Connecting test equipment to energized motors through an easy access Motor Test Access Panel (MTAP) has greatly improved the safety and efficiency of electric motor testing. However, when it comes to medium voltage VFD’s some considerations are important.
Line Side of the VFD:
– The Line Side of the VFD can be monitored using an MTAP2 and 5A rated CTs provided there are line side PTs that typically output 120V Phase-Phase (~35:1 ratio).
– To monitor the Line Side Voltage, simply connect the MTAP2 voltage leads to the PT output.
– To monitor the Line Side Current of the VFD, connect the MTAP2 CT’s to the existing Secondary CTs that are typically present.
Because the line side of the VFD operates at the standard 50/60 Hz frequency, there are no additional considerations or test limits. On the next Tip we will discuss the Load Side VFD monitoring, which adds a variety of considerations.