### How to define the Q(V) characteristic droop within a generator or station controller

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Summary

The Q(V) characteristic is available as option for the reactive power control for load flow calculation in the generator models and in the station controller model. The slope of the characteristic is entered via droop input.

Die Q(U)-Kennlinie ist als Option für die Blindleistungsregelung in den Generator-Modellen und dem Anlagenregler für die Lastflussberechnung verfügbar. Die Steigung der Kennlinie wird über die Statik eingegeben.

The Q(V) characteristic is available as reactive power controller for load flow calculation within the generator models as well as within the station controller. The slope of the control curve can be entered as ‘droop’.

The droop is defined as reciprocal value of the change in reactive power as a function of voltage deviation.

In absolute values (kV/Mvar), the droop is calculated as follows:

Droop [kV/Mvar] = 1 /(Delta Q / Delta U) = Delta U / Delta Q = (U-Uset) / (Q-Qset)

Usually, the droop is given as a relative quantity, this means that the voltage as well as the reactive power has to be applied as relative values. The voltage is related to the nominal voltage, the reactive power is related to the generators nominal power, therefore the droop is given to:

Droop [p.u./p.u.] = ((U-Uset)/Un) / ((Q-Qset)/Sn) = (U-Uset) / (Q-Qset) * Sn/Un

Since the Droop is defined in %, a multiplication with 100% has to be applied.

Droop [%] = 100% * ((U-Uset)/Un) / ((Q-Qset)/Sn) = 100% * (U-Uset) / (Q-Qset) * Sn/Un

Within the Q(V) characteristic, the droop is only used, whenever the voltage is outside the dead band between Umin and Umax. If no deadband is required, Umn should equal Umax. The reactive power setpoint has to be entered in the reactive power operational point field directly.

Allowed Q(V) characteristic settings are defined in many grid codes around the world, where you will find further information on how to properly consider them within the FAQ system.

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