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
8/19/2014 CHỨC NĂNG CÁC HỆ THỐNG TRUYỀN TẢI VÀ PHÂN PHỐI ĐIỆN NĂNG Chương GIỚI THIỆU CHUNG VỀ HỆ THỐNG ĐIỆN Võ Ngọc Điều Bộ môn Hệ Thống Điện Email: vndieu@gmail.com 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 Distribution Substation Underground Distribution Substation Substation Functions Substation Equipment Transmission Lines Overhead Transmission Lines Subtransmission Lines Underground Transmission Lines Distribution Systems Industrial Customer Commercial Customer Residential Customer Transportation Customer 8/19/2014 Power Generation Plants - 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 from solar (photovoltaic) cells • Chemical energy from: Power Generation Plant to transmission line fuel cells batteries 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 8/19/2014 Power Generation Plants Solar thermal power plant Nuclear power plant Power Generation Plants Geothermal power plant Wind power towers 8/19/2014 Substations - A substation is 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 8/19/2014 Step-up Transmission Substation - 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 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 10 8/19/2014 Step-up Transmission Substation Step-up AC transmission substation Step-up transmission substation to AC transmission lines 11 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 12 8/19/2014 Step-down Transmission Substation Step-down power transformer 13 Distribution Substation - 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 14 8/19/2014 Distribution Substation Distribution substation Distribution substation 15 Distribution Substation Distribution substation Distribution substation 16 8/19/2014 Underground Distribution Substation - Underground distribution substations are 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: Conduits Duct Runs Manholes High-Voltage Underground Cables Transformer Vault Riser Transformers Underground Distribution Substation - From here the power is distributed to industrial, commercial, and residential customers 17 Conduits - Conduits are hollow tubes running from manhole to manhole in an underground transmission or distribution system They can 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 Conduit 18 8/19/2014 Duct Runs - 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 to 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 19 Manholes - A manhole is 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 20 10 8/19/2014 Underground Transmission Lines Heat is generated when electricity flows through cables, limiting the power transmission capacity in tunnels To increase the capacity, a tunnel cooling system can be installed The system above circulates cold water through the tunnels Cable snaking through underground transmission tunnel 85 Underground Transmission Lines Cable installation of underground transmission line Cross section of underground transmission line 86 43 8/19/2014 Distribution Systems - A distribution system originates at a distribution substation and includes the lines, poles, transformers and other equipment needed to deliver electric power to the customer at the required voltages Customers are classed as: Industrial Customer Commercial Customer Residential Customer Transportation Customer 87 Distribution Systems - A distribution system consists of all the facilities and equipment connecting a transmission system to the customer's equipment - A typical distribution system can consist of: Substations Distribution Feeder Circuits Switches Protective Equipment Primary Circuits Distribution Transformers Secondaries, and Services 88 44 8/19/2014 Distribution Feeder Circuits - Distribution feeder circuits are the connections between the output terminals of a distribution substation and the input terminals of primary circuits The distribution feeder circuit conductors leave the substation from a circuit breaker or circuit recloser via underground cables, called substation exit cables The underground cables connect to a nearby overhead primary circuit outside the substation This eliminates multiple circuits on the poles adjacent to the substations thereby improving the overall appearance of the substation - Several distribution feeder circuits can leave a substation extending in different directions to serve customers The underground cables are connected to the primary circuit via a nearby riser pole - The distribution feeder bay routes power from the substation to the distribution primary feeder circuits 89 Distribution Feeder Circuits - In the photo of the distribution main feeder the primary circuit is fed underground to a nearby distribution system overhead line The yellow cables are the primary feeder lines going underground 3-phase distribution feeder bay Distribution main feeder 90 45 8/19/2014 Distribution Feeder Circuits Distribution feeder recloser 91 Switches - Distribution systems have switches installed at strategic locations to redirect or cut-off power flows for load balancing or sectionalizing Also, this permits repairing of damaged lines or equipment or upgrading work on the system The many types of switches include: circuit-breaker switches single-pole disconnect switches three-pole group-operated switches pad-mounted switchgear Air-break isolator switch Air circuit-breaker switches 92 46 8/19/2014 Switches Circuit switchers Single-pole disconnect switch combined with a fuse is called a fused cutout 93 Switches Pad mounted switchgear Circuit breakers 94 47 8/19/2014 Switches Group-operated three-pole air break switch 95 Protective Equipment - Protective equipment in a distribution system consists of protective relays, cutout switches, disconnect switches, lightning arresters, and fuses These work individually or may work in concert to open circuits whenever a short circuit, lightning strikes or other