Renewable and Efficient
`Electric Power Systems
`
`Gilbert M. Masters
`Stanford University .
`
` “M)INTERSCIENCE
`
`JOHN WILEY & SONS, INC., PUBLICATION
`
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`Copyright © 2004 by John Wiley & Sons, Inc., Hoboken, New Jersey. All rights reserved.
`
`Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
`Published simultaneously in Canada.
`
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`Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best
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`
`Library of Congress Cataloging-in-Publication Data
`
`Masters, Gilbert M.
`Renewable and efficient electric power systems / Gilbert M. Masters.
`p. cm.
`Includes bibliographical references and index.
`ISBN 0-471-28060-7 (cloth)
`.
`1. Electric power systems—Energy conservation. 2. Electric power systems—Electric
`losses. I. Title
`
`TK1005.M33 2004
`621.31-de22
`
`Printed in the United States of America.
`
`10987654
`
`2003062035
`
`ii
`
`

`

`3.10 TRANSMISSION AND DISTRIBUTION
`
`TRANSMISSION AND DISTRIBUTION
`
`145
`
`While the generation side of electric power systems usually receives the most
`attention, the shift toward utility restructuring, along with the emergence ofdis-
`tributed generation systems, is causing renewed interest in the transmission and
`distribution (T&D) side of the business.
`.
`Figure 3.33 showsthe relative capital expenditures on T&D over time com-
`_
`_ pared with generation by U.S. investor-owned utilities. The moststriking feature
`__ of the graph is the extraordinary period of power plant construction that lasted
`from the early 1970s through the mid-1980s, driven largely by huge spending for
`~ nuclear powerstations. Except for that anomalous period, T&D construction has
`generally cost utilities more than they have spent on generation. In the latter half
`of the 1990s, T&D expenditures were roughly double that of generation, with
`
`
`most of that being spent on the distribution portion of T&D.
`ae
`Theutility grid system starts with transmission lines that carry large bios:
`
`power, at voltages ranging from 161 kV to 765 kV, over relatively long
`
`distances from central generating stations toward major load centers. Lower-
`
`oltage subtransmission lines may carry it to distribution substations located
`
`
`oser to the loads. At substations, the voltage is lowered once again, to typi-
`
`ally 4.16 to 24.94 kV and sent out over distribution feeders to customers. An
`
`example of a simple distribution substation is diagrammedin Fig. 3.34. Notice
`combination of switches, circuit breakers, and fuses that protect key com-
`
`ents and which allow different segments of the system to be isolated for
`rntenance or during emergency faults(short circuits) that may occur in the
`
`
`
`—— Transmission and distribution ~-- Generation
`
`
`
`
`
`
`
`30.+1995 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 19961998
`
`Year
`
`
`Transmission and distribution (T&D) construction expenditures at U.S.
`edutilities compared with generation. Except for the anomalous spurt in
`struction during the 1970s and early 1980s, T&D costs have generally
`ration. From Lovins et al. (2002), using Edison Electric Institute data.
`
`
`
`

