China
Africa
Explore chapters and articles related to this topic
Electrical Generators
Published in Mukund R. Patel, Omid Beik, Wind and Solar Power Systems, 2021
Figure 5.1 depicts common construction features of electrical machines. Typically, there is an outer stationary member (stator) and an inner rotating member (rotor). The rotor is mounted on bearings fixed to the stator. Both the stator and the rotor carry cylindrical iron cores, which are separated by an air gap. The cores are made of magnetic iron of high permeability and have conductors embedded in slots distributed on the core surface. Alternatively, the conductors are wrapped in the coil form around salient magnetic poles. Figure 5.2 is a cross-sectional view of a rotating electrical machine with the stator made of salient poles and the rotor with distributed conductors. The magnetic flux, created by the excitation current in one of the two coils, passes from one core to the other in a combined magnetic circuit always forming a closed loop. Electromechanical energy conversion is accomplished by interaction of the magnetic flux produced by one coil with the electrical current in the other coil. The current may be externally supplied or electromagnetically induced. The induced current in a coil is proportional to the rate of change in the flux linkage of that coil.
Capacitors, Inductors, and Duality
Published in Nassir H. Sabah, Circuit Analysis with PSpice, 2017
The definition of λ can be extended to a coil of N turns. However, when the coil is in a medium of small relative permeability, as in air or other nonmagnetic, or weakly magnetic material, not all the flux lines will pass through all the turns. Some of the flux lines will loop back around some of the turns of the coil without passing through all the turns of the coil, as illustrated in Figure 7.14a. λ can be formally defined as λ=∑j=1Nϕnj where ϕnj, the normal component of flux through the jth turn, is summed over all the N turns. In other words, flux linkage is the total flux through all the turns of the coil in the direction normal to the plane of each turn.
Electromagnetic Fields
Published in Martin J. N. Sibley, Introduction to Electromagnetism, 2021
where N is the number of turns in the coil and Nϕ is known as the flux linkage. So, the induced emf depends on the rate of change of flux linkages, i.e., the higher the frequency, the higher the rate of change, the larger the induced emf. As this emf serves to oppose the voltage that produces it, Equation (3.42) is often modified to e=−ddt(Nϕ)
Physically motivated lumped-parameter model for proportional magnets
Published in International Journal of Fluid Power, 2018
Electromagnetic actuators convert the supplied electric energy into mechanical energy, magnetic energy and heat. The magnetic energy is stored in the magnetic field while dissipation is due to hysteresis losses and the ohmic resistance of the coil R. The supplied energy W can be calculated out of the supplied voltage u(t) and current i(t) by Equation 1. Moreover, assuming that hysteresis effects may be neglected, the energy stored in the magnetic field Wmag can be calculated out of the electrical signals, current i(t) and inductive voltage uL(t), by using Equations 2 and 3. Herein, the inductive voltage equals the time derivative of the magnetic flux linkage λ(t). The magnetic flux linkage describes the total magnetic flux passing the surface spanned by the coil’s windings multiplied with its number of turns. It is an integral parameter of the magnetic field describing the interaction of electric, magnetic and mechanical system. For electromagnetic actuators, it depends on the supplied current and the actuator’s stroke as well as on their history due to material hysteresis, fringing effects and eddy current losses.