Technical Aspects of Grid Interconnection - Revision history

Lisafeldmann: /* References */

2024-11-06T09:06:20Z

References

Lisafeldmann at 13:04, 31 October 2024

2024-10-31T13:04:01Z

Lisafeldmann at 10:50, 30 October 2024

2024-10-30T10:50:58Z

Lisafeldmann at 10:48, 30 October 2024

2024-10-30T10:48:34Z

Show changes

Ranisha: /* Future Information */

2018-09-11T13:09:38Z

Future Information

Johanna von Behaim at 15:17, 10 March 2017

2017-03-10T15:17:04Z

Show changes

Wiki Gardener: /* Future Information */

2014-08-11T12:02:40Z

Future Information

Wiki Gardener: /* Alternating Current (AC) and Direct Current (DC) */

2014-08-11T10:33:21Z

Alternating Current (AC) and Direct Current (DC)

Wiki Gardener at 10:32, 11 August 2014

2014-08-11T10:32:31Z

Wiki Gardener: /* Transformers and Substations */

2014-08-11T09:41:23Z

Transformers and Substations

@@ Line 350: / Line 350: @@
 == References ==
-This information is originally from the document [http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf Technical Aspects of Grid Interconnection]<br/>
+This information is originally from the chapter [http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf Technical Aspects of Grid Interconnection], published in UN DESA (2006): Multi Dimensional Issues in International Electric Power Grid Interconnections.<br/>
 <references /><br/>
 [[Category:Grid]]

@@ Line 338: / Line 338: @@
 <br/>
-== Future Information ==
+== Further Information ==
 *[[Portal:Grid|Grid Portal on energypedia]]

