Influence of Electrical Parameters on INSOCOAT Insulated Bearings

Influence of Electrical Parameters INSOCOAT Electrically Insulated Bearings behave differently in DC and AC applications. In DC applications, INSOCOAT bearings act as normal (pure ohmic) resistors. The alumina coating is an insulator, so its ohmic resistance value (R) is important. The breakdown voltage of the standard coating is 3,000 VDC and the resistance is greater than 200 M, making INSOCOAT bearings highly efficient insulating properties. In AC applications, especially when the frequency converter provides high frequencies, the bearing behaves differently. Electrically insulating coatings, such as INSOCOAT ceramic coatings, act as parallel resistors and capacitors. Therefore, impedance (Z) must also be considered, as described in Equation 1: Equation 1: Electrical Impedance of a Capacitor in Parallel with an Ohmic Resistor. Equation 1 shows that the higher the frequency, the larger the term containing capacitance in the equation, and the lower the impedance. In this case, the electrical impedance depends on the resistor's ohmic resistance (R), capacitance (C), and the frequency of the applied voltage (f). The capacitance of an INSOCOAT bearing (Equation 2) depends on the bearing's coated surface area (A), the thickness of the insulating coating (s), the material of the coating itself (r) and the dielectric constant (0, a material constant) . Equation 2: Capacitance of a parallel plate capacitor. To increase the bearing resistance, the capacitance of the coating should be as small as possible. In practice, this means that the inner ring coating will always have a higher resistance than the outer ring coating. The same is true for coating thickness. The electrical impedance of the VL0246 is much higher than that of the VL0241 (Figure 2). How SKF measures the electrical parameters of INSOCOAT bearings Effective ohmic resistance measurements can only be obtained under controlled environmental conditions, as the measurement results can be affected by many different factors such as humidity, cleanliness, temperature and contact surfaces. Figures 1 and 2 describe the measurement principle of INSOCOAT bearings with outer ring coating and inner ring coating respectively, which are in line with the actual installation conditions. Therefore, the electrical parameters described in Table 1 are only valid under mounting conditions, in a dry and clean environment and with the relevant shaft and housing dimensions in accordance with the requirements of the General Catalogue.