Decentralised Frequency Inverters With Safe Stop from Nord

Operator safety is essential for plant operation. After a safety circuit is actuated by opening a safety cover or door, it must be ensured that no rotating system components can lead to accidents. However the high availability of machinery is also very important and a rapidstart-up after safety-related interruptions is essential for economy.

In spite of their cost-optimised design, NORD SK 200E series decentralised frequency inverters are equipped with various safety functions.

Depending on the switching device which is used safe shut-down method can be achieved for high risk categories according to Category 4 or Performance Level e as per EN 13849-1. While with conventional frequency inverters of this power class restarting of the motor was prevented with a complete switchoff of the 24V control voltage orthe mains voltage, the types SK 21xE and SK 23xE are equipped with a certified safe pulse block and have digital inputs for the functions "disable voltage" and "emergency stop". By this method the frequency inverters can implement Stop Category 1 (controlled braking of the drive unit compliant with SIL1) with subsequent torque switch-off (compliant with SIL3) or Stop Category 0 (corresponding to SIL3) in accordancewith EN 60204-1.

As the control and power electronics are not switched off on activation of the pulse block, the devices remain online and are immediately available again without re-initialisation once the safety circuit has been closed. As well as the high level of availability, the safety technology of the inverters has additional economic advantages: Circuit breaker components are not required and the electronic circuit for the safety function eliminates regular maintenance and the replacement of worn electro-mechanical contacts.