Abstract- Nowadays, Offshore Wind Energy have more attention due to its advantages such as, speed is high, nolimitation of area for construction, environmental friendly and high stability, on the other hand high reactive powergenerated in the submarine cables for long distance, which mad the transmitting of the generated power fromoffshore to onshore grid is a challenge. The regulation of reactive power and voltage control must comply with gridcode requirements. The main objective of this paper is to study some of this challenges, when using High VoltageAlternating Current (HVAC) transmission from offshore grid to onshore grid. The focus will be on two issues,reactive power and voltage control in steady state operation. Static Synchronous Compensator (STATCOM) hadbeen implemented to solve these issues. In this paper proportional and integral (PI) controllers is tuning forSTATCOM to use for reactive power compensation and voltage control. To investigate the influence of STATCOMon the system, a simulation model of a system consists of offshore wind farm connected to the grid through longsubmarine HVAC transmission cable had been developed by MATLAB Simulink. The results are obtained with andwithout considering STATCOM effect. The simulation results show the beneficial operation of STATCOM with PIcontrollers for long distance HVAC submarine cable.KEY WORDSOffshore Wind Energy, Reactive Power control, Voltage Control, STATCOM, DFIG, PI ControllersI. IntroductionWind energy is a leading source of renewable energy resources 12. The offshore wind farms are rapidlygrowing in the last years, which illustrated in Figure 1, due to the decrease of onshore available area and also thegreat advantages of offshore wind resources 345. As the number of offshore wind farms have increased ininstallation, many challenges appeared in transmitting the generated power from offshore to onshore grid. Reactivepower and voltage control are the big challenge when transmitting the produced power to the utility for longdistance of submarine cables 6. Doubly fed induction generators (DFIG) is the most commonly used in offshorewind parks, due to the several advantages comparing with the singly-fed generators, DFIG can work in variablespeed of wind energy. This means that it can work when the speed is up to 30% over the synchronous speed, anddown to -30% of the synchronous speed 7. For any changes of system frequency, DFIG has no direct effect likesynchronous generators and singly-fed induction generators, also it can give high power quality features 8. Theinterface between the generated power and the grid is a must, as the produced power changed according to thechange of wind speed and high harmonics in voltage and current, so three phase AC/DC/AC converter is applied inthe system 9 10 11. Currently there are two methods for transmitting the generated power to the point ofcoupling in the onshore grid. First method, HVAC transmission cable, Second method, high voltage direct current(HVDC) 12 13. For HVDC interconnections, there are two available technologies: line commutated converterbased HVDC (HVDC-LCC) and voltage source converter based HVDC (HVDC-VSC).In this paper HVAC transmission cable is applied to transmit the generated power from offshore grid to onshore grid6. Transmitting the generated power with HVAC transmission submarine cable has more features compared withHVDC transmission. It gives ease of maintenance, installation, reliability of operation and low cost 14. Somedrawbacks like limitation for power transmission, due to the charging current on cable, which will make limitationof long distance 15. To overcome of this problem, the compensation should be applied for long distance oftransmission submarine cable. The interface of offshore wind parks with the onshore grid must meet therequirements of the grid, which is defined with the grid code requirement 16 17. Power electronics devices playan important role in solving the problem of the generated reactive power during transmitting the power to theonshore grid. Flexible Alternating Current Transmission Systems (FACTS), which is defined as a power electronicbased system and other static equipment that provide control of one or more AC transmission system parameters toenhance controllability and increase power transfer capability, there are two methods of compensation, seriescompensator FACTS, shunt compensator FACTS like Static Var Compensator (SVC) 6, and Static SynchronousCompensator (STATCOM) 18. In this paper we will focus on shunt compensation FACTS using STATCOM 19.STATCOM acts as a source of reactive power injection (STATCOM capacitive) when the system voltage is low,and acts as a source of reactive power consumption (STATCOM inductive) when the system voltage is high 2021 22.In this paper tuning PI controller is applied in STATCOM to show the best control of reactive power compensationand voltage control into the grid.