Managing Director, HVPD Ltd Combined Power Quality and Condition Monitoring of Offshore HV Cable Networks EWEA 2013 6th February 2013 Presented by: Dr Lee Renforth Managing Director, HVPD Ltd lee.renforth@hvpd.co.uk

Key Messages  to achieve this The UK offshore wind farm industry has (to date) suffered a higher-than-expected number of medium voltage (MV) and high voltage (HV) cable faults. MV and HV cable faults presently make up over 80% of UK offshore wind farm insurance claims with many faults occurring during the construction phase. The UK Government (DECC) have stated that they require the (presently high) Capital, Operational and Maintenance Costs to fall by 25%* by 2020 to make this offshore renewables electricity more affordable to the UK consumer It is argued that a radical rethink of existing offshore HV network asset management practices is needed to achieve this through the use with of ‘holistic’ condition monitoring (CM) solutions. *(DECC) Levelised Cost of Electricity (LCOE) model predicts the total cost over the 20-year lifetime of the asset.

A Proposal for a ‘Holistic’ Subsea HV Cable Network Condition Monitoring System Illustration of a typical ‘Round 2’ (500MW+) UK Offshore Wind Farm MV & HV Network. 33kV inter-array cables from the turbine arrays feed back to the offshore 33/132kV GIS substation and then, via 132kV land-sea export HV cables, back to the grid connection onshore.

Offshore Wind Farm ‘Holistic’ Subsea MV & HV Cable Monitoring System Main hubs in the 132kV onshore and offshore substations. Remote monitor units located at strategic locations within the 33kV cable array. The monitor system provides an ‘early warning’ system to detect ‘incipient’ HV insulation faults. Can be used to direct preventative maintenance activity to avoid unplanned outages.

Wind Turbine ‘Holistic’ Electrical Monitoring Solution Concept ‘Quadplex’ SMART sensors are used that are suitable for wideband electrical measurements (0-100 MHz) to detect: On-line Partial Discharge (OLPD) Transient Earth Faults (TEF) Transient Voltage Monitoring (TVM) Power Quality Monitoring (PQM) Voltage & Current Monitoring (V/A) Current Signature Analysis (CSA)

On-line Partial Discharge Sensing Techniques and Measurement Systems Inductive High Frequency Current Transformers (HFCT) – to detect partial discharge in cables and remote plant. Capacitive Transient Earth Voltage sensors (TEV) – to detect ‘local’ PD activity. By combining these two sensors, good sensitivity to different types of PD can be obtained. TEV HFCT

A ‘Round 1’ 90MW Offshore UK Wind Farm Case Study 1 OLPD Cable Testing, Location, Monitoring with Preventative Maintenance on a 33kV Land-Sea Wind Farm Export Cable The weak points on a land-sea MV/HV export cable susceptible to failure from partial discharge (PD) A ‘Round 1’ 90MW Offshore UK Wind Farm

Case Study 1: 33kV Wind Farm Export Cable – OLPD Test and Mapping Data High levels of PD (of up to 10,000pC/10nC) measured on Circuit B, Phase L3. Cable mapping (location) tests identified the source at Joint 7, 800m out on Phase L3 of Circuit B. Due to the high level of PD activity and the high risk of failure, a cable repair project was instigated. L1 L2 L3

Case Study 1: 33kV Wind Farm Export Cables High PD Detected on L3 PD Located 200 400 600 800 1,000 1,200 1,400 1,600 Location (meters) Lower-level sporadic PD signals from different site after joint replacement Joint with PD removed and replacement cable section installed

Case Study 1: 33kV Wind Farm Export Cable – Summary The joints on both circuits A & B were replaced at Joint Pit 7 were replaced as part of a preventative maintenance repair project. Extended OLPD monitoring after replacement, showed the high PD activity had ceased. This preventative maintenance repair during a planned maintenance outage removed the risk of failure and confirmed the cable insulation was now in a healthy state for service. Circuit A- Insufficient mastic around connector Circuit B- Defects along XLPE surface due to bad fitting heatshrink stress control

Conclusions The increasing installation rate of offshore wind farms in Europe, combined with the high MV and HV cable fault rates reported in the UK, has led to a ‘market need’ for better cable condition monitoring (CM) technology. Offshore wind farm subsea cable owners need to consider radically better power quality and ‘holistic’ condition monitoring (CM) systems to help drive down their presently (very high) operational and maintenance (O&M) costs. The purpose of any CM system is to provide an ‘early warning’ of ‘incipient’ cable faults to enable preventative maintenance to avoid unplanned outages A move towards Condition Based Management (CBM) of the MV and HV subsea cable networks (using data from ‘holistic’ CM technologies) is the key to help reduce these O&M costs over the 20-year service life of these assets).