@@ Line 104: / Line 104: @@
 <br/>
-== Impedance, Reactance, Inductance, Capacitance ==
+=== Impedance, Reactance, Inductance, Capacitance ===
 AC circuits involve not only resistance but other physical phenomena that impede the flow of current. These are inductance and capacitance, referred to collectively as reactance. When AC currents pass through a reac tance (e.g. in transmission and distribution lines, in transformers, or in end-use equipment such as electric motors) some of the energy is temporarily stored in electro-magnetic fields.
@@ Line 120: / Line 120: @@
 <br/>
-== Complex Power: Real, Reactive, Apparent ==
+=== Complex Power: Real, Reactive, Apparent ===
 For AC systems, there are three kinds of power: real, reactive, and apparent. Real power (sometimes called active power) is what is consumed by resistances, and is measured in W (or kW, or MW). Reactive power is consumed by reactances, and is measured in volt-amperes reactive, or VAR (sometimes kVAR, or MVAR). Apparent power is the complex sum of real and reactive power, and is measured in voltamperes, or VA (or kVA or MVA). S = √(P2 + Q2), where S is apparent power, P is real power, and Q is reactive power. Apparent power is what must be supplied by the generators in a power system to meet the system’s electrical load, whereas end-use is generally measured in terms of real power only. Utilities always seek to minimize reactive power consumption, among other reasons because it is difficult to measure and be compensated for reactive power by customers.
@@ Line 126: / Line 126: @@
 <br/>
-== Loads and Power Factors ==
+=== Loads and Power Factors ===
 An electrical load is the power drawn by an end-use device or customer connected to the power system. (Sometimes, “load” is used to refer to the end-use devices or customers themselves, but among engineers it usually refers to the power demand.) Loads can be resistive or reactive, and are often a combination of both. The extent to which a load is resistive is measured by its power factor, (p.f.), which is equal to the cosine of the phase difference between the current and voltage through the load: p.f. = cos φ. When the power factor is at its maximum value of one, the load is purely resistive. On the other hand, the smaller the power factor, the greater the phase difference and the greater the reactive power component of the load. Inductive loads, such as electric motors, have a lagging power factor (see 2.1.9), and are said to consume reactive power. Capacitive loads have a leading power factor and are said to be sources of reactive power. Given the voltages and currents through a circuit element, apparent, real, and reactive power can be calculated respectively as follows: S = IRMS * VRMS P = S * p.f. = IRMS * VRMS * cos φ Q = IRMS * VRMS * sin φ
@@ Line 134: / Line 134: @@
 <br/>
-== Three-Phase Systems ==
+=== Three-Phase Systems ===
 House current is generally single-phase AC power, but the rest of the power system from generation to secondary distribution employs 3-phase AC. This means that transmission lines have three separate conductors, each carrying one-third of the power. The waveforms of the voltage in each phase are separated by 120°.
@@ Line 149: / Line 149: @@
 <br/>
-== Basic Design Features ==
+=== Basic Design Features ===
 <u>The basic design features of an interconnection include the following elements:</u>
@@ Line 224: / Line 224: @@
 <br/>
-== Technical Issues for AC Interconnection ==
+=== Technical Issues for AC Interconnection ===
 One way of thinking about the technical issues of AC interconnections is to group them into those associated with the transmission interconnection itself, and those associated with operating the larger interconnected system. Transmission issues are discussed in <span style="color:#008000">[[Technical Aspects of Grid Interconnection#Transmission Issues|Key issues include thermal limits]], </span>stability limits, and voltage regulation, which are the main constraints on transmission line operation. Other transmission issues include loop and parallel path flows, available transfer capacity, and FACTS technologies. System-wide issues are discussed in [http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf,_page_16 including frequency regulation,]<span style="color:#008000">p</span>ower quality, the coordination of planning and operations, political and institutional cooperation, systems that are aging or in poor repair, and the operation of nuclear power plants. The implications of electricity market liberalization for interconnected systems are also discussed.
@@ Line 276: / Line 276: @@
 <br/>
-== Systems Issues ==
+=== Systems Issues ===
 Key technical systems issues that must be addressed in planning and implementing a grid interconnection include frequency regulation, coordination of operations, interconnections of power systems with weak grids, and aspects of interconnection that are associated with electricity market liberalization. Frequency Regulation Controlling frequency in a synchronous network is ultimately an issue of precisely matching generation to load. This load-matching occurs on several time scales. System planners and operators plan generation from hours to months in advance, coordinating the dispatch of generating units and power exchanges with other systems based on factors such as historical load patterns, weather predictions, maintenance
@@ Line 286: / Line 286: @@
 <br/>
-== Coordinating Operations ==
+=== Coordinating Operations ===
 The basic geographical unit of a power system is the control area, which typically has a single control center responsible for monitoring system conditions and scheduling the dispatch of all generation. In interconnected systems, transmission lines to neighboring control areas are metered and the incoming and outgoing power flows are scheduled and continuously monitored. A continuous record of the balance of load, generation, and exchanges with other control areas called the '''Area Control Error (ACE)''' is used to plan real-time corrections to maintain load-generation balance. Interconnections create a number of coordination challenges, both institutional and technical. For example, reliability standards and constraints may differ, and there may be differences in regulation and control schemes and technologies. It is important for the operators and planners of interconnected systems to be aware of the conditions and practices in their neighboring control areas. Good communication between different system operators is important for agreeing on and coordinating interchange schedules, transmission loading, maintenance schedules, procedures for fault clearing, and emergency protocols<ref>John Casazza (998), “Blackouts: Is the Risk Increasing?”. Electrical World , April 998, p.62</ref>. As interconnected systems expand to encompass large geographical scales, technology is striving to keep up with the associated complexities and risks.<br/>

@@ Line 357: / Line 357: @@
 *[[Rural Electrification - Minimum Safety Standards for Household Connection|Rural Electrification - Minimum Safety Standards for Household Connection]]
 *[[Permissible_Voltage_Drop|Permissible Voltage Drop]]<br/>
 <br/>
 = References<br/> =

@@ Line 336: / Line 336: @@
 *Clearly define the rights and obligations of all parties
 *Monitor behavior and rigorously enforce rule
@@ Line 342: / Line 343: @@
 *[[Portal:Grid|Grid Portal on energypedia]]
+*[[Rural_Electrification_-_Minimum_Safety_Standards_for_Household_Connection|Rural Electrification - Minimum Safety Standards for Household Connection]]

