A. Basak

Investigation of magnetizing inrush current in a single-phase transformer

The magnetizing inrush current which occurs at the time of energization of a transformer is due to temporary overfluxing in the transformer core. Its magnitude mainly depends on switching parameters. A system for measuring the inrush current is described. The system is also capable of presetting various combinations of switching parameters for energizing of a transformer. Data sampling of the magnetizing inrush current has been achieved by using a microcomputer, and a software package has been developed to perform harmonic analysis of each of the first few transient current cycles. The effects of the remanent flux density, the switching angle, and the primary winding resistance on the magnetizing inrush current of a 2.5-kVA single-phase transformer are presented. >

Flux distribution in three phase transformer cores with various T-joint geometries

Software developed at the Rutherford and Appleton Laboratories, U.K. and based on a finite element technique has been used to compute the magnetic fields in electrical steel sheets in various types of transformer cores. Initially isotropic steels were considered but later an attempt was made to include the effect of magnetic anisotropy in a simple manner. Some of the cores considered possessed joints (modelled as .02cm air gaps) in the corners and T-sections. The computed results have been compared with experimental results taken from practical cores possessing identical geometries.

The spatial distribution of flux waveform across the limbs in a three-phase transformer core

A scale model of three-phase three-limbed transformer cores, in which the magnetic path length varied significantly within the width of the limbs, was instrumented to observe the flux distribution in the laminations. Across the width of the center limb the local field was found to decrease monotonically with distance from the window and was minimum at the middle of the limb. In the outside limbs the local field was maximum near the window and gradually decreased across the width. The harmonic components varied in a similar fashion, although those in the center limb were 65 percent higher than those in the outside limbs. The experimental results confirmed that the magnetic material locally traverses a characteristic hysteresis loop.

Fundamental and harmonic flux behaviour in a 100 KVA distribution transformer core

A commercial 100 KVA, 3-phase distribution transformer core has been investigated in order to obtain a detailed study of flux distribution in various packets of the limbs and yokes. The core was chosen to be compatible with model cores used earlier in various experimental works. Variations of flux density from packet to packet at low excitation of 0.9 Tesla were 46% in the yokes and 28% in the limbs. At a higher core excitation, 1.7 Tesla, variation in the yokes dropped to about 16% while in the limbs it remained roughly the same. The largest third and fifth harmonic components of flux density occured in the central limb. Their magnitudes were 7% and 4.9% of the fundamental components respectively at a core excitation of 1.7 Tesla. In the yokes the harmonic contents were of much smaller magnitudes.

Leakage flux in the steel tank of a 2.5-kVA single phase transformer

The effects of aluminum magnetic shielding and mild steel magnetic shunts on the leakage flux in the steel tank of a single-phase 50-Hz 2.5-kVA transformer and consequently on the tank temperature have been investigated.

Measurement of loss in stator cores built with silicon-iron laminations cut at various angles to the rolling direction

Three model cores of the stator of a large turbogenerator were built with grain-oriented silicon-iron laminations, with rolling directions tangential and perpendicular to the circumference of the stator and also non-oriented silicon-iron laminations. Three more models were built with combinations of two of these three types of material. The total iron loss in each of them was measured and the results have been compared with one another. It has been found that the cores built with combinations of different types of material had lower losses than those built with one type of material, especially at 1.4 T. The effect of two different types of lapping arrangement on the total iron losses was also considered.

Thin Film Senses Magnetic Flux And Loss In Rotary Electric Motors

The existing methods of measurement of the flux and loss distribution in the laminations of rotary electrical motor is to employ arrays of search coils made from 40 Standard Wire Gauge (s.w.g.) enamelled copper wire and arrays of miniature thermistors. These introduce unacceptable air gaps between laminations and consequently make the core building difficult. To overcome this drawback, thin film sensors have been deposited on electrical steel sheets which build up the stack of the core of a rotary motor.

Analysis and reformation of characteristic of linear electromagnetic solenoid

The distribution of thrust in linear electromagnetic solenoids (LESs) is exponential rather than constant with displacement. In order to make the solenoids widely useful the thrust is calculated from first principles and its distribution is reformed to be flat by changing the magnetic circuit. The magnetic flux density and thrust are calculated using the finite element method. The results are compared with the experimental results obtained from the LES. >