Impact of a HVDC Link on the Reliability of the Bulk Nigerian Transmission Network

Abstract

Regular and reliable access to energy is critical to the foundations of a stable and growing economy. The Nigerian transmission network generates more electricity than is consumed but, due to unpredicted outages, customers are often left without electrical power for several hours during the year. This paper aims to assess the present reliability indices of the Nigerian transmission network, and to determine the impact of HVDCs on system reliability. In the first part of this paper, the reliability of the Nigerian transmission system is quantified by building a model in DIgSILENT PowerFactory and carrying out a reliability study based on data provided by the Nigerian transmission-system operator. Both network indices and load-point indices are evaluated, and the weakest points in the network are identified. In the second part of the paper, an HVDC model is built and integrated into the existing network at the locations identified by the reliability study. A comparative study using two different HVDC connections is then carried out, to determine the critical impact of HVDC on system reliability. The reliability results indicate that the weakest points of the transmission system are the radial feeders, and the highest impact could be achieved by spanning an HVDC line between two busbars located at the two extremes of a radial feeder: Azura and Yola.

Evaluation of a HVDC Interconnection to Improve the Voltage Stability of the Nigerian Transmission Network

“…More specifically, both PV and QV analysis indicate that Yola and Gombe are the critical buses, and these two bus bars are now considered for the HVDC connection. The power flow and reliability analysis of this network, presented in [7,22], identified these two buses as having the lowest voltage magnitude and the lowest reliability, respectively.…”

“…The network under study consists of 64 transmission lines, including 21 double circuit lines with a total length of 6575.30 km, 50 bus bars, 20 generators (two of which were out of service based on the data provided), and 22 loads. More details about the Nigerian transmission network can be found in [22], while the transmission network single-line diagram is given in Figure 2. The Nigeria Energy System Operator (NESO) supplied data for active power demand for each load and generator for both the summer and winter scenarios in 2019.…”

“…Vdc− cosϕ2/P−Q: the rectifier controls Vdc and cosϕ2 and the inverter controls P and Q. IV. Vdc−Q/P−Q: the rectifier controls Vdc, and Q, while the inverter reference output is P and Q [33] The adopted model is described more in detail in [22]. Using the control modes described above, the impact of HVDC on system stability was assessed.…”

“…N-1 contingency is a common standard for assessing the security of power systems -according to this criterion, power system should withstand any single component failure with no violations of operating constrains, while supplying all loads [36]. N-1 contingency analysis was carried out for the Nigerian power system, based on outage data used in a previous work [22].…”

“…Given the decreasing costs of HVDC technology, this may be a viable solution to replace transmission lines. The impact of HVDC on voltage profile and reliability indices has been addressed in [7] and [22], respectively. To the Authors' knowledge, this is the first work where the impact of HVDC connections on the Nigerian Transmission system is studied in detail.…”