PQ curves#
Stations#
All producing stations contain a piecewise linear PQ curve that describes the relationship between the discharge and the generation of the station. The PQ curve is normally given with a reference head.
The PQ-curve should be concave during a standard ProdRisk iteration (forward simulation and backward recursion). That is, the first PQ-segment has the highest efficiency, and the subsequent segments have equal or lower efficiencies than the previous one. If a non-concave PQ-curve is defined by the user, ProdRisk establishes a concave approximation for his purpose by removing non-concave points on the curve. During the final simulation, the default choice is to use the original PQ-curve when finding the total production. In case the original PQ-curve does not have successive lower efficiency with higher discharge, the total production will typically be lower than if we used the concave approximation. In the file Prodrisk.CPAR, there is a parameter called PQValg. If PQValg is set to 0, ProdRisk will use the concave approximation in the final simulation. If PQValg is set to 2, the final simulation uses a non-convex PQ curve.
The PQ curve is scaled according to the head coefficiernt, as described in [3]:
Pumps#
There is no PQ curve for pumps: as the power usage is modelled as a constant, but the flow is dependent on the water head and subject to the same head update as all other Prodrisk head dependencies.