Three-phase electric power

Three-phase transformer with four wire output for 208Y/120volt service: one wire for neutral, others for A, B and C phases

Three-phase electric power is a common methodof alternating-current electric power generation,transmission, and distribution.[1] It is a type of polyphasesystem and is the most common method used byelectrical grids worldwide to transfer power. It is alsoused to power large motors and other heavy loads. Athree-phase system is usually more economical than anequivalent single-phase or two-phase system at the sameline to ground voltage because it uses less conductormaterial to transmit electrical power.[2] The three-phasesystem was independently invented by Galileo Ferraris,Mikhail Dolivo-Dobrovolsky, Jonas Wenstrm andNikola Tesla in the late 1880s.

1 PrincipleIn a symmetric three-phase power supply system, threeconductors each carry an alternating current of the samefrequency and voltage amplitude relative to a commonreference but with a phase dierence of one third theperiod. The common reference is usually connected toground and often to a current-carrying conductor calledthe neutral. Due to the phase dierence, the voltage onany conductor reaches its peak at one third of a cycle af-ter one of the other conductors and one third of a cyclebefore the remaining conductor. This phase delay givesconstant power transfer to a balanced linear load. It alsomakes possible to produce a rotating magnetic eld in an

120

Phase 1 Phase 2 Phase3

120

90 270

1.0

0.5

0

-0.5

-1.0

180 360

Normalized waveforms of the instantaneous voltages in a three-phase system in one cycle with time increasing to the right. Thephase order is 123. This cycle repeats with the frequency of thepower system.

Three-phase electric power transmission lines

electric motor and generate other phase arrangements us-ing transformers (For instance, a two phase system usinga Scott-T transformer).The symmetric threephase systems described here aresimply referred to as threephase systems because, al-though it is possible to design and implement asymmetricthreephase power systems (i.e., with unequal voltages orphase shifts), they are not used in practice because theylack the most important advantages of symmetric sys-tems.In a threephase system feeding a balanced and linearload, the sum of the instantaneous currents of the threeconductors is zero. In other words, the current in eachconductor is equal in magnitude to, but with the oppositesign of, the sum of the currents in the other two. The

1

2 3 TRANSFORMER CONNECTIONS

return path for the current in any phase conductor is theother two phase conductors.Compared to a single-phase AC power supply that usestwo conductors (phase and neutral), a three-phase supplywith no neutral, the same phase-to-ground voltage andcurrent capacity per phase can transmit three times asmuch power using just 1.5 times as many wires (i.e., threeinstead of two). Thus, the ratio of capacity to conductormaterial is doubled. The same (but not the other prop-erties of three-phase power) can also be attained with acenter-grounded single-phase system.[3]

Three-phase systems may also utilize a fourth wire, par-ticularly in low-voltage distribution. This is the neutralwire. The neutral allows three separate single-phase sup-plies to be provided at a constant voltage and is com-monly used for supplying groups of domestic proper-ties which are each single-phase loads. The connec-tions are arranged so that, as far as possible in eachgroup, equal power is drawn from each phase. Furtherup the distribution system, the currents are usually wellbalanced. Transformers may be wired in a way thatthey have a fourwire secondary but a threewire primarywhile allowing unbalanced loads and the associated sec-ondaryside neutral currents.Three-phase supplies have properties that make themvery desirable in electric power distribution systems:

The phase currents tend to cancel out one another,summing to zero in the case of a linear balancedload. This makes it possible to reduce the size ofthe neutral conductor because it carries little or nocurrent. With a balanced load, all the phase conduc-tors carry the same current and so can be the samesize.

Power transfer into a linear balanced load is con-stant, which helps to reduce generator and motor vi-brations.

Three-phase systems can produce a rotating mag-netic eld with a specied direction and constantmagnitude, which simplies the design of electricmotors.