`

`146
`
`THE ELECTRIC POWER INDUSTRY
`
`Bus Breaker
`
`Radial
`
`‘
`
`Overcurrent
`Feeder
`ete
`
`.
`.
`Distribution.
`Disconnect Relay
`Disconnect
`Substation
`Transformer—=I
`Substation
`Z\ A
`t
`Dis
`cc!
`a
`isconnect
`;
`=
`_ : ee+Distribution
`
`Buse &
`Feeders
`e
`g QO
`QO
`4.16 kV —
`=
`= Overcurrent
`Bho kY
`_.
`vee
`—
`Relay
`Lightning.
`Arrestors
`
`_.
`Subtransmission
`System
`34.5 kV - 138 kV
`
`Main Bus
`
`‘
`C)
`
`Feeder
`Breakers
`
`Voltage
`Regulators
`
`Figure 3.34
`<A simple distribution station. For simplication, this is drawn as a one-line
`diagram, which meansthat a single conductor on the diagram corresponds to the three
`lines in a three-phase system.
`
`3.10.4 The National Transmission Grid
`The United States has close to 275,000 miles of transmission lines, most of which .
`
`carry high-voltage, three-phase ac power. Investor owned utilities (IOUs) own
`—
`
`three-fourths of those lines (200,000 miles), with the remaining 75,000 miles :
`- owned by federal, public, and cooperative utilities. Independent power produ
`ers do not own transmission lines so their ability to wheel power to custor
`
`
`depends entirely on their ability to have access to that grid. As will be described
`in the regulatory section of this chapter, Federal Energy Regulatory Commissi
`
`(FERC) Order 2000 is attempting to dramatically change the utility-ownershi
`
`of the grid as part of its efforts to promote a fully competitive wholesale.po
`market. Order 2000 encourages the establishment of independent regionaltr
`
`mission organizations (RTOs), which could shift transmission line ownershi
`a handful of separate transmission companies (TRANSCOs), or it could
`
`continued utility ownership but withcontrol turned over to independent,
`operators (ISQs).
`:
`As shown in Fig. 3.35, the transmission network in the United States
`
`
`nized around three major power grids:
`the Eastern Interconnect,
`the We
`
`
`Interconnect, and the Texas Interconnect. Texas is unique in that its powe
`not cross state lines so it is not subject to control by the Federal Ener;
`
`ulatory Commission (FERC). Within each of these three interconnection ;
`utilities buy and sell power among themselves. There are very limite
`
`connections between the three major power grids. After a major blac
`the Northeastern United States in 1965, the North American Electric
`
`ity Council (NERC) was formed to help coordinate bulk power pol
`affect the reliability and adequacy ofservice within 10 designatedrc
`US. grid.While almost all power in the United States is transmitted0
`
`phase ac transmission lines,
`there are circumstances in which hig
`
`
`
`
`

`

`
`
`
`
`
`
`Texas Interconnect
`
`TRANSMISSION AND DISTRIBUTION
`
`147
`
`
`
`
`Western
`
`Interconnect
`
` Eastern
`interconnect
`
`_Figure 3.35 Transmission of U.S. electric power is divided into three quite separate
`power grids, which are further subdivided into 10 North American Electric Reliability
`
`
`Council Regions. ECAR, East Central Area Reliability Coordination Agreement; ERCOT,
`
`Electric Reliability Council of Texas; FRCC, Florida Reliability Coordinating Council;
`
`MAAC, Mid-Atlantic Area Council; MAPP, Mid-Continent Area Power Pool; MAIN,
`
`Mid-America Interconnected Network; NPCC, Northeast Power Coordinating Council;
`SERC, Southeastern Electric Reliability Council; SPP, Southwest Power Pool; WSCC,
`festern‘Systems Coordinating Council. (FTA 2001).
`
`HVDC) lines have certain benefits. They are especiaily useful for inter-
`
`
`necting the power grid in one part of the country to a grid in another
`_since problems associated with exactly matching frequency, phase, and
`
`
`ages are eliminated in dc. An example of such a system is the 600-
`6000-MW Pacific Intertie between the Pacific Northwest and South-
`alifornia. Similar situations occur between countries, and indeed many
`
`-HVDC.
`links around the world are used to link the grid of one
`
`to another—examples include: Norway—Denmark, Finland—Sweden,
`
`
`Denmark, Canada—United States,
`.Germany—Czechoslovakia, Aus-
`
`wary, Argentina—Brazil, France—England, and Mozambique—South
`control and interfacing simplicity of de makes HVDClinks particu-
`uitedfor connecting ac grids that operate with different frequencies,
`
`se,for example, in Japan, with its 50-Hz and 60-Hz regions.
`inks. require converters at both ends of the dc transmission line to
`
`0 de and then to invert de back to ac. The converters at each end
`either as a rectifier or as an inverter, which allows power flow
`
`
`

