If a capacitor is rated at 100 MVAR and the system voltage is .9 PU, what is the output of the capacitor bank?

To determine the output of a capacitor bank rated at 100 MVAR when the system voltage is 0.9 per unit (PU), it's important to apply the formula for calculating the reactive power output based on the system voltage.

The formula for the output of a capacitor at a specific voltage is given by:

[ \text{Output} = \text{Rated MVAR} \times (\text{Voltage Ratio})^2 ]

In this case, the rated MVAR (100 MVAR) is multiplied by the square of the voltage ratio (0.9 PU):

[ \text{Output} = 100 , \text{MVAR} \times (0.9)^2 = 100 , \text{MVAR} \times 0.81 = 81 , \text{MVAR} ]

This calculation shows that the output of the capacitor bank decreases with the reduction in voltage; thus, if the voltage is lower than the nominal value (1 PU), the available reactive power output is less than the full rating.

Therefore, the output of the capacitor bank, when operating at 0.9 PU, is correctly calculated to be 81 MVAR. This illustrates the principle that reactive power