Most household loads are single-phase. In North Ameri-can residences, three-phase power might feed a multiple-unit apartment block, but the household loads are con-nected only as single phase. In lower-density areas, onlya single phase might be used for distribution. Some largeEuropean appliances may be powered by three-phasepower, such as electric stoves and clothes dryers.Wiring for the three phases is typically identied by colorcodes which vary by country. Connection of the phasesin the right order is required to ensure the intended di-rection of rotation of three-phase motors. For example,pumps and fans may not work in reverse. Maintainingthe identity of phases is required if there is any possi-bility two sources can be connected at the same time; a

direct interconnection between two dierent phases is ashort-circuit.

2 Generation and distribution

Animation of three-phase current ow

At the power station, an electrical generator convertsmechanical power into a set of three AC electric cur-rents, one from each coil (or winding) of the generator.The windings are arranged such that the currents varysinusoidally at the same frequency but with the peaks andtroughs of their wave forms oset to provide three com-plementary currents with a phase separation of one-thirdcycle (120 or 2 3 radians). The generator frequency istypically 50 or 60 Hz, varying by country.Further information: Mains power systems

At the power station, transformers change the voltagefrom generators to a level suitable for transmission mini-mizing losses.After further voltage conversions in the transmission net-work, the voltage is nally transformed to the standardutilization before power is supplied to customers.Most automotive alternators generate three phase AC andrectify it to DC with a diode bridge.[6]

3 Transformer connectionsA delta connected transformer winding is connectedbetween phases of a three-phase system. A wye (star)transformer connects each winding from a phase wire toa common neutral point.In an open delta or V system, only two transformersare used. A closed delta system can operate as an opendelta if one of the transformers has failed or needs to beremoved.[7] In open delta, each transformer must carrycurrent for its respective phases as well as current for thethird phase, therefore capacity is reduced to 87%. Withone of three transformers missing and the remaining twoat 87% eciency, the capacity is 58% ((2/3) 87%).[8][9]

3Where a delta-fed system must be grounded for detec-tion of stray current to ground or protection from surgevoltages, a grounding transformer (usually a zigzag trans-former) may be connected to allow ground fault cur-rents to return from any phase to ground. Another vari-ation is a corner grounded delta system, which is aclosed delta that is grounded at one of the junctions oftransformers.[10]

4 Three-wire and four-wire cir-cuits

Y configuration

Neutral (optional)

Delta configuration

L1

L2

L3

L1

L2

L3

Wye (Y) and Delta () circuits

There are two basic three-phase congurations: deltaand wye (star). As shown on the left, a delta congu-ration requires only 3 wires for transmission but a wye(star) conguration may utilise a fourth wire. The fourthwire, if present, is provided as a Neutral and is normallyGrounded. The 3-wire and 4-wire designations donot count the ground wire used above many transmis-sion lines, which is solely for fault protection and doesnot carry current under non-fault conditions.

L1 L2

L3

N

A transformer for a high-leg delta system; (Assuming a 200V, 3-phase supply) 200 V 3-phase motors would be connectedto L1, L2 and L3. 200 V single-phase load would be connectedbetween L1 and L2. Single-phase 100 V supplies (180 degreesout of phase) would be obtained between either L1 or L2 andthe neutral (N). L3 (wild or high leg) will be 173.2 V with respectto the neutral.

A four-wire system with symmetrical voltages betweenphase and neutral is obtained when the neutral is con-nected to the common star point of all supply wind-ings. In such a system, all three phases will have the samemagnitude of voltage relative to the Neutral. Other non-symmetrical systems have been used.The four-wire wye system is used when ground refer-enced voltages or the exibility of more voltage selec-tions are required. Faults on one phase to ground willcause a protection event (fuse or breaker open) locally andnot involve other phases or other connected equipment.An example of application is local distribution in Europe(and elsewhere), where each customer may be only fedfrom one phase and the neutral (which is common to thethree phases). When a group of customers sharing theneutral draw unequal phase currents, the common neutralwire carries the currents resulting from these imbalances.Electrical engineers try to design the system so the loadsare balanced as much as possible within premises where3-phase power is utilized.[11] These same principles ap-ply to the wide scale distribution of power to individualpremises. Hence, every eort is made by supply author-ities to distribute all three phases over a large number ofpremises so that, on average, as nearly as possible a bal-anced load is seen at the point of supply. For domesticuse, some countries such as the UKmay supply one phaseand neutral at a high current (up to 100A) to one property,while others such as Germany may supply 3 phases and

