Line Drop Compensation - On-Line Tap Changer 1

[Adam1980]

Dear members,

i am trying to simulate the calculations done by the line drop compensator of a tap changer in order to estimate the voltage at the end of a 110 kV 120 km line based on local measurements of voltage, current and current phase angle.

The supplier of the tap changer insists that the remote voltage will be estimated correctly once the LDC parameters are defined correctly and an offset to the voltage set-point of the tap changer to compensate the no-load voltage rise across the cable is applied.

However based on my simulations and when i am using the measured current and current phase angle the remote voltage will not be estimated correctly since the charging current of the cable is not defined in the LDC equations that I found in literature. This error will in crease with decreased loading of the cable.

My main question is: Do the LDC calculation or measurement circuit have certain methods of removing the charging current from the local measured current and phase angle?

I would appreciate any pointers.
Thank you.
Adham

 

[jghrist]

The LDC will compensate for the charging current in the same manner as it does for load current. It simulates the voltage drop through the R and X of the line for the measured current. The measured current includes the charging current and the load current. The difference will be that LDC is based on a load at the end of the line and the charging current is distributed along the line.

 

[davidbeach]

So, why not move the regulation to the load end of the cable and just let the cable do what the cable does?

 

[Adam1980]

Thank you for the reply.

magoo2
the capacitance is about 150 nF/km. the transformer impedance is not important here since i want the drop only across the line.

david
i am considering the case where can have measurement at the remote end and only rely on local measurement and LDC.

I reached the conclusion that in this case the capacitive current is so large that the reactive part of the current is still capacitive even when i am considering a full load.
The LDC will always consider the reactive part which is multiplied with X of the line as inductive. correct?

Thank you.

 

[jghrist]

I believe that the LDC will consider the current to be whatever is measured, either inductive or capacitive. The LDC calculates what the voltage drop would be for the measured current (which includes both load and charging current) flowing through a line with R and X as set. The problem is, in reality, the current is not constant in the actual line. The charging current is higher at the source end where it is measured. The LDC will calculate a lower voltage drop (or higher voltage rise) that what will actually occur in the line.