Non-contact Measurement for Shaft Voltages

There is a trend in electric drive systems for the voltage of inverters to become higher. And the shaft voltages generated by the potential between the motor shaft and the case increases in proportion to the inverter voltages. Shaft voltages are known to cause problems such as electromagnetic noises. To select the reduction methods for electromagnetic noises, we need to understand the shaft voltages generated in the motor. Commonly, we use the brush when measuring shaft voltage. However, in some motors, it may not be possible to measure shaft voltage due to the lack of a contact surface for the brush. This paper develops the antenna that can measure the shaft voltage in a non-contact. We design the antenna using the electromagnetic field simulation (ANSYS Q3D). The antenna creates electrostatic coupling by facing it towards the rotor. One of the problems is the electrostatic coupling between the coils and the antenna, which results in the generation of voltage in the antenna from the coils. This is the noise for the measurement of shaft voltage. Therefore, we design the antenna stay to reduce the electrostatic coupling between the coils and the antenna, thereby reducing the voltage from the coils. With the above structural design, the antenna capable of receiving the shaft voltage from 100 kHz to 30 MHz with an error of 6 dB or less has been completed.