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Reference Number NIA_UKPN0002
Title Directional Earth Fault Passage Indicator Trial
Status Completed
Energy Categories OTHER POWER and STORAGE TECHNOLOGIES(Electricity transmission and distribution) 100%;
Research Types Applied Research and Development 100%
Science and Technology Fields ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering) 100%
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Project Contact
No email address given
UK Power Networks
Award Type Network Innovation Allowance
Funding Source Ofgem
Start Date 01 January 2014
End Date 01 January 2018
Duration 48 months
Total Grant Value £483,764
Industrial Sectors Power
Region London
Programme Network Innovation Allowance
Investigators Principal Investigator Project Contact , UK Power Networks (100.000%)
Web Site
Objectives 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.
Abstract Faults occur on HV (11kV and 6. 6kV) networks. Faulty sections on radial circuits are conventionally identified using fault passage indicators that operate to show the passage of fault current up to the faulty section, whereas indicators located on the circuit past the fault would not operate. The LPN network has a number of HV circuits operated as closed rings where the feeders are connected together through switchgear fitted with circuit breakers and relay operated directional protection, commonly known as DOC. Any fault current will pass along both feeders of the closed ring and therefore all fault passage indictors operate making it impossible to determine the faulty section. The normal switchgear used on HV rings is the Ring Main Unit (RMU), although a wide variety of switchgear manufacturers and types are used in LPN. Communication between the RMU and the control centre is via Remote Terminal Units (RTU). Not all secondary substations in London are fitted with an RTU. The problem is therefore to be able to identify the faulty section of cable in a closed ring and communicate satisfactory information back to a control centre to enable the faulty section to be isolated for supplies / capacity to be restored. Any additional equipment must be relatively cheap and easy to install. On radial HV circuits, the fault passage indicator is connected to the RTU, where there is an RTU fitted, and its operation is indicated on the control room diagrams. This project will develop a fault passage indicator capable of reporting the direction of the fault current and displaying the direction on the control diagram in an easy to understand format. To enable the direction of the fault to be determined, both the HV voltage and HV current needs to be measured in terms of magnitude and phase at the indicator position to calculate the effective power flow direction of the HV fault current. The current is measured using current transformers (CT). Modern RMUs have individual CTs on each phase conductor in at least one ring switch or end box. The legacy switchgear has a single core balance CT around the HV cable which can only detect earth faults. HV voltages are traditionally measured using a dedicated voltage transformer but these are not standard on RMUs so alternative methods of detecting the HV waveform are required. Modern RMUs have a Voltage Presence Indicator Socket (VPIS) which is derived from capacitive bushings around the HV conductor. This gives a low voltage representation of the HV voltage waveform. Legacy RMUs do not have VPIS but a large number feed the low voltage distribution network via standard transformers ranging from 500kVA to 1000kVA. Because of the variety in RMUs two workstreams were proposed. The first to develop a device to use on modern RMUs while the second could be used on legacy RMUs: Workstream 1A number of manufacturers were contacted and Nortech were selected to add a directional facility to their existing NX41 fault passage indicator. The device would use the VPIS as the voltage source and either the three fault passage CTs to enable phase-phase and earth fault detection, or a core balance CT to enable earth fault detection only depending on what CTs are fitted to the RMUs. Workstream 2 Ricardo (previously PPA Energy) are currently involved in the UK Power Networks’ Distribution Network Visibility (DNV) project, which is being integrated into Business as Usual. This project utilises HV and LV data, part of which investigated power flow directions. This project enables Ricardo to build on the experience of DNV and to develop a Directional Earth Fault Passage Indicator (DEFPI). It will derive the earth fault current from a core balance CT. The voltage will be taken from the LV side of a distribution transformer and converted to represent the HV voltage by sequence component transformations and transformer and network data.Note : Project Documents may be available via the ENA Smarter Networks Portal using the Website link above
Publications (none)
Final Report (none)
Added to Database 09/08/18