Testing the current waveform on the input of the frequency converter can assist in troubleshooting mains phase loss conditions or suspected problems with the

SCR/diode modules. Phase loss caused by the mains supply can be easily detected. In addition, the rectifier section is controlled by SCR/diode modules. Should

one of the SCR/diode modules become defective or the gate signal to the SCR lost, the frequency converter will respond the same as loss of one of the phases.

The following measurements require an oscilloscope with voltage and current probes.

Under normal operating conditions, the waveform of a single phase of input AC voltage to the frequency converter appears as in the illustration below.

Illustration 6.3: Normal AC Input Voltage Waveform

The waveform shown in the illustration below represents the input current waveform for the same phase as in the Illustration above while the frequency converter

is running at 40% load. The two positive and two negative jumps are typical of any 6 diode bridge. It is the same for frequency converters with SCR/diode modules.

Illustration 6.4: AC Input Current Waveform with Diode Bridge

High Power Service Manual for Unit Sizes 6x

Table of Contents