Power systems analysis for unmanned offshore platform fed via a very long 13.8 kV submarine cable

One of Saudi Aramco´s gas exploration expansion plans consists of powering an unmanned offshore platform via a 13.8 kV submarine cable. The closest available source substation (SS) is located onshore; approximately 107 km from the platform. Power systems analyses were conducted under various loading conditions. Upon starting the 11500 HP motor, at the onshore SS, severe system voltage drops were observed. This led to a problematic voltage fluctuation at the offshore platform. The installation of a 13.8 kV shunt capacitor bank (SCB) and shunt reactor bank (SRB) at the offshore platform were initially introduced to remedy voltage control. During transient analysis, under faulty conditions adjacent to the SCB, the 13.8 kV circuit breaker (CB) will be exposed to an excessive transient recovery voltage (TRV) exceeding the limit of the 13.8 kV CB. The harmonic analysis indicated high values on the 5th, 7th and 11th harmonic voltage distortion. As a mitigation measures, the segregation of motor loads and non-motor loads at the SS eliminated the severe voltage drop. The installation of a static synchronous shunt compensator (STATCOM) at the offshore platform was also retained as it will eliminate the need for an SCB and SRB with the high TRVs and resolve the harmonic problems.