Beperkingen bij lage frequenties

Standaard draaistroommotoren zijn voorzien van een koelventilator die door de motor zelf wordt aangedreven. Dit betekent voor de ventilator dat de luchtopbrengst kwadratisch met het toerental toe/afneemt. Hierdoor heeft de koelventilator bij gebruik onder de 20 Hz. niet genoeg luchtopbrengst om de motor bij het volle koppel te koelen. Een richtlijn is dat bij gebruik onder de 10 Hz. het koppel niet hoger dan 60 % mag zijn. Wanneer er toch een hoger koppel nodig is moet er een andere ventilator bij gemonteerd worden.

Sommige frequentieregelaars kunnen zelf rekening houden met dit koelprobleem en beschermen de motor tegen oververhitting.

                             Technology originated from EMERSON and HUAWEI

Simon Fan Sales Manager

ShenZhen VTdrive Technology Co.,Ltd.

Mail:simon.fan@vtdrive.com

Tel:+86-0755-23060667

Fax:+86-0755-33671802

Site: http://www.vtdrive.com

Skype:simon.fan0611

Address:3F&4F, Xihe Industrial Zone,

TangTou Load, Shiyan Town,

Baoan District, Shenzhen, China.

Kunt U ook op energie besparen?

Er zijn vele manieren om op energie te besparen.
Waar ik graag uw aandacht voor wil vragen, is het volgende:
Werkt u met elektromotoren?
Denk aan machines, als ventilatoren, lopende banden, pompen, zaagmachines, freesmachines, enz.
Nemen we als voorbeeld een ventilator in een stal of droogschuur.
Die staat vaak op volle toeren te draaien, terwijl dat alleen maar nodig is bij hogere temperaturen.
Door een frequentieregelaar op de ventilator te plaatsen en deze afhankelijk van de hoogte van de temperatuur te laten draaien, kunt u onder omstandigheden tot meer dan de helft van de energie besparen.
Rekensom:
Ventilator 3 kW.
Draait 24 uur
Verbruikt per 24 uur dus 72 kWh.
Een kWh kost plusminus 0,23 eurocent.
24 uren draaien kost dus 72x0,23= 16,56 euro per etmaal.
Gaat u deze ventilator temperatuurafhankelijk regelen, dan scheelt u dat snel 2500 euro.
Hoe kom ik daar aan?
Hartje zomer:
8 uren volop draaien van de ventilator, kosten 5,52 euro
16 uren op halve kracht, kosten 5,52 euro
Etmaal kost 11,04 euro.
Hartje winter:
24 uren draaien op halve kracht, kosten 8,28 euro per etmaal.
voorjaar/najaar:
4 uren volop, kosten 2,76 euro
20 uren op halve kracht, kosten 6,90 euro
Kosten etmaal 9,66 euro
Kosten per jaar zonder regelaar:
365x24x3x0,23 kost 6044,44 euro (1 ventilator een jaar laten draaien).
Kosten per jaar met regelaar:
365:4=91,25 dagen
91,25 dagen zomer kosten 1007,40 euro
91,25 dagen winter kosten 755,55 euro
182,5 dagen voor/najaar kosten 1762,95 euro
Totaal kosten jaar met regelaar: 3525,90 euro

U bespaart: 6044,44 - 3525,90 = 2518,54 euro.
Heeft u dus bespaart met het temperatuurafhankelijk regelen van 1 ventilator van 3kW over een jaar.

Vindt u dat allemaal niet zo belangrijk, doe het dan voor het milieu, voor de toekomst van onze kinderen en voor het behoud van onze kostbare/kwetsbare aarde.

Natuurlijk is dit een voor de vuist weg berekening en geldt dat lang niet voor alle ventilatoren.
Maar toch het overdenken waard.
Past dit in een gewone huishouding?
Nee.
Past dit voor industrie, landbouw of veeteelt, of aan boord van schepen (machinekamers)?
Jazeker en vaak in een veelvoud, omdat er meerdere ventilatoren gebruikt worden.