`

`148
`
`THE ELECTRIC POWER INDUSTRY
`
`AC Generators
`
`Loads
`
`AC System
`
`HVDC Link
`CKO DC Line
`
` Transformer
`
`Transformer
`
`Rectifier
`
`Inverter en
`AC System
`
`Figure 3.36 A one-line diagram of a dc link between ac systems. The inverter and
`rectifier can switch roles to allow bidirectional power flow.
`
`:
`On
`te 4
`
`in either direction. A simple one-line drawing of an HVDC link is shownin
`Fig. 3.36. HVDC lines offer the most economic form of transmission over very
`long distances—that is, distances beyond about 500 miles or so. For these longer
`distances, the extra costs of converters at each end can be more than offset by
`the reduction in transmission line and towercosts.
`|
`
`
`
`3.10.2 Transmission Lines
`The physical characteristics of transmission lines depend very much on the volt- |
`ages that they carry. Cables carrying higher voltages must be spaced further apart
`from each other and from the ground to prevent arcing from line to line, and:
`higher current levels require thicker conductors. Table 3.5 lists the most common_
`
`
`
`
`voltages in use in the United States along with their usual designation as being
`ae
`transmission, subtransmission, distribution, or utilization voltages.
`
`Figure 3.37 shows examples of towers used for various representative trans- .
`mission and subtransmission voltages. Notice that the 500-kV tower has three
`
`suspended connections for the three-phase current, but it also shows a fourth
`connection, namely, a ground wire above the entire structure. This groundwir
`not only serves as a return path in case the phases are not balanced, butalso
`pROvaneS a certain amountof lightning protean:
`
`eee sae
`
`TABLE 3.5 Nominal Standard T&D System Voltages
`Transmission (kV)
`Subtransmission (kV) Distribution (kV) Utilization(V)
`
`765
`500
`345
`230
`161
`
`.
`
`138
`115
`69
`AG
`34.5
`
`24.94
`22.86
`13.8
`13.2.
`12.47
`8.32
`4.16
`
`600...
`480.
`240.
`208.
`120
`
`
`
`
`

`

`pooscvnbdeam
`
`CHAPTER6
`
`
`
` WIND POWER SYSTEMS
`
`
`
`6.1 HISTORICAL DEVELOPMENT OF WIND POWER
`
`
`Wind has been utilized as a source of power for thousands of years for such
`asks as propelling sailing ships, grinding grain, pumping water, and powering
`
`ctory machinery. The world’s first wind turbine used to generate electric-
`
`ity was built by a Dane, Poul
`la Cour, in 1891. It is especially interesting
`
`note that La Cour used the electricity generated by his turbines to elec-
`
`
`lyze water, producing hydrogen for gas lights inthe local schoolhouse. In
`
`at regard we could say that he was 100 years ahead of his time since the
`
`sionthat many have for the twenty-first century includes photovoltaic and
`
`indpower systems making hydrogen by electrolysis to generate electric power
`fuelcells.
`
`
`. In1941 one of the largest wind-powered systems ever built went into
`
`
`tion at Grandpa’s Knob in Vermont. Designed to produce 1250 kW from
`
`
`Viniles per hour before it catastrophically failed in 1945 in a modest 25-
`nd(one ofits 8-ton blades broke loose and was hurled 750 feet away).
`
`
`é andd Efficient Electric Power Systems. By Gilbert M. Masters
`471-28060-7 © 2004 John Wiley & Sons, Inc.
`
`307
`
`

`

`308
`
`WIND POWER SYSTEMS
`
`‘Subsequent interest in wind systems declined as the utility grid expanded and
`became morereliable and electricity prices declined. The oil shocks of the 1970s,
`which heightened awareness of our energy problems, coupled with substantial
`financial and regulatory incentives for alternative energy systems, stimulated a
`renewal of interest in windpower. Within a decade or so, dozens of manufac-
`turers installed thousands of new wind turbines (mostly in California). While
`many of those machines performed below expectations, the tax credits and other
`incentives deserve credit for shortening the time required to sort out the best
`technologies. The wind boom in California was short-lived, and when the tax
`credits were terminated in the mid-1980s, installation of new machines in the
`United States stopped almost completely for a decade. Since most of the world’s
`wind-power sales, up until about 1985, were in the United States,
`this sud- .
`den drop in the market practically wiped out the industry worldwide until the |
`early 1990s.
`Meanwhiley, wind turbine technology development continued—especially in~
`Denmark, Germany, and Spain—and those countries were ready when sales.
`began to boom in the mid-1990s. As shown in Fig. 6.1,
`the global installed
`capacity of wind turbines has been growing at over 25% per year.
`.
`Globally, the countries with the most installed wind capacity are shown in
`Fig. 6.2. As of 2003, the world leader is Germany, followed by Spain, the United _
`States, Denmark, and India. In the United States, California continuesto have the_
`most installed capacity, but as shownin Fig. 6.3, Texas is rapidly closing the gap.
`Large numbersof turbines have beeninstalled along the Columbia River Gorge in_
`the Pacific Northwest, and the windy Great Plains states are experiencing mayor_
`growth as well.
`
`35,000
`
`30,000
`
`25,000
`
`20,000
`
`
`
`Capacity(MW)
`
`15,000.
`
`10,000
`
`5000
`
`| 0
`
`Figure 6.1 Worldwide installed wind-power capacity and net annual additionstto ci
`ity have grown by over 25% per year since the mid-1990s. Data from AWEA.
`
`
`
`: 40,000
`
`
`
`E} Installed Capacity
`
`B® Net Additions
`
`=
`
`

