http://en.wikipedia.org/wiki/Electric_power_transmission

Electric power transmissionFrom Wikipedia, the free encyclopedia"Electric transmission" redirects here. For vehicle transmissions, see diesel-electric transmission.

Two-circuit, single-voltage power transmission line; "Bundled" 4-ways

Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to electrical substations located near demand centers. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. Transmission lines, when interconnected with each other, become transmission networks. The combined transmission and distribution network is known as the "power grid" in North America, or just "the grid". In the United Kingdom, the network is known as the "National Grid".

A wide area synchronous grid, also known as an "interconnection" in North America, directly connects a large number of generators delivering AC power with the same relative frequency, to a large number of consumers. For example, there are four major interconnections in North America (the Western Interconnection, the Eastern Interconnection, the Quebec Interconnection and the Electric Reliability Council of Texas (ERCOT) grid), and one large grid for most of continental Europe.

The same relative frequency, but almost never the same relative phase as ac power interchange is a function of the phase difference between any two nodes in the network, and zero degrees difference means no power is interchanged; any phase difference up to 90 degrees is stable by the "equal area criteria"; any phase difference above 90 degrees is absolutely unstable; the interchange partners are responsible for maintaining frequency as close to 60.0000 Hz as is practical, and the phase differences between any two nodes significantly less than 90 degrees; should 90 degrees be exceeded, a system separation is executed, and remains separated until the trouble has been corrected.

Historically, transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.[1]

Contents

1 System 2 Overhead transmission 3 Underground transmission 4 History 5 Bulk power transmission

o 5.1 Grid input o 5.2 Losses o 5.3 Subtransmission o 5.4 Transmission grid exit

6 High-voltage direct current 7 Capacity 8 Control

o 8.1 Load balancing o 8.2 Failure protection

9 Communications 10 Electricity market reform 11 Cost of electric power transmission 12 Merchant transmission 13 Health concerns 14 United States government policy 15 Special transmission

o 15.1 Grids for railways o 15.2 Superconducting cables o 15.3 Single wire earth return o 15.4 Wireless power transmission

16 Security of control systems 17 Records 18 See also 19 References 20 External links

System

Most transmission lines are high-voltage three-phase alternating current (AC), although single phase AC is sometimes used in railway electrification systems. High-voltage direct-current (HVDC) technology is used for greater efficiency at very long distances (typically hundreds of miles (kilometers)), or in submarine power cables (typically longer than 30 miles (50 km)). HVDC links are also used to stabilize and control problems in large power distribution networks where sudden new loads or blackouts in one part of a network can otherwise result in synchronization problems and cascading failures.

Diagram of an electric power system; transmission system is in blue

Electricity is transmitted at high voltages (120 kV or above) to reduce the energy losses in long-distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations.

A key limitation of electric power is that, with minor exceptions, electrical energy cannot be stored, and therefore must be generated as needed. A sophisticated control system is required to ensure electric generation very closely matches the demand. If the demand for power exceeds the supply, generation plant and transmission equipment can shut down, which in the worst case may lead to a major regional blackout, such as occurred in the US Northeast blackout of 1965, 1977, 2003, and other regional blackouts in 1996 and 2011. It is to reduce the risk of such a failure that electric transmission networks are interconnected into regional, national or continent wide networks thereby providing multiple redundant alternative routes for power to flow should such equipment failures occur. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line (ordinarily less than its physical or thermal limit) to ensure spare capacity is available should there be any such failure in another part of the network.

Overhead transmission

3-phase high-voltage lines in Washington State

Four-circuit, two-voltage power transmission line; "Bundled" 2-ways

A typical ACSR. The conductor consists of seven strands of steel surrounded by four layers of aluminium.Main article: Overhead power line

High-voltage overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, made into several strands and possibly reinforced with steel strands. Copper was sometimes used for overhead transmission, but aluminum is lighter, yields only marginally reduced performance and costs much less. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor

sizes range from 12 mm2 (#6 American wire gauge) to 750 mm2 (1,590,000 circular mils area), with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed. Bundle conductors are also used at high voltages to reduce energy loss caused by corona discharge.

Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages, such as 66 kV and 33 kV, are usually considered subtransmission voltages, but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 765 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages.

Since overhead transmission wires depend on air for insulation, the design of these lines requires minimum clearances to be observed to maintain safety. Adverse weather conditions, such as high wind and low temperatures, can lead to power outages. Wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply.[2] Oscillatory motion of the physical line can be termed gallop or flutter depending on the frequency and amplitude of oscillation.

Underground transmission

Main article: Undergrounding

Electric power can also be transmitted by underground power cables instead of overhead power lines. Underground cables take up less right-of-way than overhead lines, have lower visibility, and are less affected by bad weather. However, costs of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. Underground lines are strictly limited by their thermal capacity, which permits less overload or re-rating than overhead lines. Long underground AC cables have significant capacitance, which may reduce their ability to provide useful power to loads beyond 50 miles. Long underground DC cables have no such issue and can run for thousands of miles.

History

Main article: History of electric power transmission

New York City streets in 1890. Besides telegraph lines, multiple electric lines were required for each class of device requiring different voltages

In the early days of commercial electric power, transmission of electric power at the same voltage as used by lighting and mechanical loads restricted the distance between generating plant and consumers. In 1882, generation was with direct current (DC), which could not easily be increased in voltage for long-distance transmission. Different classes of loads (for example, lighting, fixed motors, and traction/railway systems) required different voltages, and so used different generators and circuits.[3][page needed]

Due to this specialization of lines and because transmission was inefficient for low-voltage high-current circuits, generators needed to be near their loads. It seemed, at the time, that the industry would develop into what is now known as a distributed generation system with large numbers of small generators located near their loads.[4]

In 1886, in Great Barrington, Massachusetts, a 1 kV alternating current (AC) distribution system was installed. That same year, AC power at 2 kV, transmitted 30 km, was installed at Cerchi, Italy. At an AIEE meeting on May 16, 1888, Nikola Tesla delivered a lecture entitled A New System of Alternating Current Motors and Transformers, describing the equipment which allowed efficient generation and use of polyphase alternating currents. The transformer, and Tesla's polyphase and single-phase induction motors, were essential for a combined AC distribution system for both lighting and machinery. Ownership of the rights to the Tesla patents was a key advantage to the Westinghouse Company in offering a complete alternating current power system for both lighting and power.

Regarded as one of the most influential electrical innovations, the universal system used transformers to step-up voltage from generators to high-voltage transmission lines, and then to step-down voltage to local distribution circuits or industrial customers.[3] By a suitable choice of utility frequency, both lighting and motor loads could be served. Rotary converters and later mercury-arc valves and other rectifier equipment allowed DC to be provided where needed. Generating stations and loads using different frequencies could be interconnected using rotary converters. By using common generating plants for every type of load, important economies of

scale were achieved, lower overall capital investment was required, load factor on each plant was increased allowing for higher efficiency, a lower cost for the consumer and increased overall use of electric power.

Nikola Tesla's alternating current polyphase generators on display at the 1893 World's Fair in Chicago. Tesla's polyphase innovations revolutionized transmission

By allowing multiple generating plants to be interconnected over a wide area, electricity production cost was reduced. The most efficient available plants could be used to supply the varying loads during the day. Reliability was improved and capital investment cost was reduced, since stand-by generating capacity could be shared over many more customers and a wider geographic area. Remote and low-cost sources of energy, such as hydroelectric power or mine-mouth coal, could be exploited to lower energy production cost.[3]

The first transmission of three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. A 25 kV transmission line, approximately 175 km long, connected Lauffen on the Neckar and Frankfurt.

