Learnings

Outcomes

Technical Papers

          B. O. Brewin, S. Pinkerton-Clark, S. C. E. Jupe, S. R. Hoda, S. J. Hodgson: “Directional Power Flow Monitoring in Overhead Line Distribution Networks with High Penetrations of DER, Session 2022 C6 - PS2 Innovative planning and operation of active distribution systems (CIGRE), 2022 (accepted for presentation)

Reports

Factory Acceptance Testing of OHL Power Pointer Solution

­   Factory acceptance testing of the OHL monitoring sensor was completed and witnessed by National Grid’s Innovation team. The report documents details of the tests that were carried out, conclusions, and evaluation of the testing.

Cyber Penetration Testing Assessment

­   National Grid’s cyber security team completed the cyber penetration testing of the Smart Navigator 2.0 clip-on OHL sensor. This report documents the findings of the testing, and recommendations from the cyber security team.

Site Selection Methodology

­   This report documents the methodology for the selection of the locations of sites for the field trials. Preference was given to circuits most likely to record disturbances, and other relevant network activity, for optimal analysis of each of the methods.

Analysis of SCADA Data

­   The Time Series Data Store (TSDS) is an archive system, that captures historical records of the instantaneous digital and analogue inputs reported from field transducers (over the SCADA system) to the Network Management System (NMS). An exercise to assess the quality and suitability of data for use in the state estimation module was carried out and the findings, including frequency, step-change and erroneousness of data, are presented in this report.

 Site Visits to Substations in the Shrewsbury Primary Network

­   This report documents the data captured from the site visits to each primary substation in the Shrewsbury 33kV network, for the purposes of validation of the impedance model for the directional power flow state estimation method.

Completion of Test Field Trials

­   This report summarises the performance of the OHL Power Pointer solution following the completion of the test trials. Diagnostics of the performance of the monitoring equipment and initial results from the field are presented. The design of the solution was later optimised from learning generated during the test trials.

          Method 1: Directional Power Flow Detection

• ­ this report summarises the analysis and evaluation of the directional power flow detection method by the OHL Power Pointer solution. Changes in power flow direction were observed through circuits during the main project trials. This report presents the validation of the method and shows the seasonal trends in the directional power flow data captured by the solution.

          Method 2: Directional Power Flow State Estimation

• ­ This report summarises the analysis and evaluation of the directional power flow state estimation method. The state estimation module uses directional (MW, MVAr) and non-directional measurements (Amps) from SCADA-connected transducers across the distribution network and provides blanket visibility of power flow direction through circuits, including circuits where there are no directional power flow sensors (or any sensors) present. The report presents the findings of online state estimation of National Grid’s Shrewsbury 33kV primary network.
•           Method 3: Detection of Auto-recloser Operations
• ­   This report summarises the analysis and evaluation of the auto-recloser detection method and quantification of short interruptions by the OHL Power Pointer solution. Individual auto-reclosing circuit breaker operations were quantified in response to attempts to clear faults on the network. The quantification of short interruptions has been presented, with minor software development work required to deliver a robust function.

          Method 4: Directional Fault Detection

• ­   This report summarises the analysis and evaluation of the directional fault detection method recorded by the OHL Power Pointer solution. The direction of fault passage is presented for several fault events observed on the network. Backfeeding into faults from synchronous embedded generation was not observed.

          Method 5: Conductor Temperature Monitoring

• ­   This report summarises the analysis and evaluation of the real-time conductor temperature data recorded by the OHL Power Pointer solution. The report also documents the development, implementation and evaluation of a short-term post-fault rating algorithm which demonstrates the safe ’10-minute’ uplift in conductor capacity along higher-voltage distribution circuits.

Documents 

•           Draft Standard Technique relating to the ‘Installation & Maintenance of Overhead Line Monitoring Devices’.
•           Draft Standard Technique relating to the ‘Operation & Control of Overhead Line Monitoring Devices’.

Systems

•  Automated software for performing online state estimation (and load flow) simulations to provide visibility of directional power flows through circuits, integrated into Nortech’s iHost platform.
•           Automated software for the derivation and application of a short-term post-fault rating for OHL conductors based on real-time conductor temperature measurements, integrated into National Grid’s iHost platform.

Processes

•           Process for the installation and commissioning of the OHL Power Pointer solution as defined by the Standard Technique.
•           Process for the installation of monitoring equipment on live OHLs as defined by an amendment to C5 of Standard Technique OH7F/6 – Live Line Techniques for Hot Stick Working, Groups C & D.