4 5 BALANCED CIRCUITS

neutral to each customer, but at a lower fuse rating, typ-ically 32 A per phase, and shued to avoid the eectthat more load tends to be put on the rst phase.In North America, a high-leg delta supply is sometimesused, where one winding of a delta connected transformerfeeding the load is center-tapped and that center tap isgrounded and connected as a Neutral, as shown on theright. This setup produces three dierent voltages. If thevoltage between the center tap (neutral) and each of thetwo adjacent phases is 120 V (100%), the voltage acrossany two phases is 240 V (200%), and the neutral to highleg voltage is 208 V (173%).[7]

The reason for providing the delta connected supply isusually to power large motors requiring a rotating eld.However, the premises concerned will also require thenormal North American 120 V supplies, two of whichare derived (180 degrees out of phase) between theNeutral and either of the center tapped phase points.

5 Balanced circuitsIn the perfectly balanced case all three lines share equiva-lent loads. Examining the circuits we can derive relation-ships between line voltage and current, and load voltageand current for wye and delta connected loads.In a balanced system each line will produce equal volt-age magnitudes at phase angles equally spaced from eachother. With V1 as our reference and V3 lagging V2 lag-ging V1, using angle notation, we have:[12]

V1 = VLN\0;

V2 = VLN\120;V3 = VLN\+120:These voltages feed into either a wye or delta connectedload.

5.1 WyeFor the wye case, all loads see their respective line volt-ages, and so:[12]

I1 =V1

jZtotalj\();

I2 =V2

jZtotalj\(120 );

I3 =V3

jZtotalj\(120 );

where Z is the sum of line and load impedances (Z= ZLN + ZY), and is the phase of the total impedance(Z).

V1

V3

V2n

+--

++-

n

Zy

ZyZy

I1

I2

I3

Three-phase AC generator connected as a wye source to a wye-connected load

The phase angle dierence between voltage and currentof each phase is not necessarily 0 and is dependent onthe type of load impedance, Z. Inductive and capacitiveloads will cause current to either lag or lead the voltage.However, the relative phase angle between each pair oflines (1 to 2, 2 to 3,and 3 to 1) will still be 120.By applying Kirchhos current law (KCL) to the neutralnode, the three phase currents sum to the total current inthe neutral line. In the balanced case:

I1 + I2 + I3 = IN = 0:

5.2 Delta

Z

V1

V3

V2n

+--

++- I12I2

I3

I23 I31

I1

Three-phase AC generator connected as a wye source to a delta-connected load

In the delta circuit, loads are connected across the lines,and so loads see line-to-line voltages:[12]

6.1 Unbalanced loads 5

V12 = V1 V2 = (VLN\0) (VLN\120)=p3VLN\30 =

p3V1\(V1 + 30);

V23 = V2 V3 = (VLN\120) (VLN\120)=p3VLN\90 =

p3V2\(V2 + 30);

V31 = V3 V1 = (VLN\120) (VLN\0)=p3VLN\150 =

p3V3\(V3 + 30):

Further:

I12 =V12jZj\(30

);

I23 =V23jZj\(90

);

I31 =V31jZj\(150

);

where is the phase of delta impedance (Z).Relative angles are preserved, so I31 lags I23 lags I12 by120. Calculating line currents by using KCL at eachdelta node gives:

I1 = I12 I31 = I12 I12\120=p3I12\(I12 30) =

p3I12\()

and similarly for each other line:

I2 =p3I23\(I23 30) =

p3I23\(120 );

I3 =p3I31\(I31 30) =

p3I31\(120 );

where, again, is the phase of delta impedance (Z).

