In 1870, the first direct current (DC) was developed by Thomas Alva Edison. We know that electricity is a flow of electrons. If electrons flow inversely (if starts from the battery ‘’+’’ terminal to the load and back to the battery ‘’- ‘’ terminal) which called DC or direct current. However, there are two main types of transmission systems AC transmission systems and DC transmission systems. However, in this journey, we will try to learn about when DC transmission is required, how to make high voltage DC power transmission, why DC transmission is required, and others.
What is High Voltage DC Power Transmission (HVDC)?
HVDC stands for high voltage direct current. If High voltage DC (50KV, 100KV, 300KV or more) is transferred over a long distance (2000 Km, 3000 Km, 5000 Km or more) through overhead or submarine cable to meet the load demand.
This power transmission system is called high voltage DC power transmission system. Many large countries (USA, Russia, Canada, China, India) use the HVDC power transmission process to send power over a very long distance to minimize power losses and economic considerations.
How to Make High Voltage DC Power Transmission?
To transmit the power in a very long distance some losses and drawbacks appeared. For this reason, a high-voltage DC (HVDC) transmission system is used. In that case, some common improvements can be followed, such as efficiency, stability, low power losses, high transmission capacity, and others.
However, let’s try to figure out how to make high-voltage DC power transmission, how to transmit it, and how does HVDC transmission system works. In this stage, we have referred to some crucial steps to make it clear perfectly.
1. Power Generating Station
We know that our entire power network is an AC (alternating current) system. That’s why AC power is generated in the power station. It is noted that for a long-distance DC transmission, high-voltage DC power cannot be generated in the electrical power plant due to commutation problems. AC power is generated and sent to the nearer electrical substation or generation substation to convert AC power into DC power to transmit over a long distance.
2. Converting Stations or Rectification Station
A converting substation or converting station is used to convert the power from AC to DC or DC to AC. To convert high voltage AC power into high voltage DC power. In that case, rectifiers, converters, harmonic filters, and synchronous condensers can be used. Let’s see an example, suppose in a three-phase three-wire system a 400KV output power is obtained from the output of the transformer.
This power is converted into a 2-wire 400KV HVDC line with the help of a rectifier, converter, or synchronous condenser. And sent to the destination through a 2-wire HVDC transmission system. It is noted that the converting substation is only used to convert AC to DC, it is not the right one. This type of station can be used to convert DC to AC power.
3. DC Transmission Line
High-voltage DC transmission lines can be run in two main ways: overhead and underground. Indeed, most high-voltage direct current transmission lines are connected to bipolar converters. For this reason, the high-voltage DC power lines have two terminal conductors: a positive terminal and a negative terminal.
This two-wire HVDC transmission system runs over a long distance in another converting station. Whereas this HVDC power needs to be converted into AC power for use. Because our entire electrical network system is AC system.
4. DC to AC Inversion station
Indeed, both converter and inverter or inversion stations work for the conversion and inversion of electric power. In short, a conversion or inversion station has a rectifier and inverter. Whenever HVDC power comes to the inversion or inverting station invert DC power into AC power using an inverter.
It is noted that the inverter has some controlling and switching electronic devices, such as Thyristor, IGBT, and other semiconductor devices. This high-voltage AC power is transferred to the grid system and transmitted to the different substations through the transmission line.
5. HVDC Transformers
HVDC transformer converting transformer is a type of transformer. It plays an essential role in the converting station. HVDC transformer is different from some other commercial transformer. There are three main configurations of a converting transformer, such as
- Three-phase 2 winding system.
- Single phase 2 winding system.
- Single 3 winding system.
Transformers provide isolation and impedance matching between the converter equipment and the grid. High-voltage DC transformers are also used in the converter stations to match the voltage levels between the AC grid system and the HVDC transmission system.
HVDC Configuration System
HVDC configuration system refers to AC power generation and conversion into HVDC. This power is inverted into HVAC systems for commercial or residential use. Indeed, there are three main types of HVDC line configuration, such as
- Mono polar link
- Bipolar link
- Homopolar link
Economic Aspect of HVDC Transmission Systems
HVDC transmission systems offer crucial economic advantages such as long-distance high-power transmission systems. Although the HVDC system’s initial installation cost can be higher due to the need for converting stations, and other conversion materials. This system is the best for long-term savings.
