# Changing transmission line voltages?

Hi everyone,

Currently working on GMD project and need to figure out how to change transmission line voltages.

To rule out some questions, some background info. Right now our university software license doesn't have the GIC model. This is irrelevant, anyway, because we are working with another team from the College of Earth, Ocean, and Atmospheric Sciences' GIC algorithm. GOAL: We would like to add their induced voltages to the ACTIVSg10k test case and run a power flow

So far, we discovered three options:

1) Convert transmission line voltages to substation voltages and change the substation voltage through API

2) Manually change all transmission line voltages

3) Add induced transmission line voltages to existing transmission line voltages

The problem with (1) is that there isn't a good way to tell how the transmission line voltage affects the substations on either end. Does it affect, e.g., substation1 more, or substation2? or just substation1 and not substation2?

The only problem with the (2)&(3) is that I have not found any information through their documents on how to change transmission voltages only substation, which is why I am posting here :]

Any information is greatly appreciated. My eyes are hurting from scanning those 500+ page documents!!! Maybe (I'm hoping) I just simply missed something :D

• Chris
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What results are you trying to obtain from running a powerflow with the induced DC voltages added?

In powerflow we have 4 types of busses: PQ (Load), PV (generator), and V/angle (slack). Most busses are load busses where the active and reactive power are specified and we solve for the voltage and angle.

As a result you cannot set the voltage at these busses in powerflow, it is solved for. You can change the nominal voltage of a bus but this will only affect how parameters are converted to per-unit, not the voltage of the bus directly. PSSE is phasor-domain fundamental frequency model so if you're trying to apply a DC voltage offset to your powerflow model this is not the software to use.

In GIC simulations a DC network is created using only DC resistances of equipment. Using faradays law, the electric-field magnitude and angle, and the orientation of the lines the DC voltage induced in each line is calculated. These DC voltages are added to the DC resistive network and the currents (GIC) in each branch and the DC voltages at each node are solved for using KVL/KCL. No powerflow data (besides topology) is used for this.

In the GIC studies I have done we use the DC currents found in the transformers to calculate the reactive power loss in transformers (from half-cycle saturation) using linear k-factors (specified in the GIC data file). These Mvar losses are then added to the powerflow case to study voltage stability.

If you want to study the effects of GIC DC voltage offset for something like insulation coordination or protection and control settings you need to use an EMTP software I think.

In my experience these DC voltage offsets will generally be much smaller than the nominal AC voltage of the equipment (by something like 1000 times).

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