6 Single-phase loadsSingle-phase loads may be connected across any twophases, or a load can be connected from phase toneutral.[13] Distributing single-phase loads among thephases of a three-phase system balances the load andmakes most economical use of conductors and transform-ers.In a symmetrical three-phase four-wire, wye system, thethree phase conductors have the same voltage to the sys-tem neutral. The voltage between line conductors is 3times the phase conductor to neutral voltage:[14]

VLL =p3VLN:

The currents returning from the customers premises tothe supply transformer all share the neutral wire. If the

loads are evenly distributed on all three phases, the sum ofthe returning currents in the neutral wire is approximatelyzero. Any unbalanced phase loading on the secondaryside of the transformer will use the transformer capacityineciently.If the supply neutral is broken, phase-to-neutral voltage isno longer maintained. Phases with higher relative loadingwill experience reduced voltage, and phases with lowerrelative loading will experience elevated voltage, up to thephase-to-phase voltage.A high-leg delta provides phase-to-neutral relationship ofVLL = 2 VLN , however, LN load is imposed on onephase.[7] A transformer manufacturers page suggests thatLN loading to not exceed 5% of transformer capacity.[15]

Since 3 1.73, dening VLN as 100% gives VLL 100% 1.73 = 173%. If VLL was set as 100%, thenVLN 57.7%.

6.1 Unbalanced loads

When the currents on the three live wires of a three-phasesystem are not equal or are not at an exact 120 phase an-gle, the power loss is greater than for a perfectly balancedsystem. The method of symmetrical components is usedto analyze unbalanced systems.

6.2 Non-linear loads

With linear loads, the neutral only carries the current dueto imbalance between the phases. Devices that utilizerectier-capacitor front-end such as switch-mode powersupplies, computers, oce equipment and such producethird-order harmonics that are in-phase on all the supplyphases. Consequently, such harmonic currents add in theneutral, which can cause the neutral current to exceed thephase current.[13][16]

7 Three-phase loadsAn important class of three-phase load is the electric mo-tor. A three-phase induction motor has a simple design,inherently high starting torque and high eciency. Suchmotors are applied in industry for many applications. Athree-phase motor is more compact and less costly thana single-phase motor of the same voltage class and rat-ing and single-phase AC motors above 10 HP (7.5 kW)are uncommon. Three-phase motors also vibrate less andhence last longer than single-phase motors of the samepower used under the same conditions.Line frequency icker in light can be reduced by evenlyspreading three phases across line frequency operatedlight sources so that illuminated area is provided lightfrom all three phases. The eect of line frequency

6 9 ALTERNATIVES TO THREE-PHASE

icker is detrimental to super slow motion cameras usedin sports event broadcasting. Three phase lighting hasbeen applied successfully at the 2008 Beijing Olympicsto provide consistent light level for each frame for SSMcameras.[17] Resistance heating loads such as electricboilers or space heating may be connected to three-phasesystems. Electric lighting may also be similarly con-nected.Rectiers may use a three-phase source to produce a six-pulse DC output.[18] The output of such rectiers is muchsmoother than rectied single phase and, unlike single-phase, does not drop to zero between pulses. Such rec-tiers may be used for battery charging, electrolysis pro-cesses such as aluminium production or for operation ofDC motors. Zig-zag transformers may make the equiv-alent of six-phase full-wave rectication, twelve pulsesper cycle, and this method is occasionally employed to re-duce the cost of the ltering components, while improv-ing the quality of the resulting DC.One example of a three-phase load is the electric arc fur-nace used in steelmaking and in rening of ores.In many European countries electric stoves are usuallydesigned for a three-phase feed. However, the individ-ual heating units are often connected between phase andneutral to allow for connection to a single-phase circuite.g. if within an older domestic property a three-phasefeed is not yet available.[19] Other usual three-phase loadsin the domestic eld are tankless water heating systemsand storage heater. However, since those references ap-peared homes in Europe and the UK have standardisedon a single-phase supply with a nominal 230 V (in prac-tice 240 V in the UK), which is used for all purposes.Most groups of houses are fed from a three-phase supplyso that individual premises with above-average demandcan be fed with a second or third phase connection, al-though domestic appliances are invariably designed for asingle-phase supply.

