AkaHammer said:
I didn't see anyone mention overload setting, if you lost a phase the current should have went higher on other phases. And if your brake was on again current should have went higher. If overload was set properly it should detect a rise in current, in theroy 1.732 times normal current should be present on other two phases.
Also suggest above add a means to detect fuse or breakers tripping
Not mentioned, no, and for good reason. What you are describing would be typical for a single-phasing issue on the motor side of a VFD (Variable Frequency Converter). The typical current imbalance one would see here on the motor leads is not relatable to the loss of a supply side phase. The Overload Fault on these drives only monitors the current in the output section and not the input section. It would or could never detect a loss or imbalance on the input supply side.
The input phases on a VFD service the full wave bridge rectifier. The rectifier section is composed of six diodes which are semiconductors designed to conduct current in one direction. The purpose of the diodes is to convert AC current to DC current to supply the DC bus. The DC current, through the bus, is then connected to a circuit of specialized transistors called insulated gate bipolar transistors (IGBT) with the motor coil connected in between them. It is the IGBT that directly controls the voltage and frequency sent to the motor coil.
When you lose an input phase on the supply side, the bridge rectifier continues to convert AC current to DC current through 4 of the diodes instead of the optimum 6 diodes. This results in DC current continuing to be supplied to the IGBT section. However, the bridge rectifier may now be under further duress and may overheat. There may also be significant DC bus ripple and the danger of overheating the DC bus capacitors. But, once the IGBT section still has sufficient current available to it, it will continue to regulate the voltage and frequency output to the motor coil. All this excess heat will continue once the load is maintained at its original current values. This will in time fatigue the drive components and likely shorten its life. This is why we derate the permissible output current where only a single phase supply is available for a normally 3 phase supply VFD i.e. less load, less heat, less stress. This single phase loss on the supply side, while potentially causing significant duress within the drive supply and power components, will not adversely affect the resultant current being produced by the IGBT output.
And again, the Overload Fault for these drives will not detect such a phase loss on the supply side as the motor side current, which the fault monitors, is continuing to be supplied and regulated by the IGBT. The very design of the bridge rectifiers for the supply section is exactly how and why we are able to run a 3 phase motor off a single phase supply without issue (once either derating is applied or a single phase supply VFD model is being used).
In short, we cannot relate the circuit-wide current characteristics we "see" in a typical direct online (DOL) starter with the current characteristics we "see" only on the output section of a VFD.
Regards,
George