The reluctance of any part of a magnetic circuit may be defined as the ratio of the drop in magnetomotive force to the flux produced in that part of the circuit. It is measured in ampere-turns/Weber and is denoted by S. Reluctance = m.m.f ⁄ flux
Sudden changes of load on synchronous motors may sometimes set up oscillations that are superimposed upon the normal rotation, resulting in periodic variations of a very low frequency in speed. This effect is known as hunting or phase-swinging.
Given Data Voltage Va = 200 v Armature Resistance Ra = 0.5Ω Armature Current Ia = 20 A Induced EMF = Ea = ? The Induced EMF of a DC machine working as a Motor is Ea = Va − IaRa Ea = 200 − 20 × 0.5 Ea = 190 V
Magnetic Field Strength (H) gives the quantitative measure of strongness or weakness of the magnetic field. H = B/μo Where B = Magnetic Flux Density μo = Vacuum Permeability Magnetic field due to infinite Linear current-carrying conductor is B = μoI/2πr B/μo = I/2πr H = (I/2πr)A/m
The average value of the sine wave over one complete cycle is actually zero. Hence, for a sine wave, the average value is defined over half the period. The average value expressed in terms of peak value is given by Average value = 0.637 × peak value
EXAMIANS