8 Phase convertersPhase converters are used when three-phase equipmentneeds to be operated on a single-phase power source.They are used when three-phase power is not availableor cost is not justiable. Such converters may also allowthe frequency to be varied (resynthesis) allowing speedcontrol. Some railway locomotives use a single-phasesource to drive three-phase motors fed through an elec-tronic drive.[20]

8.1 MechanicalOnemethod to generate three-phase power from a single-phase source is the rotary phase converter, essentiallya three-phase motor with special starting arrangementsand power factor correction that produces balanced three-

phase voltages. When properly designed, these rotaryconverters can allow satisfactory operation of a three-phase motor on a single-phase source. In such a device,the energy storage is performed by the inertia (ywheeleect) of the rotating components. An external ywheelis sometimes found on one or both ends of the shaft.A three-phase generator can be driven by a single-phasemotor. This motor-generator combination can providea frequency changer function as well as phase conver-sion, but requires two machines with all their expense andlosses. The motor-generator method can also form anuninterruptable power supply when used in conjunctionwith a large ywheel and a battery-powered DC motorfor really constant power, a standby generator set givesmore frequency drop until standby generator kicks in.

8.2 Non-mechanicalA second method that was popular in the 1940s and1950s was the transformer method. At that time, ca-pacitors were more expensive than transformers, so anautotransformer was used to apply more power throughfewer capacitors. Separated it from another commonmethod, the static converter, as both methods have nomoving parts, which separates them from the rotary con-verters.Another method often attempted is with a device referredto as a static phase converter. This method of runningthree-phase equipment is commonly attempted with mo-tor loads though it only supplies 2/3 power and can causethe motor loads to run hot and in some cases overheat.This method does not work when sensitive circuitry is in-volved such as CNC devices or in induction and rectier-type loads.Variable-frequency drives (also known as solid-stateinverters and adjustable speed drives) are used to provideprecise speed and torque control of three-phase motors.Some models can be powered by a single-phase supply.VFDs work by converting the supply voltage to DC andthen converting the DC to a suitable three-phase sourcefor the motor.Digital phase converters are designed for xed-frequencyoperation from a single-phase source. Similar to avariable-frequency drive, they use a microprocessor tocontrol solid-state power switching components to main-tain balanced three-phase voltages.

9 Alternatives to three-phase Split-phase electric power is used when three-phasepower is not available and allows double the nor-mal utilization voltage to be supplied for high-powerloads.

Two-phase electric power, like three-phase, gives

7constant power transfer to a linear load. For loadsthat connect each phase to neutral, assuming theload is the same power draw, the two-wire sys-tem has a neutral current that is greater than neu-tral current in a three-phase system. Also motorsare not entirely linear, which means that despite thetheory, motors running on three-phase tend to runsmoother than those on two-phase. The genera-tors in the Adams Power Plant at Niagara Falls thatwere installed in 1895 were the largest generatorsin the world at the time and were two-phase ma-chines. True two-phase power distribution is obso-lete for new work applications, but still exists forold work applications, perhaps most particularlyin Bualo and Niagara Falls, NY, Toronto and Ni-agara Falls, Ontario, Philadelphia and Reading, PA,and Camden, NJ. New work three-phase installa-tions may be supplied by old two-phase feeders, andold work two-phase installations may be suppliedby new three-phase feeders using a Scott-T trans-former, invented by Charles F. Scott.[21] Special-purpose systemsmay use a two-phase system for fre-quency control.

Monocyclic power was a name for an asymmetricalmodied two-phase power system used by GeneralElectric around 1897, championed by Charles Pro-teus Steinmetz and Elihu Thomson. This systemwas devised to avoid patent infringement. In thissystem, a generator was wound with a full-voltagesingle-phase winding intended for lighting loads andwith a small fraction (usually 1/4 of the line voltage)winding that produced a voltage in quadrature withthe main windings. The intention was to use thispower wire additional winding to provide startingtorque for induction motors, with the main windingproviding power for lighting loads. After the expi-ration of the Westinghouse patents on symmetricaltwo-phase and three-phase power distribution sys-tems, the monocyclic system fell out of use; it wasdicult to analyze and did not last long enough forsatisfactory energy metering to be developed.

High-phase-order systems for power transmissionhave been built and tested. Such transmission linestypically would use six phases or twelve phases.High-phase-order transmission lines allow transferof slightly less than proportionately higher powerthrough a given volume without the expense of ahigh-voltage direct current (HVDC) converter ateach end of the line. However, they require corre-spondingly more pieces of equipment.

