Dear Amir Sam,

welcome,

I think you intend the effects of the DC transmission during the switching phases where the transmission line will be empty and it will be charged during the transmission. If the transmission line is strictly terminated at its characteristic impedance it will generate a transient current during its charge which will end when the voltage wave reaches to the termination. So during it charge it will generate strong electromagnetic wave. You can model the transmission line during these transients and calculate the waveform during the switching periods. Sure it is interesting especially when there is missmatch on the transmissionline.

This in only a short note on the solution.

Best wishes

Hi Amirsam Dalir , I'm not an expert in the domain of DC power transmission but from following the path of a former student of mine, I know at least of one problem:

In the usual AC grid, feedback control is limited to the voltage and frequency of the generators while the transformers between transmission line and end users are just passive (i.e. have constant properties). With DC transmission, obviously one need active voltage converters, and it seems to make sense to provide a constant output voltage by local feedback control, within certain limits independently of the input voltage at the converter.

However for a given constant load which determines the output power of the converter, this means that also the input power is about constant, and so with decreasing input voltage the input current increases.

Thus, the converter (+ constant load) represents a negative differential resistance, and the grid could start to oscillate, a very undesirable effect.

I have to admit that this is not a problem specific to electromagnetism but the core of the problem would be the same with hydraulic or pneumatic power transmission, for example.

I think that phenomena like reflection follow the same laws as they generally do, e.g. on the power supply traces of high speed logic boards which constitute DC power transmission on a small scale.

This cannot be answered in all details in 1 minute..BUT...HV DC power transmission is good for transmission of large amount of power over distances ..say >1000 km (e.g China about 2000 km from large hydroelectric installations in the mountains to Shanghai).One of basics reasons to go for DC is stability (keep in mind that 50 hz is 6000 km wavelength and when the length of the line is approaching lamda/8 ,stability issue become important..its like RF engineering)..and there is no skin effect (Ohmic losses) and the next step would be Wikipedia...to check and then you find a lot in IEEEE proceedings.

Dear,

I suggest you read the article: Computation of Electromagnetic Fields Around HVDC Transmission Line Tying Egypt and KSA .

Abstract —The aim of this work is to compute the electromagnetic fields of a proposed high voltage direct current transmission line (HVDC) tying Egypt and KSA. The line is flat configuration with a stressed voltage of ±500 kV, bundle four, normal height of 30.2 m from ground level to pole conductors and clearance between positive and negative pole of 31.1m. The line is analysed and simulated. The charge simulation method (CSM) is used to calculate the electric field at ground level for that line while the current simulation technique is used to calculate the magnetic fields. The maximum electric and magnetic fields of the line are affected by changing the height from ground level to pole conductors. The effect of pole outage of the line on the spatial distribution of the magnetic and electric field is also studied.

Keywords — Electrical Interconnection; Charge Simulation Method; Current Simulation Technique; Extra High Voltage DC Transmission Lines; Electric Fields; Right of Way; Electromagnetic Field Effects and Hazards.