Reliable operation of synchronous generators during grid faults

The increase in volatile generation and large‐scale energy wheeling leads to a highly loaded transmission system. Due to the decrease in thermal production and especially caused by the shutdown of many nuclear power plants in Germany situations arose where the voltages in the transmission system dropped to very low levels during the last year. In order to bring the system voltage back to normal levels reactive power must be fed and  consequently the transmission system operators (TSOs) instruct the power stations to produce more reactive power. However, a severe voltage drop can cause power plants to disconnect from the grid which could trigger cascading effects and voltage collapse. So it is in the best interest of the TSOs to prevent any unnecessary disconnection of power plants during a contingency.At the moment the TSOs cannot predict determined cascading outages of power plants due to out‐of‐tolerance grid voltages in their online security assessment. Therefore it is not detectable if the system is close to such a situation. But there is a growing need to be able to evaluate the situation in the control rooms.

In the course of the research project the following targets are being pursued:

• Analysis of options to guarantee a reliable operation of synchronous generators during grid contingencies.
• Definition of criteria that prevent power plants from unnecessarily disconnecting fromthe grid.
• Specification of requirements for a tool that is suited to observe these criteria as part of
  the online security assessment
  
  

To realistically describe the controls and limitations in the grid advanced steady‐state models are defined compared to those typically applied in power flow analysis. It will be analyzed how these models can be implemented in power‐flow programs. Furthermore simple criteria for use in the control center will be created, preventing synchronous generators to disconnect needlessly from the grid during situations with conceptual grid contingencies. To verify the defined criteria and to test the advanced power station models extensive Contingency Analysis calculations will be performed. Based on the gained findings
the state of the art control and protection schemes will be critically discussed. Furthermore the specifications for a tool to observe the defined criteria as part of the online security assessment will be developed.

M. Sc. Hendrik Acker