©Električne mašine kroz praktična pitanja i odgovore – Deo 3

Autor: Radoje Jankovic.

II. OSNOVNA ZNANJA O ROTACIONIM ELEKTRIČNIM MAŠINAMA MOTORIMA I GENERATORIMA, DEFINICIJE I SLIKE – Nastavak

© Electrical machines through practical questions and answers – Part 3

Author: Radoje Jankovic.

II. BASIC KNOWLEDGE OF ROTARY ELECTRICAL MACHINES MOTORS AND GENERATORS, DEFINITIONS AND IMAGES – Continued

10. Priključna pločica asinhronih elektromotora!

Priključna pločica rotacionih električnih mašina je konstruktivni deo mašine na koju su priključeni izvodni krajevi statorskih namotaja za priključivanje mašine na mrežni napon napajanja elektromotora. Elementi za priključivanje su svornjaci (bolcnovi sa narezanim navojima) koji su trajno pričvršćeni na  kućište ili sklop električne mašine. Pravougaone priključne pločice sa 6 priključnih svornjaka su standardizovane  a izrađuju se od visokokvalitetnog izolacionog materijala. Polno preklopivi elektromtori imaju 6, 9, ili 12 stezaljki.

Naravno, u svetu proizvodnje električnih rotacionih mašina postoje različita konstruktivna rešenja priključnih pločica. Na sledećim slikama prikazano je nekoliko detalja iz prakse priključivanja kablova na priključne pločice u priključnim kutijama elektromotora.

10. Connection plate for asynchronous electric motors!

The connection plate of rotary electric machines is a constructive part of the machine to which the output ends of the stator windings are connected for connecting the machine to the mains supply voltage of the electric motor. Connecting elements are bolts (threaded bolts) which are permanently attached to the housing or assembly electrical machines. electrical machines. Rectangular connection plates with 6 connection bolts are standardized and are made of high quality insulating material. Pole-changing electric motors have 6, 9, or 12 terminals.

Of course, in the world of production of electric rotary machines, there are various constructive solutions for connection plates. The following figures show some details from the practice of connecting cables to the terminal boards in the terminal boxes of electric motors.

11. Uležištenje električnih mašina!

Električne mašine izrađuju se sa valjkastim ili kliznim ležajevima. Elektromotori do otprilike 630 kW pri 3000 1/min i do otprilike 1600 kW pri 1500 1/min imaju kotrljajuće ležajeve. Motori većih snaga opremaju se kliznim ležajevima. Manji motori mogu u posebnim pogonskim uslovima biti takođe opremljeni kliznim ležajevima. To se po pravilu radi kod određenih  vrsta spojnica (spojki) ako se zahteva ili kad se elektromotor postavlja na mesto gde se javljaju vibracije van motora. U poslednjem slučaju postoji opasnost da se pri dužem stajanju motora kotrljajuća tela (kugle) kotrljajućih ležajeva utisnu u  valjanju stazu. Na slikama su prikazani neki tipovi ležajeva koji se koriste kod elektromotora.

Ležaj je konstruktivni element predviđen da nosi (podupire) rotirajuću osovinu elektromotora i ako je potrebno da ograniči njen aksijalni pomeraj u toku rada.

11. Bearing of electric machines!

Electric machines are made with roller or sliding bearings. Electric motors up to approx. 630 kW at 3000 rpm and up to approx. 1600 kW at 1500 rpm have  rolling bearings. Higher power motors are equipped with plain bearings. Smaller motors can also be equipped with plain bearings in special operating conditions.   This is usually done with certain types of couplings if required or when the electric motor is placed in a place where vibrations occur outside the motor. In the latter case, there is a danger that the rolling bodies (balls) of the rolling bearings will be pressed into the rolling track during longer engine downtime. The pictures show some types of bearings used in electric motors.  

The bearing

is a structural element designed to carry (support) the rotating shaft of the electric motor and, if necessary, to limit its axial displacement during operation.

12. Klizni ležajevi!

Klizni ležajevi se koriste kod velikih električnih mašina, kao I kod niza specijalnih malih i srednjih električnih mašina.

Mikromotori i mali motori (izuzev motora sa sinterovanim ležajevima) izrađuju se i sa kliznim ležajevima, koji se podmazuju pomoću fitilja. Na dodrinom mestu pritisne se fitilj pomoću opruge lagano na osovinu. On mora uvek biti tatopljen uljem koje nije suviše gusto a koje po pravilu preporučuje proizvođač elektromotora. Klizni ležajevi su najčešće od bronze, a oni kod univerzalnih elektromotora su od sinterovanog metala koji zahvaljujući kapilarnom delovanju imaju osobinu samopodmazivanja. U tuljku sinterovanog ležaja postavljen je uljem natopljen pusteni prsten, koji služi kao spremnik ulja.

Kod srednjih elektromotora, slika 12.1. se klizni ležaji u normalnoj izvedbi s belom kovinom (mašću). Oni se podmazuju podmazuju pomoću slobodnog prstena za podmazivanje. Pokazivač ulja na kućištu ležaja omogućava kontrolu nivoa ulja.

Kod velikih električnih mašina podmazivanje i hlađenje kliznih ležajeva prikazanih na slici 12.2 vrši se pomoću pumpe. Za sprečavanje ležajnih struja treba pričvrstiti ležaj na strani suprotnoj od pogonske izolovano na temeljnu ploču ili noseću konstrukciju.

Ulje za podmazivanje mora biti bez smola i kiselina a po pravilu ga preporučuju proizvođači elektromotora u svom tehničkom uputstvu.

Normalni klizni ležajevi ne podnose aksijalni pritisak pa se zbog toga ne smeju upotrebljavati kod elektromotora za vertikalno ili koso postavljanje.

Definiciona terminologija za klizne ležajeve:

Klizni ležaj je cilindrični ili delimično cilindrični ležaj koji nosi (podupire) rukavac osovine.

Klizni ležaj sa prstenom za podmazivanje je ležaj, u kome prsten okružuje rukavac i vrti se snjim, podižući ulje za podmazivanje iz spremnika, u koji se umače prsten.

