What Could Be Causing Negative Reactive Power in a Three Phase Power System?

[Nick Kuza]

In a three phase power system,delta connected 66kV transmission line,the reactive power in one of the line/phase is negative(capacitive) while the reactive power in the other two lines/phases is positive.What is causing the reactive power to be negative(capacitive) in this phase?What are some possible solutions towards mitigating this negative(capacitive) reactive power?

 

[dlgoff]

Welcome to Physics Forums.

Adding capacitors will decrease the Vars, adding inductors will increase the Vars, or you can use the what's called a Synchronous Condenser which will either increase or decrease Vars.

In electrical engineering, a synchronous condenser (sometimes called a synchronous capacitor or synchronous compensator) is a device identical to a synchronous motor, whose shaft is not connected to anything but spins freely.[1] Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid's voltage, or to improve power factor.

 

[Windadct]

This could be caused by many things - How much are you talking about? How many VAR relative to Watts, if it is a small amount(near unity - or very low real power flowing) this could be a "normal" system condition, one line is actually more capacitive than the other lines. However is it is a significant amount of VARs at significant power - I would check that the CTs/PTs , instruments are connected properly. Is the POWER in that leg reversed as well?
What device is being used to tell you that the PF is +/-? Is there any way to get a complete vector diagram of the readings.