T. Glinka

A method for determining the field shape influence upon parameters of a DC micromotor

ABSTRACT A method for determining the magnetic field shape influence upon the average values and ripple content in induced voltage, current and the electromagnetic torque of a dc micromotor is presented. The dc micromotor with three slots and six different field shapes is analyzed and described analytically. The analysis shows that by using a shape function X(θ) one can find the best motor performance, i.e., highest average values of torque and the lowest ripple component. Using this approach a rectangular magnetic field shape provides the optimum solution for a wide range of tolerances. With this waveform the motor has no ripple on the induced voltage and as a result the torque pulsation are eliminated.

Impact of PWM control frequency on efficiency of drive with 1 kW permanent magnet synchronous motor

Purpose The paper presents the impact of Pulse Width Modulation (PWM) control frequency for specific Permanent Magnet Synchronous Motors (PMSMs) on the efficiency of the entire driving unit. Examinations were carried out for a PMSM unit with a power of 1 kW, rated speed of 1000 rpm, and rated torque of 6 Nm. Design/methodology/approach The PWM frequency ranged from 4 to 20 kHz with increments of 1 kHz. Measurements were taken for each of the foregoing frequencies, for the different load torques, and for the different rotation speeds including overspeed. The results achieved allow the PWM control frequency to be properly adjusted for each PMSM to operate the entire driving unit in the most efficient way and, in consequence, save energy consumed by the drive. Findings Obtained results may be used as a kind of background for the design of drive system. Research limitations/implications For a specific PMSM-based drive system one can find the optimal PWM control frequency. This frequency depends on the rotatio...

Capacitance and Resistance of Turn-to-Turn Insulation—Measurements in Transformers

Transformers operating in the power grid are subjected to different types of overvoltages, generated by lightning discharges or by switchings in the network. The overvoltage wave voltage is distributed unevenly across transformer’s winding. The maximum voltage rise rate occurs at beginning of winding. This maximum rate depends on insulation parameters such as insulation to ground capacitance and turn-to-turn insulation capacitance. Measurements of insulation to ground parameters: resistance R g and capacitance C g have been known and conducted for many years, mostly for diagnostic purposes. Capacitance C z and resistance R z of turn-to-turn insulation of transformer windings are used in analysis of voltage wave distribution across the windings during overvoltages and in diagnostics of insulation system. Method of measuring parameters R z and C z is demonstrated in the paper. The measurement is based on recording of dc current course after the winding has been short-circuited and of winding voltage after the dc current (of identical value) has been instantaneously switched off. The procedure is illustrated with example, the test object was a dry-type transformer rated at 160 kVA.