Analytical approach and solution for start-up behavior of line-start permanent magnet synchronous machines (LSPSM)
This paper presents a derivation for the maximum transient current and torque peak values for small non-salient line starting permanent magnet synchronous machine (LSPSM) on base of permissible approximations. First the equations for locked rotor operation and secondly for constant speed operation are deduced. This paper is focused on derivation of the analytical calculation process to get an approach for transient current and torque. Saturation and speed dependency of parameters are not considered. With the derived equations, effects of parameters on the peak values of torque and current at starting can be shown.
Line start permanent magnet motors - Starting, standards and application guidelines
The advantages of using permanent magnets (PM) in electric motors to increase efficiency are well documented [1]. Due to the synchronous operating nature of a PM motor, most motors of this type are used in combination with a variable frequency drive (VFD). PM motors capable of direct on line (DOL) starting have been manufactured for over 30 years [2], but the application of this technology has historically been limited to low horsepower, niche applications. In an effort to provide motors with higher than premium efficiency levels, this technology is now making its way into much larger motors. This paper discusses the transients associated with DOL starting this type of motor and the potential challenges they pose. These include transient torque, inrush current and corresponding dips in voltage. The same issues exist with induction motors and comparisons of the two technologies are offered. In addition, the ability to synchronize a given load must be considered. Test results from line starts of this type of motor are presented. Various techniques to diminish the effects of the starting process, including application guidelines, are discussed. Ongoing efforts to establish industry standards for this type of motor are reviewed.
Nuclear spin-lattice relaxation in transition metal compounds with local tetragonal symmetry.
We report on the various contributions to the total spin-lattice relaxation rate in metallic materials with local tetragonal symmetry. The analytical formulae are given in the tight-binding approximation. The calculations show the relation between various partial electron densities of states and corresponding contributions to the relaxation rates. The presented formulae can be used to compare theoretically calculated electron band structure parameters with those obtained from NMR spin-lattice relaxation time measurements.