Voltages used for electric power transmission increased throughout the 20th century. By 1914, fifty-five transmission systems each operating at more than 70 kV were in service. The highest voltage then used was 150 kV.[5]

The rapid industrialization in the 20th century made electrical transmission lines and grids a critical infrastructure item in most industrialized nations. The interconnection of local generation plants and small distribution networks was greatly spurred by the requirements of World War I, with large electrical generating plants built by governments to provide power to munitions factories. Later these generating plants were connected to supply civil loads through long-distance transmission.[6]

Bulk power transmission

A transmission substation decreases the voltage of incoming electricity, allowing it to connect from long distance high voltage transmission, to local lower voltage distribution. It also reroutes power to other transmission lines that serve local markets. This is the PacifiCorp Hale Substation, Orem, Utah, USA

Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy. These networks use components such as power lines, cables, circuit breakers, switches and transformers. The transmission network is usually administered on a regional basis by an entity such as a regional transmission organization or transmission system operator.

Transmission efficiency is greatly improved by devices that increase the voltage, (and thereby proportionately reduce the current) in the line conductors, thus allowing power to be transmitted with acceptable losses. The reduced current flowing through the line reduces the heating losses in the conductors. According to Joule's Law, energy losses are directly proportional to the square of the current. Thus, reducing the current by a factor of two will lower the energy lost to conductor resistance by a factor of four for any given size of conductor.

The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size, which states that the size is at its optimum when the annual cost of energy wasted in the resistance is equal to the annual capital charges of providing the conductor. At times of lower interest rates, Kelvin's law indicates that thicker wires are optimal; while, when metals are expensive, thinner conductors are indicated: however, power lines are designed for long-term use, so Kelvin's law has to be used in conjunction with long-term estimates of the price of copper and aluminum as well as interest rates for capital.

The increase in voltage is achieved in AC circuits by using a step-up transformer. HVDC systems require relatively costly conversion equipment which may be economically justified for particular projects such as submarine cables and longer distance high capacity point to point transmission. HVDC is necessary for the import and export of energy between grid systems that are not synchronized with each other.

A transmission grid is a network of power stations, transmission lines, and substations. Energy is usually transmitted within a grid with three-phase AC. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. In the 19th century, two-phase transmission was used but required either four wires or three wires with

unequal currents. Higher order phase systems require more than three wires, but deliver little or no benefit.

The synchronous grids of the European Union

The price of electric power station capacity is high, and electric demand is variable, so it is often cheaper to import some portion of the needed power than to generate it locally. Because loads are often regionally correlated (hot weather in the Southwest portion of the US might cause many people to use air conditioners), electric power often comes from distant sources. Because of the economic benefits of load sharing between regions, wide area transmission grids now span countries and even continents. The web of interconnections between power producers and consumers should enable power to flow, even if some links are inoperative.

The unvarying (or slowly varying over many hours) portion of the electric demand is known as the base load and is generally served by large facilities (which are more efficient due to economies of scale) with fixed costs for fuel and operation. Such facilities are nuclear, coal-fired or hydroelectric, while other energy sources such as concentrated solar thermal and geothermal power have the potential to provide base load power. Renewable energy sources, such as solar photovoltaics, wind, wave, and tidal, are, due to their intermittency, not considered as supplying "base load" but will still add power to the grid. The remaining or 'peak' power demand, is supplied by peaking power plants, which are typically smaller, faster-responding, and higher cost sources, such as combined cycle or combustion turbine plants fueled by natural gas.

Long-distance transmission of electricity (thousands of kilometers) is cheap and efficient, with costs of US$0.005–0.02/kWh (compared to annual averaged large producer costs of US$0.01–0.025/kWh, retail rates upwards of US$0.10/kWh, and multiples of retail for instantaneous suppliers at unpredicted highest demand moments).[7] Thus distant suppliers can be cheaper than local sources (e.g., New York often buys over 1000 MW of electricity from Canada).[8] Multiple local sources (even if more expensive and infrequently used) can make the transmission grid more fault tolerant to weather and other disasters that can disconnect distant suppliers.

A high-power electrical transmission tower, 230 kV, double-circuit, also double-bundled

Long-distance transmission allows remote renewable energy resources to be used to displace fossil fuel consumption. Hydro and wind sources cannot be moved closer to populous cities, and solar costs are lowest in remote areas where local power needs are minimal. Connection costs alone can determine whether any particular renewable alternative is economically sensible. Costs can be prohibitive for transmission lines, but various proposals for massive infrastructure investment in high capacity, very long distance super grid transmission networks could be recovered with modest usage fees.

Grid input

At the power stations, the power is produced at a relatively low voltage between about 2.3 kV and 30 kV, depending on the size of the unit. The generator terminal voltage is then stepped up by the power station transformer to a higher voltage (115 kV to 765 kV AC, varying by the transmission system and by country) for transmission over long distances.

Losses

Transmitting electricity at high voltage reduces the fraction of energy lost to resistance, which varies depending on the specific conductors, the current flowing, and the length of the transmission line. For example, a 100 mile 765 kV line carrying 1000 MW of power can have losses of 1.1% to 0.5%. A 345 kV line carrying the same load across the same distance has losses of 4.2%.[9] For a given amount of power, a higher voltage reduces the current and thus the resistive losses in the conductor. For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the I2R losses by a factor of 100, provided the same sized conductors are used in both cases. Even if the conductor size (cross-sectional area) is reduced 10-fold to match the lower current, the I2R losses are still reduced 10-fold. Long-distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. At extremely high voltages, more than 2,000 kV exists between conductor and ground, corona discharge losses are so large that they can offset the lower resistive losses in the line conductors. Measures to reduce corona losses include conductors having larger diameters; often hollow to save weight,[10] or bundles of two or more conductors.

Transmission and distribution losses in the USA were estimated at 6.6% in 1997[11] and 6.5% in 2007.[11] By using underground DC transmission, these losses can be cut in half.[citation needed] Underground cables can be larger diameter because they do not have the constraint of light weight that overhead conductors have. In general, losses are estimated from the discrepancy

between power produced (as reported by power plants) and power sold to the end customers; the difference between what is produced and what is consumed constitute transmission and distribution losses, assuming no theft of utility occurs.

As of 1980, the longest cost-effective distance for direct-current transmission was determined to be 7,000 km (4,300 mi). For alternating current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this.[7]

In any alternating current transmission line, the inductance and capacitance of the conductors can be significant. Currents that flow solely in 'reaction' to these properties of the circuit, (which together with the resistance define the impedance) constitute reactive power flow, which transmits no 'real' power to the load. These reactive currents, however, are very real and cause extra heating losses in the transmission circuit. The ratio of 'real' power (transmitted to the load) to 'apparent' power (sum of 'real' and 'reactive') is the power factor. As reactive current increases, the reactive power increases and the power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor. Utilities add capacitor banks, reactors and other components (such as phase-shifting transformers; static VAR compensators; physical transposition of the phase conductors; and flexible AC transmission systems, FACTS) throughout the system to compensate for the reactive power flow and reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'.

Subtransmission

danger subtransmission line above

subtransmission line, wood H-frame construction

Subtransmission is part of an electric power transmission system that runs at relatively lower voltages. It is uneconomical to connect all distribution substations to the high main transmission voltage, because the equipment is larger and more expensive. Typically, only larger substations connect with this high voltage. It is stepped down and sent to smaller substations in towns and neighborhoods. Subtransmission circuits are usually arranged in loops so that a single line failure does not cut off service to a large number of customers for more than a short time. Loops can be "normally closed", where loss of one circuit should result in no interruption, or "normally open" where substations can switch to a backup supply. While subtransmission circuits are usually carried on overhead lines, in urban areas buried cable may be used. The lower-voltage subtransmission lines use less right-of-way and simpler structures; it is much more feasible to put them underground where needed. Higher-voltage lines require more space and are usually above-ground since putting them underground is very expensive.

