Jan 2014
Electricity Distribution
Directional Earth Fault Passage Indicator Trial
Jan 2014
Jan 2018
UK Power Networks and London Power Networks
Peter Lang
Click here to send a question to the contact.
Network Innovation Allowance
Fault Level
The project requires a satisfactory demonstration of the techniques proposed, followed by installation of trial units on the live network to monitor their operation under true fault conditions.

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.

The project intends to develop devices that can confidently identify the direction of fault current on closed HV rings and correctly display on the control diagram to enable the correct isolation of faulty sections of HV circuits, thus minimising disruption to customers and minimizing CIs and CMLs.

The devices must be able to be fitted to existing standard RMUs and communicate via standard RTUs as installed on UK Power Networks’ LPN network.

The devices must be able to be installed with the minimum resource and network outage requirement.

During the trial, the operation of the device under fault will initially be treated in the same way as a non-direction device until such time as UK Power Networks has confidence in direction being reported correctly.

During initial trials a number of improvements were identified to ensure more consistent and accurate direction indications from the DEFPI units.. A subsequent firmware upgrade has been developed for both types of unit and an additional trial phase planned to collect and assess additional evidence to demonstrate that the units do provide correct direction indications consistently.  It is expected that this monitoring phase could last an additional 12 months.  

The following will be considered when assessing if the project has been successful:

  • 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.