Investigation of Resonance Condition in OFF Shore Wind Park during Energization Events

Abstract

Transformer energisation in offshore High-Voltage Alternating Current (HVAC) transmission systems can result in significant transient and temporary overvoltages due to the interaction between transformer magnetising inrush currents and network resonances. A detailed Electromagnetic Transient (EMT) model comprising a Thevenin-equivalent grid, frequency-dependent cable representation, and a saturable transformer model was developed to analyse the switching behaviour of the system. Wind Turbine Transformers (WTTs) are experiencing high dielectric stress due to transients induced during energization and de-energization events in offshore wind parks. This paper investigates the energisation of WTT connected to an onshore grid through a HVAC export cable under weak-grid conditions, the resonance potential on the terminal of WTT is assessed. A black box model of a 300 kVA transformer is derived by measurement and implemented in ATP. Vector fitting is used in establishing the frequency domain model and lumped parameter RLC description of the transformer is introduced in ATP as a user specified component. More Emphasis is given on the accurate modeling of cable-transformer energization as well as cable ground fault. Finally, transients induced during switching in an array of Wind Park are simulated in ATP to identify resonance situations and transformer terminal voltages.