There is no fixed cutoff between subtransmission and transmission, or subtransmission and distribution. The voltage ranges overlap somewhat. Voltages of 69 kV, 115 kV and 138 kV are often used for subtransmission in North America. As power systems evolved, voltages formerly used for transmission were used for subtransmission, and subtransmission voltages became distribution voltages. Like transmission, subtransmission moves relatively large amounts of power, and like distribution, subtransmission covers an area instead of just point to point.[12]

Transmission grid exit

At the substations, transformers reduce the voltage to a lower level for distribution to commercial and residential users. This distribution is accomplished with a combination of sub-transmission (33 kV to 132 kV) and distribution (3.3 to 25 kV). Finally, at the point of use, the energy is transformed to low voltage (varying by country and customer requirements—see Mains electricity by country).

High-voltage direct current

Main article: High-voltage direct current

High-voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is to be transmitted over very long distances, the power lost in AC transmission becomes appreciable and it is less expensive to use direct current instead of alternating current. For a very long transmission line, these lower losses (and reduced construction cost of a DC line) can offset the additional cost of the required converter stations at each end.

HVDC is also used for submarine cables because over about 30 kilometres (19 mi) lengths AC cannot be supplied[citation needed]. In these cases special high-voltage cables for DC are used. Submarine HVDC systems are often used to connect the electricity grids of islands, for example, between Great Britain and mainland Europe, between Great Britain and Ireland, between

Tasmania and the Australian mainland, and between the North and South Islands of New Zealand. Submarine connections up to 600 kilometres (370 mi) in length are presently in use.

HVDC links can be used to control problems in the grid with AC electricity flow. The power transmitted by an AC line increases as the phase angle between source end voltage and destination ends increases, but too large a phase angle will allow the systems at either end of the line to fall out of step. Since the power flow in a DC link is controlled independently of the phases of the AC networks at either end of the link, this phase angle limit does not exist, and a DC link is always able to transfer its full rated power. A DC link therefore stabilizes the AC grid at either end, since power flow and phase angle can then be controlled independently.

As an example, to adjust the flow of AC power on a hypothetical line between Seattle and Boston would require adjustment of the relative phase of the two regional electrical grids. This is an everyday occurrence in AC systems, but one that can become disrupted when AC system components fail and place unexpected loads on the remaining working grid system. With an HVDC line instead, such an interconnection would: (1) Convert AC in Seattle into HVDC; (2) Use HVDC for the 3,000 miles of cross-country transmission; and (3) Convert the HVDC to locally synchronized AC in Boston, (and possibly in other cooperating cities along the transmission route). Such a system could be less prone to failure if parts of it were suddenly shut down. One example of a long DC transmission line is the Pacific DC Intertie located in the Western United States.

Capacity

The amount of power that can be sent over a transmission line is limited. The origins of the limits vary depending on the length of the line. For a short line, the heating of conductors due to line losses sets a thermal limit. If too much current is drawn, conductors may sag too close to the ground, or conductors and equipment may be damaged by overheating. For intermediate-length lines on the order of 100 km (62 mi), the limit is set by the voltage drop in the line. For longer AC lines, system stability sets the limit to the power that can be transferred. Approximately, the power flowing over an AC line is proportional to the cosine of the phase angle of the voltage and current at the receiving and transmitting ends. Since this angle varies depending on system loading and generation, it is undesirable for the angle to approach 90 degrees. Very approximately, the allowable product of line length and maximum load is proportional to the square of the system voltage. Series capacitors or phase-shifting transformers are used on long lines to improve stability. High-voltage direct current lines are restricted only by thermal and voltage drop limits, since the phase angle is not material to their operation.

Up to now, it has been almost impossible to foresee the temperature distribution along the cable route, so that the maximum applicable current load was usually set as a compromise between understanding of operation conditions and risk minimization. The availability of industrial distributed temperature sensing (DTS) systems that measure in real time temperatures all along the cable is a first step in monitoring the transmission system capacity. This monitoring solution is based on using passive optical fibers as temperature sensors, either integrated directly inside a high voltage cable or mounted externally on the cable insulation. A solution for overhead lines is also available. In this case the optical fiber is integrated into the core of a phase wire of overhead

transmission lines (OPPC). The integrated Dynamic Cable Rating (DCR) or also called Real Time Thermal Rating (RTTR) solution enables not only to continuously monitor the temperature of a high voltage cable circuit in real time, but to safely utilize the existing network capacity to its maximum. Furthermore it provides the ability to the operator to predict the behavior of the transmission system upon major changes made to its initial operating conditions.

Control

To ensure safe and predictable operation the components of the transmission system are controlled with generators, switches, circuit breakers and loads. The voltage, power, frequency, load factor, and reliability capabilities of the transmission system are designed to provide cost effective performance for the customers.

Load balancing

The transmission system provides for base load and peak load capability, with safety and fault tolerance margins. The peak load times vary by region largely due to the industry mix. In very hot and very cold climates home air conditioning and heating loads have an effect on the overall load. They are typically highest in the late afternoon in the hottest part of the year and in mid-mornings and mid-evenings in the coldest part of the year. This makes the power requirements vary by the season and the time of day. Distribution system designs always take the base load and the peak load into consideration.

The transmission system usually does not have a large buffering capability to match the loads with the generation. Thus generation has to be kept matched to the load, to prevent overloading failures of the generation equipment.

Multiple sources and loads can be connected to the transmission system and they must be controlled to provide orderly transfer of power. In centralized power generation, only local control of generation is necessary, and it involves synchronization of the generation units, to prevent large transients and overload conditions.

In distributed power generation the generators are geographically distributed and the process to bring them online and offline must be carefully controlled. The load control signals can either be sent on separate lines or on the power lines themselves. Voltage and frequency can be used as signalling mechanisms to balance the loads.

In voltage signaling, the variation of voltage is used to increase generation. The power added by any system increases as the line voltage decreases. This arrangement is stable in principle. Voltage-based regulation is complex to use in mesh networks, since the individual components and setpoints would need to be reconfigured every time a new generator is added to the mesh.

In frequency signaling, the generating units match the frequency of the power transmission system. In droop speed control, if the frequency decreases, the power is increased. (The drop in line frequency is an indication that the increased load is causing the generators to slow down.)

Wind turbines, vehicle-to-grid and other distributed storage and generation systems can be connected to the power grid, and interact with it to improve system operation.[citation needed]

Failure protection

Under excess load conditions, the system can be designed to fail gracefully rather than all at once. Brownouts occur when the supply power drops below the demand. Blackouts occur when the supply fails completely.

Rolling blackouts (also called load shedding) are intentionally engineered electrical power outages, used to distribute insufficient power when the demand for electricity exceeds the supply.

Communications

Operators of long transmission lines require reliable communications for control of the power grid and, often, associated generation and distribution facilities. Fault-sensing protective relays at each end of the line must communicate to monitor the flow of power into and out of the protected line section so that faulted conductors or equipment can be quickly de-energized and the balance of the system restored. Protection of the transmission line from short circuits and other faults is usually so critical that common carrier telecommunications are insufficiently reliable, and in remote areas a common carrier may not be available. Communication systems associated with a transmission project may use:

Microwaves Power line communication Optical fibers

Rarely, and for short distances, a utility will use pilot-wires strung along the transmission line path. Leased circuits from common carriers are not preferred since availability is not under control of the electric power transmission organization.