Zo zijn er veel meer grotere en kleinere installaties te bedenken, waar gretig bezuinigd kan worden.
Neem gerust contact met ons op. Wij helpen u (en waar mogelijk onze zo kwetsbare aarde) graag.

                             Technology originated from EMERSON and HUAWEI

Simon Fan Sales Manager

ShenZhen VTdrive Technology Co.,Ltd.

Mail:simon.fan@vtdrive.com

Tel:+86-0755-23060667

Fax:+86-0755-33671802

Site: http://www.vtdrive.com

Skype:simon.fan0611

Address:3F&4F, Xihe Industrial Zone,

TangTou Load, Shiyan Town,

Baoan District, Shenzhen, China.

Wat is een frequentieregelaar?

Een frequentieregelaar is een apparaat opgebouwd uit  vermogenselektronica met een besturing welke wordt toegepast voor het traploos regelen van de snelheid ofwel toerental van een wisselstroom elektromotor.

Het regelen van de snelheid bespaart energie, beschermd machines en zorgt voor een gelijkmatigere belasting van het elektriciteitsnet. Daarnaast verhoogt en verbetert het de productiviteit en kwaliteit.

Een frequentieregelaar regelt de snelheid van een inductie- of een synchroonmotor door het varieren van de frequentie van de voeding van de motor. Een frequentieregelaar wordt ook wel aangeduidt met:

• ASD : adjustable speed drive
• AFD : adjustable frequency drives
• VFD : variable frequency drives
• VSD : variable speed drives
• FC : frequency converters
• FO : frequentieomvormer

De eerste wisselstroommotor werd ontworpen in 1899. Wisselstroommotoren zetten elektrische energie om in mechanische energie d.m.v. elektromagnetische inductie.
Wisselstroommotoren hebben de volgende eigenschappen:

• Vaste snelheid, bepaald door de frequentie van de voedende spanning.
• Vast koppel

Vanzelfsprekend is een vaste snelheid niet geschikt voor alle processen onder alle omstandigheden. Er is dus een behoefte aan het regelen van de snelheid/toerental afhankelijk van de vraag.

Industriële machines worden vaak aangedreven met behulp van een elektromotor welke een voorziening hebben voor het regelen van de snelheid. Deze motoren zijn simpelweg een grotere uitvoering van de elektromotoren welke worden toegepast in bekende toepassingen als boormachines of mixers die normaal gesproken op een vaste snelheid of toerental werken.

Een regeling welke een snelheids/toerenregeling mogelijk maakt wordt een frequentieregelaar genoemd. Frequentieregelaars worden toegepast over een breed gebied in de industie zoals bijvoorbeeld voor het regelen van het toerental van ventilatoren en daarmee de luchtstroom in klimaatinstallaties of het regelen van de doorstroming van water of chemicaliën door het regelen van de snelheid/toerental van pompen.

Daarnaast worden frequentieregelaars ook veelal toegepast in complexere en moeilijkere aandrijvingen zoals bij papiermolens, tunnelboormachines, boorplatforms, voorstuwing op schepen, hijskranen, lieren etc. 

Procesregeling en energie besparing zijn de voornaamste redenen om een frequentieregelaar toe te passen. Frequentieregelaars werden primair ontwikkeld voor procesregeling maar door de toenemende behoefte aan energiebesparing worden ook hiervoor steeds meer frequentieregelaars toegepast.

Energiebesparen met frequentieregelaars.

Een aandrijving met frequentieregelaar verbruikt veelal minder energie dan een aandrijving met een vaste snelheid/toerental en een andere manier van regelen. Pompen en ventilatoren zijn de bekenste applicaties waar energie bespaard kan worden. Wanneer een ventilator aangedreven wordt door een motor met een vaste snelheid dan kan de benodigde luchtstroom groter zijn dan daadwerkelijk nodig is. De luchtstroom kan dan via een klepregeling geregeld worden echter is het veel efficiënter de luchtstroom te regelen door de snelheid/toerental van de motor te regelen.

