GIỚI THIỆU CHUNG VỀ HỆ THỐNG ĐIỆN

A power generation plant is a facility designed to produce electric energy from another form of energy, such as: • Heat (thermal) energy generated from: fossil fuels; coal petroleum natural gas solar thermal energy geothermal energy nuclear energy • Potential energy from falling water in a hydroelectric facility • Wind energy • Solar electric

GIỚI THIỆU CHUNG VỀ

HỆ THỐNG ĐIỆN

CH Ứ C N Ă NG CÁC H Ệ TH Ố NG TRUY Ề N T Ả I

VÀ PHÂN PH Ố I Đ I Ệ N N Ă NG

Võ Ngọc Điều

Bộ môn Hệ Thống ĐiệnEmail: vndieu@gmail.com

Chương 1

Power System Structure

- A typical power generation, transmission and distribution system has these

components:

Power Generation Plants

Substations

Step-up Transmission Substation

Step-down Transmission Substation

Power Generation Plants

- A power generation plantis a facility designed to produce electric energy

from another form of energy, such as:

•Heat (thermal) energy generated from:

•Solar electric from solar (photovoltaic) cells

•Chemical energy from:

Power Generation Plants

- There are many different types of electric power generating plants The

major types generating electric power today are shown below

Fossil fuel power plant Hydroelectric power plant

Power Generation Plants

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Solar thermal power plant Nuclear power plant

Power Generation Plants

6

Geothermal power plant

Wind power towers

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- A substationis a high-voltage electric system facility It is used to switch

generators, equipment, and circuits or lines in and out of a system It also is

used to change AC voltages from one level to another, and/or change

alternating current to direct current or direct current to alternating current

Some substations are small with little more than a transformer and associated

switches Others are very large with several transformers and dozens of

switches and other equipment There are three aspects to substations:

Typical substation

Substations

- Substation Types: Although, there are generally four 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

Step-up Transmission Substation

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- A step-up transmission substation receives electric power from a nearby

generating facility and uses a large power transformer to increase the voltage

for transmission to distant locations A transmission bus is used to distribute

electric power to one or more transmission lines There can also be a tap on the

incoming power feed from the generation plant to provide electric power to

operate equipment in the generation plant

- A substation can have circuit breakers that are used to switch generation and

transmission circuits in and out of service as needed or for emergencies

requiring shut-down of power to a circuit or redirection of power

Step-up Transmission Substation

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The specific voltages leaving a step-up transmission substation are determined

by the customer needs of the utility supplying power and to the requirements

of any connections to regional grids Typical voltages are:

High voltage (HV) ac: 69 kV, 115 kV, 138 kV, 161 kV, 230 kV

Extra-high voltage (EHV) ac: 345 kV, 500 kV, 765 kV

Ultra-high voltage (UHV) ac: 1100 kV, 1500 kV

Direct-current high voltage (dc HV): ±250 kV, ±400 kV, ±500 kV

- Direct current voltage is either positive or negative polarity A DC line has

two conductors, so one would be positive and the other negative

Step-up Transmission Substation

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Step-up AC transmission substation

Step-up transmission substation to AC transmission lines

Step-down Transmission Substation

- Step-down transmission substations are located at switching points in an

electrical grid They connect different parts of a grid and are a source for

subtransmission lines or distribution lines The step-down substation can

change the transmission voltage 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

distribution substation

Step-down Transmission Substation

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Step-down power transformer

Distribution Substation

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-Distribution substations are located near to the end-users Distribution

substation transformers change the transmission or subtransmission voltage to

lower levels for use by end-users Typical distribution voltages vary from

34,500Y/19,920 volts to 4,160Y/2400 volts

- 34,500Y/19,920 volts is interpreted as a three-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 wires The voltage between the

three phase conductors or wires would be 34,500 volts and the voltage

between one phase conductor and the neutral ground would be 19,920 volts

- From here the power is distributed to industrial, commercial, and residential

customers

Underground Distribution Substation

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- Underground distribution substationsare also located near to the end-users

