Consulting Stories Part. IV

 

A solar panel manufacturer contacted our engineering office to carry a study concerning the implementation of a PV plant on Transmission system in Africa. The main concern was the effect of this new solar plant on Power System stability and harmonic production.

 

Modelling

 

Powersys began by modelling the industrial Power System where the solar plant will be connected. In order to provide the most realistic results as possible, the accuracy of the model was a major concern. The solar plant model took into account all V-I curves with dependences on irradiance and temperature. The model even included the relation between connection bus voltage and produced reactive power. Various protections were integrated to the model. These protections concerned several types of electrical parameters and had different temporizations

Powersys Engineering Team had to face a lack of data. Typical values were proposed and used with the agreement of the client.

 

Figure 1 Power system single-line diagram

 

Simulation of Impacting events

 

Powersys simulated several stressful events for the stability of the system consisting in:

  • Instantaneous modifications of the load,
  • Instantaneous modifications of the production,
  • Instantaneous connection/disconnection of solar plant

A fault analysis was then realized. This study began by identifying buses where the occurrence of a fault could have a major impact on Power System. To cover a wide range of possible faults, the occurrence of three-phase and one-phase fault was simulated on two critical buses.

In each case, Powersys carefully examined the evolution of main buses voltages and frequency.

Some events could provoke the triggering of a protection at National Power System connection level. Nonetheless, our engineering team concluded that no stability problem was likely to happen

Figure 2 Voltage evolution in time

 

Evaluation of harmonic emissions

 

Then, Powersys carried a harmonic study. The question we had to answered was whether the harmonics the solar panel injects on Power network at the connection bus of solar plant and at the Point of Common Coupling will violate standard limitations. To ensure all cases are considered, two analyses were carried: with maximal solar plant production and with reduced solar plant production.

Powersys determined that in both configurations (maximal power and reduced power) harmonic production remains far below limits of IEEE 519-2014. It was then concluded that no mitigation issue was recommended.

Figure 3 Current harmonics at PCC level

 

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