Een aantal voordelen kunnen van belang zijn bij het regelen van een proces.

• Gelijkmatigere processen
• Acceleratie en deceleratie controle
• Verschillende snelheden/toerentallen voor verschillende processen
• Compensatie voor veranderende procesvariabellen
• Lage toerentallen voor installatie en inregel doeleinden
• Aanpassing van de productie snelheid
• Toepassen van nauwkeurige positionering
• Regelen van koppel en trekkracht

Voorbeeld

Een frequentie geregelde aandrijving heeft veelal een gelijkmatigere belasting in vergelijking tot een aandrijving met een vaste snelheid. In bijvoorbeeld een rioolwaterzuivering komt het rioolwater via een leidingsysteem in een groot basin terecht. Daar vandaan wordt het rioolwater naar het zuiveringsproces gepompt.

Bij installaties met pompen die draaien op een vaste snelheid worden deze pompen gestart en gestopt als het waterniveau in het basin een bepaald maximaal resp. minimaal niveau heeft bereikt. Het telkens starten van de pompen resulteert in regelmatig terug kerende piekstromen om de pompen te starten wat weer als gevolg heeft dat er (elektro)mechanische en thermische "stress" optreedt in de motoren en de overige elektrische componenten. De pompen en leidingen ondervinden mechanische en hydraulische "stress".
In het zuiveringsproces dient rekening te worden gehouden met piekbelastingen omdat er telkens een toename is van de doorstroming van rioolwater.

Wanneer er frequentiegeregelde aandrijvingen worden toegepast draaien de pompen continu waarbij de snelheid/toerental zal toenemen naarmate het niveau in het basin hoger/lager wordt. Hierdoor wordt de doorstroming van rioolwater naar het zuiveringsproces geoptimaliseerd en kan er een gelijkmatiger en verbeterd reinigingsproces plaatsvinden.

                             Technology originated from EMERSON and HUAWEI

Simon Fan Sales Manager

ShenZhen VTdrive Technology Co.,Ltd.

Mail:simon.fan@vtdrive.com

Tel:+86-0755-23060667

Fax:+86-0755-33671802

Site: http://www.vtdrive.com

Skype:simon.fan0611

Address:3F&4F, Xihe Industrial Zone,

TangTou Load, Shiyan Town,

Baoan District, Shenzhen, China.

VTdrive frequentieregelaars

VTdrive® Energiebesparing

Nu is de tijd om serieus energie te besparen

Als u ooit serieus heeft moeten nadenken over het besparen van energie, is het nu wel. Niet alleen vanwege het klimaat en bijvoorbeeld het terugdringen van de CO2 uitstoot, maar natuurlijk ook vanwege de noodzaak kosten te besparen.

Door het toepassen van VTdrive frequentieregelaars is het energieverbruik in elektrische aandrijfinstallaties relatief eenvoudig te verminderen. De investering zal zich in veel gevallen zelfs in korte tijd terugverdienen.

Energie efficiënt

De VTdrive frequentieregelaars hebben een bijzonder hoge energie efficiëntie van 98% . Dat betekent dat minder dan 2% van de energie verloren gaat in de regelaar. Als gevolg daarvan produceren de VTdrive regelaars ook minder warmte waardoor er ook nog eens minder energie nodig is voor het koelen van de regelaar en de ruimte waar deze geplaatst wordt.

Pompen en ventilatoren
Bij alle vormen van elektrische aandrijftechniek zorgt de VLT frequentieregelaar
voor een vermindering van het energieverbruik. Maar bij het aandrijven van pompen en ventilatoren
gaat het extra hard, omdat bij dergelijke variabel koppel aandrijvingen
het energieverbruik met de 3e macht van het toerental toeneemt. Wordt in een dergelijk geval het toerental met 10% verlaagd, dan bespaart al direct meer dan 25% energie. Bij een toerental vermindering van 20% wordt het energieverbruik
zelfs gehalveerd.

