Understand Ehv DC Transmission: I2R Losses Explained

In summary: Using an Earth return instead of a conventional wire for high voltage transmission lines reduces the number of wires and insulators in the system, which in turn makes the towers and equipment lighter. Additionally, the absence of an AC voltage peak reduces the vulnerability of the system to solar flare induced magnetic storms.
  • #1
asad1111
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i have read that in high voltage transmission line dc is preffered on ac and i know all advantages and disadvantages but one main disadvantage that i cannot find was I^2*R losses which was the main reason why we use ac on the first place can someone please explain that?
 
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  • #2
asad1111 said:
i have read that in high voltage transmission line dc is preffered on ac and i know all advantages and disadvantages but one main disadvantage that i cannot find was I^2*R losses which was the main reason why we use ac on the first place can someone please explain that?

You're mistaken, I^2*R losses are much the same for both AC and DC. Reducing I^2R losses is the reason for going to higher voltages in either case (both AC and DC).

I^2R losses are "series" losses. These losses decrease with the use of higher voltage due to the fact that you need less current for the same amount of power.

It's parallel losses that increase with with increasing voltage, however here there is much asymmetry between the AC and the DC case. This is because the shunt conductance that would cause parallel losses are typically not simple conductances, but rather are lossy dielectrics. Like a lossy capacitor this is an AC phenomenon. So the shunt losses are far greater for AC than they are for DC, that's the real advantage of DC at extremely high voltages.
 
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  • #3
For a given transmission line, if the DC current and the RMS current are the same, then the heat dissipation of the line will be the same for DC or AC.

So, this sets an upper limit on how much current the line can carry.

The voltage drop also depends on this current and the resistance of the wires.

Using a higher voltage (AC or DC) results in more total power being delivered and better efficiency.

Developing this higher voltage, and using it at the consumer end of the line, is currently easier using AC and transformers, but DC has some advantages, particularly if the transfer of power is between countries that use different electrical standards for domestic power supply.
 
  • #4
The transmission line can use cheaper insulators because there's no AC peak voltage in DC - 1000 kv is 1000kv not 1414kv.

By using Earth for return they reduce # of wires and insulators , so the towers can be of lighter construction.
 
  • #5
jim hardy said:
The transmission line can use cheaper insulators because there's no AC peak voltage in DC - 1000 kv is 1000kv not 1414kv.

By using Earth for return they reduce # of wires and insulators , so the towers can be of lighter construction.

In my country, AC transmission does not use the Earth as a conductor. It is used for safety reasons, but does not normally carry a current.

There used to be some single wire transmission systems in remote areas, but these have been phased out for reasons of safety and reliability.
 
  • #6
""In my country, AC transmission does not use the Earth as a conductor. It is used for safety reasons, but does not normally carry a current.""

same here. i was describing hvdc which in its real early days used Earth for return. i assume it still does.

sorry about the confusion.

one wonders whether that Earth return would make HVDC more vulnerable to those solar flare induced magnetic storms discussed in another thread... sure increases the area available for induction.
 
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1. What is Ehv DC transmission?

Ehv DC (Extra High Voltage Direct Current) transmission is a method of transmitting electrical power at high voltage levels using direct current (DC) instead of alternating current (AC). This allows for more efficient and cost-effective long-distance power transmission.

2. Why is understanding I2R losses important in Ehv DC transmission?

I2R losses, also known as resistive losses, occur when current flows through a conductor, causing a loss of energy in the form of heat. In Ehv DC transmission, these losses can be significant due to the high voltage and long distances involved. Understanding I2R losses is important in order to minimize them and ensure efficient power transmission.

3. How are I2R losses calculated in Ehv DC transmission?

I2R losses are calculated using Ohm's law, which states that the power loss (in watts) is equal to the current squared (I2) multiplied by the resistance (R) of the conductor. In Ehv DC transmission, the resistance of the conductor is affected by factors such as its material, length, and temperature.

4. What are some methods for reducing I2R losses in Ehv DC transmission?

One method for reducing I2R losses is by using conductors with lower resistance, such as copper instead of aluminum. Another method is to increase the diameter of the conductor, which decreases its resistance. Additionally, using superconducting materials or insulating the conductors can also help reduce I2R losses.

5. Are there any other factors that can contribute to power losses in Ehv DC transmission?

Yes, there are other factors that can contribute to power losses in Ehv DC transmission, such as skin effect, which causes the current to be concentrated near the surface of the conductor, and proximity effect, which occurs when multiple conductors are closely placed together. These effects can be mitigated by using hollow conductors or arranging the conductors in a specific configuration.

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