10 Color codesSee also: Electrical wiring Colour code

Conductors of a three-phase system are usually identi-ed by a color code, to allow for balanced loading andto assure the correct phase rotation for motors. Colorsused may adhere to International Standard IEC 60446(now merged into IEC 60445), older standards or to nostandard at all and may vary even within a single installa-tion. For example, in the U.S. and Canada, dierent colorcodes are used for grounded (earthed) and ungroundedsystems.

11 See also Three-phase AC railway electrication Charging station Frequency converter Industrial & multiphase power plugs & sockets International Electrotechnical Exhibition John Hopkinson Y- transform

12 Notes[1] In Australia and New Zealand, active conductors can be

any color except green/yellow, green, yellow, black or lightblue. Yellow is no longer permitted in the 2007 revision ofwiring code ASNZS 3000. European color codes are usedfor all IEC or ex cables such as extension leads, applianceleads etc. and are equally permitted for use in buildingwiring per AS/NZS 3000:2007.

[2] The international standard green-yellow marking ofprotective-earth conductors was introduced to reduce therisk of confusion by color blind installers. About 7%to 10% of men cannot clearly distinguish between redand green, which is a particular concern in older schemeswhere red marks a live conductor and green marks pro-tective earth or safety ground.

[3] In Europe, there still exist many installations with oldercolors but, since the early 1970s, all new installationsuse green/yellow earth according to IEC 60446. (E.g.Phase/Neutral+Earth German: black/grey + red Francegreen/red + White Russia: Red/ Grey + Black; Switzer-land: Red/ Grey +Yellow or yellow & red Denmark:White/Black + Red

[4] See Paul Cook: Harmonised colours and alphanumericmarking. IEE Wiring Matters, Spring 2006.

[5] In the U.S., a green/yellow striped wire may indicate anisolated ground. In most countries today, green/yellowstriped wire may only be used for protective earth (safetyground) and may never be unconnected or used for anyother purpose.

8 13 REFERENCES

[6] Since 1975, the U.S. National Electric Code has not spec-ied coloring of phase conductors. It is common practicein many regions to identify 120/208 (wye) conductors asblack, red, and blue, and 277/480 (wye or delta) conduc-tors as brown, orange, yellow. In a 120/240 delta systemwith a 208v high leg, the high leg (typically B phase) isalways marked orange, commonly A phase is black andC phase is either red or blue. Local regulations mayamend the N.E.C. The U.S. National Electric Code hascolor requirements for grounded conductors, ground, andgrounded-delta 3-phase systems which result in one un-grounded leg having a higher voltage potential to groundthan the other two ungrounded legs.

13 References[1] William D. Stevenson, Jr. Elements of Power System

Analysis Third Edition, McGraw-Hill, New York (1975).ISBN 0-07-061285-4, p. 2

[2] Three-phase power systems : Polyphase Ac Circuits -Electronics Textbook. Allaboutcircuits.com. Retrieved2015-05-13.

[3] Cotton, H, Electrical Technology, 6th Ed., Pitman, Lon-don, 1950, p. 268

[4] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.,1917, vol. 4, Ch. 46: Alternating Currents, p. 1026, g.1260.

[5] Hawkins Electrical Guide, Theo. Audel and Co., 2nd ed.,1917, vol. 4, Ch. 46: Alternating Currents, p. 1026, g.1261.

[6]

[7] Fowler, Nick (2011). Electricians Calculations Manual2nd Edition. McGraw-Hill. pp. 35. ISBN 978-0-07-177017-0.

[8] McGraw-Hill (1920). Power 51 (17) http://books.google.com/books?id=u91QAAAAYAAJ&pg=PA673&lpg=PA673. Retrieved 21 December 2012.Missing or empty |title= (help)

[9] H. W. Beaty, D.G.Fink (ed) Standard Handbook forElectrical Engineers Fifteenth Edition,McGraw-Hill, 2007ISBN 0-07-144146-8, p. 1011

[10] Schneider

[11] http://www.rapid-tech.com.au/Fluke-2_Saving%20energy%20through%20load%20balancing.pdf

[12] J. Duncan Glover; Mulukutla S. Sarma; Thomas J. Over-bye (April 2011). Power System Analysis & Design. Cen-gage Learning. pp. 6068. ISBN 978-1-111-42579-1.

