Improvement of protective relaying efficiency for motor drives at mineral processing plants

The article suggests a new way of improving the protective relaying and control systems used for motor drives in electric utilities. The authors made the conclusion that symmetrical component filters are widely used in the measuring part of protection against the open phase condition. In most cases, such filters receive signals from current transformers connected to the electric motor protected. The current transformers have some shortcomings that may result in the lack of accuracy and selectivity of relaying devices and cause problems for relaying algorithms development. The improvement of protective means can be implemented with the use of instrument current transducers designed by the authors. The primary current transducer in the suggested design is the Rogowski coil. The results of the research show that the reliability of the system can be improved and the quantity of the protection devices can be decreased. Such conclusion is also confirmed by results of practical experiments with the instrument current transducer described in the article.