The project will trial 100 units at various secondary substations on closed HV rings.

The sites will be chosen subject to various criteria:

• Number of substations on the closed ring;

• Number of customers on the closed ring;

• Profile of customers on the closed ring;

• Fault history of the feeders;

• Workstream 1 – Modern RMUs with three fault current CTs and VPIS (Lucy VRN2A and Schneider RN2C) and RTU installed;

• Workstream 2 – Legacy RMUs with a core balance CT, a distribution transformer feeding the low voltage network and an RTU installed.

Workstream 1 uses an existing proven fault passage indicator (NX41) that has been widely used on UK distribution networks. The enhancements to the device to enable directional functions was successfully simulated as a desk top demonstration using variable voltage and current inputs at Bengeworth Road on 17 September 2014.

Workstream 2 Ricardo utilized the UK Power Networks’ training centre’s network at Sundridge which is equipped with standard secondary network transformers and RMUs to successfully demonstrate the directional capabilities. For safety reasons, the training network is very limited in capacity, although it operates at 11kV. For demonstration purposes, the network was energized at a reduced voltage to enable a measurable fault current to be detected. This was carried out on 17 October 2014.

Since the device will be install on a ring switch on an RMU, it will report when a fault is detected in one of three states;

• Fault detected direction INTO the RMU,

• Fault detected direction AWAY FROM the RMU,

• Fault detected but direction UNKNOWN.

Benefits

• Faults experienced on closed rings where a trial DEFPI has been installed give correct directional information by the end of the trial.

• CI and CML values can be saved once the DEFPI indications are used during fault restorations.

• If proven, an understanding of how use of the device could be expanded to radial HV circuits with interconnected LV meshed networks where reverse power flows from the LV network during phase-phase HV faults cause existing fault passage indicators to give misleading information.