Modeling and Mitigation for High Frequency Switching Transients Due to Energization in Offshore Wind Farms

Abstract

This paper presents a comprehensive investigation on high frequency (HF) switching transients due to energization of vacuum circuit breakers (VCBs) in offshore wind farms (OWFs). This research not only concerns the modeling of main components in collector grids of an OWF for transient analysis (including VCBs, wind turbine transformers (WTTs), submarine cables), but also compares the effectiveness between several mainstream switching overvoltage (SOV) protection methods and a new mitigation method called smart choke. In order to accurately reproduce such HF switching transients considering the current chopping, dielectric strength (DS) recovery capability and HF quenching capability of VCBs, three models are developed, i.e., a user-defined VCB model, a HF transformer terminal model and a three-core (TC) frequency dependent model of submarine cables, which are validated through simulations and compared with measurements. Based on the above models and a real OWF configuration, a simulation model is built and several typical switching transient cases are investigated to analyze the switching transient process and phenomena. Subsequently, according to the characteristics of overvoltages, appropriate parameters of SOV mitigation methods are determined to improve their effectiveness. Simulation results indicate that the user-defined VCB model can satisfactorily simulate prestrikes and the proposed component models display HF characteristics, which are consistent with onsite measurement behaviors. Moreover, the employed protection methods can suppress induced SOVs, which have a steep front, a high oscillation frequency and a high amplitude, among which the smart choke presents a preferable HF damping effect.

Impact Factor Identification for Switching Overvoltage in an Offshore Wind Farm by Analyzing Multiple Ignition Transients

“…The test results show that severe HF SOVs are induced on T G , when VCB G is switched off while WTG is connected. Thus, to reveal the mechanism for the occurrence of SOV in this scenario, and investigate the impact of system configurations on SOV, such as the length of submarine cable [13], the topology of the collector system [14], the setting of reactive power compensation capacity [15], and the arcing characteristic of VCB [16], a HF simulation model for an OWF is built in PSCAD/EMTDC. In the developed model, the voltage source is replaced by an ideal power grid with an infinite capacity.…”

“…The parameters of the three-core submarine cable are set according to the actual geometric structure of the cable used in tests. The HF model of T G is designed with the method in [14], in which the inter-phase stray capacitance and the phase-to-ground capacitance under the HF state are considered. The solution time step in PSCAD is set 0.5 µs, and it is small enough to calculate SOVs, in which the HF component is around dozens of kilohertz.…”

“…According to the parameters of cable (Fig. 3) and the recommended value in [14], C = C C +C T = 0.15 nF m×80 m+3 nF = 15 nF. To verify the relationship of (3), namely whether the impact of the HF current and the total phase-to-ground capacitance on the steepness of SOV is in accordance with the relationship in (3), the SOV and HF current in phase A/B during ten ignitions are calculated in Fig.…”

Study on Transient Overvoltage of Offshore Wind Farm Considering Different Electrical Characteristics of Vacuum Circuit Breaker

“…The HF current starts with a high rate of change that the VCB cannot turn off. However, with the attenuation of HF current, when the di/dt is less than a critical value when the current is crossing zero, the VCB will cut off HF current and turn it into a disconnected state, which is generally between 100-600 A/µs [24].…”

Analysis of Switching Transients during Energization in Large Offshore Wind Farms

“…It was found that the simulation results can be improved greatly if an appropriate VCB model was included in PSCAD, whereas little improvement was found in DigSILENT. Based on the above discoveries, the authors of [9][10][11][12][13] used a PSCAD/EMTDC simulation to calculate TOVs when VCBs were operated in different configurations, and the results showed that TOVs were affected by many factors, such as the operating scenarios of OWFs, the transformer locations, the cable length, and the wave propagations in the cables.…”