Klizni ležaj sa diskom za podmazivanje

je ležaj, u kome je na osovini koncentrično postavlje disk umočen u spremnik za ulje. Pri obrtanju osovine ulje s površine diska ulazi u ležaj.

Ležaj sa fitiljem za podmazivanje

je ležaj, u kome se podmazivanje uljem vrši kapilarnim delovanjem pomoću fitlja umočenog u posudi (spremniku) za ulje.   

12. Sliding bearings!

Sliding bearings are used in large electric machines, as well as in a number of special small and medium electric machines. Micromotors and small motors (except for motors with sintered bearings) are also made with sliding bearings, which are lubricated with a wick.

At the point of contact, the wick is pressed lightly on the shaft with the help of a spring. It must always be immersed in oil that is not too thick and which is usually recommended by the electric motor manufacturer. Sliding

bearings are usually made of bronze, and those with universal electric motors are made of sintered metal, which, thanks to their capillary action, have the property of self-lubrication. An oil-soaked felt ring is placed in the sleeve of the sintered bearing, which serves as an oil tank.

For medium electric motors, Figure 12.1. are plain bearings in the normal version with white metal (grease). They are lubricated with a free lubrication ring. The oil indicator on the bearing housing allows control of the oil level.

For large electrical machines, the lubrication and cooling of the plain bearings shown in Figure 12.2 is done by means of a pump. To prevent bearing currents, the bearing should be fastened on the side opposite to the drive in isolation to the foundation plate or supporting structure.

Lubricating oil must be free of resins and acids, and as a rule it is recommended by the manufacturers of electric motors in their technical instructions. Normal plain bearings do not withstand axial pressure and must therefore not be used with electric motors for vertical or oblique mounting.

Definition terminology for plain bearings:

Sliding bearing is a cylindrical or partially cylindrical bearing that carries (supports) the shaft sleeve.

A sliding bearing with a lubricating ring is a bearing, in which the ring surrounds the sleeve and rotates with it, lifting the lubricating oil from the tank, into which the ring is dipped.

A sliding bearing  with a lubricating disc is a bearing in which a disc dipped in an oil tank is concentrically placed on the shaft. When the shaft rotates, oil enters the bearing from the surface of the disc.

Bearing with lubricating wick is a bearing in which oil lubrication is performed by capillary action using a wick dipped in an oil container.

13. Kotrljajući ležajevi!

Kod električnih mašina kotrljajući ležajevi su pretežno kuglični ili  valjkasti. U odnosu na  klizne ležajeve, njihove prednosti su manje dimenzije, jednostavnije održavanje, zaštita protiv onečišćenja i znatno manje trenje pri pokretanju elektromotora. Vazdušni zazor motora s kotrljajućim ležajevima se ne menja, jer se ti ležaji troše samo neznatno. Normalni kotrljajući ležajevi mogu preuzeti ograničen aksijalni pritisak koji je naveden u katalozima proizvođača.

Mali elektromotori imaju sa obe strane kuglične ležajeve. Ugrađeni elastični prstenovi obezbeđuju miran rad elektromotora i sprečavaju oštećenja ležaja prilikom transportovanja.

Srednji motori najčešće imaju na pogonskoj strani valjkasti ležaj, a na suprotnoj strani kuglični ležaj, slika 13.1. 

Veliki elektromotori imaju na pogonskoj strani pored valjkastog i kuglični ležaj, slika 13.2. koji služi za fiksiranje položaja rotora i za preuzimanje eventualnih dodathnih aksijalnih sila. Sklopovi kotrljajućih ležajeva srednjih i velikih eletromotora opremljeni su regulatorom količine masti i mazalicama koje omogućavaju podmazivanje za vreme rada mašine.

Na slici 13.3. prikazani su detalji ugradnje kugličnih ležajeva sa elastičnim prstenovima  na prednjoj i suprtnoj strani osovine manjih elektromotora.

Na sliki 13.4. prikazani su detalji ugradnje istih kotrljajućih ležajeva bez elastičnih prstenva  i na prednjoj i na suprotnoj strani osovine elektromotora.

Standardne definicije za ležajeve bi bile:

Kuglični ležaj

je ležaj koji ima obujmicu sa kuglicama.

Valjkasti ležaj

je ležaj koji ima obujmicu sa valjcima.

Aksijalni uporni ležaj

je ležaj predviđen za sprečavanje aksijalnog pomaka osovine i preuzimanje

aksijalnog opterećenja.

Vodeći ležaj

je ležaj predviđen za ograničenje poprečnog pomicanja vertikalne osovine.

Centrirajući ležaj

je ležaj koji služi za ograničavanje aksijalnog pomicanja horizontalne osovine ali koji nije predviđen da preuzima bilo kakvo trajno opterećenje osovine. Može biti kombinovan s ležajem koji preuzima opterećenje osovine.

13. Rolling bearings!

In electric machines, the roller bearings are mostly ball or roller. Compared to plain bearings, their advantages are smaller dimensions, easier maintenance, protection against pollution and significantly less friction when starting the electric motor. The air gap of the motor with roller bearings does not change, because these bearings wear only slightly. Normal roller bearings

can take on the limited axial pressure specified in the manufacturer’s catalogs.

Small electric motors have ball bearings on both sides. Built-in elastic rings ensure smooth operation of the electric motor and prevent damage to the bearings during transport. Medium engines usually have a roller bearing on the drive side and on the opposite side ball bearing, Figure 13.1.

Large electric motors have a ball bearing on the drive side next to the roller, Figure 13.2. which serves to fix the position of the rotor and to take over any additional axial forces. Rolling bearing assemblies for medium and large electric motors are equipped with a grease regulator and lubricators that allow lubrication during machine operation.

In Figure 13.3. details of the installation of ball bearings with elastic rings on the front and opposite side of the shaft of smaller electric motors are shown.

In Figure 13.4. details of the installation of the same roller bearings without elastic rings on both the front and opposite sides of the electric motor shaft are shown.

The standard definitions for bearings would be:

A ball bearing is a bearing that has a ball clamp.

