Background. The operation of electric motors in variable‑frequency drive systems is associated with the problem of premature failure of rolling bearings due to parasitic currents flowing through them. One way to address this issue is to bypass the bearing using a special brush that electrically connects the bearing shield to the motor shaft. However, this method has several significant drawbacks: unstable transition resistance, arcing, the need for maintenance, limited applicability in explosive environments. In this regard, developing a method for shunting bearing currents that is free from the aforementioned drawbacks is an important scientific task.
Materials and methods. To create an electrical contact between the shaft and the housing of the electric motor, an electrically conductive ferrofluid has been used. This fluid is obtained by adding graphite or graphene particles to a nanodispersed ferrofluid. The influence of such a conductive ferrofluid ring on bearing current has been studied using an equivalent electrical circuit for common‑mode current developed in MatLab.
Results. A method has been proposed to create a stable electrical contact between the housing and the shaft of an electric motor using an electrically conductive ferrofluid. The influence of the electrically conductive ferrofluidic ring on bearing current has been studied using an equivalent electrical circuit for the common‑mode current of a frequency‑converter‑driven electric motor, developed in MatLab Simulink and taking into account the stray capacitances between its components. It has been found that when an active resistance of Rму = 2,1 Ω (simulating a conductive magnetic fluid ring) has been introduced into the circuit and connected in parallel with the bearing capacitance, the current through the bearing has decreased by 23 times from 9,33 to 0,4 mA.
Conclusions. The obtained data confirm the effectiveness of a ferrofluid seal with an electrically conductive ferrofluid as a bypass element to reduce parasitic currents in bearings. A ferrofluid seal with an electrically conductive ferrofluid is a promising alternative to brush-based shaft grounding systems. The proposed method provides a stable electrical contact without dry mechanical friction or arcing, which enhances reliability and expands the range of applications for electric motors, including use in explosive environments.