Simulator 16 User Guide - PowerWorld

QV Curves
The QV Curves tool provides the ability to compute QV curves for any bus in the system. A QV analysis
studies how variations in reactive power (Q) injection at a bus affects the voltage (V) at that same
bus. Other system parameters can also be monitored as the reactive power injection changes.
To create a QV curve, a fictitious generator (synchronous condenser) is placed at a bus that is being
studied. The voltage set-point of this generator is varied and its var output is allowed to be any valued
needed to meet this voltage set-point. The vertical axis (y-axis) of a QV curve depicts the output of the
fictitious generator in Mvar. The horizontal (x-axis) depicts the respective voltage under this condition.
The base case operating point of the system is represented by the x-intercept of the curve. This is the
point where the fictitious generator is at 0 Mvar output and represents the base case. There are
situations in which the output of the fictitious generator is not 0 Mvar in the base case, but these will
be explained with the appropriate option settings. When considering a contingency scenario in
the QV analysis, the term base case operating point will also be used. This is the starting
case that represents the system prior to performing any analysis for the curve tracing.
Tracing down the curve from higher to lower voltage set-points represents a decrease in the fictitious
generator's Mvar output which is representative of an increase in Mvar load. The curve is then tracing
what the voltage would be as the Mvar load increases. At some point the Mvar value of the generator
will stop decreasing and the bottom of the curve will be reached. This point represents the maximum
increase in load Mvar that can occur at this bus before voltage collapse is reached.
The following shows a typical QV curve. The plot is actually a VQ curve, but this is traditionally called
the QV curve.
The following plot shows a situation in which there is not enough Mvar reserve. There is no base case
operating point as the curve never crosses the x-axis. The difference between the bottom of the curve
and the x-axis is the amount of Mvar injection needed to achieve a solvable case and to come out of
collapse.
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