The influence of external fault on input side, such as bus voltage drop caused by external power grid fault, on the operation of high voltage inverter. A power plant unit in Guangdong Province once had such an accident: due to the transient fault of the external power grid, the auxiliary power bus voltage flickered and dropped, leading to the shutdown of the auxiliary frequency converter. Although the fault of the external power grid was removed quickly, the important auxiliary equipment driven by the frequency converter stopped, which led to the unit load rejection. Therefore, the re start function of instantaneous power failure should be a reliable guarantee to improve the bearing capacity of external fault of high-voltage inverter of auxiliary equipment of power plant.

The influence of external faults on the output side, such as cable breakdown and short circuit, single-phase grounding or even phase to phase short-circuit fault on high-voltage inverter. The high-voltage inverter shall be equipped with single-phase grounding fault detection function, and set alarm or trip protection according to site conditions. According to statistics, there are about 20 sets of phase to phase short circuit fault caused by insulation damage of high-voltage motors in Guangdong Province every year. Although the relative probability is small, the impact of short-circuit current on the equipment of high-voltage inverter with extremely limited over-current capacity is huge, which may lead to serious fault of equipment damage. The bearing capacity and protection technology of high voltage inverter to output phase to phase short circuit is an important factor to be considered in equipment selection and equipment safety assurance.

Equipment faults can be divided into two types: one is the fault that can be recovered instantly. Once the fault occurs, it can recover itself in a short time. The frequency conversion device with automatic speed tracking function can significantly improve the operation ability and reliability under such fault conditions. Some of the high-voltage inverters in Guangdong Province are frequently shut down when lightning strikes in thunderstorm season;

The other is the recovery time of the device after permanent failure. The power unit modularization can replace the standby module in a short time, so that the equipment can resume operation in a short time.