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Power Delivery Systems: Transmission and Distribution
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
The converter station can also be operated in a reverse fashion to invert a DC input to an AC output with the same thyristor valve circuits used for rectification. With a DC input, the output of a thyristor valve is a square wave. With commutating circuit components, a simple thyristor bridge is made to produce an alternating square wave. The use of 6-pulse and 12-pulse designs yields a more trapezoidal-shaped alternating waveform that is the result of summing the square wave outputs of the various thyristor valves (which are fired in time sequence stages). This output consists of the fundamental frequency (e.g., 60 Hz) plus harmonics, the content of which depends on the number of valves utilized in the converter station. AC filters are used to absorb the harmonic currents. The resulting AC output current leads the voltage, and thus the converter requires compensating reactive power.
DC Transmission
Published in Amitava Sil, Saikat Maity, Industrial Power Systems, 2022
Principles of HVDC transmission system is shown in Figure 14.1. In the HVDC station, the converter transformer steps up the generated AC voltages to the required level. The converter station rectifies AC to DC, which is then transmitted through overhead lines (or cables). At the receiving end of the converter station, an inverter converts the DC voltage back to AC, which is stepped down to the distribution voltage levels at various consumer ends.
The Smart Grid Concept
Published in Francisco C. De La Rosa, Harmonics, Power Systems, and Smart Grids, 2017
Converter stations usually include converter transformers, thyristor valves, smoothing reactors, AC filters, and DC filters. The so-called light HVDC version8 replaces the line commutated thyristor valves with self-commutated IGBT valves. Among other advantages, it further offers independent power transfer and voltage control, low power operation, power reversal, reduced power losses and increased transfer capacity.
Integrated floating method based on four-bucket jacket foundation for offshore substations and converter stations
Published in Ships and Offshore Structures, 2023
Yaohua Guo, Yue Zhao, Shengxiao Zhao, Haijun Wang, Jijian Lian
However, the large-scale development of offshore wind farms is facing the problem of long-distance power transmission. In general, the capacity of a single offshore wind farm is between 200 and 300 MW. When its distance to the shore is longer than 15 km, it is necessary to set up an offshore substation, where current is boosted and transported to the shore through AC power transmission. Once the distance exceeds 80 km, problems related to high-voltage AC transmission in terms of voltage, frequency, and loss become more severe. In this case, the flexible high voltage direct current (HVDC) technology is required (Warnock et al. 2019; MacIver et al. 2016), with which the AC power generated by offshore wind turbines is boosted by the offshore substation and then collected by the offshore converter station. After being commutated, the power is sent to the onshore converter station as DC current via a submarine cable. Finally, it is merged into the AC grid through the inverter (Figure 1(a)) (Alstom 2014). It is clear that both modes require an offshore AC substation. However, HVDC is still a novel technical solution for integrating the substation with the converter station or only retaining the converter station (Figure 1(b)) (GE 2020; GE 2021; TenneT 2018a).