A roller bearing is a bearing that has a clamp with rollers.

An axial thrust bearing is a bearing designed to prevent axial displacement of the shaft and take axial load.

The guide bearing is a bearing designed to limit the transverse movement of the vertical shaft.

The centering bearing is a bearing that serves to limit the axial movement of the horizontal axis but which is not designed to take any permanent axle load. It can be combined with a bearing that takes on the axle load.

14. O aktivnim delovima rotacionih električnih mašina!

Aktivni deo svake električne mašine sastoji se od magnetnog i električnog dela.

Magnetni deo (magnetno jezgro) služi za provođenje magnetnog toka (fluksa).

Električni deo sastoji se od električno provodljivog  dela (namotaj) koji služi za provođenje električne struje, i električno neprovodljivog dela (izolacionog sistema) koji služi za odvajanje pojedinih delova električne mašine između kojih postoji električni napon. Izradaedba aktivnih delova električnih mašina zavisna je od vrste električne mašine, njene veličine, nazivnog napona mašine i dr. 

U narednim pitanjima sa odgovorima biće prikazane osnovne i tipične izvedbe aktivnog dela električnih mašina.

Usvojene definicije aktivnih delova električnih mašina bile bi sledeće:

Magnetno jezgro

je deo magnetnog kola električne mašine, na koje ili oko njega se po pravilu postavlja namotaj.

Paket limova

je magnetno jezgro koje se sastoji iz lameliranog magnetnog lima.

Pol

je deo magnetnog jezgra, na kojem je postvljen ili u koji je uložen pobudni namotaj. Pol može biti izrađen i kao trajni magnet.   

Namotaj

je grupa navojaka (svitaka) koji čine električnu mrežu ili deo električne mreže u električnoj mašini.

Izolacioni system

je raspored odgovarajućih izolacionih materijala.

14. About the active parts of rotary electric machines!

The active part of each electrical machine consists of a magnetic and an electrical part. The magnetic part (magnetic core) is used to conduct magnetic flux. The electrical part consists of an electrically conductive part (coil) that serves to conduct electricity, and an electrically non-conductive part (insulation system) that serves to separate individual parts of the electrical machine between which there is electrical voltage.

The production of active parts of electrical machines depends on the type of electrical machine, its size, rated voltage of the machine, etc. In the following questions with answers, the basic and typical performances of the active part of electrical machines will be presented.

The adopted definitions of the active parts of electrical machines would be as follows:

A magnetic core is a part of the magnetic circuit of an electrical machine, on or around which a winding is usually placed.

The sheet metal package is a magnetic core consisting of a laminated magnetic sheet.

The pole is the part of the magnetic core, on which the excitation coil is placed or in which it is inserted. The pole can also be made as a permanent magnet.

A coil is a group of coils (sections) that form an electrical network or part of an electrical network in an electrical machine.

The insulation system is the arrangement of appropriate insulation materials.

15. O statorima električnih mašina jednosmerne struje?

Stator jednosmernih motora, slika 15.1., sastoji se od jarma, glavnih i pomoćnih polova koji su pričvršćeni na njega. Kroz glavne polove prolazi magnetni fluks naizmenog polariteta u rotor (armaturu) i nose glavni namotaj.

Jaram stvara magnetni povratni put. Između glavnih polova nalaze se pomoćni polovi kroz čiji namotaj protiče struja rotora. Magnetni fluks u jarmu je vremenski stalan, ako se ne uzme u obzir promena pobude. Kod malih jednosmernih mašina izrađuje se masivni jaram. Sve velike jednosmerne mašine kao i srednje predviđeni za napajanje valovitom strujom iz ispravljača imaju radi smanjenja gubitaka lamelirani jaram, tj. izrađen od limova. Kriva pobude, tj. raspodela magnetnog polja ispod luka glavnog pola, izobličuje se pri opterećenju zbog uticaja rotra kroz koji teče električna struja. Kako bi se što više smanjilo ovo izobličenje polja kod srednjih, a naročito kod velikih jednosmernih mašina ugrađuje se kompenzacioni namotaj, u žlebove polne papuče glavnog pola, što se vidi na slici 15.2.    

Prema definicijiama;

-Izraženi pol (naziva se i istaknuti pol)je vrsta magnetnog pola koji strči iz jarma glavčine prema vazdušnom zazoru.

-Polna papuča je deo izraženog pola okrenut prema vazdušnom zazoru.

Na slikama 15.3. do 15.14. prikazani su stvarni detalji statora mašina jednosmerne struje. O rotorima (armaturi) više ćemo govoriti u sledećem pitanju.

15. About stators of electric machines of direct current?

The stator of DC motors, Figure 15.1., consists of a yoke, main and auxiliary poles attached to it. A magnetic flux of alternating polarity passes through the main poles into the rotor (armature) and carries the main winding.

The yoke creates a magnetic return path. Between the main poles there are auxiliary poles through whose winding the rotor current flows. The magnetic flux in the yoke is time constant, if the change in excitation is not taken into account. With small one-way machines, a massive yoke is made. All large DC machines, as well as medium ones, intended for power supply with wave current from the rectifier, have a laminated yoke in order to reduce losses, ie. made of sheet metal. The excitation curve, ie. the distribution of the magnetic field under the arc of the main pole, is distorted under load due to the influence of the rotor through which the electric current flows. In order to reduce this field distortion as much as possible in medium, and especially in large DC machines, a compensating winding is installed in the grooves of the main pole’s full slipper, which can be seen in Figure 15.2.

By definition;

-The sailent is a type of magnetic pole that protrudes from the yoke of the hub towards the air gap.

-The full slipper is the part of the salient half facing the air gap.

In Figures 15.3. to 15.14. the actual details of the machine stator are shown direct currents. We will talk more about rotors (armature) in the next question.

16. O rotorima električnih mašina jednosmerne struje

U prethodnom pitanju smo dali najvažnija znanja o statorima jednosmernih električnih mašina, pa je red da nešto kažemo i o njihovim rotorima.