`

`
`500
`
`Minnesota
`
`Wasnington
`
`Oregon.
`
`Wyoming
`
`Kansas
`
`Texas
`
`lowa
`
`gCc_
`
`2c
`
`I
`oO
`
`
`
`
`_ Figure 6.3
`
`Installed wind capacity in the United States in 1999 and 2002.
`
`YPES OF WIND TURBINES
`
`
`
`early wind turbines were used to grind grain into flour, hence the name
`Ki mill.” Strictly speaking, therefore, calling a machine that pumps water or
`eselectricity a windmill is somewhat of a misnomer. Instead, people are
`
`TYPES OF WIND TURBINES
`
`309
`
`Germany
`12,001
`
`Figure 6.2. Total installed capacity in 2002, by country. AWEA data.
`
`2000
`
`
`
` 1500
`
`1000
`
`
`
`

`

`310
`
`WIND POWER SYSTEMS
`
`using more accurate, but generally clumsier, terminology: ‘““Wind-driven gener-
`a>
`66.
`ator,”
`“wind generator,” “wind turbine,” “wind-turbine generator”? (WTG), and
`“wind energy conversion system” (WECS) all are in use. For our purposes,
`“wind turbine” will suffice even though often we will be talking about system
`components (e.g., towers, generators, etc.) that clearly are not part of a “turbine.”
`' One way to classify wind turbines is in terms of the axis around which the
`turbine blades rotate. Most are horizontal axis wind turbines (HAWT), butthere
`are some with blades that spin around a vertical axis (VAWT). Examples of the
`two types are shownin Fig. 6.4.
`The only vertical axis machine that has had any commercial success is the
`Darrieus rotor, named after. its inventor the French engineer G. M. Darricus,
`who first developed the turbines in the 1920s. The shape of the blades is that
`which would result from holding a rope at both ends and spinning it around a
`vertical axis, giving it a look that is not unlike a giant eggbeater. Considerable
`developmentof these turbines, including a 500-kW, 34-m diameter machine,was
`undertaken in the 1980s by Sandia National Laboratories in the United States.
`An American company, FloWind, manufactured and installed a number ofthese
`wind turbines before leaving the business in 1997.
`The principal advantage of vertical axis machines, such as the Darrieusrotor,
`is that they don’t need any kind of yaw control to keep them facing into the
`wind. A second advantage is that the heavy machinery contained in the nacelle
`(the housing around the generator, gear box, and other mechanical components)
`can be located down on the ground, where it can be serviced easily. Since the
`heavy equipment is not perched on top of a tower, the tower itself need not
`be structurally as strong as that for a HAWT. The tower can be lightened even
`further when guy wires are used, which is fine for towers located on land but not
`for offshore installations. The blades on a Darrieus rotor, as they spin around,are
`almost always in pure tension, which meansthat they can berelatively lightweight
`
`Gear
`
`
`/ box Generator
`
`secs
`
`
`
`|| Tower
`
`
`
`Guy wires
`a
`
`Wind
`
`Wind
`
`> -
`_—
`
` Rotor bladesaoeef 4
`Wind
`|| Nacele
`Wing
`ae
`
`
`
`
`Generator,
`Gear Box
`
`Darrieus
`VAWT
`
`Rotor
`blades
`
`i ih ;
`
`Upwin
`HAWT
`
`SHEER
`
`Downwind
`HAWT
`
`(a)
`
`(b)
`
`(c)
`
`Figure 6.4 Horizontal axis wind turbines (HAWT) are either upwind machines (a) of
`downwind machines (b). Vertical axis wind turbines (VAWT)accept the wind from any
`direction (c).
`
`
`
`
`
`

