Save your DC drive`s thyristors

Siemens has developed a system that protects DC drives against the effects of commutation failure which can destroy a drive`s thyristors. It also prevents fuses from blowing and cuts service and maintenance costs.

DC drives operating in the regenerative mode can suffer commutation failures if the voltage dips or fails - as a result of disturbances such as electrical storms, uncontrolled switching operations or high loads in weak systems. A large current is generated in the power supply in the feedback direction, or a transverse current is generated in the converter. In either case, a fuse trips and the thyristors can be destroyed.

Siemens` answer has been to enhance the software in its Simoreg DC Master converters to detect a commutation failure as it starts. The software sends a command to switch off the power semiconductors, thus limiting the currents and protecting the fuses and thyristors. The drive also absorbs the magnetic energy stored in the driven motor as electrical energy.