Rotor električnih motora jednosmerne struje sastoji se od osovine i na njoj pričvršćenog  paketa limova, kolektora, ventilatora i ležajeva koji se mogu skidati sa osovine. Paket limova je u obliku cilindričnog valjka sa žlebovima na spoljašnjoj strani u koju je postavljen namotaj električno povezan sa kolektorom. Kolektor se sastoji od bakarnih segmenata (lamela) postavljenih po obodu i međusobno izolovanih. Kolektor ima zadatak da sa četkicama koje naležu i po njemu klize da izvrši ispravljanje unutrašnje naizmenične napone rotora (armature) i da u njega dovodi električnu struju tako da gledano sa statorske strane raspodela struje ostane nepromenjena nazaviasno od promenljivog položaja rotora. Ispod glavnih polova istog polarriteta, prema tome protiču uvek rotorske struje istog smera. 

Na kolektor se dovodi struja preko grafitnih ili ugljenih četkica koje se nalaze u držačima a njihov pritisak se tačno podešava. Držači četkica učvršćeni su na provodne bolcnove sa navojima (svornjake) koji su izolovano fiksirani na jaram (nosač) za četkice. Svornjaci istog polariteta su međusobno električno povezani.

 Prema definicijiama;

Četkica je element koji prvodi struju, po pravilu nepomičan, predviđen da pomoću kliznog kontakta osigurava električnu vezu između pokretnih i nepokretnih delova električne mašine. 

Držač četkica je deo konstrukcioni deo električne mašine koji drži četkice i omogućava održavanje njihovog kontakta pod pritiskom s rotirajućom površinom.

Ormarić četkice je deo držača četkica u kojem je smeštena četkica.

Opruga držača četkice je deo držača četikace koji osigurava potreban pritiska na četkicu za održavanjem njenog kontaktra sa kliznom površinom.

Na slici 16.3. prikazan je kompletan sklop četkica sa svim gore pomenutim delovima jednog jednosmernog elektromotora ili generatora.

Kolektor je komplet lamella međusobno izolovanih u radialno aksialnoj ravni na koje su smeštene četkice koje omogućavaju preko kliznog kontakta prelaz struje iz jednog dela električnog kola u drugi električne mašine.

Zastavica kolektora je strujno provodljiv element za spajanje lamele kolektora sa sekcijom namotaja.

Na slikama 16.1. do 16.5. prikazan je rotor jedne veće jednosmerne mašine, od spremnog rotora za namotavanje pa do kraja.

Na slici 16.6 prikazan je poklopac jednosmerne mašine otvorene konstrukcije sa nosačima četkica.

16. About rotors of electric machines of direct current

In the previous question, we gave the most important knowledge about the stators of DC electric machines, so it is time to say something about their rotors.

The rotor of DC electric motors consists of a shaft and a package of sheets, collectors, fans and bearings attached to it, which can be removed from the shaft. The package of sheets is in the form of a cylindrical roller with slots on the outside in which the coil is placed electrically connected to the collector. The collector is consists of copper segments (lamellae) placed along the perimeter and mutually insulated. The collector has the task of correcting the internal alternating voltage of the rotor (armature) with the brushes that rest and slide on it and to bring electric current into it so that seen from the stator side, the current distribution remains unchanged depending on the variable position of the rotor. Below the main poles of the same polarity, therefore, rotor currents always flow in the same direction.

Electricity is supplied to the collector via graphite or carbon brushes located in the holders and their pressure is precisely adjusted. The brush holders are fixed to the conductive bolts with threads (bolts) which are fixed to the yoke (carrier) for the brushes in isolation. Bolts of the same polarity are electrically connected to each other.

By definition;

A brush is an element that conducts electricity, as a rule fixed, designed to provide an electrical connection between moving and immovable parts of an electrical machine by means of a sliding contact.

The brush holder is a structural part of an electrical machine that holds the brushes and allows them to maintain their contact under pressure with the rotating surface.

The brush cabinet is the part of the brush holder in which the brush is placed.

The brush holder spring is the part of the brush holder that provides the necessary pressure on the brush to maintain its contact with the sliding surface.

In Figure 16.3. a complete set of brushes with all the above-mentioned parts of one DC electric motor or generator is shown. The collector is a set of lamellae insulated from each other in the radially axial plane, on which brushes are placed, which enable the passage of current from one part of the electrical circuit to another electrical machine via a sliding contact.

The collector flag  is a current-carrying element for connecting the collector lamella to the winding section.

In Figures 16.1. to 16.5. the rotor of a larger DC machine is shown, from the ready rotor for winding to the end.

Figure 16.6 shows the cover of a one-way machine of open construction with brush holders.

17. Šta znate o sinhronim električnim mašinma?

Sinhrone električne mašine slične u obliku sinhronih generatora zastupljene su oblasti proizvodnje električne energije.

Prema pogonskoj mašini sinhroni generatori se dele na:

• Turbogeneratore,
• Hidrogeneratore,
• Dizel generatore,
• Gasne generatore,
• Vetrogeneratori,
• Sinhroni kompenzatori,
• Sinhroni elektromotori.

Turbogeneratori se pokreću turbinama sa vodenom parom. Hidrogeneratori se pokreću snagom vode.

Dizel generatori ili dizel agregati se pokreći pomoću dizel motora.

Gasni generatori se pokreću pomoću gasnih turbina. 

Vetrogeneratori se pokreću snagom vetra preko jednoelisne, dvoelisne ili troelisne turbine. Koriste se sihnroni generatori sa stalnim magnetima ili sa pobudnim namotajem.

Na narednim slikama prikazane različite konstrukcije sinhronih generatora koji se koriste u termoelektranama I hidroelektranama sa kraćim a jasnim opisima razumljivim svakom stručnjaku, bez teoretisanja.

Ove električne mašine, prvenstveno se koriste kao generatori, a ređe kao elektromotori. Sinhroni generatori su najveće električne mašine koje se danas proizvode. Maksimalna snaga jedne jedinice kreće se preko 1000 MW. S druge strane, sinhroni motori se rade za snage od nekoliko delova vata do više megavata.

Sinhrone mašine se primenjuju u pogonu i kao mašine pobudne jalove-reaktivne) snage a nazivaju se sinhroni kompenzatori.