`

`336
`
`WIND POWER SYSTEMS
`
`
`
`
`
`Powerdelivered(kW)
`
`500
`
`400
`
`100
`
`300
`
`200
`
`Wind speed (m/s)
`
`Figure 6.20 Example of the impact that a three-step rotational speed adjustment has
`on delivered power. For winds below 7.5 m/s, 20 rpm is best; between 7.5 and 11 m/s,
`30 rpm is best; and above 11 m/s, 40 rpm is best.
`
`
`
`
`
`
`
`
`
`shows the impact of varying rotor speed from 20 to 30 to 40 rpm for a 30-m
`rotor with efficiency given in Fig. 6.19, along with an assumed gear and generator
`efficiency of 70%.
`_ While blade efficiency benefits from adjustments in speed as illustrated in
`Figs. 6.19: and 6.20, the generator may need to spin at a fixed rate in order to
`deliver current and voltage in phase with the grid that it is feeding. So, for
`grid-connected turbines, the challenge is to design machines that can somehow
`accommodate variable rotor speed and somewhat fixed generator speed—or at
`least attempt to do so. If the wind turbine is not grid-connected, the generator
`electrical output can be allowed to vary in frequency (usually it is converted to _
`dc), so this dilemma isn’t a problem.
`—
`
`
`
`
`
`Induction generators spin at a frequency that is largely controlled by the number
`of poles. A two-pole, 60-Hz generator rotates at very close to 3600 rpm; with
`four poles it rotates at close to 1800 rpm; and so on. If we could change the
`
`number of poles, we could allow the wind turbine to have several operating
`speeds, approximating the performance shown in Figs. 6.19 and 6.20. A key f
`
`this approach is that as far as the rotor is concerned, the number ofpoles it
`
`the stator of an induction generator is irrelevant. That is, the stator can have
`external connections that switch the number of poles from one value to anotbet
`
`without needing any change in the rotor. This approach is common in household
`appliance motors such as those used in washing machines and exhaust fans
`give two- or three-speed operation.
`
`6.7.2 Pole-Changing Induction Generators
`
`
`
`

