A novel bus bar protection for complicated bus arrangements without using isolator status wiring

Abstract

In this paper, the experience in engineering, logic development, testing and commissioning of bus bar protection relay applicable for 400kV and 220kV substations, for a complicated bus arrangement executed at Madhya Pradesh power transmission corporation limited (MPPTCL) is discussed. For decades, the isolator/disconnector position from switch yard is replicated in the bus bar protection relay for zone selectivity functionality. Bus bar protection for 28 sub stations in MPPTCL was to be implemented with a challenge that the isolator images were not available at site and up-gradation of the same was also not possible, however the implementation of bus bar protection for discriminative buses are a must owing to the statutory requirements. This was possible to be implemented without sacrificing the protection requirement by employing the inbuilt push buttons available on the IEDs to perform the zone selection / CT switching functionality. The philosophy of utilizing the isolator position (for zone selection and CT switching) from switch yard being replaced with built in push button and a novel solution is implemented and executed by General Electric (GE) and demonstrated to MPPTCL for more than 28 substations with GE make B90-IED. The advantage of this solution is to overcome the limitation in upgrading the existing disconnectors and associated copper cabling laid between switch yard to control room on a live station functioning fully well. Further challenges were encountered while providing the bus bar protection for one of the 400kV SS where the bus configuration is with a split bus having two bypass arrangements to facilitate better operational convenience. The challenges were, multiple zones of protection, switching of CTs, positioning of CTs creating blind spots, tripping algorithm, enhanced security and operation for appropriate zones. The challenges were effectively addressed by using state of the art technology like dual algorithm and decision making, internal push button based CT switching, increasing the number of zones by adopting partial differential principle. These complications are well addressed by B90/B30-IEDs working on a low impedance principle with the internal logic capability. Further the effects of inadvertent mistakes of operators (human error) on the protection system are also addressed by employing enhanced security logics to a certain extent is also discussed in this paper.