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Power System Stability Case Study

 Powersys performed in 2016 a power system study for an electrical utility located in Central Africa. Following a first study performed in 2013 where some weaknesses and instabilities were highlighted, investments were made during the last few years to strengthen their system: production increase, new transmission lines, new substations, and improved reactive compensation. The aim of the study conducted by Powersys in 2016 was to validate through simulation the improvement of the power system reliability and to forecast future system performance.

 

In particular, Powersys was asked to:
   - Update and validate the simulation model of the power system to take into account the new configuration and equipment,
   - Perform load-flow and dynamic studies,
   - Update the voltage plan.

 

All the relevant aspects of the model are considered: generators (including regulation), loads, transformers, lines, cables, and capacitor banks. Static loads (essentially residential) are aggregated per feeder. Protection relays are not modeled in details but the frequency and voltage variations are compared with the relays’ settings.

 

Two system configurations are analyzed: when the load level is minimum and when it’s maximum.
For each configuration, a load-flow is performed on the nominal network and on the N-1 contingency cases (due to equipment failure or maintenance) and the voltages and power flows are compared with the limits recommended by the utility. A dynamic study is also performed for each configuration. It consists in simulating the power system after a short circuit or after a generator failure. The exact list of events to investigate was discussed and validated with the utility.

 

Some unstable and out-of-the-limits cases are identified and load-shedding scenarios are proposed to mitigate them. The study is repeated with a total load increase of 7% which correspond to the utility forecast for the next year.

 

The study demonstrated that the global reliability of the system is drastically improved thanks to the new transmission lines and generators. As the transmission power system is now more meshed, the list of contingencies leading to unstable scenario is reduced, even in the case of a load increase.