Explosion protected electrical drives - risk assessment and technical diagnostics

In this paper the application of motors in plants at risk of explosive atmospheres, and the special requirements of such applications from the standpoint of explosion protection are considered. The application of motors with type of protection increased safety, marked as “EEx e”, with and without associated safety systems, are analyzed for zone 2. Risk assessment of such applications, based on the requirements of ATEX Directive, is the main part of this paper. There is a specific example which illustrates the results of selection and application of motors with type of protection “EEx e” without the application of additional safety systems, which is the traditional approach. Possible application, in special cases, of the mentioned motor with the application of additional safety systems, which is the new approach, is also analyzed. The concept of the new approach is used in cases where diagnostic methods have determined that the basic explosion protection of an “EEx e” motor has been undermined. To establish the actual condition of a rotor squirrel cage, a diagnostic method based on the spectrum analysis of the stator current is used. This diagnostic test can ascertain the deteriorated condition of the rotor cage which directly affects its explosion protection. Damage to the rotor cage can be a serious source of ignition of explosive atmospheres.