It reduces transmission losses and lowers HVDC infrastructure costs. It is economically beneficial like in underwater cables, cross-border connections, and remote renewable energy integration systems (offshore wind farms and solar plants to the grid). However, let’s see some economic considerations of the HVDC system.
- Operational savings lower infrastructure costs
- Reduced transmission losses
- Grid interconnection and stability and economic integration system.
- Renewable energy integration system.
- Long-term savings or economic viability.
- Strategic investments and national and regional benefits.
HVDC system Cost in the USA
For the USA, the cost of implementing an HVDC system can vary widely depending on the transmission line length, the capacity of the system, and the specific technology used. It is noted that the costs break down into two main reasons: the converter stations and the transmission line.
For Converter Stations
- The cost of HVDC converter stations ranges from $200 million to $1 billion per station (AC to DC and back to AC).
Transmission Lines
- HVDC transmission lines cost around $1 million to $3 million per mile for overhead lines in the USA.
- For underground or submarine cables, the cost is around $5 million to $20 million per mile depending on installation complexity.
These costs can be higher for HVDC systems, but long-distance and high-capacity power transmission is more beneficial.
What should be the Distance for HVDC transmission lines?
In most cases, the high voltage direct current transmission line distance is greater than 300 miles (about 500 kilometers). This distance can be 600 kilometers to 10000 kilometers. However, for distances beyond 300 miles, HVDC’s reduced power losses and lower infrastructure requirements.
Recently, the world’s longest HVDC transmission line has been in the China Zhundong–Wannan UHVDC (Ultra High Voltage Direct Current). This transmission line distance is approximately 3,293 kilometers or 2,046 miles and has a transmission capacity of 12,000 MW. This line is built to transmit electricity to China’s remote western regions.
Voltage Range of Long Distance HVDC Transmission Line
The long-distance high voltage direct current HVDC transmission lines voltage or HVDC voltage ranges from ±500 kV to ±1,100 kV. The ultra-high voltage DC transmission or ultra-high voltage direct current (UHVDC) lines are used for extremely long distances and large power capacities. This power can reach up to ±1100 kV.
How Efficient is High Voltage DC Power Transmission?
High Voltage DC (HVDC) power transmission is highly efficient around 3% or 3.5% per 1,000 kilometers (620 miles). This is significantly lower than the 6-8% losses. Therefore, HVDC and UHVDC systems are more economical and efficient than AC transmission systems for long-distance transmission.
Advantages of High Voltage DC Transmission System
The advantages of high-voltage power transmission are indescribable. These benefits let the engineers know make high-voltage DC power transmission systems. So, let’s see some essential advantages of the HVDC or UHVDC system.
- Lower transmission losses.
- Efficient long-distance DC current transmission.
- Reduced infrastructure costs.
- Easy and better ability to connect asynchronous grids.
- Improved grid stability and reliability.
- Easier integration of renewable energy sources.
- Higher power capacity per line.
- Better control over power flow.
- Lower electromagnetic interference.
- Easy to transmit power for underwater and underground cables.
Disadvantages of High Voltage DC Transmission System
- The high initial cost of converter stations.
- Complex and expensive maintenance and multi-terminal configurations.
- Converter station and space requirements.
- Higher complexity in fault management.
- Potential for higher electromagnetic interference near converter stations.
- Require longer construction and commissioning times.
How Does High Voltage DC Transmission Impact Grid Stability?
Grid stability is the ability of an electrical grid to maintain. Grid stability also refers to a steady and reliable power supply in various disturbances. However, the high voltage DC power lines can enhance grid stability in several ways such as isolation of AC grids, precise power control, stability during disturbances, reduced risk of cascading failures, and frequency regulation.
Final Thought
HVDC voltage or HVDC current is more beneficial and economical for transmitting power over a long distance. In the above section, I have shown how to make high voltage DC power transmission by following high-voltage DC power transmission technology. Hopefully, this section will be the best one to get crucial information about the HVDC transmission system. So, get in touch with OPEN READ, get the creative information, and share your opinion.