Transmission lines can also be used to carry data: this is called power-line carrier, or PLC. PLC signals can be easily received with a radio for the long wave range.

Optical fibers can be included in the stranded conductors of a transmission line, in the overhead shield wires. These cables are known as optical ground wire (OPGW). Sometimes a standalone cable is used, all-dielectric self-supporting (ADSS) cable, attached to the transmission line cross arms.

Some jurisdictions, such as Minnesota, prohibit energy transmission companies from selling surplus communication bandwidth or acting as a telecommunications common carrier. Where the regulatory structure permits, the utility can sell capacity in extra dark fibers to a common carrier, providing another revenue stream.

Electricity market reform

Main article: Electricity market

Some regulators regard electric transmission to be a natural monopoly [13] [14] and there are moves in many countries to separately regulate transmission (see electricity market).

Spain was the first country to establish a regional transmission organization. In that country, transmission operations and market operations are controlled by separate companies. The transmission system operator is Red Eléctrica de España (REE) and the wholesale electricity market operator is Operador del Mercado Ibérico de Energía – Polo Español, S.A. (OMEL) [1]. Spain's transmission system is interconnected with those of France, Portugal, and Morocco.

In the United States and parts of Canada, electrical transmission companies operate independently of generation and distribution companies.

Cost of electric power transmission

The cost of high voltage electricity transmission (as opposed to the costs of electric power distribution) is comparatively low, compared to all other costs arising in a consumer's electricity bill. In the UK, transmission costs are about 0.2p/kWh compared to a delivered domestic price of around 10p/kWh.[15]

Research evaluates the level of capital expenditure in the electric power T&D equipment market will be worth $128.9bn in 2011.[16]

Merchant transmission

Merchant transmission is an arrangement where a third party constructs and operates electric transmission lines through the franchise area of an unrelated utility.

Operating merchant transmission projects in the United States include the Cross Sound Cable from Shoreham, New York to New Haven, Connecticut, Neptune RTS Transmission Line from Sayreville, N.J., to Newbridge, N.Y, and Path 15 in California. Additional projects are in development or have been proposed throughout the United States, including the Lake Erie Connector, an underwater transmission line proposed by ITC Holdings Corp., connecting Ontario to load serving entities in the PJM Interconnection region. [17]

There is only one unregulated or market interconnector in Australia: Basslink between Tasmania and Victoria. Two DC links originally implemented as market interconnectors, Directlink and Murraylink, have been converted to regulated interconnectors. NEMMCO

A major barrier to wider adoption of merchant transmission is the difficulty in identifying who benefits from the facility so that the beneficiaries will pay the toll. Also, it is difficult for a

merchant transmission line to compete when the alternative transmission lines are subsidized by other utility businesses.[18]

Health concerns

Main article: Electromagnetic radiation and health

Some large studies, including a large United States study, have failed to find any link between living near power lines and developing any sickness or diseases, such as cancer. A 1997 study found that it did not matter how close one was to a power line or a sub-station, there was no increased risk of cancer or illness.[19]

The mainstream scientific evidence suggests that low-power, low-frequency, electromagnetic radiation associated with household currents and high transmission power lines does not constitute a short or long term health hazard. Some studies, however, have found statistical correlations between various diseases and living or working near power lines. No adverse health effects have been substantiated for people not living close to powerlines.[20]

There are established biological effects for acute high level exposure to magnetic fields well above 100 µT (1 G). In a residential setting, there is "limited evidence of carcinogenicity in humans and less than sufficient evidence for carcinogenicity in experimental animals", in particular, childhood leukemia, associated with average exposure to residential power-frequency magnetic field above 0.3 µT (3 mG) to 0.4 µT (4 mG). These levels exceed average residential power-frequency magnetic fields in homes, which are about 0.07 µT (0.7 mG) in Europe and 0.11 µT (1.1 mG) in North America.[21][22]

The Earths natural geomagnetic field strength varies over the surface of the planet between 0.035 mT - 0.07 mT (35 µT - 70 µT or 0.35 G - 0.7 G) while the International Standard for the continuous exposure limit is set at 40 mT (40,000 µT or 400 G) for the general public.[21]

Tree Growth Regulator and Herbicide Control Methods may be used in transmission line right of ways[23] which may have health effects.

United States government policy

The examples and perspective in this article may not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (March 2013)

Historically, local governments have exercised authority over the grid and have significant disincentives to encourage actions that would benefit states other than their own. Localities with cheap electricity have a disincentive to encourage making interstate commerce in electricity trading easier, since other regions will be able to compete for local energy and drive up rates. For example, some regulators in Maine do not wish to address congestion problems because the congestion serves to keep Maine rates low.[24] Further, vocal local constituencies can block or slow permitting by pointing to visual impact, environmental, and perceived health concerns. In

the US, generation is growing four times faster than transmission, but big transmission upgrades require the coordination of multiple states, a multitude of interlocking permits, and cooperation between a significant portion of the 500 companies that own the grid. From a policy perspective, the control of the grid is balkanized, and even former energy secretary Bill Richardson refers to it as a third world grid. There have been efforts in the EU and US to confront the problem. The US national security interest in significantly growing transmission capacity drove passage of the 2005 energy act giving the Department of Energy the authority to approve transmission if states refuse to act. However, soon after the Department of Energy used its power to designate two National Interest Electric Transmission Corridors, 14 senators signed a letter stating the DOE was being too aggressive.[25]

Special transmission

Grids for railways

Main article: Traction power network

In some countries where electric locomotives or electric multiple units run on low frequency AC power, there are separate single phase traction power networks operated by the railways. Prime example are the countries of Europe, which utilize the older AC technology based on 16 2/3 Hz.

Superconducting cables

High-temperature superconductors (HTS) promise to revolutionize power distribution by providing lossless transmission of electrical power. The development of superconductors with transition temperatures higher than the boiling point of liquid nitrogen has made the concept of superconducting power lines commercially feasible, at least for high-load applications.[26] It has been estimated that the waste would be halved using this method, since the necessary refrigeration equipment would consume about half the power saved by the elimination of the majority of resistive losses. Some companies such as Consolidated Edison and American Superconductor have already begun commercial production of such systems.[27] In one hypothetical future system called a SuperGrid, the cost of cooling would be eliminated by coupling the transmission line with a liquid hydrogen pipeline.

Superconducting cables are particularly suited to high load density areas such as the business district of large cities, where purchase of an easement for cables would be very costly.[28]

HTS transmission lines[29]

Location Length (km) Voltage (kV) Capacity (GW) DateCarrollton, Georgia 2000Albany, New York[30] 0.35 34.5 0.048 2006Long Island[31] 0.6 130 0.574 2008Tres Amigas 5 Proposed 2013Manhattan: Project Hydra Proposed 2014Essen, Germany[32][33] 1 10 0.04 2014

Single wire earth return

Main article: Single-wire earth return

Single-wire earth return (SWER) or single wire ground return is a single-wire transmission line for supplying single-phase electrical power for an electrical grid to remote areas at low cost. It is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps. Single wire earth return is also used for HVDC over submarine power cables.

Wireless power transmission

Main article: Wireless energy transfer

Both Nikola Tesla and Hidetsugu Yagi attempted to devise systems for large scale wireless power transmission in the late 1800s and early 1900s, with no commercial success.

In November 2009, LaserMotive won the NASA 2009 Power Beaming Challenge by powering a cable climber 1 km vertically using a ground-based laser transmitter. The system produced up to 1 kW of power at the receiver end. In August 2010, NASA contracted with private companies to pursue the design of laser power beaming systems to power low earth orbit satellites and to launch rockets using laser power beams.