`

`(cid:14)(cid:12)(cid:5)(cid:5)(cid:4)(cid:19)(cid:3)(cid:11)(cid:10)(cid:15)(cid:13)(cid:11)(cid:8)(cid:19)(cid:6)(cid:11)(cid:13)(cid:19)(cid:9)(cid:2)(cid:7)(cid:9)(cid:16)(cid:9)(cid:19)(cid:12)(cid:11)(cid:17)(cid:5)(cid:13)(cid:19)
`SPEED CONTROL FOR MAXIMUM POWER
`
`(cid:1)(cid:1)(cid:18)(cid:19)
`33)
`
`(cid:7)(cid:2)(cid:9)(cid:2)(cid:4)(cid:35) (cid:14)(cid:32)(cid:24)(cid:31)(cid:22)(cid:28)(cid:23)(cid:21)(cid:35)(cid:12)(cid:21)(cid:17)(cid:29)(cid:18)(cid:27)(cid:33)(cid:21)(cid:30)(cid:35)
`6.7.3 Multiple Gearboxes
`(cid:33)(cid:95)(cid:84)(cid:51)(cid:134) (cid:123)(cid:74)(cid:90)(cid:45)(cid:134) (cid:113)(cid:120)(cid:101)(cid:39)(cid:74)(cid:90)(cid:51)(cid:112)(cid:134) (cid:68)(cid:38)(cid:121)(cid:51)(cid:134) (cid:113)(cid:123)(cid:95)(cid:134) (cid:67)(cid:51)(cid:38)(cid:102)(cid:39)(cid:95)(cid:126)(cid:51)(cid:112)(cid:134) (cid:123)(cid:74)(cid:113)(cid:68)(cid:134) (cid:112)(cid:51)(cid:97)(cid:38)(cid:102)(cid:38)(cid:113)(cid:51)(cid:134) (cid:67)(cid:51)(cid:90)(cid:51)(cid:102)(cid:38)(cid:113)(cid:95)(cid:102)(cid:112)(cid:134) (cid:38)(cid:113)(cid:113)(cid:38)(cid:40)(cid:68)(cid:51)(cid:45)(cid:134) (cid:113)(cid:95)(cid:134)
`Some wind turbines have two gearboxes with separate generators attached to
`(cid:51)(cid:38)(cid:40)(cid:68)(cid:3)(cid:134)(cid:67)(cid:74)(cid:121)(cid:74)(cid:90)(cid:67)(cid:134)(cid:38)(cid:134)(cid:83)(cid:95)(cid:123)(cid:5)(cid:123)(cid:74)(cid:90)(cid:45)(cid:6)(cid:112)(cid:97)(cid:51)(cid:51)(cid:45)(cid:134)(cid:67)(cid:51)(cid:38)(cid:102)(cid:134)(cid:102)(cid:38)(cid:113)(cid:74)(cid:95)(cid:134)(cid:38)(cid:90)(cid:45)(cid:134)(cid:67)(cid:51)(cid:90)(cid:51)(cid:102)(cid:38)(cid:113)(cid:95)(cid:102)(cid:134)(cid:97)(cid:83)(cid:118)(cid:112)(cid:134)(cid:38)(cid:134)(cid:68)(cid:74)(cid:67)(cid:68)(cid:6)(cid:123)(cid:74)(cid:90)(cid:45)(cid:6)(cid:112)(cid:97)(cid:51)(cid:51)(cid:45)(cid:134)
`each, giving a low-wind-speed gear ratio and generator plus a high-wind-speed
`(cid:67)(cid:51)(cid:38)(cid:102)(cid:134)(cid:102)(cid:38)(cid:113)(cid:74)(cid:95)(cid:134)(cid:38)(cid:90)(cid:45)(cid:134)(cid:67)(cid:51)(cid:90)(cid:51)(cid:102)(cid:38)(cid:113)(cid:95)(cid:102)(cid:11)(cid:134)
`gear ratio and generator.
`
`(cid:7)(cid:3)(cid:9)(cid:2)(cid:5)(cid:35) (cid:16)(cid:17)(cid:29)(cid:22)(cid:17)(cid:18)(cid:24)(cid:21)(cid:1)(cid:15)(cid:24)(cid:22)(cid:28)(cid:35)(cid:13)(cid:26)(cid:20)(cid:32)(cid:19)(cid:31)(cid:22)(cid:27)(cid:26)(cid:35)(cid:12)(cid:21)(cid:26)(cid:21)(cid:29)(cid:17)(cid:31)(cid:27)(cid:29)(cid:30)(cid:35)
`_ 6.7.4 Variable-Slip Induction Generators
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`A normal induction generator maintains its speed within about 1% of the syn-
`(cid:40)(cid:68)(cid:102)(cid:95)(cid:90)(cid:95)(cid:118)(cid:112)(cid:134)(cid:112)(cid:97)(cid:51)(cid:51)(cid:45)(cid:10)(cid:134) (cid:22)(cid:112)(cid:134)(cid:74)(cid:113)(cid:134)(cid:113)(cid:118)(cid:110)(cid:112)(cid:134)(cid:95)(cid:118)(cid:113)(cid:3)(cid:134) (cid:113)(cid:68)(cid:51)(cid:134)(cid:112)(cid:83)(cid:74)(cid:97)(cid:134)(cid:74)(cid:90)(cid:134)(cid:112)(cid:118)(cid:40)(cid:68)(cid:134)(cid:67)(cid:51)(cid:90)(cid:51)(cid:102)(cid:38)(cid:113)(cid:95)(cid:102)(cid:112)(cid:134)(cid:74)(cid:112)(cid:134)(cid:38)(cid:134)(cid:60)(cid:120)(cid:90)(cid:40)(cid:113)(cid:74)(cid:95)(cid:90)(cid:134)(cid:95)(cid:58)(cid:134)(cid:113)(cid:68)(cid:51)(cid:134)