      

Nog meer besparingen

Door het vermogen van de aandrijving aan te passen aan de vraag of behoefte bespaart u veel energie.

Maar er zijn meer voordelen:

• minder slijtage

• hogere bedrijfszekerheid

• minder onderhoud

• langere levensduur

• minder onverwachtte stilstand

• betere werkomstandigheden

                             Technology originated from EMERSON and HUAWEI

Simon Fan Sales Manager

ShenZhen VTdrive Technology Co.,Ltd.

Mail:simon.fan@vtdrive.com

Tel:+86-0755-23060667

Fax:+86-0755-33671802

Site: http://www.vtdrive.com

Skype:simon.fan0611

Address:3F&4F, Xihe Industrial Zone,

TangTou Load, Shiyan Town,

Baoan District, Shenzhen, China.

The difference function between E5, V5 and V6 series frequency inverter

	E5	V5	V6
Hardware
Digital input terminal	X1~X4	X1~X7/DI	X1~X7/DI
Support DI input	NO	YES	YES
Digital putput terminal	1（Y1）	2（Y1 and Y2/DO）	2（Y1 and Y2/DO）
Relay	1（RA-RB-RC)	1（RA-RB-RC)	1（RA-RB-RC)
Analog	2（AI1 and AI2）	3（AI1、AI2、AI3）	3（AI1、AI2、AI3）
Analog input support +10V~-10V	NO	YES(AI3)	YES(AI3)
Analog output	2	2	2
Support DO output	NO	YES(Y2/DO)	YES(Y2/DO)
Support dual 485	NO (*)	YES	YES
Support operation panel 485	YES	YES	YES
Support extension card	NO(*)	YES	YES
Support built in braking unit	15kw and  below power built in as standard.	15kw and below power built in as standard.	15kw and below power built in as standard.
	Other power class only support external braking unit.	18.5kW~75kW braking unit can be optional.	18.5kW~75kW braking unit can be optional.
		90kW and above only support external braking unit	90kW and above only support external braking unit
(*)Note：If E5 series need terminal 485 or support extension card, should order non-standard control board.
Vector control 1 without encoder speed feedback
P0.03=0	YES	YES	YES
P0.03=1	YES	YES	YES
P0.03=2	NO	YES	YES
P0.03=3	NO	YES	YES
Vector control 2 without encoder speed feedback
P0.03=4	NO	YES	YES
P0.03=5	NO	YES	YES
P0.03=6	NO	YES	YES
P0.03=7	NO	YES	YES
Vector control 2 with encoder speed feedback
P0.03=8	NO	NO	YES
P0.03=9	NO	NO	YES
P0.03=10	NO	NO	YES
P0.03=11	NO	NO	YES
Torque control
Torque control without encoder	NO	NO	YES
Torque control with encoder	NO	NO	YES
Other
Default braking voltage	750	720	720
X1/X2 terminal delay	YES	NO	NO
Y1 terminal and relay delay and pulse width setting	YES	NO	NO
Pump and fan control	YES	NO	NO
Sleep and wake up	YES	NO	NO
Acceleration and deceleration time auto switch	YES	NO	NO
View user continuous running time	YES	NO	NO
View user total running time	YES	NO	NO
Output if continuous running time arrive	YES	NO	NO
Output if total running time arrive	YES	NO	NO
Force energy saving rate setting	YES	NO	NO
Force waking up	YES	NO	NO
Output sleeping status	YES	NO	NO
PID function	YES	YES	YES
Setting pressure reference Mpa	YES	NO	NO
Statis auto-tuning	YES	YES	YES
Rotating auto-tuning	NO	YES	YES

    

                             Technology originated from EMERSON and HUAWEI

Simon Fan Sales Manager

ShenZhen VTdrive Technology Co.,Ltd.

Mail:simon.fan@vtdrive.com

Tel:+86-0755-23060667

Fax:+86-0755-33671802

Site: http://www.vtdrive.com

Skype:simon.fan0611

Address:3F&4F, Xihe Industrial Zone,

TangTou Load, Shiyan Town,

Baoan District, Shenzhen, China.