[13] Lowenstein, Michael. The 3rd Harmonic Blocking Fil-ter: A Well Established Approach to Harmonic CurrentMitigation. IAEI Magazine. Retrieved 24 November2012.

[14] The boy electrician by J W Sims M.I.E.E. (Page 98)

[15] Federal pacic

[16] Enjeti, Prasad. Harmonics in Low Voltage Three-PhaseFour-Wire Electric Distribution Systems and Filtering So-lutions (PDF). Texas A&MUniversity Power Electronicsand Power Quality Laboratory. Retrieved 24 November2012.

[17] Hui, Sun. Sports Lighting Design Considerations ForThe Beijing 2008 Olympic Games (PDF). GE Lighting.Retrieved 18 December 2012.

[18] IEEE

[19] British and European practices for domestic appliancescompared, Electrical Times, volume 148, page 691,1965.

[20] Japan Railway & Transport Review (PDF). No. 58: 58.Oct 2011 http://www.jrtr.net/jrtr58/pdf/51-60web.pdf.Missing or empty |title= (help)

[21] Brittain, J. E. (2007). Electrical Engineering Hall ofFame: Charles F. Scott. Proceedings of the IEEE 95 (4):836839. doi:10.1109/JPROC.2006.892488.

[22] Canadian Electrical Code Part I, 23rd Edition, (2002)ISBN 1-55324-690-X, rule 4-036 (3)

[23] Canadian Electrical Code 23th edition 2002, rule 24-208(c)