Wireless power transmission has been studied for transmission of power from solar power satellites to the earth. A high power array of microwave or laser transmitters would beam power to a rectenna. Major engineering and economic challenges face any solar power satellite project.

Security of control systems

The examples and perspective in this article may not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (March 2013)

The Federal government of the United States admits that the power grid is susceptible to cyber-warfare.[34][35] The United States Department of Homeland Security works with industry to identify vulnerabilities and to help industry enhance the security of control system networks, the federal government is also working to ensure that security is built in as the U.S. develops the next generation of 'smart grid' networks.[36]

Records

Highest capacity system: 6.3 GW HVDC Itaipu (Brazil/Paraguay) (±600 kV DC)[37]

Highest transmission voltage (AC): o planned: 1.20 MV (Ultra High Voltage) on Wardha-Aurangabad line (India) -

under construction. Initially will operate at 400 kV.[38]

o worldwide: 1.15 MV (Ultra High Voltage) on Ekibastuz-Kokshetau line (Kazakhstan)

Largest double-circuit transmission, Kita-Iwaki Powerline (Japan). Highest towers: Yangtze River Crossing (China) (height: 345 m or 1,132 ft) Longest power line: Inga-Shaba (Democratic Republic of Congo) (length: 1,700

kilometres or 1,056 miles) Longest span of power line: 5,376 m (17,638 ft) at Ameralik Span (Greenland, Denmark) Longest submarine cables:

o NorNed , North Sea (Norway/Netherlands) – (length of submarine cable: 580 kilometres or 360 miles)

o Basslink , Bass Strait, (Australia) – (length of submarine cable: 290 kilometres or 180 miles, total length: 370.1 kilometres or 230 miles)

o Baltic Cable , Baltic Sea (Germany/Sweden) – (length of submarine cable: 238 kilometres or 148 miles, HVDC length: 250 kilometres or 155 miles, total length: 262 kilometres or 163 miles)

Longest underground cables: o Murraylink , Riverland/Sunraysia (Australia) – (length of underground cable: 180

kilometres or 112 miles)

See also

Energy portal

General:

Distributed generation Electricity distribution Green power grid Overhead power line Power outage

Electricity market:

Electricity market Dynamic demand (electric

power) Demand response List of energy storage projects

Transport:

Traction power network

Technical:

Conductor marking lights Double-circuit transmission line Electromagnetic Transients Program (EMTP) Flexible AC transmission system (FACTS) Geomagnetically induced current , (GIC) Grid-tied electrical system High-voltage direct current (HVDC) List of high voltage underground and submarine

cables Load profile Power line communications (PLC) Radio frequency power transmission Submarine power cable Three-phase electric power Wheeling (electric power transmission)

References

Notes

1. "A Primer on Electric Utilities, Deregulation, and Restructuring of U.S. Electricity Markets" (pdf). United States Department of Energy Federal Energy Management Program (FEMP). May 2002. Retrieved December 27, 2008.

2. Hans Dieter Betz, Ulrich Schumann, Pierre Laroche (2009). Lightning: Principles, Instruments and Applications. Springer, pp. 202–203. ISBN 978-1-4020-9078-3. Retrieved on May 13, 2009.

3. Thomas P. Hughes (1993). Networks of Power: Electrification in Western Society, 1880–1930. Baltimore: Johns Hopkins University Press. pp. 119–122. ISBN 0-8018-4614-5.

4. National Council on Electricity Policy. "Electricity Transmission: A primer" (pdf).5. Bureau of Census data reprinted in Hughes, pp. 282–2836. Hughes, pp. 293–2957. Paris, L.; Zini, G.; Valtorta, M.; Manzoni, G.; Invernizzi, A.; De Franco, N.; Vian, A.

(1984). "Present Limits of Very Long Distance Transmission Systems" (pdf). CIGRE International Conference on Large High Voltage Electric Systems, 1984 Session, 29th August-6th September. Global Energy Network Institute. Retrieved March 29, 2011. 4.98 MB

8. "NYISO Zone Maps" . New York Independent System Operator. Retrieved January 10, 2014.

9. American Electric Power, Transmission Facts, page 4: http://www.aep.com/about/transmission/docs/transmission-facts.pdf

10. California Public Utilities Commission Corona and induced currents11. "Where can I find data on electricity transmission and distribution losses?" . Frequently

Asked Questions – Electricity. U.S. Energy Information Administration. November 19, 2009. Retrieved March 29, 2011.

12. Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers (15th Edition) McGraw-Hill, 2007 ISBN 978-0-07-144146-9 section 18.5

13. Raghuvir Srinivasan (August 15, 2004). "Power transmission business is a natural monopoly". The Hindu Business Line. The Hindu. Retrieved January 31, 2008.

14. Lynne Kiesling (August 18, 2003). "Rethink the Natural Monopoly Justification of Electricity Regulation". Reason Foundation. Retrieved January 31, 2008.

15. What is the cost per kWh of bulk transmission / National Grid in the UK (note this excludes distribution costs)

16. The Electric Power Transmission & Distribution (T&D) Equipment Market 2011–2021 17. How ITC Holdings plans to connect PJM demand with Ontario's rich renewables, Utility

Dive, Dec. 8, 2014, http://www.utilitydive.com/news/how-itc-holdings-plans-to-connect-pjm-demand-with-ontarios-rich-renewables/341524/

18. Fiona Woolf (February 2003). Global Transmission Expansion. Pennwell Books. pp. 226, 247. ISBN 0-87814-862-0.

19. Power Lines and Cancer , The Health Report / ABC Science - Broadcast on June 7, 1997 (Australian Broadcasting Corporation)

20. Electromagnetic fields and public health , World Health Organization21. "Electromagnetic fields and public health" . Fact sheet No. 322. World Health

Organization. June 2007. Retrieved January 23, 2008.22. "Electric and Magnetic Fields Associated with the Use of Power" (PDF). National

Institute of Environmental Health Sciences. June 2002. Retrieved January 29, 2008.

23. Transmission Vegetation Management NERC Standard FAC-003-2 Technical Reference Page 14/50. http://www.nerc.com/docs/standards/sar/FAC-003-2_White_Paper_2009Sept9.pdf

24. National Council on Electricity Policy. "Electricity Transmission: A primer" (pdf). p. 32 (41 in pdf).

25. Wald, Matthew (August 27, 2008). "Wind Energy Bumps Into Power Grid's Limits". New York Times. p. A1. Retrieved December 12, 2008.

26. Jacob Oestergaard et al. (2001). "Energy losses of superconducting power transmission cables in the grid". IEEE Transactions on Applied Superconductivity 11: 2375. doi:10.1109/77.920339.

27. 600m superconducting electricity line laid in New York 28. Superconducting cables will be used to supply electricity to consumers 29. Superconductivity's First Century 30. Albany HTS Cable Project 31. High-Temperature Superconductors 32. High-Temperature Superconductor Technology Stepped Up 33. Operation of longest superconducting cable worldwide started 34. BBC: Spies 'infiltrate US power grid' 35. CNN: Video 36. Reuters: US concerned power grid vulnerable to cyber-attack 37. "Energy Systems, Environment and Development" . Advanced Technology Assessment

Systems (Global Energy Network Institute) (6). Autumn 1991. Retrieved December 27, 2008.

38. "India Steps It Up" . Transmission & Distribution World. January 2013.

Further reading

Grigsby, L. L., et al. The Electric Power Engineering Handbook. USA: CRC Press. (2001). ISBN 0-8493-8578-4

Hughes, Thomas P. , Networks of Power: Electrification in Western Society 1880–1930, The Johns Hopkins University Press,Baltimore 1983 ISBN 0-8018-2873-2, an excellent overview of development during the first 50 years of commercial electric power

Reilly, Helen (2008). Connecting the Country – New Zealand’s National Grid 1886–2007. Wellington: Steele Roberts. pp. 376 pages. ISBN 978-1-877448-40-9.