Active Harmonic Filter

What is the Active Harmonic Filter?

An Active Harmonic Filter is an electronic power inverter using IGBT semiconductors with various control loops to increase Power Factor and reduce harmonics by injecting a dynamic cancellation signal into the power line.  Thereby reducing amperage, KVA, KVAR, circulating currents, harmonic resonance, line voltage imbalance and closed delta-winding losses.  The Active Harmonic Filter solution from Power Correction Systems improves the efficiency and operation of AC Motor Systems, AC Variable Frequency Drive (VFD) Systems and works well with virtually every Electrical and Electronic Device in your facility.  Conforms to IEEE 519-1996 and IEC 1000-2-2.

Who needs the Active Harmonic Filter Solution?

You do, if you are operating with today’s sophisticated automation using VFDs DC Drives, SCRs, Process Controllers, computer-based Robotics, rectifier-based equipment or any other non-linear loads in commercial or industrial application.  Any facility, from the oldest to the newest, which incorporates non-linear process controls and VFDs In its operation, is a potential beneficiary of an Active Harmonic Filter solution.

You also need this solution, if you would like to reduce the costs of your electrical operation of your facility.  In the past, efficiency was increased by installing and using standard capacitors on power lines.  However, with the implementation of modern sophisticated automation, the increase in the amount of switching supplies and rectifier circuits now being used in manufacturing has caused efficiency to decrease.  These switching supplies and rectifier circuits create harmonics that can overheat capacitors.  Industry engineers and consultants agree that the application of standard capacitors to these systems is NOT always possible or feasible, and in some cases detrimental to the electrical systems.  A detrimental system resonance can occur and cause 100% over-voltage conditions when there are harmonics circulating.

Power Correction Systems offers advanced solutions to the problems of harmonics, Power Factor and voltage imbalance, the Active Harmonic Filter series provides economic savings and enhanced systems reliability due to Power Quality.  Installation of the Active Harmonic Filter is quick and easy, requiring no mechanical break to the power lines.

Typical Return Of Investment from 1 to 3 years.

ECONOMIC BENEFITS:

·         Lower Electric bills and KVA charges up to 30%

·         Reduce peak energy demand charges

·         Eliminate Power Factor penalties while improving electrical system efficiency

·         Longer equipment life – less maintenance, repair and replacement cost of contactors, heaters, motors and transformers

·         Improve safety – lower temperature of cables, generators, motors and transformers

·         Decrease production losses and downtime of operations

·         Increase power system equipment capacity for future expansion  

Please do not hesitate to contact us should you required further assistant.

AC Drives or What Is a drive anyway.......? [By James M. Shumberg]

On with the AC drives article:

About AC Drive Technicians"A good AC drive technician understands the operation of the variable speed drive and the functions of its components. An outstanding AC drive technician also understands the effects of the load on the drive and the effects of the drive on the load." ...James Shumberg

Understanding AC Motor-Drive Systems (Sometimes called Variable Frequency Drives or VFDs) Maybe your objective is to learn how to troubleshoot variable frequency drives or maybe you want to know how to properly set-up a drive through programming. Maybe you just want the question answered: how does an AC variable frequency drive work? During this article I will definitely cover the theory of operation of the variable frequency drive (VFD) and several typical AC drive applications including multi-motor AC drive applications. In any case, to gain a useful working knowledge of the drive it is mandatory that you understand how AC induction motors produce mechanical force, called torque, and the limitations of AC motors. Therefore, what follows includes quite a lot of AC motor theory followed by heavy AC drive theory. The very first thing you need to know is that the AC drive does not produce any torque - in fact, it does not produce even one ounce of load moving torque. All the mechanical force that moves your machine and al of the mechanical force that is produced by the motor & drive system is produced by the motor. The drive itself just has to provide the motor with the proper voltage and current necessary in a form that is usable by the motor. The drive itself, is only an electrical power supply. The motor is the all-important prime mover. If a particular motor does not have the capability to produce the required torque and speed there is absolutely nothing you can do to the drive, programmatically or otherwise, to enable the motor to power your machine! Therefore, when designing a motor-drive system proper motor selection is crucial. Above all never, never, never match a "High Efficient" design motor to an AC drive! I am emphatic about this because I see it happen all the time and it is the worst thing you can do. (Well, not really the worst thing you can do, but I do want to get my point across.) Do not buy a high-effecient motor to operate on an AC drive! Interested?If you have an interest in this topic you should consider registering in my AC drive seminar and bring a co-worker (because no one else back on the job is going to believe what I told you during the seminar.) Also, keep reading, I will tell you things about AC drives you never before heard and never will hear anywhere else.

