A new method of condition monitoring on electrical contact endurance of power switch
Prediction of the remaining electrical endurance of a power switch is important for the reliable performance of power switches. The erosion of contact material is one of the most important indexes for the electrical life of a contact. Previous methods of contact material life prediction are introduced. They mainly consider the relationship between erosion volume and current amplitude. A new idea is presented to diagnose the life of electrode material from the waveform characteristics of the make and break currents. LabVIEW is used to sample and store the current and voltage signals. Current waveforms, break/make current arc duration and contact resistance are discussed. As a result, the occurrence probability of fluctuating phenomena of the break current, contact resistance and make arc duration change with the number of contact operations. The break arc duration is determined by the break current.
Interruption life of vacuum circuit breakers
Over the past few years, there has been an increased interest in the number of short circuit interruptions a vacuum circuit breaker is capable of before excessive wear occurs on the contacts. Several methods have been proposed for recording or extrapolating the interruption life of vacuum circuit breaker contacts and these have resulted in many different claims. As a means of reconciling these, and for providing a common ground for axial magnetic type vacuum circuit breaker contacts, a recommendation is made for a new means of measuring contact life. This new method is based on the interruption level and the amount of time in which the arcing between the contacts occurs. This is then compared against test results for vacuum circuit breaker contacts from Cooper Power Systems.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.