Requirement
Prior to the stability study described here, CAPSIM had produced power flow calculations and calculations of the short-circuit currents for the operator of an industrial electrical power grid. These calculations had been used to validate the sizing of equipment and to put in place a protection plan for the grid.
The turbine generators for that network could operate either independently or coupled to the public distribution grid and simulations were carried out for the two operating configurations. Events acting on the islanded configuration could more easily result in a grid instability because the short-circuit power of the sources was lower.
The objective of the study was to validate the protection plan put in place by CAPSIM as well as to perform a study of the dynamic behaviour of the turbine generators when subject to disruption events. The outdated nature of the generators and their excitation raised questions regarding their robustness and their effectiveness when faced with such events.
Realization
The presence of high power generators therefore led Capsim to carry out a stability study. This study was both able to validate the adjustments to the previously established protection plan (simulation of three phase and single pole short-circuits) and also to validate the stability of the grid in the event of disruptions such as :
- Start-up of an islanded high-power motor
- Load shedding by power consuming units
- Dip in voltage on connection of the public distribution grid
CAPSIM modelled a simplified version of the refinery using PSIM software. A complete version of the network was produced using ETAP for the power flow and short-circuit current calculations. The simplified PSIM version was sufficient for the phenomena studied. Nine calculation scenarios were carried out. These scenarios allowed the changes in the electromagnetic values of the network to be visualized during disruption events.
Results
The results of the study made it possible to refine the adjustment of the grid protections for optimum operation. The study has also led the operator to consider replacement of the excitation system for the generators to provide better support of the grid voltage in the event of a short-circuit in islanded configuration.
Power supplied by a turbine generator coupled to the public grid during a dip in voltage on the public distribution grid
