Abstract- This paper deals with the circulating current distribution calculation and its resultant ohmic losses in a large synchronous generator. Circulating currents are produced by the induced voltage differences between parallel strands in a bar that cause high ohmic losses in high power synchronous generators. In this paper, three different cases are assumed for the armature end winding structure, and a 3-D finite element model is adopted to calculate the effectiveness and resultant losses of these cases. As mentioned later, by the use of an appropriate transposition in slot area, both main and leakage fluxes inside the machine are the same for all transposed strands bundle in active part and consequently the induced voltage difference in each strand in a bundle is negligible. However, the currents flowing in the end winding of the generator produce leakage flux in the slot region that causes circulating currents in strands, and consequently electrical power losses in the machine.
Index terms— Synchronous generator, slot region, end winding, circulating current, finite element method.
I. INTRODUCTION
Circulating currents are produced by the induced voltage differences between parallel strands in a bar due to different linkage magnetic flux. In large synchronous generator with high power density, the Roebel bars are used for the stator windings in which strands in a bundle are completely transposed in slot region by different arrangement.
By the use of this procedure, the overall physical position of each strand in a bundle is the same. Therefore, the both main and leakage fluxes are the same for each strand in each bundle, and consequently the induced voltage difference in each strand is negligible. Anyway, the curr...
... middle of paper ...
...gren X, Lijian T, Dangun Z, Yi X. “Calculation of end region magnetic field and circulating losses for turbo-generators using a coupled field and circuit equations method”, IEEE Trans Magn 1990;26:497–500.
[5] K. Takahashi, M. Takahashi, and M. Sato, “Calculation Method for Strand Current Distributions in Armature Winding of a Turbine Generator”, Electrical Engineering in Japan, Vol. 143, No. 2, 2003 Translated from Denki Gakkai Ronbunshi, Vol. 122-D, No. 4, April 2002, pp. 323–329.
[6] Hitachi, Ltd., Japan M. A. Mueller, “Design and Performance of a 20kW, 100rpm, Switched Reluctance Generator for a Direct Drive Wind Energy Converter”, IEEE International Conference on Electric Machines and Drives, page(s): 56-63, 2005.
[7] J. Haldemann, “Transpositions in Stator Bars of Large Turbogenerators” IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 19, NO. 3, SEPTEMBER 2004
Muller, S., Prowse, D. L., & Soper, M. E. (2012, September 25). CompTIA A+ Cert Guide: Power Supplies and System Cooling | Foundation Topics | Pearson IT Certification. Retrieved March 20, 2014, from http://www.pearsonitcertification.com/articles/article.aspx?p=1945640
Dennis Grant Turbo Fundamentals. How Turbos Work or The Closest Thing to a Free Lunch. Http://www.turboclub.com/turboFun1.htm
A direct current in a set of windings creates a polar magnetic field. A torque acts on the rotor due to its relation to the external magnetic field. Just as the magnetic field of the rotor becomes fully aligned with the external magnetic field, the direction of the current in the windings on the armature reverses, thereby reversing the polarity of the rotor's electromagnetic field. A torque is once again exerted on the rotor, and it continues spinning.
United States International Trade Commission (2009, June). Wind Turbine Industry and Trade Report. Retrieved, August 12, 2011 from http://www.usitc.gov/publications/332/ITS-2.pdf
The PSS is an additional control system, which is often applied as a part of an excitation control system. The basic function of the PSS is to apply a signal to the excitation system, producing electrical torques to the rotor in phase with speed differences that damp out power oscillations. They perform within the generator’s excitation system to create a part of electrical torque, called damping torque, proportional to speed change. A CPSS can be modeled by a two stage (identical), lead-lag network which is represented by a gain K and two time constants T1 and T2. This network is connected with a washout circuit of a time constant Tw. The signal washout block acts as a high-pass filter with the time constant Tw that allows the signal associated with the oscillations in rotor speed to pass unchanged. Furthermore, it does not allow the steady state changes to modify the terminal voltages. The phase compensation blocks with time constants T1i – T4i supply the suitable phase-lead characteristics to compensate the phase lag between the input and the output signals. The commonly used structure of the PSS is shown in Fig
Their performance can be modelled, predicted and analyzed using equivalent circuits, and this experiment examines one of these circuits. MEASUREMENTS ------------ Short-circuit test: Primary voltage (Vsc) = 26V Primary current (I1) =
In order to calculate such wind turbines, it depends on three main variables: the size of the turbine, the speed of the wind, and the efficiency of the turbine as well as the generator. The formula in order to calculate the wind power is: P=½ρAV³.