Pansini, Anthony J, E.E., P.E. undergrounding electric lines. USA Hayden Book Co, 1978. ISBN 0-8104-0827-9

Westinghouse Electric Corporation, "Electric power transmission patents; Tesla polyphase system". (Transmission of power; polyphase system; Tesla patents)

The Physics of Everyday Stuff - Transmission Lines

External links

Wikimedia Commons has media related to Electric power transmission.

Look up grid electricity in Wiktionary, the free dictionary.

Japan: World's First In-Grid High-Temperature Superconducting Power Cable System - Link broken

A Power Grid for the Hydrogen Economy: Overview/A Continental SuperGrid Global Energy Network Institute (GENI) – The GENI Initiative focuses on linking

renewable energy resources around the world using international electricity transmission. Union for the Co-ordination of Transmission of Electricity (UCTE) , the association of

transmission system operators in continental Europe, running one of the two largest power transmission systems in the world

Non-Ionizing Radiation, Part 1: Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields (2002) by the IARC – Link Broken.

A Simulation of the Power Grid – The Trustworthy Cyber Infrastructure for the Power Grid (TCIP) group at the University of Illinois at Urbana-Champaign has developed lessons and an applet which illustrate the transmission of electricity from generators to energy consumers, and allows the user to manipulate generation, consumption, and power flow.

Map of U.S. electric power generation and transmission

Maps

Electric power transmission systems (worldwide) based on Openstreetmap-Data

https://hitechtabai.wordpress.com/2012/04/27/power-system-loss-one-of-the-7-wonders-in-our-electricity-bill/

Power System Loss– One of the "7 Wonders" in our Electricity   Bill By Jun Tariman April 27, 2012 electrical pilferage electricity theft eletricity EPIRA ERC HVDC system loss VECO       

1 Vote

Don’t mistakenly understood the “7 Wonders” in the title of this post as something outstanding or astonishing. In the contrary, it makes you wonder why it’s there in our monthly electricity bill and shouldered by many consumers.

SYSTEM LOSSThe EPIRA (Electric Power Industry Reform Act/RA 9136) is not mentioning the System Loss nor the Anti-Electricity and Electric Transmission Lines/Materials Pilferage Act of 1994 (RA 7832) is discussing thoroughly about it. So, what the hell is a SYSTEM LOSS?

System Loss is an operational cost in the power generation that is pass on to the consumers at a rate determined by the Energy Regulatory Commission (ERC) every year and collected by the power utility companies in its monthly bill to the consumers.

In this VECO electric bill,the Systems Loss is shown as part of the Generation and Transmission Charges.

Still confused how the System Loss became part of our monthly bill? Thanks to the EPIRA and the RA 7832 for allowing power utilities to recover that operational cost by passing it on to consumers. The ERC, as the implementing agency of the EPIRA, determines every year the ceiling how much System Loss shall be collected by the power companies like VECO (Visayan Electric Company). The rate is now pegged at 8.5% from as high as 14.5% of the total System Loss incurred by a power company.

Our monthly electricity bill is now unbundled by means of segregating the various components in the electricity bill such as generation, transmission and distribution. It gives us also the chance to be informed how much are we paying in every aspect of our electrical consumption including the taxes.

“7 WONDERS”In our monthly bill, there are seven (7) operational costs that have been passed on to the consumers. Here are the rates for each charge and the sample costs for each charge based on my bill above which totalled to P435.74:

System Loss Charge @ P0.9853/kWh (P212.82) Subsidy on Lifeline Charge @ P0.0986/kWh (P21.30) Senior Citizen Subsidy Rate @ P0.0002/kWh (P0.04) Missionary Electrification @ P0.1163/kWh (P25.12) Environmental Charge @ P0.0025/kWh (P0.54) ICERA (Incremental Currency Exchange Rate Adjustment) @ P0.0159/kWh (P3.43) Local Franchise Tax and Value Added Taxes @ 12% for Generation, Transmission,

System Loss, Distribution, Others (P122.49)

Subsidy on Lifeline Charge, is used by our power company (VECO) to defray the discount given to small electricity consumers or those who consumed below 100kWh every month. If your consumption is higher than 100kWh you’ll be part of those subsidizing the bills of the small consumers. So, VECO is not the one giving the discount! lol

Chart from VECO website.

Senior Citizen Subsidy Rate, is also used by VECO to defray the discount given to consumers who are Senior Citizens. So, old folks must be thankful to the rest of the consumers not to VECO.

Missionary Electrification, is also used by VECO in providing electricity to “Unviable Areas” where there are less consumers like the mountain and remote areas. So, mountain folks must be thankful to their counterparts in the flat lands.

Environmental Charge, is not clear how VECO used this fund. I’m just guessing they might used it to defray the expenses in protecting the environment from possible destruction by their operations.

ICERA, is the mechanism allowed by ERC that is used to recover the “increase in principal payments of foreign denominated loans that may be brought about by the peso devaluation”. If the current exchange rate shows that the peso is devaluating, then more ICERA charge shall be paid by the consumers in order for VECO to recover that additional amount added to their loans.

Local Franchise Tax, is collected by VECO to “recover the local franchise tax imposed by the local government in your city or municipality from 1994-2000, which was not passed on the consumers”. So, the consumers are made to pay the Franchise Tax.

Value Added Tax, as we all knew is a pass-it-on tax aimed to ensure tax collection. VECO is able to recover their paid input taxes by charging it to us in the form of VAT. Unfortunately, the ordinary consumers has no one to pass on  the VAT ending him the one paying partly VECO’s taxes to the government.

HOW SYSTEM LOSS OCCUR?The System Loss we help paying for VECO is both technical and non-technical system losses. It is the electricity that is lost during the distribution of power from the generating plants to VECO’s receiving point up to our electrical meters.

I tried also scanning the 100-page Implementing Rules and Regulations of the EPIRA but there is no mention about System Loss. It’s not even included in the Definition of Terms. So, i have to scan this technical report on “Losses in Electric Power Systems” at the School of Electrical Engineering of the Purdue University in Indiana to know more about System Loss.

According to the report, losses in the transmission system could incur due to the resistance of the conductors like electrical wires used in transmitting the power. This is line resistance. The losses can be reduced by increasing the voltage level that the line is carrying but would incur substantial expenses in transformers and insulators.

Transmission lines would incur high losses when carrying full load of current while the electricity demand of the area served is only modest. In order to reduces losses, transformers are employed in carrying electricity. However, transformers have also losses on its own.

Another contributor in System Loss during transmission is the use of AC Transmission System. To reduce losses, transmission system used the High Voltage Direct Current (HVDC) Transmission System which allows high voltage transmission and is only limited by the amount of heat that the line can tolerate.

In summary, System Loss is too complex to be understood by the consumers. What most of us thought of System Loss are the pilferages of electricity like electrical theft which VECO maybe charging us to recover the losses. Understanding all of those charges i enumerated above would derive a conclusion that VECO is really doing business without spending much losses. :(

http://business.inquirer.net/109847/nea-taps-jica-expertise-to-reduce-systems-losses-of-power-cooperatives

NEA taps JICA expertise to reduce systems losses of power cooperatives

Philippine Daily Inquirer

7:17 PM | Wednesday, February 27th, 2013More News from Amy R. Remo

MANILA, Philippines—The state-run National Electrification Administration has tapped Japan International Cooperation Agency (JICA) for a technical cooperation project aimed at reducing systems losses and improving the operational efficiencies of electric cooperatives.