Distribution substation transformers change the subtransmission voltage to

lower levels for use by end-users Typical distribution voltages vary from

34,500Y/19,920 volts to 4,160Y/2400 volts

- An underground system may

consist of these parts:

- From here the power is distributed to

industrial, commercial, and residential customers

Underground Distribution Substation

Conduits

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-Conduits are hollow tubes running from manhole to manhole in an

underground transmission or distribution system They can contain one or

more ducts (SeeDuct Runs) They can be made of plastic (PVC), fiberglass,

fiber, tile, concrete, or steel PVC and fiberglass are most commonly used

Conduit

Duct Runs

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-Duct runs are hollow tubes running from manhole to manhole inside a

conduit (see conduits) in an underground system They are of various sizes

usually from 2 to 6 inches in diameter Electrical cables are run through ducts

and the ducts are sized accordingly The diameter of a duct should be at least

1/2 to 3/4 inch greater than the diameter of the cable(s) installed in the duct

They can be made of plastic (PVC), fiberglass, fiber, tile, concrete, or steel

PVC and fiberglass are most commonly used

Duct run within conduit showing

drainage in both directions

Conduit on a grade

Manholes

- A manholeis the opening in the underground duct system which houses

cables splices and which cablemen enter to pull in cable and to make splices

and tests Also called a splicing chamber or cable vault

Manholes

Manhole cover

High-Voltage Underground Cables

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-High-Voltage underground cables are constructed in many different ways, but

are usually shielded cables They are made with a conductor, conductor-strand

shielding, insulation, semi-conducting insulation shielding, metallic insulation

shielding, and a sheath The sheath can be metallic and may then serve as the

metallic insulation shielding and be covered with a nonmetallic jacket to

protect the sheath This sheath helps to reduce or eliminate inductive reactance

Such cables are commonly used in circuits operating at 2400 volts or higher

High-voltage underground cables High-voltage underground cables

Transformer Vault

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- A transformer vault is a structure or room in which power transformers,

network protectors, voltage regulators, circuit breakers, meters, etc are

housed

An underground transformer vault

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- A riseris a set of devices that connects an overhead line to an underground

line A riser has a conduit from the ground up the pole where potheads are used

to connect to the overhead lines

Transformer - Underground

- An underground transformer is essentially the same as an aboveground

transformer, but is constructed for the particular needs of underground

installation Vault type, pad-mounted, submersible, and direct-buried

transformers are used in underground systems Pad-mounted transformers are

installed on a concrete pad on the surface near the end-user

Pad-mounted transformer for underground system Transformer in underground vault

Substation Functions

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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 the circuits

Substation Equipment

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Air Circuit Breaker Distribution Bus Potheads

Batteries Duct Runs Power-line Carrier

Bus Support Insulators Frequency Changers Power Transformers

Capacitor Bank Grounding Resistors Rectifiers

Circuit Switchers Grounding Transformers Relays

Concrete Foundation High-Voltage Underground Cables SF6 Circuit Breakers

Conduits High-Voltage Fuses Shunt Reactors

Control House Lightning Arresters Steel Superstructures

Control Panels Manholes Supervisory Control

Control Wires Metal-clad Switchgear Suspension Insulators

Converter Stations Meters Synchronous Condensers

Coupling Capacitors Microwave Transmission Bus

Current Transformers Oil Circuit Breakers Vacuum Circuit Breakers

Disconnect Switches Potential Transformers

Air Circuit Breakers

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- Air circuit breakers are used to interrupt circuits while current flows through

them Compressed air is used to quench the arc when the connection is broken

Air circuit breaker

Batteries

- Batteries are used in the substation control house as a backup to power the

control systems in case of a power blackout

Backup batteries in the control house

Bus Support Insulators

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- Bus support insulators are 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 insulators used in substations and transmission

poles and towers

Bus support insulators

Capacitor Bank

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- Capacitorsare used to control the level of the voltage supplied to the

customer by reducing or eliminating the voltage drop in the system caused by

inductive reactive loads

Capacitor bank, end view Capacitor bank, side view

Circuit Switchers

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- Circuit switchers provide equipment protection for transformers, lines,