@@ Line 51: / Line 51: @@
 <br/>
 == Alternating Current (AC) and Direct Current (DC)<br/> ==
-Electric power comes in two forms: alternating current (AC) and direct current (DC). These forms are characterized by the behavior of their waveforms: AC alternates between positive and negative polarity with respect to ground, while DC does not.
+Electric power comes in two forms:
 In power systems, AC is generally a sine wave, while DC is a constant value. Early electricity systems, such as Thomas Edison’s Pearl Street Station in New York City, which provided the world’s first public electric service in 1882, were DC. However, by the beginning of the 20th century AC systems had become standard worldwide. The main reason for the adoption of AC was that it is relatively simple to change AC voltage levels by using transformers, while it is difficult to change DC voltages. The development of solid-state power electronics in recent years has allowed an increased use of DC in the form of HVDC interconnections, but otherwise power systems remain AC.
 <br/>
 == Frequency (Hz)<br/> ==

@@ Line 1: / Line 1: @@
-= Overview - The Evolution of Interconnected Systems<br/> =
+= Overview - The Evolution of Interconnected Systems<ref name="Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, ">Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, </ref><br/> =
 Electricity grid interconnections have played a key role in the history of electric power systems. Most national and regional power systems that exist today began many decades ago as isolated systems, often as a single generator in a large city. As power systems expanded out from their urban cores, interconnections among neighboring systems became increasingly common<ref name="T. Hughes (983),Networks of Power: Electrification in Western Society, 1880-1930, Johns Hopkins University, Baltimore, MD">T. Hughes (983),Networks of Power: Electrification in Western Society, 1880-1930, Johns Hopkins University, Baltimore, MD</ref> . Groups of utilities began to form power pools, allowing them to trade electricity and share capacity reserves. The first power pool in the United States was formed in the Connecticut Valley in 1925<ref name="Rincliffe, R.G. (967), “Planning and Operation of a Large Power Pool.”.IEEE Spectrum: 9-96. January 967. The PJM (Pennsylvania/New Jersey/Maryland) grid was next to be developed, in 927.">Rincliffe, R.G. (967), “Planning and Operation of a Large Power Pool.”.IEEE Spectrum: 9-96. January 967. The PJM (Pennsylvania/New Jersey/Maryland) grid was next to be developed, in 927.</ref>.<br/>
@@ Line 14: / Line 14: @@
 <br/>
-= General Potential Benefits of Grid Interconnections<ref name="http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf">http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf</ref><br/> =
+= General Potential Benefits of Grid Interconnections<ref name="Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, ">Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, </ref><br/> =
 There are number of technical rationales for grid interconnections, many of which have economic components as well.<br/>
@@ Line 30: / Line 30: @@
 <br/>
-= Technical Complexities and Risks of Grid Interconnections<ref name="http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf">http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf</ref><br/> =
+= Technical Complexities and Risks of Grid Interconnections<ref name="Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, ">Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, </ref><br/> =
 The fact that interconnections between power systems are increasingly common does not imply that they are as simple as connecting a few wires. Interconnections obviously entail the expense of constructing and operating transmission lines and substations, or in the case of HVDC, converter stations. Interconnections also entail other costs, technical complexities, and risks. For AC interconnections especially, a power system interconnection is a kind of marriage, because two systems become one in an important way when they operate in synchronism. To do this requires a high degree of technical compatibility and operational coordination, which grows in cost and complexity with the scale and inherent differences of the systems involved. To give just one example, when systems are interconnected, even if they are otherwise fully compatible, fault currents (the current that flows during a short circuit) generally increase, requiring the installation of higher capacity circuit breakers to maintain safety and reliability. To properly specify these and many other technical changes required by interconnection requires extensive planning studies, computer modeling, and exchange of data between the interconnected systems.<br/>
@@ Line 44: / Line 44: @@
 <br/>
-= Technical Parameters of Interconnection<ref name="http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf">http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf</ref><br/> =
+= Technical Parameters of Interconnection<ref name="Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, ">Technical Aspects of Grid Interconnection - http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf, </ref><br/> =
 == Basic Electrical Parameters<br/> ==
@@ Line 184: / Line 184: @@
 <br/>
 == Transformers and Substations ==
@@ Line 195: / Line 196: @@
 <br/>
 == Protection Systems ==
-Protection systems are an extremely important part of any power system. Their primary function is to detect and clear faults, which are inadvertent electrical connections – that is, short circuits – between system components at different voltages. When faults occur, very high currents can result, typically 2-10 times as high as normal load currents. Since power is proportional to I2, a great deal of energy can be delivered to unintended recipients in a very short time. The goal of protection systems is to isolate and de-energize faults before they can harm personnel or cause serious damage to equipment. Note that protection systems are designed to protect the power system itself, rather than end-user equipment. The key components of protection systems are circuit breakers, instrument transformers, and relays. Circuit breakers are designed to interrupt a circuit in which high levels of current are flowing, typically within three voltage cycles (about 50 milliseconds in a 60 Hz system). <br/>