JICA also tapped the expertise of the Tokyo Electric Power Co. (Tepco) for the project entitled, “System Loss Reduction for Philippine Electric Cooperatives,” NEA said in a statement issued on Wednesday.

NEA stressed the significance of bringing down the systems losses—or power lost either in transmission through power lines or pilferage—as this would be a “comprehensive approach to mitigate the total amount of energy losses from power generation to distribution.” This will likewise bring down the cost of systems loss charges, which are being billed to end power consumers.

One of the key outputs of technical project was the “System Loss Reduction Manual,” which aims to develop the technical capability and planning strategies of both the NEA and the electric cooperatives, in reducing distribution system losses. This manual is being launched on Thursday, through a final workshop being conducted for about 80 electric cooperatives.

Takahiro Sasaki, chief representative of JICA Philippines, said he expected the project to serve as a means to attain the desired end of a better system loss management of local electric cooperatives.

“The manual and the forum are just tools to face the challenges of effective system loss management. Electric cooperatives should make extensive use of the manual to better manage their system losses for the benefit of the general public,” Sasaki said.

“We enjoin all electric cooperatives to make use of the Manual on System Loss Reduction to help them in their technical operation, thus ensuring the continuing reduction of their system losses,” added NEA Administrator Edita S. Bueno.

NEA previously established the System Loss Reduction Program (SLRP) through which the electric cooperatives’ system losses are closely monitored. On the national average, the system loss has always been within the cap of 13 percent as set by the Energy Regulatory Commission.

Currently, roughly 70 percent of the electric cooperatives have system losses below the 13-percent cap, while 19 other electric coops have posted single-digit system losses.

“With the System Loss Reduction Manual as a tool, more electric cooperatives are expected to reduce their losses and improve their technical performance,” the NEA added.

Read more: http://business.inquirer.net/109847/nea-taps-jica-expertise-to-reduce-systems-losses-of-power-cooperatives#ixzz3WnzyYhFk Follow us: @inquirerdotnet on Twitter | inquirerdotnet on Facebook

http://electrical-engineering-portal.com/total-losses-in-power-distribution-and-transmission-lines-1

Home / Technical Articles / Total Losses in Power Distribution and Transmission Lines (1)

Total Losses in Power Distribution and Transmission Lines (1)Posted Aug 19 2013 by jiguparmar in Transmission and Distribution with 20 Comments

Total Losses in Power Distribution and Transmission Lines (on photo: Power sunset over Kampala City, Uganda)

Introduction

Power generated in power stations pass through large and complex networks like transformers, overhead lines, cables and other equipment and reaches at the end users. It is fact that the unit of electric energy generated by Power Station does not match with the units distributed to the consumers. Some percentage of the units is lost in the distribution network.

This difference in the generated and distributed units is known as Transmission and Distribution loss. Transmission and Distribution loss are the amounts that are not paid for by users.

T&D Losses = (Energy Input to feeder(Kwh) – Billed Energy to Consumer(Kwh)) / Energy Input kwh x 100

Distribution Sector considered as the weakest link in the entire power sector. Transmission Losses is approximate 17% while Distribution Losses is approximate 50%.

There are two types of Transmission and Distribution Losses:

1. Technical Losses2. Non Technical Losses (Commercial Losses)

1. Technical Losses

The technical losses are due to energy dissipated in the conductors, equipment used for transmission line, transformer, subtransmission line and distribution line and magnetic losses in transformers.

Technical losses are normally 22.5%, and directly depend on the network characteristics and the mode of operation.

The major amount of losses in a power system is in primary and secondary distribution lines. While transmission and sub-transmission lines account for only about 30% of the total losses. Therefore the primary and secondary distribution systems must be properly planned to ensure within limits.

The unexpected load increase was reflected in the increase of technical losses above the normal level

Losses are inherent to the distribution of electricity and cannot be eliminated.

There are two Type of Technical Losses.

1. Permanent / Fixed Technical losses

Fixed losses do not vary according to current. These losses take the form of heat and noise and occur as long as a transformer is energized

Between 1/4 and 1/3 of technical losses on distribution networks are fixed losses. Fixed losses on a network can be influenced in the ways set out below

Corona Losses Leakage Current Losses Dielectric Losses Open-circuit Losses Losses caused by continuous load of measuring elements Losses caused by continuous load of control elements

2. Variable Technical losses

Variable losses vary with the amount of electricity distributed and are, more precisely, proportional to the square of the current. Consequently, a 1% increase in current leads to an increase in losses of more than 1%.

Between 2/3 and 3/4 of technical (or physical) losses on distribution networks are variable Losses.

By increasing the cross sectional area of lines and cables for a given load, losses will fall. This leads to a direct trade-off between cost of losses and cost of capital expenditure. It has been suggested that optimal average utilization rate on a distribution network that considers the cost of losses in its design could be as low as 30 per cent.

Joule losses in lines in each voltage level Impedance losses Losses caused by contact resistance.

Main Reasons for Technical Losses

1. Lengthy Distribution lines

In practically 11 KV and 415 volts lines, in rural areas are extended over long distances to feed loads scattered over large areas. Thus the primary and secondary distributions lines in rural areas are largely radial laid usually extend over long distances.

This results in high line resistance and therefore high I2R losses in the line.

Haphazard growths of sub-transmission and distribution system in to new areas. Large scale rural electrification through long 11kV and LT lines.

2. Inadequate Size of Conductors of Distribution lines

The size of the conductors should be selected on the basis of KVA x KM capacity of standard conductor for a required voltage regulation, but rural loads are usually scattered and generally fed by radial feeders. The conductor size of these feeders should be adequate.

3. Installation of Distribution transformers away from load centers

Distribution Transformers are not located at Load center on the Secondary Distribution System.

In most of case Distribution Transformers are not located centrally with respect to consumers. Consequently, the farthest consumers obtain an extremity low voltage even though a good voltage levels maintained at the transformers secondary.

This again leads to higher line losses. (The reason for the line losses increasing as a result of decreased voltage at the consumers end therefore in order to reduce the voltage drop in the line to the farthest consumers, the distribution transformer should be located at the load center to keep voltage drop within permissible limits.)

4. Low Power Factor of Primary and secondary distribution system

In most LT distribution circuits normally the Power Factor ranges from 0.65 to 0.75. A low Power Factor contributes towards high distribution losses.

For a given load, if the Power Factor is low, the current drawn in high  And  the losses proportional to square of the current will be more. Thus, line losses owing to the poor PF can be reduced by improving the Power Factor.

This can be done by application of shunt capacitors.

Shunt capacitors can be connected either in secondary side (11 KV side) of the 33/11 KV power transformers or at various point of Distribution Line.

The optimum rating of capacitor banks for a distribution system is 2/3rd of the average KVAR requirement of that distribution system.

The vantage point is at 2/3rd the length of the main distributor from the transformer. A more appropriate manner of improving this PF of the distribution system and thereby reduce

the line losses is to connect capacitors across the terminals of the consumers having inductive loads.

By connecting the capacitors across individual loads, the line loss is reduced from 4 to 9% depending upon the extent of PF improvement.

5. Bad Workmanship

Bad Workmanship contributes significantly role towards increasing distribution losses.

Joints are a source of power loss. Therefore the number of joints should be kept to a minimum. Proper jointing techniques should be used to ensure firm connections.

Connections to the transformer bushing-stem, drop out fuse, isolator, and LT switch etc. should be periodically inspected and proper pressure maintained to avoid sparking and heating of contacts.

Replacement of deteriorated wires and services should also be made timely to avoid any cause of leaking and loss of power.