Exactly what is an AC drive? The word "drive" is used loosely in the industry. It seems that people involved primarily in the world of gear boxes and pulleys refer to any collection of mechanical and electro-mechanical components, which when connected together will move a load, as a "drive". When speaking to these people, an AC drive may be considered by them as the variable frequency inverter and motor combination. It may even include the motor's pulley - I am not sure. People in the electrical field and electrical suppliers usually refer to a variable frequency inverter unit alone, or an SCR power module alone (when discussing DC drives) as the "drive" and the motor as the "motor". Manufacturers of variable frequency drives (VFD) used to refer to the drive as just that, a "variable frequency drive". More manufacturers are referring to their drive as an "adjustable speed AC drive". To make matters worse when a motor is included in the package it may be referred to as an "adjustable speed AC drive system". A variable frequency drive is an adjustable speed drive. Adjustable speed drives include all types; mechanical and electrical. Now is it clear? Don't worry about it. It's not clear to anyone. As you read on, when I refer to the "drive" I  am referring to the variable frequency inverter alone.

---

A Little About AC Drives The main power components of an AC drive, have to be able to supply the required level of current and voltage in a form the motor can use. The controls have to be able to provide the user with necessary adjustments such as minimum and maximum speed settings, so that the drive can be adapted to the user's process. Spare parts have to be available and the repair manual has to be readable. It's nice if the drive can shut itself down when detecting either an internal or an external problem. It's also nice if  the drive components are all packaged in a single enclosure to aid in installation but that's about it.

The Dumb Trap The paradox facing drive manufacturers today is that as they make their drives easier to use,  the amount of training with which they must provide their users increases. This is because as drives become easier to use they are purchased more and more by people of less and less technical capability. As less technical people get involved in drive purchases the number of misapplications goes way up. I call this phenomenon the "dumb trap". (When manufactures discover this phenomenon they simultaneously discover how dumb they've been. Some have not yet discovered it.)

---

Ambiguous Motor Theory The real action in an AC variable frequency drive system is in the motor. This is really where it all happens. To be an AC drive application Wizard (which is several levels higher then Guru) one must understand how motors use electric power. It is essential. I cannot emphasize the importance of this. All loads moved by electric motors are really moved by magnetism. The purpose of every component in a motor is to help harness, control, and use magnetic force. When applying an AC drive system it helps to remember you are actually applying magnets to move a load. To move a load fast does not require more magnets, you just move the magnets fast. To move a heavier load or to decrease acceleration time (accelerate faster) more magnets (more torque) are needed. This is the basis for all motor applications.   Where does the real action happen in a AC drive system?
Above is a cross-sectional view a motor rotor and field magnetic core. Looking from the side would look something like a looking at a can:
We can add magnets (and torque) to our drive system by using a motor with a core that is either longer, larger in cross-sectional diameter, or some combination of both.