Na slici 17.1. i 17.2.  vidimo Vestinghausove dvofazne generatore, montirane u hidroelektrani Edward Dean Adams na Nijagarinim vodopadima 1895. godine, naizmenične struje faznog napona 2200 (2250 V), 25 c/se, 775 A, 5000 HP, 250 1/min. Polovi su na statoru, a dvofazni namotaj na rotoru. Kasnije su ovi generatori prerađeni na trofazne i za viši napon. 

17. What do you know about synchronous electric machines?

Synchronous electrical machines similar in form to synchronous generators are represented in the field of electricity production.

According to the driving machine, synchronous generators are divided into:

– Turbogenerators,

– Hydrogenerators,

– Diesel generators,

– Gas generators,

– Wind generators,

– Synchronous compensators,

– Synchronous electric motors.

Turbogenerators are driven by steam turbines. Hydro generators are powered by water power.

Diesel generators or diesel aggregates are powered by diesel engines.

Gas generators are powered by gas turbines.

Wind generators are driven by the power of the wind through a single, double or triple turbine.

Synchronous generators with permanent magnets or with an excitation coil are used.

The following pictures show different constructions of synchronous generators used in thermal power plants and hydroelectric power plants with short and clear descriptions understandable to every expert, without theorizing.

These electric machines are primarily used as generators, and less often as electric motors. Synchronous generators are the largest electrical machines produced today.

The maximum power of one unit is over 1000 MW. On the other hand, synchronous motors are made for powers from a few fractions of a watt to several megawatts.

Synchronous machines are also used in operation as machines of excitation (reactive) power and are called synchronous compensators.

In Figure 17.1. and 17.2. we see Westinghouse’s two-phase generators, installed in the Edward Dean Adams hydroelectric plant at Niagara Falls in 1895, alternating currents of phase voltage 2200 (2250 V), 25 c/s, 775 A, 5000 HP, 250 1/min. The poles are on the stator, and the two-phase winding is on the rotor. Later, these generators were converted to three-phase and for higher voltage.

18. Statori sinhronih električnih mašina

Statori sinhronih mašina su praktično identični statorima asinhronih mašina. Razlike u konstrukciji su posledica veličine mašina i brzine obrtanja.

Magnetno kolo sinhronog generatora sastoji se iz dva glavna (osnovna) dela:

• Statora koji je uvek nepokretni deo i
• Rotora koji je obrtni deo,

 

Stator sinhrone električne mašine je u obliku šupljeg cilindra koji se radi od visokokvalitetnih dinamo limova (debljinje 0.5 mm, ređe debljeg lima). Limovi su međusobno izolovani kako bi se smanjili gubici usled vrtložnih struja. Limovi statora slažu se u pakete – segmente između kojih se nalaze promajišta za efikasnije hlađenje. Limovi se štancaju na posebnoj mašini za štancanje limova svih tipova rotacionih električnih mašina. Žlebovi statora sinhronih električnih  mašina manjih snaga su poluzatvoreni, a po obliku trapezni ili pravougaoni. S druge strane, žlebovi statora sinhronih mašina srednjih i velikih snaga uvek otvoreni pravougaonog a ne retko i trapeznog oblika. U žlebove se ulažu, najčešće štapni namotaji u toku montaže hidrogeneratora na samom gradilištu i koji su polusekcijski. Kod manjih sinhronih mašina namotaji jedne sekcije su iz jednog dela, što se može videti na narednim slikama. Prednost otvorenih žlebova, posebno kod generatora za više i visoke napone u fabrici vakuumiraju, čime su odstranjeni mehurići vazduha, koji mogu dovesti do tinjavog pražnjenja a time i do oštećenja izolacije. Sinhroni generatori velikih snaga se na gradilište elektrana dopremaju u delovima; statorska jezgra su najčešće u segmentima a ređe se limovi slažu na samom gradilištu, namotaji se dopremaju u polusekcijama spremnim za ulaganje u statorske žlebove, a ređe celim sekcijama (sekcija iz jednog dela), takođe i elementi za spajanje namotaja kao i elementi za hlađenje namotaja ako je hlađenje namotaja vodom ili vodonikom.     

Turbogeneratori se proizvode sa cilindirčnim rotorom, obično sa p=1, ređe p=2, tako da pri frekvenciji napna od 50 Hz imaju broj obrtaja respektivno 3000 1/min i 1500 1/min, dok pri frekvenciji od 60 Hz su respektno brzine obrtanja 3600 1/min i 1800 1/min. Pri ovako velikim brzinama obrtanja velike su periferne brzine, pa kod turbogeneratora zbog velike obrtne mase i dužine između ležišta dolazi do velikih mehaničkih naprezanja. Ovo je razlog zbog koga se turborotiri ne grade sa velikim prečnicima i da se namotaj rotora raspodeljuje što ravnomernije po obimu rotora. Pogonske mašine za ovako velike brzine su parne ili gasne turbine.

Turbogeneratori se uvek montiraju horizontalno.  

Hidrogeneratori se grade sa istaknutim polovima na rotoru, od sasvim sporohodih do brzohodih sa p=2. Kako raste broj pari polova, brzina obrtanja se smanjuje. Što je brzina manja, veći je prečnik rotora, koji je takođe ograničen mehaničkim naprezanjima usled delovanja centrifugalnih sila. Ova mehanička naprezanja nisu toliko velika pa nije potrebna ravnomerna raspodela namotaja po obimu rotora, tako da se može koristiti rotor sa istaknutim polovima. Kod velikih snaga pogon se vrši Kaplanovom ili Francisovom turbinom.

Kao što se vidi hidrogeneratori i turbogeneratori se mnogo razlikuju po svojim konstrukcijama. Primera radi, kod turbogeneratora snage 100 MW i 200 MW dužina rotora je 5 do 6 puta veća od prečnika. S druge strane, kod hidrogeneratora snage 100 MW i 130 MW prečnik rotora je 6 do 7 puta veći od osne dužine magnetnog kola. Sve se ovo može videti iz fotorgrafija i crteža u prilogu sa opisima.

