Akio Kaga

Prevention of harmonic torques in squirrel cage induction motors by means of soft ferrite magnetic wedges

It is well known that the harmonic torques in squirrel cage induction motors are caused by the space harmonic waves in air-gap flux distribution. The soft ferrite magnetic wedges inserted into the stator slot openings reduce the ripple of air-gap permeance. Therefore, this wedges reduce the magnitude of harmonic torques. A trial was performed on prevention of harmonic torques in squirrel cage induction motors, by inserting a soft ferrite magnetic wedges into its stator slot openings. Results obtained were as follows; (1) The soft ferrite magnetic wedges made it possible to decrease by about 40% the 17th and 19th asynchronous torques. (2) The magnitude of 17th and 19th asynchronous torque on the induction motor with the soft ferrite magnetic wedges and the unskewed rotor is approximately equivalent to that on the induction motor with the rotor skewed through 0.4 stator slot pitch. (3) The soft ferrite magnetic wedges were incapable of decreasing the 5th asynchronous and synchronous torque. The authors suggest that the utilization of soft ferrite magnetic wedges will become important to prevent the harmonic torques in induction motors.

One Method For Calculating Flux-MMF Relations Hip Of Orthogonal-core

One method for calculating flux-MMF relationship of an orthogonal core is described. The calculation is based on a three-dimensional magnetic circuit model of the orthogonal core. The model is derived by dividing the orthogonal core, inclusive of the surrounding region, into elements comprising a three-dimensional magnetic circuit. Using this model, the flux-MMF relationship of the orthogonal core with arbitrary dimensions can be calculated from the B-H characteristic of the core material. The calculation method presented is useful for optimum design of devices using an orthogonal core. >

The efficiency improvement of capacitor motor with ferrite magnetic wedges

With the development of condenser materials, single-phase capacitor motors for domestic use have been made smaller, and the utility for it has been raised in these days. For saving electric energy consumed in motors, the authors have carried out experimental discussions on the capacitor motor. In short, with wedging of soft ferrite materials into the motor slots, the characteristics in locked, no-loaded and loaded motor have been investigated. Owing to ferrite magnetic wedges, Carters coefficient estimated by the finite element method was reduced, and iron loss of the motor decreased. As the result, efficiency of the motor was improved about 6 % or above.

Fundamental Characteristics of AC Flashover on Contaminated Insulators Covered with Ice

The fundamental characteristics of ac contaminated flashover on iced insulators were studied for the three icing states, i.e., glaze, hard rime and soft rime, which are observed most frequently in service conditions. The results showed that thawed snow with a relatively low salt concentration can produce a salt deposit density (SDD) high enough for flashover on an iced insulator. For the same concentration of contamination liquid, average values of SDD for icing states are 5 to 9 times higher than those for icing-free conditions. The results also showed that the minimum flashover stress of the soft rime condition is 20% lower than that of icing-free conditions. For this reason, we deduced that the number density of Na atoms in the discharge space at flashover tends to become highest under the soft rime conditions.

Calculation on Flux-MMF Relationship of Orthogonal-Core

Orthogonal-cores have various potential applications, for instance in parametric transformers and dc-ac converters. The operating characteristics of the devices can be calculated on the basis of the measured relationship of flux to MMF of the orthogonal -core. To achieve optimal design of the applied device, the relationship of flux to MMF must be determined; however, this involves solving a three dimensional nonlinear problem. In this paper, we calculate the flux-MMF relationship based on a magnetic circuit model for the orthogonal-core. The computed results agree well with experiment. The method of this study is shown to be valid for calculation of characteristics and useful for optimal design of application devices.

A research of efficiency improvement by means of wedging with soft ferrite in small induction motors

To save electric power to be consumed in small induction motors, its efficiency improvement is required. As one of methods to improve the efficiency of small induction motors, magnetic materials have been wedged into the stator slots of the induction motors. Experiments have been performed on fabricated induction motors with soft ferrite wedged into stator slots. As the results, the decreasing of starting torques for the induction motors was found to be only 3 %. The efficiency of the ferrite wedged induction motors was improved by about 4 % at the rated output and 11 % at a quarter output, as compared with that without the soft ferrite.

An Analysis of the Behavior of Orthogonal-Core Type Push-Pull Parametric Transformer with Iron and Copper Losses

This paper describes an analysis of the behavior of orthogonal-core type push-pull parametric transformers, taking the iron loss of the orthogonal-cores and the copper loss of the windings into consideration. The analysis was performed for the magnetic circuit of the orthogonal-core under magnetic saturation and with hysteresis. To improve the accuracy of calculations, the saturation characteristic was approximated by a series which includes terms of up to 21st order in the flux, and the hysteresis curve by a series including terms of up to 5th order in the exciting voltage. The calculated results show good agreement with experimental data. The analytical method presented here is useful for optimizing the design of push-pull parametric transformers.

Effects of Power Loss Reduction with Ferrite Magnetic Wedge on Capacitor Motor.

The authors have inserted ferrite magnetic wedges into the stator slot openings of the capacitor motor to decrease the pulsation of flux density distribution in the air gap. As a result, the iron loss was reduced greatly to increase the motor efficiency and to improve other running characteristics.

AC Flashover Characteristics on Trapezoidal Contamination Models of Actual Insulators

The fundamental characteristics of an ac contaminated flashover were investigated by using a simplified model which consists of a trapezoidal unit and a series of units in order to simulate the current density distribution on actual insulators. It is found that the lowest flashover voltage decreases with an increase in the voltage build-up rate, and after passing a minimum, tends to increase. Experiments also show that, if the leakage length is equal, a disc insulator string model having a metal plate on the connected area of units tends to flashover at a lower voltage than a long rod insulator model having no metal plate. The results are discussed according to the characteristics of the ac reignition voltage on contaminated surfaces in previous reports. It is deduced that the accumulation of Na ions in the discharge space at flashover dominates the reduction of contaminated flashover voltage.

Effect of ferrite magnetic wedge on capacitor motor characteristics under triac control

The running characteristics of the split-phase capacitor motor in which a triac is connected in series with the motor circuit to control the applied voltage in accordance with the load conditions are studied. Ferrite magnetic wedges are inserted into the slot openings on the motor stator. The wedging effect on the motor characteristics is studied. When the ferrite wedges are inserted into the slot openings, the flux density pulsation in the air gap is decreased greatly to decrease the inner power losses, resulting in the improvement of motor efficiency and characteristics. >