# what is shunt charging in power systems?

I am currently working with Power World Simulator. When inserting transmission lines, there is a parameter called shunt charging. What is this and what effect does it have on power loss in the line?

• Capacitance per metre or mile between line and earth. – Andy aka Sep 14 '15 at 17:31

A transmission line is a wire suspended above the ground. Since the wire is insulated from ground, and is at a different voltage to the ground, the transmission line forms a capacitor between the wire and the ground. This is the shunt charging capacitance of the transmission line.

The size of the capacitor can be measured either as a capacitance, $\mu F . km ^{-1}$, or as an admittance, $\Omega ^ {-1} . km^{-1}$.

The shunt capacitance causes a reactive power flow on the line. You could think of it as injecting reactive power into the line, just like a capacitor bank, though much weaker.

The capacitive power is reactive power (VARs) so does not, itself, represent a loss of real power (Watts.) However, the flow of reactive power does incur losses due to $P=I^{2}R$.

An analogous situation occurs with insulated cables. It is normal for HV cable manufacturers to give the "conductor to screen capacitance" and the "charging current per phase" in datasheets.

From the Olex HV cable catalogue, for 6.35/11kV Three Core Ind. Screened & PVC Sheathed cable with copper conductors, we have the following table:

Interestingly, they also give figures for "dielectric loss per phase", measured in Watts/km, which really is a power loss due to the capacitance, albeit a very small one.