Empowering Progress at Hollycross ATFS – Stage 2

Empowering Progress at Hollycross ATFS – Stage 2

November 19, 2024

Last weekend (16/17 November) Enable Power Systems, with support from Network Rail Testing (NRT) and WJP Services, successfully completed the stage 2 commissioning of a new auto transformer feeder site (ATFS) at Hollycross (Bramley).

The works involved close collaboration with National Grid engineering teams to energise the 25kV grid intake substation at Hollycross, which is fed via the 400kV National Grid substation at Bramley. Stage 2 included the energisation of both National Grid and Network Rail infrastructure, specifically:

• Bramley 400kV to Bramley NG (Hollycross) 25kV National Grid HV cables, switchgear, and protection schemes: This involved the installation and testing of high-voltage cables, ensuring the integrity and reliability of the connections. The switchgear and protection schemes were tested to confirm their functionality in isolating faults and protecting the infrastructure.
• Bramley NR auto transformer feeder site cross-boundary 25kV HV feeder cables, ABB SMOS switchgear, protection schemes, busbars, and two auto transformers: The feeder cables were tested for insulation resistance and continuity. The ABB SMOS switchgear was subjected to operational tests to verify its performance under load conditions. Protection schemes were calibrated to ensure accurate fault detection and isolation. The busbars and auto transformers were tested for electrical and thermal performance.

The purpose of the stage 2 energisation was to conduct short circuit testing while recording voltage potentials on adjacent infrastructure. This ensured compliance with step and touch voltage limits, including Rise of Earth Potential (RoEP) on railway traction sites. The maximum fault current was confirmed by NRT to be within the 12kA limit of the source supply.

Technical Details:

• Short Circuit Testing: This involved creating controlled fault conditions to measure the system’s response. The tests confirmed the robustness of the protection schemes and the ability of the infrastructure to handle fault currents without damage.
• Voltage Potential Recording: Voltage potentials were recorded at various points to ensure that step and touch voltage limits were within safe thresholds. This is crucial for the safety of personnel and the integrity of the infrastructure.
• RoEP Compliance: The Rise of Earth Potential was measured to ensure that it did not exceed safe limits, preventing hazardous conditions during fault scenarios.

All equipment was energised safely, and the work was completed on time, in accordance with the approved commissioning schedule. With all stage 2 energisation tests and results recorded satisfactorily, the site was de-energised in preparation for stage 3 entry into service.