Presentations & Dissemination Events

•           CIGRE UK webinar on project findings
•           Internal stakeholder engagement workshop on project findings
•           Regional IET webinar on project findings

Lessons Learnt

Specification preparation 

•          Functional specifications have been developed for the OHL Power Pointer solution that can be adopted by Distribution System Operators (DSOs) to procure suitable solutions for OHL monitoring.
•           Whilst the functionality of the Smart Navigator 2.0 meets present requirements for network operators, the functional specification provides details of the parameters that are reported in real-time.
•           The report also details thresholds for overcurrent detection, earth fault detection and parameters for power flow direction which is derived from the phase angle between monitored voltage reference and the phase current

Installation of OHL monitoring equipment

•           Original guidance for installation of OHL monitoring equipment recommended that the master unit was installed on the central phase conductor, to maintain equal distance for local comms to the satellite units. The master unit consumes the most power, as it contains a modem to support remote communications. During the test trials, it was often found that the central phase conductor carried the lowest current, as radial tappings are normally taken from the outer phases of the main circuit. Consequently, the power harvesting from the central phase was less effective. There was no degradation in performance of the local communications between the master and satellites when the master was moved to the outer phase, therefore the guidance for installation of equipment on 11kV circuits was updated to install the master unit on the outer phase of 11kV circuits.
•           The installation of OHL monitoring equipment should always be undertaken in accordance with the relevant policies. This section documents the learning from the installation of OHL monitoring equipment in preparation for the field trials.
• ­   11kV OHL circuits (wood pole) – it was most efficient to install equipment using live-line techniques and with telescopic rods. Access to the installation location on foot. A vehicle (e.g. Unimog) caused inconvenience to landowners and was not required. Installations on 11kV circuits did not require significant planning effort.
• ­   33kV & 66kV OHL circuits (wood pole) – using live-line techniques with circuit dead. Equipment was installed using telescopic rods with the occasional support of vehicle (e.g. Unimog) where phase conductors were above 10m from the ground. Installations on 33kV circuits required significant planning effort.
• ­   132kV OHL circuits (tower structures) – installed under outage using hot sticks installed within reach of the tower structure. Installations were planned during pre-planned outages for routine maintenance (e.g. tower painting). Installations on 132kV circuits did not require significant planning effort.

Location of OHL monitoring equipment

•  Further use cases for the OHL Power Pointer monitoring solution have been identified, including equipping telecontrol-enabled equipment with the OHL Power Pointer solution for remote FPI visibility and confirmation of successful close operation. One example being Automatic Sectionalising Links which open during the dead-time of a recloser, but do not always restore successfully on each phase. The use of the OHL Power Pointer would identify which of the phases have been successfully restored and would be able to inform control of any equipment mal-operation…

Directional Power Flow Detection

•  Smart Navigator 2.0 sensors have been proven to be a reliable solution for sensing power flow direction without the requirement for a solidly earthed voltage reference.
•           The phase angle between current and voltage must be measured to determine the direction of power flow through a conductor. The Smart Navigator 2.0 uses a capacitive divider to monitor the voltage, with a cage around the sensor acting as a neutral, which negates the need for a bonded reference to earth.
•           It is also worth noting that the detection of power flow direction is reliant on the installation of the Smart Navigator 2.0 sensors being installed and commissioned correctly. The orientation of the OHL monitors and their uniformity is essential.
•           Independent directional power flow monitoring using the OHL Power Pointer devices has demonstrated how substation sensors that record real power flowing through circuits are not always installed with correct polarity, i.e. in accordance with the convention given in ST: TP6F/1.

Directional power flow state estimation

•           The direction of power flows under both normal network running arrangements, and abnormal running arrangements, was demonstrated successfully.

Conductor temperature monitoring

•           A correlation between the high loading of a conductor (>80% of seasonal static thermal rating) and conductor temperature was observed during the field trials.

Short-term post-fault ratings

•           By monitoring the conductor temperature using the OHL sensors, we are able to assess in real time the impact of increased loading and ambient temperature on the conductor. This has enabled a potential uplift in thermal ratings which often exceeds the static seasonal (probabilistic) ratings in some OHL circuits. This means that by monitoring conductor temperature in real time, we can increase capacity on our network without reinforcement. We can also develop (short-term) post fault ratings which would enable ANM (Active Network Management) schemes to reduce the amount of curtailed generation. The creation of (short-term) post fault ratings may allow more low carbon generation to be connected to our network without costly reinforcement.

Improved supply restoration response time using directional FPI

•  A previous ENWL innovation project recommended average savings of 20 minutes per fault incident by utilising FPIs on OHL circuits. The integration of the OHL Power Pointer solution into the Network Management System (NMS) has not yet been fully completed so it has not been possible to confirm the savings to be made using FPI. However, remote interrogation of the OHL Power Pointer solution was used to determine the fault classification (e.g. phase-to-phase, single phase-to-ground) and assisted field teams with fault location (e.g. distribution transformer, underground cable failure).
•   Customers Minutes Lost (CMLs) were saved with directional fault detection at a trial location on the 11kV network in the Stoke region. Overhead lines teams were notified of a loss of supply on an 11kV feeder and could not locate the fault without mobilising several field teams. The project team was contacted by one of the field team’s support with information from the OHL Power Pointer monitoring solution. The project team were able to determine that the fault was a phase to earth fault and able to confirm the direction of the fault along the circuit from the trial location. Field teams were able to quickly identify the fault location (a transformer installed on radial spur), the fault was isolated and customers were quickly restored to supply. This event occurred prior to the integration of the solution into the NMS.
•   the learning from the project has been incorporated into the planning and delivery of two ensuing Network Innovation Allowance (NIA) projects:
• ­   Pre-Fix (developing a HV pre-fault intervention capability that can be managed at scale), and;
• ­   Running Cool (developing the application of short-term post-fault ratings for use in ANM schemes)