+Protection systems are an extremely important part of any power system. Their primary function is to detect and clear faults, which are inadvertent electrical connections – that is, short circuits – between system components at different voltages. When faults occur, very high currents can result, typically 2-10 times as high as normal load currents. Since power is proportional to I2, a great deal of energy can be delivered to unintended recipients in a very short time. The goal of protection systems is to isolate and de-energize faults before they can harm personnel or cause serious damage to equipment. Note that protection systems are designed to protect the power system itself, rather than end-user equipment. The key components of protection systems are circuit breakers, instrument transformers, and relays. Circuit breakers are designed to interrupt a circuit in which high levels of current are flowing, typically within three voltage cycles (about 50 milliseconds in a 60 Hz system).<br/>
 To do this they must quench the electric arc that appears when the breaker contacts are opened; this is usually accomplished by blowing a gas, such as compressed air or sulfur hexafluoride (SF6) across the contacts. Since human operators generally could not respond to a fault in time to prevent damage, circuit breakers are operated by automatic relays that sense faults or other undesirable system conditions. To distinguish between normal operations and fault conditions, relays are connected to instrument transformers – '''voltage transformers (VT)''' and '''current transformers (CT)''' – that reflect the voltages and currents of the equipment they are connected to. Relays themselves can be either electromechanical or solid state devices. Essential aspects of protection system design include determining the specifications and placement of protection equipment, and also the correct timing and sequence of relay operations. Protection engineers must determine how long an undesirable condition should be allowed to persist before opening a circuit breaker, and the order in which circuit breakers must open to correctly isolate faults in different zones<ref name="J. Blackburn (998), Protective Relaying: Principles and Applications , 2nd ed. Marcel Dekker, New York.">J. Blackburn (998), Protective Relaying: Principles and Applications , 2nd ed. Marcel Dekker, New York.</ref>.<br/>
@@ Line 224: / Line 226: @@
 == Technical Issues for AC Interconnection<br/> ==
-One way of thinking about the technical issues of AC interconnections is to group them into those associated with the transmission interconnection itself, and those associated with operating the larger interconnected system. Transmission issues are discussed in <span style="color:#008000">Key issues include thermal limits, </span>stability limits, and voltage regulation, which are the main constraints on transmission line operation. Other transmission issues include loop and parallel path flows, available transfer capacity, and FACTS technologies. System-wide issues are discussed in
+One way of thinking about the technical issues of AC interconnections is to group them into those associated with the transmission interconnection itself, and those associated with operating the larger interconnected system. Transmission issues are discussed in <span style="color:#008000">[[Technical_Aspects_of_Grid_Interconnection#Transmission_Issues|Key issues include thermal limits]], </span>stability limits, and voltage regulation, which are the main constraints on transmission line operation. Other transmission issues include loop and parallel path flows, available transfer capacity, and FACTS technologies. System-wide issues are discussed in [http://www.un.org/esa/sustdev/publications/energy/chapter2.pdf,_page_16 including frequency regulation,]<span style="color:#008000">p</span>ower quality, the coordination of planning and operations, political and institutional cooperation, systems that are aging or in poor repair, and the operation of nuclear power plants. The implications of electricity market liberalization for interconnected systems are also discussed.
-<span style="color:#008000">including frequency regulation, p</span>ower quality, the coordination of planning and operations, political and institutional cooperation, systems that are aging or in poor repair, and the operation of nuclear power plants. The implications of electricity market liberalization for interconnected systems are also discussed.
+The capacity of transmission lines, transformers, and other equipment is determined by temperature limits. If these limits are exceeded, the equipment can be damaged or destroyed. Equipment ratings have traditionally been conservative, and operators have stayed well below the rated limits, but increased power trading in liberalized markets has created pressure for higher utilization. Instead of a single thermal limit, dynamic ratings are now often used. For example, transmission lines can carry more current when heat is effectively dissipated, and thus will have a higher rating on cold, windy days without direct sunlight. When transmission lines heat up, the metal expands and the line sags. If the sag becomes too great, lines can come into contact with surrounding objects, causing a fault. Excess sag can also cause the metal to lose tensile strength due to annealing, after which it will not shrink back to its original length. Important transmission lines are often monitored by a device called a “sagometer”, which measures the amount of sag, making system operators aware of dangerous sag conditions.
-Stability limits<br/>
+'''Stability limits'''<br/>
 The stability limit of a transmission line is the maximum amount of power that can be transmitted for which the system will remain synchronized if a disturbance occurs. The power flow through a transmission line is governed by the difference in power angle between the sending and receiving sides: P = VR ∗ VS ∗ sinδ / X
@@ Line 323: / Line 329: @@
 *Improve incentives for investing in infrastructure
 *Clearly define the rights and obligations of all parties
-*Monitor behavior and rigorously enforce rules
+*Monitor behavior and rigorously enforce rule
 = Future Information =
-[[Portal:Grid|Portal:Grid]]
+*[[Portal:Grid|Grid Portal on energypedia]]
 = References<br/> =

