Probes measure high frequency motor drive common-mode currents

Using Rogowski technology, they allow motor installers and design engineers to deal more effectively with high frequency (hf) common-mode currents caused by variable-frequency drives.

Engineers can assess the magnitude of the threat posed by hf common-mode currents, that can damage motor bearings and interfere with nearby electrical equipment. The current measurements can help determine suitable corrective action, such as fitting brushes, insulated bearings, or choke coils, and, with further measurements, assess the effectiveness of the chosen remedy.

The screened coils have excellent immunity to voltage disturbances and a low frequency (-3dB) bandwidth that attenuates unwanted 50/60Hzmagnetic fields while maximising the SNR of the measurement of the high frequency common mode currents. Available in coil sizes from 300 to 1000mm, and longer if required, making them suitable for use with a range of motor shafts. Even with a coil circumference of 1000mm the probes can achieve a high frequency (-3dB) less than 10MHz, says the company.

Three sensitivity grades are available for measuring bearing currents up to 37.5, 75 or 150A peak. The peak detected current corresponds to a maximum output voltage of ±7.5V when connected to an oscilloscope input via the BNC output provided.

PEM: PCIM Hall 7 - 122