Requirement
The French law of 23 April 2008, which specifies the conditions for connecting generating units to the public distribution grid, changed the requirements relating to disrupted voltage regimes on public grids.
Under certain conditions, the electricity producer must now leave its generating unit connected during fluctuations in frequency and voltage on the grid, where as previously it had been requested to uncouple the generator in such situations.
This part of the law applies to all generating units greater than 5 MW and may also apply to new installations with a modified existing installation or with installations for which the energy repurchasing contract comes to an end.
Article 14 sets a voltage dip profile at the point of delivery which must be tolerated without decoupling by the generating unit:
Voltage dip profile from article 14 of the law of April 2008
Our client wished to study the possible impact of this voltage dip on its equipment and, in particular, the risk of instability and loss of synchronization on the generator.
Realization
CAPSIM used PSIM to model gas turbines and their speed control as well as generators and their excitation control, in order to simulate the behaviour of cogeneration power plants during the appearance of voltage dips on the HVA network.
The simulation was able to analyze the sensitivity of the following parameters :
- The power of short-circuits at the connection point
- The characteristics of the generators
- The excitation systems
- The dynamics of the speed of the machine with its power or speed regulation and its inertia
- The initial operating conditions, particularly the contractual power factor and the voltage level at the point of delivery with respect to the contractual voltage
Results
The results of this study have been used by the leading French players in cogeneration to negotiate with the ERDF on the conditions of application of the April 2008 law. This law of 23 April 2008 is to be modified by an Amendment proposing a more favourable voltage dip profile.
Example of a gas motor and generator
