Capacitive Effect on Underground Conductors

[ncjones]

Hi everyone,

Here at the utility, we have noticed high voltage at the end of our UG feeders (We regulate to 124 V and in some instances we have recorded voltage levels of >126 V on customer loads at the end of our feeders.). I was recently asked to determine the cause for this rise in voltage.

Here is what I know:
I do know that capacitors are introduced into power systems for power factor correction purposes. The capacitors increase the power factor of the source and also reduce the apparent power. With a decrease in apparent power, the source current also decreases. All of this means lower line losses and lower line-voltage drops which improves efficiency and improves voltage regulation.

Here is what I am unsure of:
Is the rise in voltage on the UG conductors caused by a similar capacitive effect? Can the lower line losses and lower voltage drops produced by a capacitive effect actually raise voltage? If this is so, could someone help me explain why increased negative vars actually raises the voltage. I am having a hard time realizing this concept if it is true. Also, is this effect known as cable charging or is that a whole different matter?

Thanks for everyones help!!

Nate

 

[stevenal]

Attach a generator of real power to the end of this line and you will raise the local voltage as current flows toward the upstream loads. Think of capacitors as generators of reactive power. Put a reactive generator on the end of an unloaded line and var flow will be into the line looking for upstream reactive loads. The impedance of the line in both cases will cause a voltage drop from generator to load.

Cable charging current is same concept.