High Speed Main-Tie-Main Pole Top Source Transfer Application with Precise Voltage Regulation

This paper will discuss the implementation of a highspeed source transfer and voltage regulation system deployed by the Cuyahoga Falls Electric Department to increase the reliability of the 25 kV distribution grid. The feeder topology includes two line sections feeding a critical load, which are supplied by the “Thiess” and “Sub #3” substations. A main-tie-main pole top solution, along with line end voltage regulation, was implemented to minimize the potential impact on the load caused by any fault at the substation or on the feeder. The production process at the critical load facilities required the system to perform any source transfer operation within 6–7 cycles. Therefore, in the event of a fault on the line section with the critical load, the protection system was required to immediately isolate the line section to minimize the impact on the entire distribution system. Due to this requirement, the system employed fast acting differential protection instead of conventional time coordinated curves. Further analysis indicated that the transfer event might cause a significant voltage drop at the line end when both line sections are fed from a single source. The solution for this was to adjust the substation voltage regulators based on the line end voltage. This functionality required a real time interaction between the reclosers in the field and voltage regulators in the substation. This was achieved using decentralized logic architecture and IEC61850 peer-to-peer communication protocol with GOOSE messaging between all devices. The paper will discuss the following: ◾ Source transfer sequences; ◾ Fault isolation concept using jDiffTM differential protection; ◾ Voltage regulation logic; ◾ System design testing and commissioning steps; ◾ Communication and SCADA integration; Field test results.