Hidrogeneratori kod kojih je brzina obrtanja relativno velika montiraju se horizontalno, a hidrogeneratori većih i velikih snaga sa relativno malim brzinama obrtanja, montiraju se vertikalno, a hlađenje je kombinovano sa vodom i vazduhom, ređe sa vodonikom.

Sinhroni generatori sa pogonom pomoću dizel motora ili gasnim turbinama, proizvode se u širokom rasponu brzina obrtanja, od p=2 pa naviše. Snaga dizel i gasnih generatora ograničena je mogućnostima izrade dizel motora ili gasne turbine, u proseku do desetinu megavoltampera. 

 Hlađenje namotaja je vazdušno, vodeno i sa vodonikom.

18. Stators of synchronous electric machines

The stators of synchronous machines are practically identical to the stators of asynchronous machines. The differences in construction are due to the size of the machines and the speed of rotation. The magnetic circuit of the synchronous generator consists of two main (basic) parts:

– The stator, which is always a stationary part and

– Rotor, which is a rotating part, which are separated from each other by spacers. In the case of synchronous electric machines, the inductor ie. the primary is always the rotor, and the induct ie. the secondary is the stator.

The stator of the synchronous electric machine is in the form of a hollow cylinder made of high-quality dynamo sheets (thickness 0.5 mm, less often thicker sheets). The sheets are insulated from each other to reduce losses due to eddy currents. The stator sheets are arranged in packages – segments between which there are drafts for more efficient cooling. Sheets are stamped on a special machine for stamping sheets of all types of rotary electric machines.

The slots of the stator of synchronous electric machines of lower power are semi-closed, and trapezoidal or rectangular in shape. On the other hand, the slots of the stator of medium and high power synchronous machines are always open rectangular and not infrequently trapezoidal. Rod coils are inserted into the grooves during the assembly of the hydrogenerator on the construction site and are semi-sectional. In smaller synchronous machines, the windings of one section are from one part, which can be seen in the following pictures.

The advantage of open slots, especially in the case of generators for higher and higher voltages, is that they are vacuumed in the factory, which eliminates air bubbles, which can lead to smoldering discharge and thus damage to the insulation. High power synchronous generators are delivered to the power plant construction site in parts; stator cores are most often in segments, and less often the sheets are stacked on the construction site itself, the coils are delivered in half sections ready for inserting in the stator slots, and less often in whole sections and less often the sheets are stacked on the construction site itself, the windings are delivered in half sections ready for inserting in the stator slots, and less often in whole sections (section from one part), also elements for connecting the windings as well as elements for cooling the windings if the windings are cooled by water or hydrogen.

Turbogenerators are produced with a cylindrical rotor, usually with p=1, less often p=2, so that at a voltage frequency of 50 Hz they have a number of revolutions of 3000 1/min and 1500 1/min, respectively, while at a frequency of 60 Hz, the rotation speeds are 3600 1/min and 1800 1/min, respectively. At such high rotation speeds, the peripheral speeds are high, so in the case of turbogenerators, due to the large rotating mass and the length between the bearings, large mechanical stresses occur. This is the reason why turborotors are not built with large diameters and that the rotor winding is distributed as evenly as possible over the circumference of the rotor. The driving machines for such high speeds are steam or gas turbines.

Turbogenerators are always mounted horizontally. Hydrogenerators are built with salient poles on the rotor, from quite slow-moving ones to fast rotation with p=2. As the number of pole pairs increases, the rotation speed decreases. The lower the speed, the larger the diameter of the rotor, which is also limited by mechanical stresses due to the action of centrifugal forces. These mechanical stresses are not so great, so there is no need for an even distribution of windings around the circumference of the rotor.

So a rotor with salient poles can be used. At high power, the drive is made with a Kaplan or Francis turbine.

As you can see, hydrogenerators and turbogenerators differ greatly in their constructions. For example, in 100 MW and 200 MW turbo generators, the length of the rotor is 5 to 6 times greater than the diameter. On the other hand, in 100 MW and 130 MW hydro generators, the diameter of the rotor is 6 to 7 times greater than the axial length of the magnetic circuit. All this can be seen from the photos and drawings in the attached description.

Hydrogenerators with a relatively high speed of rotation are mounted horizontally, and hydrogenerators of higher and higher power with relatively low speed of rotation are mounted vertically, and the cooling is combined with water and air, less often with hydrogen.

Synchronous generators powered by diesel engines or gas turbines are produced in a wide range of rotation speeds, from p=2 and up. The power of diesel and gas generators is limited by the possibilities of making a diesel engine or a gas turbine, on average up to a tenth of a megavolt.

Coil cooling is air, water and hydrogen.

19. O rotorima sinhronih električnih mašina

Kao što smo rekli, rotor je pored statora drugi najvažniji deo sinhronih električnih mašina, pa ćemo se ovde detaljnije pozabaviti i rotorima, ali, sa praktične strane jer se u ovoj seriji ne bavimo teorijom koja je dosta komplikovana i o njoj postoji mnoštvo literature.

Rotor sinhrone električne mašine je tipičan induktor koji se izvodi dvojako.

Dvopolne mašine sa 3000 1/min za 50 Hz i 3600 1/min za 60 Hz, a eventualno i četvoropolne. Izrađuju se u obliku punog (okruglog) rotora. Kod termoelektrana ovakvi rotori se nazivaju turborotori, a generator turbogeneratrimom. Generatori sa manjim brzinama obrtanja imaju imaju izražene polove. S obzirom da se najčešće pogone hidrauličnim turbinama nazivaju se hidrogeneratora ili hidroagregati.

Turborotori su uzdužno ožljebljeni po većem delu oboda u čije se žlebovesmeštaju pobudni namotaji koji mogu biti različitih konstrukcija. Žlebovi i provodnici raspoređuju se tako da dobijen oblik magnetnog fluksa bude što približnije sinusoidalnom. U zavisnosti od tehničkih zahteva telo rotora može biti ovalno obrađeno. Krajevi pobudnih namotaja izvode se na klizne prstenove montirane na osovini rotora. Telo turborotora je masivno, izrađeno iz jednog komada zajedno sa osovinom.