`__ chronousspeed.Asit turns out, the slip in such generators is a function of the
`(cid:45)(cid:54)(cid:134)(cid:102)(cid:51)(cid:112)(cid:74)(cid:112)(cid:113)(cid:38)(cid:90)(cid:40)(cid:51)(cid:134)(cid:74)(cid:90)(cid:134)(cid:113)(cid:68)(cid:51)(cid:134)(cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:134)(cid:40)(cid:95)(cid:90)(cid:45)(cid:118)(cid:40)(cid:113)(cid:95)(cid:102)(cid:112)(cid:11)(cid:134)(cid:23)(cid:127)(cid:134)(cid:97)(cid:118)(cid:102)(cid:97)(cid:95)(cid:112)(cid:51)(cid:83)(cid:127)(cid:134)(cid:38)(cid:45)(cid:45)(cid:74)(cid:90)(cid:67)(cid:134)(cid:121)(cid:38)(cid:102)(cid:74)(cid:38)(cid:39)(cid:83)(cid:51)(cid:134)(cid:102)(cid:51)(cid:112)(cid:74)(cid:112)(cid:113)(cid:38)(cid:90)(cid:40)(cid:51)(cid:134)(cid:113)(cid:95)(cid:134)
`dc resistance in the rotor conductors. By purposely adding variable resistance to
`(cid:113)(cid:68)(cid:51)(cid:134)(cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:3)(cid:134)(cid:113)(cid:68)(cid:51)(cid:134)(cid:38)(cid:88)(cid:95)(cid:118)(cid:90)(cid:113)(cid:134) (cid:95)(cid:58)(cid:134)(cid:112)(cid:83)(cid:74)(cid:97)(cid:134) (cid:40)(cid:38)(cid:90)(cid:134) (cid:102)(cid:38)(cid:90)(cid:67)(cid:51)(cid:134) (cid:118)(cid:97)(cid:134) (cid:113)(cid:95)(cid:134)(cid:38)(cid:102)(cid:95)(cid:118)(cid:90)(cid:45)(cid:134)(cid:15)(cid:14)(cid:1)(cid:134) (cid:95)(cid:102)(cid:134) (cid:112)(cid:95)(cid:3)(cid:134) (cid:123)(cid:68)(cid:74)(cid:40)(cid:68)(cid:134)(cid:4)(cid:123)(cid:95)(cid:118)(cid:83)(cid:45)(cid:134)
`the rotor, the amount of slip can range up to around 10% or so, which would
`(cid:85)(cid:51)(cid:38)(cid:90)(cid:3)(cid:134)(cid:63)(cid:102)(cid:134)(cid:51)(cid:126)(cid:38)(cid:84)(cid:97)(cid:83)(cid:51)(cid:3)(cid:134)(cid:113)(cid:68)(cid:38)(cid:113)(cid:134)(cid:38)(cid:134)(cid:63)(cid:118)(cid:102)(cid:7)(cid:97)(cid:95)(cid:83)(cid:51)(cid:3)(cid:134)(cid:15)(cid:21)(cid:14)(cid:14)(cid:8)(cid:111)(cid:84)(cid:134)(cid:84)(cid:38)(cid:40)(cid:68)(cid:74)(cid:90)(cid:51)(cid:134)(cid:40)(cid:95)(cid:118)(cid:83)(cid:45)(cid:134)(cid:95)(cid:97)(cid:51)(cid:102)(cid:38)(cid:113)(cid:51)(cid:134)(cid:38)(cid:90)(cid:127)(cid:123)(cid:68)(cid:51)(cid:102)(cid:51)(cid:132)(cid:134)
`mean, for example, that a four-pole, 1800-rpm machine could operate anywhere
`(cid:64)(cid:95)(cid:84)(cid:134) (cid:38)(cid:39)(cid:95)(cid:118)(cid:113)(cid:134) (cid:15)(cid:21)(cid:14)(cid:14)(cid:134) (cid:113)(cid:95)(cid:134) (cid:18)(cid:14)(cid:14)(cid:14)(cid:134)(cid:111)(cid:84)(cid:10)(cid:134) (cid:32)(cid:90)(cid:51)(cid:134) (cid:123)(cid:38)(cid:127)(cid:134) (cid:113)(cid:95)(cid:134) (cid:97)(cid:102)(cid:95)(cid:121)(cid:74)(cid:45)(cid:51)(cid:134) (cid:113)(cid:68)(cid:74)(cid:112)(cid:134)(cid:40)(cid:38)(cid:97)(cid:38)(cid:39)(cid:74)(cid:83)(cid:74)(cid:113)(cid:127)(cid:134) (cid:74)(cid:112)(cid:134) (cid:113)(cid:95)(cid:134) (cid:68)(cid:38)(cid:121)(cid:51)(cid:134)
`_ from about 1800 to 2000 rpm. One wayto provide this capability is to have
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`adjustable resistors external to the generator, but the trade-off is that now an
