Cable RedundancyAnalysisNorthumbria University StudentProjectFeb 2021Page 2 of 3 © Kinewell Energy LtdFeb 2021Cable Redundancy AnalysisProject Brief (CONFIDENTIAL)1 Project Background / Introduction1.1 General information about KLOCKinewell Energy has developed the software package, Kinewell Layout Optimisation of Cable (KLOC),which optimises offshore windfarm inter-array cable layouts which enables cost savings in the regionof 20% of the cable system capital cost over the operational lifetime of the system. The software wasHighly Commended at the 2016 Innovation Awards of the Institute of Engineering and Technology(IET) in two categories; Power and Model Based Engineering.1.2 Background informationKLOC’s inter array cable layouts are currently based on two network orientations:• Radial. The substation is connected to wind turbines via cables consecutively (below, left).• Branched. The substation is connected to wind turbines via cables which may branch off andconnect to other turbines (below, right).Over the operational lifetime of the wind farms, some cables will likely fail. This could be due to anynumber of potential reasons, for example a shipping anchor might snag on a cable causing it to ripup. When a cable fails, which could be any cable in any location, circuit breakers will isolate the faultto protect the connected equipment. The number of turbines removed from service due to the faultwill depend on the location and type of isolation. When a turbine is removed from service, its energygeneration stops causing a loss in revenue for the operator and should be minimised.The typical protection philosophy used by the industry at present is:• On fault detection, the circuit breaker at the substation trips isolating the entire string• Engineers visit the wind farm, and manually isolate the fault through an isolator within theturbine immediately prior to the fault. This allows the turbines closest to the substation tobe returned to service while awaiting a full cable repair• Engineers visit the wind farm to repair the faulted cable. This allows the full string ofturbines to be brought back into servicePage 3 of 3 © Kinewell Energy LtdFeb 2021Cable Redundancy AnalysisProject Brief (CONFIDENTIAL)Both visits to the wind farm take time and are not immediate; the right people, equipment andvessels must be organised and deployed within a suitable weather window. During this time, energythat would otherwise be generated and sold, is lost, causing reduced revenue to the operator. Thesereduced revenues are the Unavailability Losses.Unavailability losses can be minimised by:1) reducing the time to isolate the fault2) reducing the number of turbines isolated when a fault occursReducing the number of turbines isolated could be achieved by using ‘redundant cables’ that linkdifferent strings together. Some wind farms do make use of redundant cables at the ends of radialstrings to create ‘loops’. The cost of these connections rarely makes economic sense on an energyexport perspective and are there for insurance purposes so that the turbine monitoring systemsremain in service (without needing emergency diesel generators). They are operated ‘normally open’and thus under normal operation the loop is disconnected making the network electrically the sameas a radial network.As the industry moves to larger turbines the unavailability losses resulting from a cable failure willalso get larger. This might make it economical to consider redundant cables for energy exportpurposes.The costs of installing redundant cables are well understood, and do not need to be consideredfurther. The benefits of redundant cables, however, is complex and dependent on many interrelated considerations:• What are the different conceptual ways that redundant cables could link multiple stringstogether? Should the links always be at the end of the string? Should there be only oneredundant link per string?• What the different ways the protection can be set-up, and how does this impact what is inand out of service during the fault and repair cycle for each of the different ways redundantcables could be configured?• How might the power flows change from the normal operation configuration to enableincreased exports under fault conditions for each protection set-up and redundant cableconfiguration?• In a fault condition, the rerouted network might mean more turbines connected to a stringthan it is designed for:o Will the turbines need to be operated at reduced power to maintain cable thermalampacity limits?o Should all the turbines have their power reduced by the same amount or bydiffering amounts?o Should larger cables with higher thermal ampacity limits be selected?Northumbria students will focus on understanding the benefits of redundant cables with the aim ofanswering the previous questions.
