Application Strategy of Distance Protections On Transmission Lines With Ibr Connections

In recent years, the installations of Inverter-Based Resources (IBR), such as battery energy storage systems (BESS), have seen significant growth in Ontario, Canada, with a continued upward trend projected for the coming years. Unlike conventional synchronous generators, IBRs are strategically located near load centers to minimize power losses over long transmission lines. In addition to radial connection to terminal stations, numerous IBRs are connected to Hydro One grid with direct T-tapped onto nearby transmission lines.

One of distinctive features of IBRs is their rapid response through their control logics, leading to distinct fault current characteristics. Compared to conventional synchronous generators, IBRs generate lower fault currents but also provide low negative sequence current.

For directly T-tapped on HV transmission lines, the interfacing transformers are usually regular Wye-Delta winding connection configuration with solidly neutrally grounded on HV side. As the grounded Wye-Delta transformer is a low impedance zero sequence current source, ground distance elements in line protections will be influenced. Leakage of zero sequence current due to the grounded transformers will increase the apparent impedance of ground distance elements, which will result in coverage reduction of the ground distance protection element.

For radial lines with only IBR connections, protection at the grid’s terminal station is straightforward when faults occur on the IBR line as the fault current is mainly supplied by the grid. But if a reverse fault occurs on the terminal station bus or on adjacent line, the distance protection element on the IBR line may lose its directionality since the fault current is solely supplied by the IBR. Therefore, the operational performance of conventional line protection schemes becomes vital when more IBRs is integrated with HV transmission systems.

This paper analyzes apparent impedance changes with IBR direct T-tap connection and radial connection with different IBR capacities through a grounded interfacing transformer. Dynamic characteristics of Mho distance element are examined with fault data with IBR model. Strategy on IBR connection on transmission lines are proposed to reduce the impact of IBR connections on phase and ground distance protection elements.

Dedicated simulation tests and actual examination of line protections application with IBRs show that distance protection schemes can reliably operate on transmission lines with suitable plans and designs.