Radio-frequency-based measurement methods for bearing current analysis in induction motors

The most common reason for a low-voltage induction motor breakdown is a bearing failure. Along with the increasing popularity of modern frequency converters, bearing failures have become the most important motor fault type. Conditions in which bearing currents are likely to occur are generated as a side effect of fast du/dt switching transients. Once present, different types of bearing currents can accelerate the mechanical wear of bearings by causing deformation of metal parts in the bearing and degradation of the lubricating oil properties.The bearing current phenomena are well known, and several bearing current measurement and mitigation methods have been proposed. Nevertheless, in order to develop more feasible methods to measure and mitigate bearing currents, better knowledge of the phenomena is required. When mechanical wear is caused by bearing currents, the resulting aging impact has to be monitored and dealt with. Moreover, because of the stepwise aging mechanism, periodically executed condition monitoring measurements have been found ineffective. Thus, there is a need for feasible bearing current measurement methods that can be applied in parallel with the normal operation of series production drive systems. In order to reach the objectives of feasibility and applicability, nonintrusive measurement methods are preferred. In this doctoral dissertation, the characteristics and conditions of bearings that are related to the occurrence of different kinds of bearing currents are studied. Further, the study introduces some nonintrusive radio-frequency-signal-based approaches to detect and measure parameters that are associated with the accelerated bearing wear caused by bearing currents.

Kuparin hitsaus kattavilla laatuvaatimuksilla

Kuparin ja kupariseosten hitsaus eroaa merkittävästi esimerkiksi terästen hitsauksesta. Suuri lämmönjohtavuus, lämpölaajeneminen, pehmeneminen ja kuparin taipumus liuottaa kaasuja sulaan asettavat hitsaukselle haasteita. Kuparia on perinteisesti hitsattu kaasuhitsaamalla ja kaasukaarihitsausprosesseilla, mutta uudemmat menetelmät kuten laserhitsaus, elektronisuihkuhitsaus ja FSW-hitsaus tarjoavat uudenlaisia käyttökohteita korkealla laadulla. ISO 3834-2 asettaa noudatettavat vaatimukset hitsaustoiminnalle laatuvaatimusten ollessa kattavia. Ydinvoimalaitoksella hitsauksessa tulee lisäksi noudattaa Säteilyturvakeskuksen YVL-ohjeita, joissa on määritetty lisävaatimuksia liitosten materiaalivalinnoille, pätevöittämiselle ja tarkastamiselle. Tässä työssä tutkittiin kuparimetallien hitsauksen mahdollisuutta Loviisan ydinvoimalaitoksella juottamisen sijasta siten, että kattavat laatuvaatimukset täyttyisivät. Hitsauskokeissa ja laboratoriotutkimuksissa testattiin hitsausta erilaisilla hitsausaineilla ja hitsausprosesseilla. Koetulosten pohjalta toteutettiin hitsausmenetelmä deoksidoidun kupariputken ja tinapronssilaipan TIG-hitsaukselle.