6. Feeder Phase Current and Load Balancing>

One of the easiest loss savings of the distribution system is balancing current along three-phase circuits.

Feeder phase balancing also tends to balance voltage drop among phases giving three-phase customers less voltage unbalance. Amperage magnitude at the substation doesn’t guarantee load is balanced throughout the feeder length.

Feeder phase unbalance may vary during the day and with different seasons. Feeders are usually considered “balanced” when phase current magnitudes are within 10.Similarly, balancing load among distribution feeders will also lower losses assuming similar conductor resistance. This may require installing additional switches between feeders to allow for appropriate load transfer.

Bifurcation of feeders according to Voltage regulation and Load.

7. Load Factor Effect on Losses

Power consumption of customer varies throughout the day and over seasons.

Residential customers generally draw their highest power demand in the evening hours. Same commercial customer load generally peak in the early afternoon. Because current level (hence, load) is the primary driver in distribution power losses, keeping power consumption more level throughout the day will lower peak power loss and overall energy losses.

Load variation is Called load factor and It varies from 0 to 1.

Load Factor = Average load in a specified time period / peak load during that time period.

For example, for 30 days month (720 hours) peak Load of the feeder is 10 MW. If the feeder supplied a total energy of 5,000 MWH, the load factor for that month is (5,000 MWh)/ (10MW x 720) =0.69.

Lower power and energy losses are reduced by raising the load factor, which, evens out feeder demand variation throughout the feeder.

The load factor has been increase by offering customers “time-of-use” rates. Companies use pricing power to influence consumers to shift electric-intensive activities during off-peak times (such as, electric water and space heating, air conditioning, irrigating, and pool filter pumping).

With financial incentives, some electric customers are also allowing utilities to interrupt large electric loads remotely through radio frequency or power line carrier during periods of peak use. Utilities can try to design in higher load factors by running the same feeders through residential and commercial areas.

8. Transformer Sizing and Selection

Distribution transformers use copper conductor windings to induce a magnetic field into a grain-oriented silicon steel core. Therefore, transformers have both load losses and no-load core losses.

Transformer copper losses vary with load based on the resistive power loss equation (P loss = I2R). For some utilities, economic transformer loading means loading distribution transformers to capacity-or slightly above capacity for a short time-in an effort to minimize capital costs and still maintain long transformer life.

However, since peak generation is usually the most expensive, total cost of ownership (TCO) studies should take into account the cost of peak transformer losses. Increasing distribution transformer capacity during peak by one size will often result in lower total peak power dissipation-more so if it is overloaded.

Transformer no-load excitation loss (iron loss) occurs from a changing magnetic field in the transformer core whenever it is energized. Core loss varies slightly with voltage but is essentially considered constant. Fixed iron loss depends on transformer core design and steel lamination molecular structure. Improved manufacturing of steel cores and introducing amorphous metals (such as metallic glass) have reduced core losses.

9. Balancing 3 phase loads

Balancing 3-phase loads periodically throughout a network can reduce losses significantly. It can be done relatively easily on overhead networks and consequently offers considerable scope for cost effective loss reduction, given suitable incentives.

10. Switching off transformers

One method of reducing fixed losses is to switch off transformers in periods of low demand. If two transformers of a certain size are required at a substation during peak periods, only one might be required during times of low demand so that the other transformer might be switched off in order to reduce fixed losses.

This will produce some offsetting increase in variable losses and might affect security and quality of supply as well as the operational condition of the transformer itself. However, these trade-offs will not be explored and optimized unless the cost of losses are taken into account.

11. Other Reasons for Technical Losses

Unequal load distribution among three phases in L.T system causing high neutral currents. leaking and loss of power Over loading of lines. Abnormal operating conditions at which power and distribution transformers are operated Low voltages at consumer terminals causing higher drawl of currents by inductive loads. Poor quality of equipment used in agricultural pumping in rural areas, cooler air-conditioners

and industrial loads in urban areas.

Recommended EE articles //

6 Transformer Types You Can See In Commercial InstallationsMarch 16, 2015

Important Generator Set Rating ConsiderationsJanuary 30, 2015

The Consumer Power Substation With Metering On Medium Voltage SideJanuary 12, 2015

8 important definitions to quantify Load DiversityOctober 31, 2014

Share with engineers //

Article Tags //

distribution network, distribution transformers, load factor, power distribution, technical losses, total losses, transformers, transmission, transmission lines,

Filed Under Category //

Transmission and Distribution

About Author //

Jignesh Parmar

jiguparmar - Jignesh Parmar has completed his B.E(Electrical) from Gujarat University. He is member of Institution of Engineers (MIE),India. Membership No:M-1473586.He has more than 12 years experience in Transmission -Distribution-Electrical Energy theft detection-Electrical Maintenance-Electrical Projects (Planning-Designing-Technical Review-coordination -Execution). He is Presently associate with one of the leading business group as a Assistant Manager at Ahmedabad,India. He has published numbers of Technical Articles in "Electrical Mirror", "Electrical India", "Lighting India", "Industrial Electrix"(Australian Power Publications) Magazines. He is Freelancer Programmer of Advance Excel and design useful Excel base Electrical Programs as per IS, NEC, IEC,IEEE codes. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & Knowledge and

help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

http://www.davaolight.com/index.php?option=com_content&view=article&catid=122:march14&id=1952:knowing-system-loss-charge-and-how-it-can-lower-down-electricity-bill

Knowing system loss charge and how it can lower down electricity bill

Paying utility bills every month is like a way of life. But, most people do not really pay attention to the charges that make up the bill.

In Davao Light and Power Co. and in all distribution utilities, the electricity bill is unbundled. Meaning, various components of electricity tariffs are itemized and segregated for transparency to paying customers. However, not all customers understand these charges. One best example of these is the system loss charge.

System loss is simply the difference between the power purchased from energy sources and the power sold to customers. It is attributed to two components; technical and non-technical losses. Technical losses occur naturally and consist mainly of power dissipation or heat generated in electricity system components such as transformers, transmission and distribution lines. Meanwhile, non-technical losses are caused by actions external to the power system and an example of which is electricity theft.

Under the R.A. 9136 or Electric Power Industry Reform Act (EPIRA) Law of 2001, electric utilities like Davao Light can recover the power lost through the system loss charge. However, a utility can only recover up to a set ceiling of 8.5% as implemented by the Energy Regulatory Commission (ERC). Otherwise, the distribution utility absorbs the system loss in excess of the cap.

Even so, Davao Light only charges its customers the actual system loss which is lower than the cap. Hence, Davao Light customers pay less in terms of amount per kWh. As of February 2013, Davao Light's cumulative system loss is only at 7.29% which is lower compared to other electric utilities and cooperatives.

For example, with Davao Light's system loss at 7.29%, the residential customer with a monthly consumption of 175 kWh currently saves P11.71 or P140.52 in a year. This would not have been enjoyed by him had the company system loss exceeded the mandated cap.

To sustain a below cap system loss, Davao Light continuously invests in state-of-the-art equipment and upgrades its systems. It also is serious in its campaign against electricity theft or pilferage. These strategies are of significance to the electric utility as it does not want to pass on its inefficiency to its customers.

he ASKDLPC BILL text broadcast of Davao Light and Power Company is currently unavailable to its customers due to some technical problems since last March 23.

The electric distribution utility is working closely with its telecommunication service providers at the moment in order to restore the SMS service at the earliest possible time.

Davao Light apologizes to those customers who will be affected by the temporary unavailability of this text messaging service.

For your billing inquiries and concerns, you may call us at 229-DLPC (3572) or email us at davaolight@aboitiz.com.

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