Provodnici se žlebovima učvršćuju zaglavcima (klinovima), a glave namotaja (bočne veze) zaštićuju se kapama od nemagnetnog čelika. Za male generatore, umesto kape se koristi bandažiranje koje se izvodi od žice i od poliesternih traka sa staklenim vlaknima.

Kada se žlebovi sa obe strane rotora sliju u po jedan žleb, dobija se rotor “školskog” tipa u obliku dvostrukog slova T, kako se vidi na slici 19.1.

Ponovićemo, brzine obrtanja sinhronih mašina su:

Za frekvenciju f= 50 Hz je:

p=1, n=3000 1/min;

p=2, n=1500 1/min;

p=3, n=1000 1/min;

p=4, n=750 1/min;

p=5, n=600 1/min;

p=6, n=500 !/min 

a za frekvenciju napona od f=60 Hz to izgleda:

p=1, n=3600 1/min;

p=2, n=1800 1/min;

p=3, n=1200 1/min;

p=4, n=900 1/min;

p=5, n=720 1/min;

p=6, n=600 1/min.       

Naravno, sinhroni generatori, posebno hidrogeneratori se grade i za još niže brzine čak od 120 1/min i prelaze snagu od 1000 MVA odnosno 1000 MW.

Ukratko, turbogeneratori se proizvode tj. grade sa cilindričnim rotorom, obično sa p=1 pari polova, ređe sa p=2 za frekvenciju od 50 Hz, brzine obrtanja 3000 1/min i 1500 1/min, odnosno za frekvenciju 6 Hz, 3600 1/min i 1800 1/min i uvek se montiraju u horizontalnom položaju.

Takođe, hidrogeneratori se grade sa istaknutim polovima na rotoru, od sasvim sporohodnih do brzohodnih sa p=2. Sa većim brojem pari polova, brzina obrtanja se smanjuje. Što je brzina obrtanja manja, prečnik rotora je veći.

Rotor sinhrone električne mašine je obrtni deo te je zbog toga dobio svoj naziv. Njegov naziv kod ovih mašina je induktor (primar) dok je indukt (sekundar) stator.

Rotor sa osovinom sinhrone mašine čini celinu, na čijoj perferiji je smešteno 2p polova koji mogu biti od masignog viskokvalitetnog gvođža za ovu namenu ili od limova, laminirani rotor. Kod sinhronih električnih mašina pobudni namotaj je uvek smešten na rotoru a napajan je jednosmernom strujom. Pored pobudnog namotaja, kod nekih sinhronih električnih mašina sa istaknutim polovima, na rotoru je postavljen i dodatni prigušni tj. amortizacioni namotaj. Zadatak ovog namotaja je: prigušenje elektromehaničke oscilacije rotora i prigušenje inverzne komponente magnetnog polja koji nastaju pri nesimetričnim opterećenjima, a koje mogu da izazovu nepoželjne gubitke i prenapone, i omogućuju asinhrono zaletanje sinhronih elektromotora i kompenzatora.

Kod sinhronih mašina sa cilindiričnim rotorom ugrađuje se prigušni namotaj kada se očekuju velika nesimetrična opterećenja. Postoje dve izvedbe oblika rotora:

• Cilindrični rotor se izrađuje od najkvalitetnijeg masivnog čelika-gvožđa, a zatim se obrađuje najčešće kovanjem. Po celoj osnoj dužini rotora se urezuju žlebovi u koje se smešta namotaj rotora sastavljen iz sekcija i raspodeljen u žlebovima. Kod cilindričnih rotora približno jedna trećina polnog koraka nije ožljebljena i čini zonu velikog zubca kroz koji prolazi glavni deo magnetnog fluksa. Namotaji za ovaj rotor se izrađuju od bakra koji na radnoj temperaturi, pored velike električne provodnosti, ima i visoku mehaničku čvrstoću. Kod sinhtronih električnih mašina sa cilindričnim rotorom međugvožđe je svuda iste dužine. Cilindrični rotor se skoro isključivo primenjuje kod velikih dvopolnih ili četvoropolnih turbogeneratora.

• Rotor sa istaknutim polovima se sastoji od:

    Osovine, magnetnog venca i magnetnih polova. Kod mašina manjih snaga i manjih brzina magnetni polovi se pričvršćuju pomoću zavrtnjeva, a kod mašina  većih snaga i većih brzina obrtanja pomoću tzv. “lastinog” repa. Ovaj tip konstrucije rotora koristi se kod hidrogeneratora sa većim brojem pari polova.

Treba naglasiti da se za razliku od cilindričnih rotora, rotori sa istaknutim polovima mogu montirati i horizontalno i vertikalno.

Rotor sinhrone električne mašine je tipičan induktor koji se izvodi dvojako. Dvopolne mašine sa 3000 1/min za 50 Hz, a eventualno i četvoropolne. Izrađuju se u obliku punog (okruglog) rotora. Kod termoelektrana ovakvi rotori se nazivaju turborotori, a generator turbogeneratrimom. Generatori sa manjim brzinama obrtanja imaju imaju izražene polove. S obzirom da se najčešće pogone hidrauličnim turbinama nazivaju se hidrogeneratora ili hidroagregati.

Turborotori su uzdužno ožljebljeni po većem delu oboda u čije se žlebove smeštaju pobudni namotaji koji mogu biti različitih konstrukcija. Žlebovi iprovodnici raspoređuju se tako da dobijen oblik magnetnog fluksa bude što približnije sinusoidalnom. U zavisnosti od tehničkih zahteva telo rotora može biti ovalno obrađeno. Krajevi pobudnih namotaja izvode se na klizne prstenove montirane na osovini rotora. Telo turborotora je masivno, izrađeno iz jednog komada zajedno sa osovinom.

Provodnici se žlebovima učvršćuju zaglavcima (klinovima), a glave namotaja (bočne veze) zaštićuju se kapama od nemagnetnog čelika. Za male generatore, umesto kape se koristi bandažiranje koje se izvodi od žice i od poliesternih traka sa staklenim vlaknima.