Basic Mathematics for Electronics seventh edition: Nelson M. Cooke, Herbert F.R Adams, Peter B. Dell, T. Adair Moore; Copyright 1960
To capture the flow physics near the engine wall we need to increase the density of the cells near the wall. A grid was generated in the computational domain of the simulations using grid generator package ICEM cfd (Ansys 14.5). The first grid layer near the engine wall was nearly 20microns and hence the grid is finer at the walls of the engine and relatively coarser away from the walls of the engine.
Wilson, D. G., & Korakianitis, T. (1998). The design of high-efficiency turbomachinery and gas turbines (2nd ed.). Upper Saddle River, NJ: Prentice Hall.
The stator is the stationary component while the rotor is the rotational component of the motor. Usually magnetic fields are created when an electric current is applied to a set of conductive wires wound together (Dixon, 2001). Magnetic fields can also be created using Permanent Magnets (PM). Electrical motors can also work as electrical generators (Correla, 1986). Electrical generators are devices capable of converting mechanical energy into electrical energy. An example would be a wind turbine which works as an electrical generator. It converts the mechanical energy of the rotating shaft caused by wind into electrical energy (Correla, 1986). The focus of this research will ...
Alternators used in central power stations also control the field current to regulate reactive power and to help stabilize the power system against the effects of momentary faults. Often there are three sets of stator windings, physically offset so that the rotating magnetic field produces a three phase current, displaced by
In this experiment, we are able to investigate the relationship between the induced current in a coil and the frequency of oscillation of a bar magnet inside the coil. In 1820, Hans Christian Oersted, a Danish physicist had discover the magnetic effect of current carrying conductor (wire) as it pass through a current, and it will effect the magnetic field around the wire. [search from references book]. His discover led to inventions of dynamo, motor and telephone is due to electromagnetism. As a bar magnet, it has its own magnetic field around it and magnetic field lines. The properties of magnetic field lines is it always flow from North pole to South pole. North pole always flow out and South pole always flow in. In addition, the magnetic field lines cannot cross each other. Similarly, the more concentration of magnetic field lines, it more strength of magnetism. The study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field on the surface of a spherical magnet using iron needles [search from Wikipedia]. Magnetic field is a region which a magnetic material experiences a force as the result of the presence of a magnet or a current carrying conductor.[search from Wikipedia]. Right-hand Grip Rule is used to determined the direction of the magnetic field. The thumbs always points in the direction of the current, while finger give the direction of magnetic field. For determined direction of the magnetic field of solenoid, thumbs always point to north pole. In this experiments also, we should use this rule to determine the current flow in solenoid. The strength of magnetic field can increases by increasing the current, increasing the number of turns of wire. Substance such a...
The wind is an incredibly valuable renewable energy source and is in the forefront of renewable energy developments. It is used to convert wind energy into energy that can be harnessed and used via a variety of methods, including; wind turbines, windmills, sails and windpumps. For a renewable energy source, however, it is wind turbines that are used to generate electricity (see figure 1). Wind power has been used for this since the end of the nineteenth century, after Professor James Blyth of the Royal College of Science and Technology first attempted it (Boyle, 2012). However, It wasn’t until the 1980s that using wind power technology was sufficient enough to experience a rapid growth of the technology.
Deal, W. (n.d.). Wind power: An emerging energy resource.Technology & Engineering Teacher, 70(1), 9-15. Retrieved from http://web.b.ebscohost.com/ehost/detail?sid=a747d6c4-9f9f-4066-be3e-d7d26a427ef2@sessionmgr115&vid=1&hid=114&bdata=JkF1dGhUeXBlPWNvb2tpZSxpcCxjcGlkJmN1c3RpZD1zc2Mmc2l0ZT1laG9zdC1saXZlJnNjb3BlPXNpdGU=