Performance of an arc-resistant medium-voltage motor control center for an in-service fault

Since the introduction of the IEEE C37.20.7 standard and predecessor documents for testing switchgear under arcing fault conditions, the use of arc-resistant equipment has increased and is now the standard in many companies in the petrochemical and oil industries. Equipment designs have evolved to be more robust under fault conditions to meet the testing criteria, but there is limited knowledge of how such equipment performs if a fault occurs while in service at an end-user facility. This paper discusses an actual fault sustained on an arc-resistant 5kV motor control center lineup at a large oil refinery and lessons learned from the incident. The paper discusses the background of the installation, provides an overview of the fault incident and discusses the causes of the incident. The considerations for proper coordination of protective relays to achieve both the desired selectivity for faults to ensure continuity of service to critical refinery processes and to properly protect the equipment in accordance with its arc rating are discussed. The testing protocol and passing criteria for arc-resistant equipment is explored, with an emphasis on providing a comparison between how a manufacturer tests the equipment and how it performs during the test versus the perception that end-users may have. Potential recommendations are offered to enhance the testing protocol and testing criteria to better align with end-user expectations. Additionally, the paper will highlight other considerations that should be part of the application, installation and maintenance of arc-resistant equipment.