Explosion-protected Electrical Drive Systems

Tasks

By an increase in the technical complexity, for example by providing longer clearances and creepage distances on insulating materials or reducing the winding temperature of machines, it is possible, compared with the standard design, to enhance the safety of electrical equipment which in normal operation does not contain sources of ignition so that their safety level is comparable with that of other types of protection. All the connection for installation, e.g. terminals and terminal boxes are designed in this type of protection. Squirrel-cage motors which form the greatest group of explosion-protected equipment as regards the number and the variety of types available are of paramount technical and economic importance. Motor test facilities serve to find out whether the maximum permissible temperature is exceeded somewhere on the motor in the case of failures, for example when the rotor is locked. As a result of the present state of development of power electronics, the converter-fed variable-speed three-phase motor is of commercial interest also for hazardous areas. Extensive basic investigations were necessary to assess the safety of such combinations. These investigtions showed that not invidivual components but only the whole assembly can be assessed. For the supervision of motors of the "increased safety" type of protection from the point of view of safety engineering, the techniques available are supported by electronic systems. In this connection, international standards are at present being prepared.

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