GENERATOR CONTROL
Coordination of Different Generator Sets
Generator sets typically have their own primary controllers. If several of them operate jointly in an island grid, they need to be coordinated. Generation control ensures the most reliable power generation possible in industry grids containing several generator sets ? both connected to an external power utility and in island mode.
Ensuring Grid Stability
Generation control establishes evenly balanced active power that enables power demand from an external grid to be set, to keep within a maximum purchasing limit from the external grid, or to stabilize the frequency in the islanded grid. It can, however, also establish evenly balanced reactive power in order to maintain a desired power factor angle at the tie-line to an external grid or to stabilize the rated voltage of the busbars in island mode. Generation control also calculates the spinning reserve in order to ensure that there is always sufficient control capacity available.
Efficient and Convenient
Generation control is totally integrated in substation automation and runs on a central computer, with optional redundancy available. As a result, there is no need for additional devices or inputs/outputs. In addition, the same user interface is used for control and monitoring as well as for power management. This provides a very transparent means of displaying numerous parameters, for example, power flows and reserves, operating modes, individual generator sets, and entire grid areas.
LOAD SHEDDING
Power-based load shedding continuously calculates the necessary reactions to critical scenarios that could occur and is therefore prepared for all eventualities at all times. This predictive approach is used for fast load shedding as well as for blocking of large loads.
Fast Power-Based Load Shedding
Critical events ? like a disconnection from the external power utility grid or the failure of a generator in island mode ? require the fastest load shedding possible in order to limit the resulting drop in power frequency and prevent triggering of the under frequency protection. The system only sheds as much load as necessary for restoring the rated frequency.
Dynamic Power-Based Load Shedding
In stable island mode, loads change as needed by the industry process. These variations are balanced by the primary control of the on-site turbines. As the power requirement increases, the spinning reserve decreases, reducing the capability for starting big loads. Dynamic load shedding monitors the spinning reserve for a defined limit value. While it is permissible to exceed the limit for short periods, load is shed if these periods last for longer in order to restore the required reserve. In addition, in island mode large consumers are monitored while in the idle state. If the spinning reserve falls below these starting power level, a signal inhibits the start and so prevents grid overload.
Frequency-Based Load Shedding
This function is available both as an independent main function for ordinary applications and as a reserve function for fast power-based load shedding. It monitors when the frequency drops below given thresholds and sheds predefined loads as required, independent of the control system. It can function in the event of multiple faults in the grid, and also sheds loads reliably even when the central unit is disconnected.
SYNCHRONIZATION
Synchronization means connecting an energy source in parallel with many other sources that is in a live system of constant voltage and constant frequency. All the sources must have the same level output voltage and frequency. Before connecting a source into the grid, following conditions must be fulfilled:
Equal voltage: The terminal voltage level of incoming must be equal to the bus-bar voltage.
Similar frequency: The frequency of generated voltage must be equal to the frequency of the bus-bar voltage.
Phase sequence: The phase sequence of the three phases of alternator must be similar to that of the grid or bus-bars.
Phase angle: The phase angle between the generated voltage and the voltage of grid must be between setting level.