Kada se žlebovi sa obe strane rotora sliju u po jedan žleb, dobija se rotor “školskog” tipa u obliku dvostrukog slova T, kako se vidi na slici 19.1.

19. About rotors of synchronous electric machines

As we said, the rotor is next to the stator the second most important part of synchronous electric machines, so here we will deal with rotors in more detail, but from the practical side because in this series we are not dealing with the theory, which is quite complicated and there is a lot of literature on it.

The rotor of a synchronous electric machine is a typical inductor that is performed in two ways.

Two-pole machines with 3000 1/min for 50 Hz and 3600 1/min for 60 Hz, and possibly four-pole. They are made in the form of a full (round) rotor. In thermal power plants, such rotors are called turborotors, and the generator is called a turbogenerator. Generators with lower rotation speeds have salient poles. Given that the most common drives with hydraulic turbines are called hydrogenerators or hydroaggregates.

Turborotors are longitudinally slotted along the larger part of the rim, in which slots are placed excitation coils that can be of different constructions. The slots and conductors are arranged so that the obtained shape of the magnetic flux is as close as possible to the sinusoidal one. Depending on the technical requirements, the rotor body can be oval-shaped. The ends of the excitation windings are led to slip rings mounted on the rotor shaft. The body of the turborotor is massive, made in one piece together with the shaft.

The conductors are secured with slots by pins, and the winding heads (side connections) are protected by caps made of non-magnetic steel. For small generators, instead of a cap, bandaging is used, which is made of wire and polyester tapes with glass fibers.

When the grooves on both sides of the rotor merge into one groove, a “school” type rotor in the shape of a double T is obtained, as seen in Figure 19.1.

To repeat, the rotational speeds of synchronous machines are:

For the frequency f= 50 Hz it is:

p=1, n=3000 1/min;

p=2, n=1500 1/min;

p=3, n=1000 1/min;

p=4, n=750 1/min;

p=5, n=600 1/min;

p=6, n=500 1/min

and for a voltage frequency of f=60 Hz it looks like:

p=1, n=3600 1/min;

p=2, n=1800 1/min;

p=3, n=1200 1/min;

p=4, n=900 1/min;

p=5, n=720 1/min;

p=6, n=600 1/min.

Of course, synchronous generators, especially hydrogenerators, are built for even lower speeds of even 120 1/min and exceed a power of of 1000 MVA or 1000 MW.

In short, turbogenerators are produced ie. they are built with a cylindrical rotor, usually with p=1 pairs of poles, less often with p=2 for a frequency of 50 Hz, rotation speeds of 3000 1/min and 1500 1/min, i.e. for a frequency of 6 Hz, 3600 1/min and 1800 1/ min and are always mounted in a horizontal position. Also, hydrogenerators are built with salient poles on the rotor, from completely slow-moving to fast-moving with p=2.

With a larger number of pole pairs, the rotation speed decreases. The lower the rotation speed, the larger the diameter of the rotor.

The rotor of a synchronous electric machine is a rotating part, which is why it got its name. Its name in these machines is the inductor (primary) while the induct (secondary) is the stator.

The rotor with the shaft of the synchronous machine forms a whole, on the periphery of which there are 2p poles that can be made of massive high-quality iron for this purpose or of sheets, a laminated rotor. In synchronous electric machines, the excitation winding is always located on the rotor and is supplied with direct current. In addition to the excitation winding, in some synchronous electric machines with salient poles, an additional damper is placed on the rotor, i.e. damping coil. The task of this winding is: damping of the electromechanical oscillation of the rotor and damping of the inverse component of the magnetic field that occur in case of asymmetric loads, which can cause undesirable losses and overvoltages, and enable asynchronous start-up of synchronous electric motors and compensators.In synchronous machines with a cylindrical rotor, a damping winding is installed when large asymmetric loads are expected. There are two versions of the rotor shape:

– The cylindrical rotor is made of the highest quality massive steel-iron, and then it is usually processed by forging. Slots are cut along the entire axial length of the rotor, in which the rotor winding assembled from sections and distributed in the slots is placed. The code cylindrical rotors, approximately one-third of the pole pitch is not grooved and forms the zone of a large tooth through which the main part of the magnetic flux passes. The windings for this rotor are made of copper, which at operating temperature, in addition to high electrical conductivity, also has high mechanical strength. In synchronous electric machines with a cylindrical rotor, the intermediate iron is everywhere the same length. The cylindrical rotor is almost exclusively used in large two-pole or four-pole turbogenerators.

– The rotor with sailent poles consists of:

Shafts, magnetic rings and magnetic poles. In machines of lower power and lower speeds, the magnetic poles are attached using screws, and in machines of higher power and higher rotation speeds, using the so-called “swallow” tail. This type of rotor construction is used in hydro generators with a larger number of pole pairs. It should be emphasized that unlike cylindrical rotors, rotors with salient poles can be mounted both horizontally and vertically. The rotor of a synchronous electric machine is a typical inductor that is performed in two ways. Two-pole machines with 3000 1/min for 50 Hz, 3600 1/min, 60 Hz and possibly four-pole machines. They are made in the form of a full (round) rotor. In thermal power plants, such rotors are called turborotors, and the generator is called a turbogenerator. Generators with lower rotation speeds have salient poles. Given that they are most often powered by hydraulic turbines, they are called hydrogenerators or hydroaggregates. The slots and conductors are arranged so that the obtained shape of the magnetic flux is as close as possible to the sinusoidal one. Depending on the technical requirements, the rotor body can be oval-shaped. The ends of the excitation windings are led to slip rings mounted on the rotor shaft. The body of the turborotor is massive, made of one piece together with the shaft. The conductors are fixed with slots by pins (pegs), and the heads of the coils (side connections) are protected by caps made of non-magnetic steel.

For small generators, instead of a cap, a banding made of wire and polyester tapes with glass fibers is used.

When the grooves on both sides of the rotor merge into one groove, a “school” type rotor in the shape of a double letter T is obtained, as seen in Figure 19.1.

Next time will be more interesting things.

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