With the upgrading of industrial automation, the frequency converter is widely used in bridge building crane. The frequency converter has a lot of protection function such asbridge girder launcher overcurrent,overvoltage and overload protection etc.

1,when maintaining, cutting off the power, and the operator must make sure the converter input the power directly.

2. cutting off the power, the electrolytic capacitor in main circuit of frequency converter still has the remain high-pressure electricity.

3. must waiting and making sure the remain high-pressure electricity release clearly and then operating.

4. measuring the output voltage of frequency converter, must use the rectifying alternating voltage because the common voltage can’t display easily.