Requirement
For the case of energetic development in sub-Saharan Africa, the construction of a 33MWp photovoltaic power station is planned. This future power station will be connected to the national electricity transmission grid of the country. This electrical grid can be interconnected with those of 2 neighbouring countries. This grid possesses several electrical thermal and hydraulic generation power units across the country.
In this context, Capsim was sought by investors and the network operator for the following :
- Analysis of the grid stability during power injection by the future power station on the interconnected national grid. In this particular case, the intermittence of the photovoltaic power station and the weaknesses already present in the current network (low production capacity, regular power cuts and black outs) are to be considered
- Assistance in technical specification precisions to include in the tender files of the key-in-hand construction contract
- Analysis of issues regarding the extension of the power station or the integration of additional power stations into the grid.
Realization
Capsim’s project team firstly created a numerical model of the national interconnected grid of the country. This step required a member of the team to recuperate all of the necessary input data on spot. The model was constituted so as to represent the various existing grid configurations as well as the N-1 contingency cases (transformer, or transmission line failures, protection tripping).
The following analyses were then executed using the numerical model :
- Power flow and system voltage study : this helped to check the static criteria regarding the voltage on the grid as well as the sizing of the main equipment (transformers, transmission lines). Energy management strategies of this new energy source were suggested. The impact analysis of contingency scenarios with and without the presence of the PV power station helped to put forward grid stability problems in some configurations and therefore to recommend solutions (reactive power compensation, energy storage systems).
- Dynamic analysis : it consisted in analyzing the dynamic stability of the grid in islanded configuration (when the grid is not connected with those of the neighbouring countries). Indeed, in islanded mode, the PV penetration level is much higher, therefore increasing the grid instability and load-shedding risks. This analysis is based on typical scenarios regarding power fluctuations of the PV power station (rise in production, appearance of clouds). From the results obtained, new energy management strategies were suggested for the islanded configuration and the actual limits of the power stations were known.
- Short-circuit calculations : it consisted in calculating the short-circuit contributions on the new PV power station and to check the validation of the onsite equipment (busbars, cables, etc...) via the maximum short-circuit values
- Harmonic analysis : in this part, the model of harmonic pollution injected by the inverters of the PV power station was established. It was thus possible to evaluate the impact of these inverters on the voltage distortion of the network substations
ETAP model of NIG 2015
Results
This study helped the grid manager to :
- Know the impact(s) of the insertion of the 33MWp PV power station on the transmission grid for all of the possible grid operation configurations
- Identify the cases in which the static criteria regarding system voltage and frequency are not respected and bring solutions to solve these issues
- Evaluate the dynamic stability of the grid during the PV power station’s generation power fluctuations and having solutions (in terms of control system of equipment) in order to manage intermittence issue
- Check whether the impact of the short-circuit currents on the new PV grid was negligible or not
- Evaluate the impact of harmonic pollution generated by the PV grid components on the grid
CAPSIM has realised this type of study on similar projects occurring in the following countries: Chad, Niger, Togo, Ivory Coast, Burkina Faso, Mali, Ethiopia, Mozambique, Gabon, Sao Tomé, Tunisia, Algerian Etc...
