978-1-7281-1078-3/20/$31.00 ©2020 Crown IEEE Optimization Modeling for Offshore Wind Farms Siti Khadijah Hamzah Sch. of Computing, Eng & Digital Technologies Teesside University Middlesbrough, UK Gill Lacey Sch. of Computing, Eng & Digital Technologies Teesside University Middlesbrough, UK g.lacey@tees.ac.uk Gobind Pillai Sch. of Computing, Eng & Digital Technologies Teesside University Middlesbrough, UK Abstract— Offshore wind farms have emerged as the biggest contributor of renewable energy to the national grid over the last decade, driven by advanced technology, higher investment, and lowering operational and maintenance costs. This demonstrates the value of improving the efficiency in wind farms, with designs to be selected for the most effective transmission system implementation. This paper describes the simulation models developed with network simulation software (IPSA and PowerWorld) for evaluating and analyzing the load flow by observing the losses, voltage magnitude and transmitted power, both active and reactive. There were three different models, one using standard inter-array cable (33 kV) and one with upgrade inter-array cable to 52 kV. The third model proposed replacing high voltage side transformers with a mechanically switched capacitor (MSC) rather than the usual static Var compensator. Results from 52 kV models revealed that high voltage cable in offshore wind farms is capable of transmitting more active power than medium voltage. Indeed, the losses in this design are in the range of theoretical value in between 0.3% and 11%. The MSC losses agreed using a value of 1.7%. the results of the third model showed that static Var produced more active power than mechanically switched capacitor. At the same time, the static Var produced the highest reactive power at export cable. Although the static Var models have performed better than mechanically switched capacitors, in terms of monetary value mechanically switched capacitors are better than static Var compensators. The parameters of the design were given by Siemens, where their supplier confirmed that initial costs including operation and maintenance cost for mechanically switched capacitor are lower compared to the transformer. Keywords—Offshore wind farm, 52 kV, mechanically switched capacitor, static Var compensator. I. INTRODUCTION The rapid development of wind power globally has led to increased focus on wind energy in many countries [1]. The global scale of wind energy grew by $24.8 billion reflecting an increase of 35% from 2010 to 2018 [2]. As reported by [2], wind power in offshore is gaining prominence and demonstrates a steady state rise over 11 years from 2019 onwards relative to other renewable sources. Offshore wind power currently accounts for 4.26% of global cumulative capacity. Wind power plants have been seen as a crucial element of sustainable energy policies, meeting green-house gas emissions goals and enhancing future power stability [3]. Today, several countries across the world are anticipated to develop higher rates of penetration as renewable energy is considered a safe, clean, sustainable alternative to traditional energy sources, and a stimulating economic choice in locations with sufficient wind resource. In other ways, the integration of high wind power penetration rates (>30%) across huge international, integrated electrical systems entail a step by step restructuring of the current electrical system and operation strategies. Indeed, it is more likely to be a financial problem rather a technical one. This integration of substantial wind power penetration rates is not only feasible but does not necessitate a lot of restructure of the current power grid. A designer of a wind plant must balance the benefit gained from reduced losses, and imposed availability against the corresponding cost of capital required to achieve such improvements [4]. This paper aims to compare three different methods of taking wind generation from offshore Wind Farms to onshore grid connection using network modelling software to indicate the effect on power quality and losses of each system. This will inform the developer of the wind farm as to the most efficient way to transmit the generated power. II. REACTIVE POWER COMPENSATION A Reactive Power Compensation (RPC) device is required to reduce the reactive power in order to enhance the efficiency of network power systems. Besides that, it also improves the stability of the system by raising the maximum active power which could be transferred to the transmission system [5]. Capacitors and inductor (or reactors) are static devices because they have no active control of the reactive power output in response to the system voltage. They just supply and consume static reactive power. Meanwhile, Flexible AC Transmission Systems (FACTS) including static Var compensators (SVC) and static compensators (STATCOM) are categories of dynamic reactive power devices. They have the capability to change their output based on pre-set limits in response to the changing system voltages. [6]. A. Mechanically Switched Capacitor Mechanically Switched Capacitor (MSC) is the most economical RPC device with simple design low speed resolution for voltage control and grid stabilization under heavy load conditions. They have little or no effect on short- circuit power, but they increase the voltage at the point of connection [7]. MSC is helpful for voltage stability by allowing the local generator to operate close to unity power factor. As a result, it maximizes fast acting reactive reserve [8]. The advantage of MSCs is that they can improve the performance, quality and efficiency of electrical systems, minimize power losses, improve the cost effective system, improve the power factor of the line, increase the active power transmission capacity and transient stability margin, attain effective voltage control and damp power oscillation [9]. MSC switching is limited to 2,000 – 5,000 cycles before the switch must be changed, limiting the use of the MSC because the required level of reactive power (var) compensation changes gradually. As MSC has lower losses, they preferred applications that consistently require capacitive injection [10]. brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Teeside University's Research Repository