disruptive event occurs - When a circuit breakers opens, the entire distribution circuit is deenergized Since this can disrupt power to many customers, the distribution system is often designed with many layers of redundancy Through redundancy, power can be shut off in portions of the system only, but not the entire system, or can be redirected to continue to serve customers Only in extreme events, or failure of redundant systems, does an entire system become deenergized, shutting off power to large numbers of customers - The redundancy consists of the many fuses and fused cutouts throughout the system that can disable parts of the system but not the entire system Lightning arresters also act locally to drain off electrical energy from a lightning strike so that the larger circuit breakers are not actuated 96 48 8/19/2014 Protective Equipment Fused cut-out Substation bus lightning arresters 97 Protective Equipment Pole mounted type - lightning arrester Substation disconnect switch 98 49 8/19/2014 Primary Circuits - Primary circuits are the distribution circuits that carry power from substations to local load areas They are also called express feeders or distribution main feeders The distribution feeder bay routes power from the substation to the distribution primary feeder circuits - In the photo of the distribution main feeder the primary circuit is fed underground to a nearby distribution system overhead line The yellow cables are the primary feeder lines going underground phase distribution feeder bay Distribution main feeder 99 Primary Circuits Overhead primary feeder Distribution primary feeder underbuild 100 50 8/19/2014 Distribution Transformers - Distribution transformers reduce the voltage of the primary circuit to the voltage required by customers This voltage varies and is usually: 120/240 volts single phase for residential customers, - 480Y/277 or 208Y/120 for commercial or light industry customers Three-phase pad mounted transformers are used with an underground primary circuit and three single-phase pole type transformers for overhead service - Network service can be provided for areas with large concentrations of businesses These are usually transformers installed in an underground vault Power is then sent via underground cables to the separate customers 101 Distribution Transformers Air Distribution transformer - commercial facility Industrial facility distribution transformer 102 51 8/19/2014 Distribution Transformers Residential distribution transformer Pad-mounted residential distribution transformer 103 Secondaries - Secondaries are the conductors originating at the low-voltage secondary winding of a distribution transformer Secondaries for residential service are three-wire single-phase circuits They extend along the rear lot lines, alleys, or streets past customer's premises The secondaries can be overhead lines or underground lines - Overhead secondary lines are usually strung below the primary lines and typically in a vertical plane When secondaries are strung in a vertical plane, they are directly attached to the support pole one above the other This is in contrast to the primary lines which are often strung on a cross bar or other attachment in a horizontal or "V" shaped plane 104 52 8/19/2014 Secondaries Secondaries in a vertical plane Cabled secondaries 105 Secondaries Cabled secondaries, primaries in a "V" plane 106 53 8/19/2014 Services - The wires extending from the secondaries or distribution transformer to a customer's location are called a service A service can be above or below ground Underground services have a riser connection at the distribution pole Commercial and residential services are much the same and can be either 120 or 220 or both Service line to residence Distribution system lines and associated equipment 107 Services Commercial service Secondary to underground service via a riser 108 54 8/19/2014 Industrial Customer - Most industries need 2,400 to 4,160 volts to run heavy machinery and usually their own substation or substations to reduce the voltage from the transmission line to the desired level for distribution throughout the plant area They usually require 3-phase lines to power 3-phase motors Industrial facility distribution transformer 109 Commercial Customer - Commercial customers are usually served at distribution voltages, ranging from 14.4 kV to 7.2 kV through a service drop line which leads from a transformer on or near the distribution pole to the customer's end use structure They may require 3-phase lines to power 3-phase motors Commercial service drop Distribution transformer to 3-phase service - commercial facility 110 55 8/19/2014 Residential Customer - The distribution electricity is reduced to the end use voltage (120/240 volts single phase) via a pole mounted or pad-mounted transformer Power is delivered to the residential customer through a service drop line which leads from the distribution pole transformer to the customer's structure, for overhead lines, or underground Residential distribution transformer and service drop Pad-mounted residential distribution transformer 111 Transportation Customer - Currently the only electric transportation systems are light rail and subway systems A small distribution substation reduces the local distribution voltage to the transportation system requirements The overhead lines supply electric power to the transportation system motors and the return current lines are connected to the train tracks Public transit train powered by overhead electric lines Substation where electricity is conditioned for powering commuter trains 112 56 8/19/2014 Transportation Customer Power runs from the substation underground to the poles where power is delivered to the power lines The circuit is completed through the train tracks, with lines returning to the substation Electric cables carry electricity to power the train's motors 113 57