Safe application of converter-powered drives

Status:

completed 04/1995

Aims:

In the course of technical and industrial development, conventional drives have been replaced by converter-powered ones in many fields of application. In the case of converter-powered drives with a high dynamic, an interruption of the power supply by means of electromechanical components is safety-technically insufficient. A new type of circuit breaking is likely to enhance the safety of machinery. The BG expert committees "Printing and paper", "Iron and Metal I", "Iron and Metal II", and "Nonmetallic minerals II" has launched a compilation of a number of example applications. This documentation is to support the work of BG expert committees providing consultancy services to companies, and also to assist standards committees in the drafting of type C standards.

Activities/Methods:

The investigations together with the expert committees aimed to identify new hazards likely to occur in connection with converter-powered drives, and to develop suitable protective measures. For this purpose several actions were taken: the hazard potential of new industrial machinery was analysed, safety requirements specified in relevant regulations and standards were compiled, malfunction and faults of converter-powered drives were investigated. Proven measures to avoid or prevent hazards in the case of control failures were compared to new approaches.

Results:

The investigations show that a safe standstill of electronic drive controls can be obtained without direct decoupling by simply cutting off the power supply for the impulse generator (with electromechanical contacts). The obtained safety level is comparable to that of a galvanic isolation. Generally, a converter does not provide reliable protection against excess of a maximum speed. Additional external control devices might therefore be necessary; otherwise the control must satisfy special requirements in terms of control level. As a rule, safe breaking cannot be ensured by the converter alone. It is therefore usual to have additional breaking devices, except cases where constructive and structural measures are taken to realise a comparable safety level. Further investigations into drive controls were carried out. It could be shown that it is possible to ensure safe standstill by electronic components only without making use of electromechanical equipment. The same is true for the safely reduced speed function which can nowadays be realised without having recourse to additional external control devices.

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