Post on 03-Jun-2018
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Introduction
Substation Types
Parts ofSubstation
Major Components
Of Substation
Substatio
ns
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When electricity leaves a power plant (1),
its voltage is increased at a step-up substation (2).
Next, the energy travels along a transmission line to thearea where the power is needed (3).
Once there, the voltage is decreased or stepped-down,at another substation (4),
and a distribution power line (5)carries the electricity until it reaches a home or business
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A substationis a high-voltage electric system facility.It is used to switch generators equipment andcircuits or lines in and out of a system. It also isused to change AC voltages from one level toanother and/or change alternating current to directcurrent or direct current to alternating current.Some substations are small with little more than atransformer and associated switches. Others arevery large with several transformers and dozens ofswitches and other equipment
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Substation Types: Although, there are generallyfour types of substations there are substations
that are a combination of two or more types.
Step-up Transmission Substation
Step-down Transmission Substation
Distribution Substation
Underground Distribution Substation
Substation Functions
Substation Equipment
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A step-up transmission substationreceiveselectric power from a nearby generating facilityand uses a large power transformer to increasethe voltage for transmission to distant locations.
A transmission bus is used to distribute electricpower to one or more transmission lines. Therecan also be a tap on the incoming power feedfrom the generation plant to provide electricpower to operate equipment in the generationplant.
A substation can have circuit breakers that are
used to switch generation and transmissioncircuits in and out of service as needed or foremergencies requiring shut-down of power to acircuit or redirection of power.
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The specific voltages leaving a step-uptransmission substation are determined by the
customer needs of the utility supplying powerand to the requirements of any connections toregional grids. Typical voltages are:
High voltage (HV) ac:69 kV, 115 kV, 138 kV, 161kV, 230 kVExtra-high voltage (EHV) ac:345 kV,500 kV, 765 kVUltra-high voltage (UHV) ac:1100kV, 1500 kVDirect-current high voltage (dc HV):250 kV, 400 kV, 500 kV
Direct current voltage is either positive or negativepolarity. A DC line has two conductors, so onewould be positive and the other negative.
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Step-down transmission substationsare
located at switching points in an electrical
grid. They connect different parts of a gridand are a source for subtransmission lines
or distribution lines. The step-down
substation can change the transmissionvoltage to a subtransmission voltage,
usually 69 kV. The subtransmission
voltage lines can then serve as a source to
distribution substations. Sometimes,
power is tapped from the subtransmission
line for use in an industrial facility along
the way. Otherwise, the power goes to a
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Distribution substationsare located near to
the end-users. Distribution substation
transformers change the transmission orsubtransmission voltage to lower levels for
use by end-users. Typical distribution
voltages vary from 34,500Y/19,920 volts to4,160Y/2400 volts.
34,500Y/19,920 volts is interpreted as athree-phase circuit with a grounded neutral
source. This would have three high-
voltage conductors or wires and one
grounded neutral conductor, a total of four
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Underground distribution substationsare
also located near to the end-users.
Distribution substation transformers
change the subtransmission voltage tolower levels for use by end-users. Typical
distribution voltages vary from
34,500Y/19,920 volts to 4,160Y/2400volts.
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An underground system may consist of these parts:
Figure 10. Underground Distribution Substation
Conduits
Duct Runs
Manholes
High-Voltage Underground Cables
Transformer Vault
Riser
Transformers
From here the power is distributed to industrial, commercial, and residential customers.
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Substations are designed to accomplish the following functions, although not all
substations have all these functions:
Change voltage from one level to another
Regulate voltage to compensate for system voltage changes
Switch transmission and distribution circuits into and out of the grid system
Measure electric power qualities flowing in the circuits
Connect communication signals to the circuits
Eliminate lightning and other electrical surges from the system
Connect electric generation plants to the system
Make interconnections between the electric systems of more than one utility
Control reactive kilovolt-amperes supplied to and the flow of reactive kilovolt-amperes in thecircuits
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The major components of a typical substation are:
Air circuit breakersare used to interrupt
circuits while current flows through them.
Compressed air is used to quench the arc
when the connection is broken.
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Batteriesare used in the substation control
house as a backup to power the control
systems in case of a power blackout
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Bus support insulatorsare porcelain or fiberglass insulators that
serve to isolate the bus bar switches and other support structures
and to prevent leakage current from flowing through the structure or
to ground. These insulators are similar in function to other insulatorsused in substations and transmission poles and towers.
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Capacitor Bank
Capacitorsare used to control the level of
the voltage supplied to the customer byreducing or eliminating the voltage drop in
the system caused by inductive reactive
loads.
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Circuit switchersprovide equipment
protection for transformers, lines, cables,
and capacitor banks. They also are used
to energize and deenergize capacitor
banks and other circuits.
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Concrete foundationsor pads are laid for
all large equipment, support structures,
and control buildings in a substation.
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Conduitsare hollow tubes running from
manhole to manhole in an underground
transmission or distribution system. Theycan contain one or more ducts (See Duct
Runs). They can be made of plastic
(PVC), fiberglass, fiber, tile, concrete, or
steel. PVC and fiberglass are most
commonly used.
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The substation control housecontains
switchboard panels, batteries, battery
chargers, supervisory control, power-linecarrier, meters, and relays. The control
house provides all weather protection and
security for the control equipment. It isalso called a doghouse.
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Control Panels
Control panelscontain meters, control
switches and recorders located in thecontrol building, also called a doghouse.
These are used to control the substation
equipment, to send power from one circuitto another or to open or to shut down
circuits when needed.
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Control wiresare installed connecting the
control house control panels to all the
equipment in the substation. A typicalsubstation control house contains several
thousand feet of conduit and miles of
control wire.
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Converter stationsare located at the terminals of a DC transmission line. Converter
stations can change alternating current into direct current or change direct current to
alternating current. Sometimes converter stations are located at a generation power
plant or at transmission substations. Two unsynchronized AC transmission systems
can be connected together with converter stations.
Converter stations are also found in most substations for converting the emergency
battery back-up system to AC power for use in an emergency.
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Coupling capacitorsare used to transmit communication signals to
transmission lines. Some are used to measure the voltage in
transmission lines. In signal transmission the coupling capacitor is
part of a power line carrier circuit as shown in the schematic below.A coupling capacitor is used in this circuit in conjunction with a line
trap. Line traps can be installed at the substation or on a
transmission line tower.
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Current Transformers
Current transformerscan be used to supply information for
measuring power flows and the electrical inputs for the operation of
protective relays associated with the transmission and distribution
circuits or for power transformers. These current transformers have
the primary winding connected in series with the conductor carrying
the current to be measured or controlled. The secondary winding is
thus insulated from the high voltage and can then be connected to
low-voltage metering circuits.
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Disconnect switchesor circuit breakers are used to isolate
equipment or to redirect current in a substation. Many different types
of disconnect switches are shown below.
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A distribution busis a steel structure
array of switches used to route powerout of a substation.
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A frequency changer is a motor-generator
set that changes power of an alternating
current system from one frequency to oneor more different frequencies, with or
without a change in the number of phases,
or in voltage. Sometimes a converter isused to accomplish this.
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High voltage fusesare used to protect the
electrical system in a substation from
power transformer faults. They areswitched for maintenance and safety.
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Lightning arresters are protective devices for limiting surge voltages
due to lightning strikes or equipment faults or other events, to
prevent damage to equipment and disruption of service. Also called
surge arresters.
Lightning arresters are installed on many different pieces of
equipment such as power poles and towers, power transformers,
circuit breakers, bus structures, and steel superstructures in
substations.
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