplying houses and suburban residences
are, more and more, being installed underground for longer life
expectancy, reduced maintenance costs, service uninterrupted by
storms, reduced fire hazards, increased safety and to conserve
valuable land. The main distribution circuits are frequently concentric
neutral power cables. They feed underground transformers at intermittent
points, and power goes to control pedestals, through service entrance
cables to electric meters at the houses.
In rural areas, distribution systems are also being installed
underground. Typically, the overhead system is replaced by 25
kV concentric neutral power cable, buried by modern cable ploughing
equipment, to a minimum depth of 1 metre (about 3 ft.). The underground
cables feed the transformers, from which the cables enter the
farms and houses along the route.
Transportation
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Transportation systems rely on main distribution systems to provide
power at key locations along their routes.
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The forms of transportation which are supplied with electrical
power from medium-voltage distribution systems include subways,
trolley buses, and L.R.T. (Light Rapid Transit) systems.
In subway systems the power is supplied by a complex installation
of cables and wiring. DC power is used for the train, but AC is
used for all the other equipment, including signals, fans, pumps,
heating, lighting and ventilation.
For L.R.T. systems, an excellent example is in Calgary. Unshielded,
XLPE insulated cable, with 500 kcmil copper conductor and PVC
jacket, is used to supply the DC power to the overhead trolley
wire. Due to the voltage drop in the trolley wire, it is necessary
to feed supplementary power from a parallel conductor, throughout
the routes.
In the Vancouver Regional Rapid Transit System, the cars have
linear induction motors in which the "stator" is a coil assembly
inside the car, and the "rotor" is a long flat rail in the centre
of the tracks, extending throughout the system. One of the main
types of cable used is copper-conductor Teck Cable for the power
supply and the other electrical circuits
Submarine Systems
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The Île-aux-Grues installation. A winch-drawn barge supplies the
cable while pulling the submerged, cable-laying plough.
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An example of a submarine cable crossing, which is about 6 km
(about 3.7 miles) long, is at Île-aux-Grues, in the St. Lawrence
River, northeast of Quebec City. It supplies power to the 25 kV
distribution system on the island. The installation is actually
two circuits, about 1 km (about 0.6 mile) apart, each circuit
consisting of three individual cables. The cables were ploughed
2.5 metres (about 8 feet) beneath the surface of the river bed,
using a special submersible cable plough, to ensure that they
were below shifting ice and ships' anchors.
Another submarine cable example, is the 28 kV installation in
Lake Erie, from Leamington, Ontario to the North Bay of Pelee
Island, a distance of about 26 km (about 16 miles). Trenches 3
metres (about 10 feet) deep were excavated 450 metres (about 1,480
feet) out into the Lake from both shores and 75 mm (about 3 inch)
diam. plastic ducts installed. The Cable was manufactured in five
5,500 metre (18,000-foot) lengths, which were spliced together
and then rewound on a specially constructed motorized reel on
the cable-laying barge. The reel weighed about 225 tonnes (250
tons) when full.
A more uncommon submarine application would be the trailing cable
for a floating dredge, such as used to deepen and maintain shipping
channels, create aquatic parks and marinas, and build-up shorelines.
These trailing cables must have minimum electrical losses, be
flexible, highly resistant to moisture, rugged to withstand the
abrasion of rocks, and the stresses of repeated reeling and dereeling.
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Return to Copper Medium-Voltage Power Cables Table of Contents.