A direct current in a p-pole field winding on the rotor will also produce a magnetic field rotating at rotor speed. The effect of the stator current is to establish a magnetic field rotating at 120 f/ p revolutions per minute for a frequency of f hertz and for p poles. The principle of operation of a synchronous motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Įlementary synchronous generator.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.From tech to household and wellness products. This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.When these "specials" are made I usually see 6 pole machines - but that may be just a manufacturer's preference. I often see name plates with things like 575VAC, 42.5 Hz etc. With the advent of variable frequency drive (VFD), you can have any frequency / rated volts you desire. Where the power of the induction motor is constant, the torque increases at the rate that the speed decreases. To determine the number of poles, you can read the data plate directly or calculate it from the RPM stated on the data plate or you can count the coils and divide by 3 (poles per phase) or by 6 (pairs of poles per phase). The actual running speed is the synchronous speed minus the slip speed.Ģ poles or 1 pair of poles = 3,000 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n)Ģ poles or 1 pair of poles = 3,600 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n) The formula is n = 60 x f / p where n = synchronous speed f = supply frequency & p = pairs of poles per phase. Here are two tables, one for a 50 Hz power supply and one for a 60 Hz power supply: When selecting a three phase motor, the number of poles is chosen to achieve the speed of rotation that you require. For example 5.5kW, 400v, 2 pole motor will run at approximately 2880 rpm.įor a four pole machine, 60 x 50 / 2 = 1500 rpm so the same size motor at 5.5kW, 400v but 4 poles will have a nominal speed of 1500rpm but will run near 1455 rpm. The induction motor will run at a slight less speed due to "slip" which is what gives the motor its torque. If you are using 50Hz and have a two pole motor 60 x 50 / 1 = 3000 rpm. Pole pairs is there because that any pole must be constructed in a pairs top and bottom / left right, so with one cycle it will move half the distance. The 60 is there to convert from revolutions per second to revolutions per minute as the frequency is in cycles per second. n (rpm) = (60 x f) / N where:- f = frequency and N = number of pole pairs. Are performances of these two motors different or the same? Please note excluding frequency and inter-coil connections all remained the same. Then we re-connect the winding coils to arrange p=4 and feed if grow 100 Hz grid. ![]() Let's we have an induction motor with p=2 and feed it from 50 Hz grid. Does the induction motor supplied by the main grid (say, 50 Hz) increases its torque capability in "p" times with growing pole number "p" since its speed decreases in "p" time (like in a gearbox)?Ģ. There are many much more interesting questions related to the pole number of induction motors, e.g.:ġ.
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