Inverter-generated bearing currents may destroy the bearings of an induction motor within a short time of operation, such as in a period of two months. The reason for bearing damage due to bearing currents is electrical discharges that take place through the lubricant between the raceways of inner and outer ring and the rolling elements of the bearing. This phenomenon is similar to the electrical discharge machining. Eventually, this leads to a bearing damage. Multiple techniques have been proposed to mitigate bearing currents. However, it is possible to measure bearing currents reliably only in a laboratory and with specially designed motors. This makes it difficult to determine if there are bearing currents present in the real operation location and if the installed mitigation techniques are working as expected. In this article, it is shown that the sparking inside the bearing can be measured outside the motor. The sparking generates a high frequency current impulse that can be measured with an antenna and oscilloscope. It is also shown that the motor operates as a radio antenna.
展开▼