`(cid:51)(cid:83)(cid:51)(cid:40)(cid:113)(cid:102)(cid:74)(cid:40)(cid:38)(cid:83)(cid:134) (cid:40)(cid:95)(cid:90)(cid:90)(cid:51)(cid:40)(cid:113)(cid:74)(cid:95)(cid:90)(cid:134) (cid:74)(cid:112)(cid:134)(cid:90)(cid:51)(cid:51)(cid:45)(cid:51)(cid:45)(cid:134)(cid:39)(cid:51)(cid:113)(cid:123)(cid:51)(cid:51)(cid:90)(cid:134) (cid:113)(cid:68)(cid:51)(cid:134) (cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:134) (cid:38)(cid:90)(cid:45)(cid:134)(cid:102)(cid:51)(cid:112)(cid:74)(cid:112)(cid:113)(cid:95)(cid:102)(cid:112)(cid:11)(cid:134)(cid:34)(cid:68)(cid:38)(cid:113)(cid:134)(cid:40)(cid:38)(cid:90)(cid:134)(cid:84)(cid:51)(cid:38)(cid:90)(cid:134)
`_.electrical connection is needed between the rotor and resistors. That can mean
`(cid:38)(cid:39)(cid:38)(cid:90)(cid:45)(cid:95)(cid:90)(cid:74)(cid:90)(cid:67)(cid:134)(cid:113)(cid:68)(cid:51)(cid:134)(cid:51)(cid:83)(cid:51)(cid:67)(cid:38)(cid:90)(cid:113)(cid:134)(cid:40)(cid:38)(cid:67)(cid:51)(cid:134)(cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:134)(cid:40)(cid:95)(cid:90)(cid:40)(cid:51)(cid:97)(cid:113)(cid:134)(cid:38)(cid:90)(cid:45)(cid:134)(cid:74)(cid:90)(cid:112)(cid:113)(cid:51)(cid:38)(cid:45)(cid:134)(cid:118)(cid:112)(cid:74)(cid:90)(cid:67)(cid:134)(cid:38)(cid:134)(cid:123)(cid:95)(cid:118)(cid:90)(cid:45)(cid:134)(cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:134)(cid:123)(cid:74)(cid:113)(cid:68)(cid:134)
`_ abandoning the elegant cage rotor concept and instead using a woundrotor with
`(cid:112)(cid:83)(cid:74)(cid:97)(cid:134)(cid:102)(cid:74)(cid:90)(cid:67)(cid:112)(cid:134) (cid:38)(cid:90)(cid:45)(cid:134) (cid:39)(cid:102)(cid:118)(cid:112)(cid:68)(cid:51)(cid:112)(cid:134) (cid:112)(cid:74)(cid:84)(cid:74)(cid:83)(cid:38)(cid:102)(cid:134) (cid:113)(cid:95)(cid:134) (cid:123)(cid:68)(cid:38)(cid:113)(cid:134) (cid:38)(cid:134) (cid:112)(cid:127)(cid:90)(cid:40)(cid:68)(cid:102)(cid:95)(cid:90)(cid:95)(cid:118)(cid:112)(cid:134) (cid:67)(cid:51)(cid:90)(cid:51)(cid:102)(cid:38)(cid:113)(cid:95)(cid:102)(cid:134) (cid:68)(cid:38)(cid:112)(cid:11)(cid:134) (cid:22)(cid:90)(cid:45)(cid:134) (cid:113)(cid:68)(cid:38)(cid:113)(cid:134)
`co lip rings and brushes similar to what a synchronous generator has. And that
`
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`_ means more maintenance will be required.
`(cid:22)(cid:90)(cid:95)(cid:113)(cid:71)(cid:51)(cid:102)(cid:134)(cid:123)(cid:38)(cid:127)(cid:134)(cid:113)(cid:95)(cid:134)(cid:97)(cid:102)(cid:95)(cid:121)(cid:74)(cid:45)(cid:51)(cid:134)(cid:121)(cid:38)(cid:102)(cid:74)(cid:38)(cid:39)(cid:83)(cid:51)(cid:134)(cid:102)(cid:51)(cid:112)(cid:74)(cid:112)(cid:113)(cid:38)(cid:90)(cid:40)(cid:51)(cid:134)(cid:63)(cid:102)(cid:134)(cid:113)(cid:68)(cid:51)(cid:134)(cid:102)(cid:95)(cid:113)(cid:95)(cid:102)(cid:134)(cid:74)(cid:112)(cid:134)(cid:113)(cid:95)(cid:134)(cid:97)(cid:68)(cid:127)(cid:112)(cid:74)(cid:40)(cid:38)(cid:83)(cid:83)(cid:127)(cid:134)(cid:84)(cid:95)(cid:118)(cid:90)(cid:113)(cid:134)
`_ Another wayto provide variable resistance for the rotor is to physically mount
`
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`_the resistors and the electronics that are needed to control them ontherotoritself.
`
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`_ But then you need some wayto sendsignalsto the rotor telling it how muchslip
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