The operating conditions of many distributed power generation plants (e.g. sugar mill cogeneration plants) sometimes require different capabilities of governor and excitation controllers when compared to that of traditional base loaded power stations. This is particularly true for distributed generation that forms some part of an industrial power system and have different performance requirements to distributed generation that are solely power producers.
In addition to the regular tasks of controlling desired power and voltage set-points the control systems for these plants must be able to:
- Isolate the generation plant from the network for network events such as short circuits or loss of supply while maintaining electricity supply for the industrial load (islanding).
- Be able to operate in continuous isochronous (island) mode while maintaining the industrial load.
- Maintain synchronism on weak rural transmission systems which may experience line to ground faults (with associated re-closer operation) and wide voltage variations.
- Maintain a range of controller tuning parameters (e.g., multiple PID groups) depending on network conditions provided by the network operator. Synchronise and load share with generators of various types and sizes within an islanded system (such as a large sugar mill or pulp and paper plant).
As with any electrical installation, system studies are generally carried out beforehand to review the desired operating scenario and typically analysis would include:
- Load flow
- Fault levels
- Protection co-ordination
The stability analysis in particular can be a useful tool in determining the likely dynamic behaviour of the generating plant in response to various scenarios, which may include:
- Network faults of various magnitudes
- Islanding at full load (load rejection)
- Sudden increase or decrease in load
- Dynamic modelling
- Excitation system modelling
- Excitation design reports