PO.ID 054 The Adoption of Best Practices for Insulation Condition Assessment and Condition Monitoring of OWF HVAC Export and MVAC Inter-array Cables: Preliminary Field Trial Results Lee Renforth Riccardo Giussani Malcolm Seltzer-Grant William Waugh HVPD HVPD HVPD Newcastle University Abstract OHVMS Prototype – Offshore Turbine System The implementation of electrical condition monitoring (CM) technology in the offshore wind farm (OWF) industry has been limited to date. There is presently no system available in the market that can effectively perform the monitoring and correlation of several electrical condition parameters to enhance the insulation condition assessment (ICA) of the network. This paper is an extension of the work published by the authors in the 2013 EWEA Offshore Conference in Nov 2013 on the importance of ‘holistic’ insulation condition monitoring (CM) and testing, both at the commissioning/acceptance phase and then into the service life of the cable networks. To further improve the CM of the cable networks in the OWF market sector, the authors present a new system (OHVMS) that is capable of monitoring the state and condition of the network. This work presents the results from the infield trial of this new technology. The system acquires and records, on a continuous basis, partial discharge (PD), power quality (PQ) and cable sheath currents (SC) data. The ongoing analysis of the data shows how correlating the effect of phenomena on differing parameters can help to increase the understanding of the real state of the systems, improving the Condition Based Management (CBM) of the assets. The data has been recorded on both 33kV inter-array cables and 132kV export cables on a number of UK offshore wind farms over a period of several months. A case study in which the system has helped to identify PD on an offshore site is reported herein. ‘Holistic’ Insulation Condition Assessment of OWF Export and Inter-array Cables – the HVPD OHVMS System Figure 2 above shows the schematic and the functionalities of an OHVMS prototype installed at an offshore wind turbine tower. The system collect simultaneously partial discharge (PD) data, power quality (PQ) data and sheath currents (SC) data from the turbine and the three interarray subsea cables connected to it. OHVMS Detection of PD on an Offshore Wind Turbine In the EWEA Offshore poster the authors highlighted the importance of carrying out electrical testing and monitoring during each phase of the lifecycle of the offshore cables network: This section reports how the OHVMS prototype helped to detect partial discharge (PD) activity on an OWF 33kV inter array network. HVAC WITHSTAND COMMISSIONING TESTS OF NEWLY INSTALLED CABLES Figure 3 below shows the extended OLPD monitoring data over 2 months recorded by the OHVMS system and Figure 4 shows the data from an online partial discharge (OLPD) diagnostic ‘spot’ test that confirmed the PD activity diagnosed by the OHVMS system. • • • Detects any poor workmanship or installation damage PD acceptance test and voltage withstand test (to 1.7 – 2.0U0), or a 24-hour soak test at U0 Off-line electrical Time Domain Reflectometry (TDR) supports future PD site localisation and/or cable fault location Figure 3: this shows the OLPD cumulative activity (top) and PD peak activity (bottom) detected over a period of two months by one of the HVPD OHVMS prototype installed on an offshore wind turbine. REPEAT ON-LINE PARTIAL DISCHARGE (OLPD) TESTING • Performed before the cable supplier/jointer warranty period expires CONTINUOUS OLPD MONITORING • • • Conducted through the service life of an asset Detects PD activity that has initiated during the service life of cable/plant Supports maintenance and operation decisions To further improve the CM of the cable network for offshore wind farms the authors presented a new CM system able to monitor and correlate several parameters. OHVMS Prototype – Onshore Grid Connection Substation Figure 4 Below shows the results of OLPD diagnostic ‘spot’ test performed on the same turbine. Respectively an example of the PD waveform detected (left) and the PRPD Pattern across the 50Hz power cycle (right) is shown, both confirming the nature of the PD. Segment Waveform 250 200 Volts (mV) 150 100 50 0 -50 -100 5 6 7 8 9 10 Time us Next Step - Combining electrical and mechanical CM Figure 5 The next generation of ‘holistic’ Condition Monitoring (CM) technology for offshore wind farm turbine array networks. will combine electrical and mechanical CM. Figure 1 above shows the schematic and the functionalities of an OHVMS prototype installed at an onshore, grid-connection substation from an offshore wind farm. The system is able to monitor partial discharge (PD) activity alongside analysing the power quality (PQ) data. Moreover the system continuously monitors the value of the sheath currents presented on the XLPE cable sheath as a function of the relative load currents. EWEA 2014, Barcelona, Spain: Europe’s Premier Wind Energy Event