@@ Line 183: / Line 183: @@
 <br/>
 == Transformers and Substations ==
@@ Line 188: / Line 189: @@
 Transformers are used to change voltage levels in AC circuits, allowing transmission at high voltages to minimize resistive losses, and low voltages at the customer end for safety. This ability, following the development of transformers by William Stanley in 1885, led to the rapid adoption of AC systems over DC systems. The essential element of a transformer consists of two coils of wire wrapped around an iron core. An alternating current in one coil produces a changing electromagnetic field that induces a current in the other. The voltages on either side are in the same ratio as the number of turns on each coil. For example, a transformer with a 10:1 “turns ratio” that is connected to a 15 kV supply on its primary side, will have a voltage of 150 kV on its secondary side. Transformers step up the voltage from generator to transmission system, and other transformers step it down, often in several stages, from transmission to sub-transmission to primary distribution to secondary distribution, and finally to the end-user voltage, such as 120 V. At the distribution level, transformers often have taps that can be used to change the turns ratio; this allows operators to maintain customer voltage levels when system voltages change. Modern transformers are extremely efficient, typically greater than 99%, but even small losses can produce a great deal of heat, which must be dissipated to prevent damage to the equipment. Large transformers are cooled by circulating oil, which also functions as an electrical insulator.
-[[File:Towers.jpg|thumb|right|300px|From Chapter 4 of US Nuclear Regulatory Commission (NRC,996), Generic Environmental Impact Statement for License Renewal of Nuclear Plants (Report # NUREG- 437 Vol. ), available as http://www. nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1437/v1/ Original source: R. L. Kroodsma and J. W. Van Dyke (985),Technical and Environmental Aspects of Electric Power Transmission, Report # ORNL-6 65, Oak Ridge National Laboratory, Oak Ridge, Tennessee]]
+[[File:Towers.jpg|thumb|right|300px|From Chapter 4 of US Nuclear Regulatory Commission (NRC,996), Generic Environmental Impact Statement for License Renewal of Nuclear Plants (Report # NUREG- 437 Vol. ), Original source: R. L. Kroodsma and J. W. Van Dyke (985),Technical and Environmental Aspects of Electric Power Transmission, Report # ORNL-6 65, Oak Ridge National Laboratory, Oak Ridge, Tennessee]]
 Large transformers are housed in substations, where sections of a transmission and distribution system operating at different voltages are joined. Larger substations have a manned control room, while smaller substations often operate automatically. In addition to transformers, important substation equipment includes switchgear, circuit breakers and other protective equipment (see next section), and capacitor banks used to provide reactive power support.
 <br/>
 == Protection Systems ==