A Side Note About Fishing, Electro-magnets, Current, and Magnetic Conductivity  When we go fishing we put bait on a hook and throw it in water knowing that according to generally accepted theory, a hungry fish will sooner or later, bite. Well the truth is we don't know why the fish bite. No one to date, has talked to a fish (well maybe a few people talk to fish). The fact the we get hungry and therefore fish must too, seems like a safe assumption. But it doesn't really matter because we do know that putting bait on a hook will get fish into the boat. Magnetism and electricity are the same way. We have some well accepted theories that we can use to explain how magnets can move our load but no one really knows what magnetism and electricity are (regardless of what they say). When it comes to using magnetic force to move our load, how it works just doesn't matter. We do know that it works. We have even noticed a few peculiar things. We have noticed that when you wrap a coil of wire around a piece of iron and apply electric current the piece of iron becomes magnetic. We call this an electro-magnet.
Schematic of Electro-Magnet	Electro-Magnet

---

About Electro-Magnets (The Torque Producers Inside Every Motor) We have noticed a lot of things about electro-magnets that are very important to the drive application wizard (you'll see why later): After we apply the electric current, the magnet field grows at a finite rate to a finite size . After voltage is applied and full current is reached, which always takes a little time, the field quits growing and becomes a constant size. If we increase the applied voltage the field grows and becomes stronger, decrease the voltage and the field weakens and shrinks. When we remove electric power to the coil the field does not just disappear. It just decreases in size until it does disappear. It collapses over time so to speak. The more current our coil draws (which we can force by increasing the applied voltage level ) the stronger and larger our magnetic field becomes. I know I said it twice. It's that important. When we increase voltage to our electro-magnet, current will increase directly proportional up to a point. After that point current increases exponentially. THIS IS IMPORTANT! Generally accepted theory says that the iron core or any material, can only conduct a limited amount of magnetic flux. Once that point is reached current can become very high with a very small increase in voltage. This is called magnetic saturation and is sometimes seen in motor applications. Motor life becomes very short when the core reaches saturation - about 15 seconds in some cases. We will look at this and some of the causes later. Some energy is consumed by simply magnetizing the iron core. Different materials consume different amounts of energy. This is usually considered an energy loss. Some energy is converted into heat within the iron core. Different materials convert different amounts of energy. This is also usually considered an energy loss. Once a core is magnetized, demagnetization and reverse polarity re-magnetization consumes more energy and takes quite a long time, relatively speaking. (Remember, an existing field has to collapse over time.) The amount of this loss is proportional to the frequency of polarization reversals. This happens 120 times per second when operating an AC motor at 60 hertz. We will touch on the importance of this later. (Are you beginning to see where all this is going?)

---

The Magnets Within the Motor and Torque
The motor stator shown below is a two-pole motor meaning it is wound with with two field coils for each phase. In the industry this would be called a "2-pole motor". For simplicity, only one phase is shown. In reality, a 3-phase,  two pole motor requires six coils, evenly spaced around the core - a minimum of two coils is required, to generate two electro-magnetic poles, for each of the three phases. (A 4-pole motor will have four coils per phase or 12 total coils for a 3-phase motor.)
Motors are designed so that the  electro-magnets are made as strong as possible with acceptable risk of core saturation. This will maximize the torque capability of the motor but also means that during normal operation every motor may at some point, operate close to saturation. How close a motor runs to saturation depends upon the amount and type of core material used. So naturally, this point varies from manufacturer to manufacturer. There really is a difference in motors and you get what you pay for.
When the voltage applied to a motor is increased current to the electro-magnets increases resulting in higher field strength and increased motor torque output. This is a commonly used technique, especially in AC drive applications. It is a very good way to gain torque capability when needed.
This technique can increase motor torque it will also cause higher than normal motor heating resulting in reduced motor life. Close monitoring of the motor is required. Avoid saturating the core!

---

All Three Phases of a 2-Pole Motor The image to the right shows all three phases wound into a 2-pole motor. Note how the end connections of each phase are connected together at the "Y" point. This allows for three lead wires to be brought out of the terminal box to be connected to a 3-phase power system.

---

A Coil-Ectomy If you could remove the coils from the above motor without breaking a connection, and lay them side-by-side, this is what you would have. What is shown are three phases: A, B, and C phase connected together (see the arrow) at a "star" or "Y" point. There are other motor connection schemes but this is the most typical:

---

AC Generator If a magnet is passed along the coils, an electric current is generated in each of the three phases. In fact, there is little difference between AC generator and motor field windings.

