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Protection Solutions for Refinery Transmission Upgrades from Radial to Looped Configuration

By Kyle Bennett, POWER Engineers

Abstract

Most industrial power systems use a radially connected transmission system to distribute power within the facility. Inverse time overcurrent protection for transmission, transformer, cable, and load protection is frequently employed. Even with the presence of multiple sources (both utility and cogeneration) coordination is typically achievable. Coordinating inverse-time overcurrent protection can become quite a challenge when the power system is fed in a looped or interconnected transmission system as the sources have parallel paths to travel during faults. Calculating the current split for each path is further complicated by the present switching configuration of the facility. This paper will present the upgrade of the protection system for a refinery that was upgraded from a radially fed medium voltage (4.16 kV) transmission system to a looped system to provide electrical redundancy for reliability. The focus will be on the design challenges faced and solutions created by the project protection team in designing and executing new protection schemes and concepts for protecting both the transmission system and power delivery centers (bus). Challenges include utilizing existing instrument transformers, protective relays, and switchgear in the design, maintaining backup level protection for system bus and feeders by applying IEC 61850 GOOSE communication aided schemes, integrating the new protection schemes with the existing schemes, and installing new equipment into existing metal clad switchgear.

This paper was presented at the 2019 Georgia Tech Protective Relaying Conference.

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