cables, and capacitor banks They also are used to energize and deenergize

capacitor banks and other circuits

Circuit switchers Circuit switcher

Concrete Foundations

- Concrete foundations or pads are laid for all large equipment, support

structures, and control buildings in a substation

Concrete foundation - step-up transmission

substation

Concrete foundations

Control House

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-The substation control housecontains switchboard panels, batteries, battery

chargers, supervisory control, power-line carrier, meters, and relays The

control house provides all weather protection and security for the control

equipment It is also called a doghouse

Control Panels

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- Control panels contain meters, control switches and recorders located in the

control building, also called a doghouse These are used to control the

substation equipment, to send power from one circuit to another or to open or

to shut down circuits when needed

Substation control panel Substation control panel, detail

Control Wires

- Control wires are installed connecting the control house control panels to all

the equipment in the substation A typical substation control house contains

several thousand feet of conduit and miles of control wire

Control wire conduit

Control wires

- Converter stations are 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

Converter station in battery room

Coupling Capacitors

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- Coupling capacitors are 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

Power line carrier schematic showing use of coupling capacitors

Coupling Capacitors

Primary coupling capacitor

Substation line traps

Current Transformers

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- 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

- Current transformers are also used for street lighting circuits Street lighting

requires a constant current to prevent flickering lights and a current

transformer is used to provide that constant current In this case the current

transformer utilizes a moving secondary coil to vary the output so that a

constant current is obtained

Current Transformers

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Metering current transformers

Pole type constant current transformer

400 kV current transformer

Disconnect Switches

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- Disconnect switches or circuit breakers are used to isolate equipment or to

redirect current in a substation Many different types of disconnect switches

are shown below

Disconnect switches on an outgoing

Frequency Changers

47

-A frequency changer is a motor-generator set that changes power of an

alternating current system from one frequency to one or more different

frequencies, with or without a change in the number of phases, or in voltage

Sometimes a converter is used to accomplish this

Frequency changers at a transportation substation

Grounding Resistors

- Grounding Resistors are designed to provide added safety to industrial

distribution systems by limiting ground fault current to reasonable levels They

are usually connected between earth ground and the neutral of power

transformers, power generators or artificial neutral transformers Their main

purpose is to limit the maximum fault current to a value which will not damage

generating, distribution or other associated equipment in the power system, yet

allow sufficient flow of fault current to operate protective relays to clear the

fault

Grounding Transformers

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-A grounding transformer is intended primarily to provide a neutral point for

grounding purposes It may be provided with a delta winding in which

resistors or reactors are connected

Grounding transformer - front view Grounding transformer - back view

High Voltage Fuses

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- High voltage fuses are used to protect the electrical system in a substation

from power transformer faults They are switched for maintenance and safety

High voltage fuses in a switch box External switch for high voltage fuses

Lightning Arresters

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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

Lightning arresters on bus structures

Lightning arrester on distribution pole

Metal-clad Switchgear

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- Switchgear can be either for outdoor use or indoor use An outdoor metal-clad

switchgearis a weatherproof housing for circuit breakers, protective relays,

meters, current transformers, potential transformers, bus conductors, and other

equipment An indoor switchgear must be protected from the environment and

contains the same types of equipment as the outdoor type

Outdoor metal-clad switchgear

Outdoor metal-clad switchgear - way view

cut-a-Metal-clad Switchgear

54

Indoor metal-clad switchgear

55

- Various types of metersare found in substation control houses They all are

measuring devices and can be an indicating meter or a recording meter An

indicating meter shows on a dial the quantity being measured A recording

meter makes a permanent record of the quantity being measured, usually by

tracing a line on a chart or graph Newer recording meters store the information

electronically The photo below left is an indicating amperage meter On the

right is a recording meter

An indicating AC amperes meter Recording power meter

Microwave

- Substations commonly use microwavecommunication equipment for

communication with local and regional electric power system control centers

This system allows for rapid communication and signaling for controlling the

routing of power

- Electric power for microwave transmission comes from special transformers

that reduce incoming transmission voltage to that required for the microwave

system