The faster you move the magnet the higher the AC output frequency. Variable frequency drives control the frequency electronically. We'll get to more on that later.

---

When an iron core is placed so a moving magnetic field passes through it, a magnet field is generated within the iron core. It takes time to generate a field therefore, the new field reaches peak strength after the peak of the generating field has passed. The bar (rotor) is "pulled" by the magnetic field thus producing torque.

The magnetic field has to pass through the rotor to generate a rotor field and pull. If the rotor travels at the same speed as the magnetic field, induction into the rotor will cease, the magnetic field will disappear and the rotor will loose its pull and slow down. Pull (torque) is obtained when fields are passed through the rotor in quick succession. Remember though, it takes a long time to generate a field. If the frequency of fields passing through the rotor is too low, effectiveness is lost.  If the frequency of the generating field is held constant, and the torque is great enough to move the rotor, the rotor will reach an equilibrium speed, where at any higher speed induction and torque are reduced and the rotor slows back down to equilibrium.

---

More About AC Induction Motors
Typical Rotor (Rotating Part)	Typical Stator (Stationary Part)
Important Motor Formula - Calculating the Synchronous Speed:
("120" is a constant in the formula - don't worry about it.)
"Synchronous RPM" is the RPM the motor would run if the rotor did not slip. All AC induction motors slip. ("Synchronous motors", a special kind of induction motor, do not slip- at least least they are not supposed to. More about synchronous motors will have to be covered in another article.) A note about nominal RPM ratings: An AC motor referred to, in the industry, as an 1800 RPM motor will be name-plated with a speed of something less, usually around 1735 RPM. 1735 RPM is a typical RPM rating but can be higher or lower but is always less than the synchronous speed (1800 RPM). The difference between the synchronous and the actual RPM is called "slip". Adjusting slip is an important technique in AC drive applications. A lot more about slip will come later.
The following is surprisingly simple but important! Don't let it scare you.You do not have to memorize it - just understand it.
Calculation of Synchronous Speed(The "Poles" are the number of electro-magnetic poles wound into the motor. Motors can have any even number of poles wound into them but a minimum of 2 poles for each of the 3 phases are required. The most common AC motors are wound with either 2, 4, 6, or 8 poles.)
Looking at the calculation above you can see that a motor name-plated approximately 3450 RPM and 60 HZ is obviously a 2-pole motor with a synchronous speed of 3600 RPM.
Calculation of % Slip(Typical induction motors slip anywhere from 3% to 5% when they are fully mechanically loaded.)
Example of % Slip Calculation

---

Why are some motors called "induction motors" and what is induction? When an electric current is applied to a conductor a magnetic field builds around that conductor. If another conductor is in close proximity so that the building magnet field "cuts" through that conductor, a current of equal potential is produced with flow in the opposite direction of the original current. This conductor is called the secondary circuit and the principal is called induction.
When an electric current is applied to a conductor a magnetic field builds around that conductor. If another conductor is in close proximity so that the building magnet field "cuts" through that conductor, a current of equal potential is produced with flow in the opposite direction of the original current. This conductor is called the secondary circuit and the principal is called induction.
If the number conductors in the secondary is increased the output potential is increased in direct proportion. The inverse is also true. This is called transformeraction. It is because of transformer action that a current is created in the rotor (secondary circuit) of an AC induction motor and a resulting magnetic force, within and around the rotor, is also created. Note: If the magnetic field reaches maximum strength and quits growing, the current flow in the secondary returns to zero regardless of the level of current flow in the primary. In other words, there is a secondary current induced only when the magnetic field around the primary is either increasing or decreasing in size. www.driveswarehouse.com Low Prices on AC & DC Drives www.automationdirect.com Low Prices on PLCs& Touchscreens www.vtdrive.com A China leading AC Drives Manufacture