914 Text and image sources, contributors, and licenses14.1 Text

Three-phase electric power Source: https://en.wikipedia.org/wiki/Three-phase_electric_power?oldid=669187389 Contributors: BryanDerksen, Timo Honkasalo, The Anome, DanKeshet, Mirwin~enwiki, Europrobe, Heron, Jaknouse, Twilsonb, Patrick, Michael Hardy, TimStarling, Nixdorf, Cameron Dewe, Karada, Mcarling, Ahoerstemeier, Williamv1138, Glenn, Reddi, Zoicon5, Bhuston, Joy, Uninvited-Company, Robbot, Greudin, Securiger, Modeha, Wjbeaty, DocWatson42, Mat-C, Wolfkeeper, BenFrantzDale, Karn, Everyking, MarkusKuhn, Crag, Darrien, Chameleon, Wmahan, Chowbok, Wangguoqin1001, Beland, Siliconwafer, Ot, Springerj, Nek, Buchs, Togo~enwiki,Glogger, Sam Hocevar, Nulzilla, Alistair1978, Mashford, Plugwash, Kgaughan, Meggar, Shenme, Cmdrjameson, Blotwell, Atlant, Pouya,Wtmitchell, BRW, Wtshymanski, Gene Nygaard, Martian, Evan C, Woohookitty, Linas, DonPMitchell, BillC, Lifung, Dionyziz, Man-darax, Graham87, Ketiltrout, Rjwilmsi, Pdelong, Hezery99, Brighterorange, Paul foord, Ichudov, Wingchi, Roboto de Ajvol, Wavelength,DMahalko, Perkinma, Ikar.us, Hellbus, Tole, CambridgeBayWeather, Pseudomonas, Bovineone, Salsb, Dhollm, Natkeeran, SFC9394,Mysid, Donbert, Curpsbot-unicodify, Benandorsqueaks, SmackBot, Incnis Mrsi, Saihtam, SparkyBuzzkill, Jester1983, Antifumo, Bluebot,Thumperward, AndrewBuck, VMS Mosaic, DMacks, Acdx, P2pauthor, Breadbox, KLLvr283, Mgiganteus1, Codacola~enwiki, Dacium,Inquisitus, DwightKingsbury, Sandothegrate, Luminaux, Chetvorno, Cydebot, DumbBOT, Oxonhutch, Epbr123, Qwyrxian, Pjvpjv, Elec-tron9, Widefox, Bigtimepeace, Soothsayer2, CPMartin, Standardcomm, UnivEducator, Davken1102, Danger, Mfrisk, Rico402, Magiola-ditis, BBar, JFine, ElectroTech, Adil zia, I B Wright, Csylcox, MottyGlicksman, Gah4, J.delanoy, James cudahy, Firemansam87, Lajos87,Mrmalsah, Mrjohns2, Laager, Davidclt, Idioma-bot, Joeinwap, Hugo999, X!, VolkovBot, JohnBlackburne, Seniorsag, Soliloquial, Kylethe bot, Davehi1, Hqb, Doug2008, Nazgul02, Don4of4, Yeokaiwei, Modal Jig, Spiral5800, Hanjabba, Jhawkinson, Vchimpanzee, Spin-ningspark, Truthanado, KjellG, Flyer22, A. Carty, Wol377, KoshVorlon,Wiki-ny-2007, Pointbonita, Dolphin51, ClueBot, Alpta, AlptaBot,Fredquint, SchreiberBike, Dusen189, Wikiuser100, Dthomsen8, Eug.galeotti, Addbot, Cantaloupe2, Michael E Hayes, Gruver777, Tiderolls, Tenth Plague, Ben Ben, Legobot, Luckas-bot, Yobot, KamikazeBot, AnomieBOT, Fmorgan98, Killiondude, TonyGraySchneider-Electric, V35b, Xqbot, J JMesserly, Garetoo, RibotBOT, IShadowed, Chongkian, Shadowjams, Stiepan Pietrov, Imveracious, Piero71,FrescoBot, Mfwitten, Interp, Biker Biker, Kukdide, Elmf, Reconsider the static, SchreyP, ElectroDrache, Tbhotch, MegaSloth, John ofReading, Joshkurien, Ndkl, Noroi, K6ka, AManWithNoPlan, Nudecline, JoeSperrazza, Peterh5322, Vvickky007, Stomar2, Teapeat, Kr-ishna santosh eee, Xanchester, Mikhail Ryazanov, ClueBot NG, MelbourneStar, Historikeren, DieSwartzPunkt, Widr, Helpful Pixie Bot,Tholme, Lowercase sigmabot, BG19bot, Sjsmith2611, Roadstoroam, Vindarmagnus~enwiki, Klilidiplomus, Pratyya Ghosh, Eatmajor7th,YFdyh-bot, Dexbot, Rezonansowy, Paresh108, Svjo, Mitchmarsh, AndreCF, GCMathTeacher, Zhao88, Jaredmporter, Monkbot, Chrisfrd,Frequencydrive, Sn maiti, Mario Casteln Castro, DarkMoon, Wardenclyetower and Anonymous: 399

14.2 Images File:3-phase_flow.gif Source: https://upload.wikimedia.org/wikipedia/commons/4/48/3-phase_flow.gif License: CC-BY-SA-3.0 Con-

tributors: Transferred from en.wikipedia; transferred to Commons by User:Zscout370 using CommonsHelper. Original artist: Originaluploader was BillC at en.wikipedia

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File:3_phase_AC_waveform.svg Source: https://upload.wikimedia.org/wikipedia/commons/c/cc/3_phase_AC_waveform.svg License:Public domain Contributors: File:3-fas-spnningar.svg Original artist: User:J JMesserly modication of original svg by User:SiriusA

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File:Hawkins_Electrical_Guide_-_3phase_Elementary_6wire.jpg Source: https://upload.wikimedia.org/wikipedia/commons/d/d0/Hawkins_Electrical_Guide_-_3phase_Elementary_6wire.jpg License: Public domain Contributors: ? Original artist: ?

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10 14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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14.3 Content license Creative Commons Attribution-Share Alike 3.0

Principle Generation and distribution Transformer connections Three-wire and four-wire circuits Balanced circuits Wye Delta

Single-phase loads Unbalanced loads Non-linear loads

Three-phase loads Phase converters Mechanical Non-mechanical

Alternatives to three-phase Color codes See also Notes References Text and image sources, contributors, and licensesTextImagesContent license