EHV Ac and Dc transmission.

Unit 1
Constitution of EHV a.c (what is EHV ac)-
EHV AC stands for Extra High Voltage Alternating Current. It refers to the transmission of
electricity at voltages significantly higher than those used in conventional power distribution
grids. The term "extra high voltage" typically denotes voltages above 345,000 volts (345 kV),
although definitions may vary slightly depending on the context and region.

Here's a detailed breakdown of EHV AC:

1. **Voltage Range**: EHV AC systems operate at voltages higher than the standard high
voltage (HV) levels used in most power grids. While there's no universally agreed-upon
threshold, voltages above 345 kV are generally considered EHV. These voltages can range
from several hundred kilovolts (kV) to over a million volts (MV).

2. **Purpose**: The primary purpose of EHV AC transmission is to efficiently transport large

amounts of electrical energy over long distances with minimal loss. By transmitting power at
higher voltages, the current required for a given amount of power is reduced, leading to
lower resistive losses in the transmission lines.

3. **Transmission Lines**: EHV AC transmission lines consist of conductors supported by

towers or poles. These lines are typically made of aluminum or aluminum alloy for its
lightweight properties and high conductivity. The conductors are often bundled together to
increase the transmission capacity and reduce corona discharge losses.

4. **Substations**: At various points along the transmission route, substations are used to
regulate voltage levels, switch power flows, and facilitate interconnections between
different transmission lines. These substations step down the voltage to levels suitable for
distribution to end-users or other lower voltage transmission systems.

5. **Insulation**: Insulation is crucial in EHV AC systems to prevent electrical breakdown

and ensure the safe and reliable operation of the transmission lines and equipment.
Insulators made of porcelain, glass, or composite materials are used to support the
conductors and maintain sufficient distance between them and the supporting structures.
6. **Challenges**: While EHV AC transmission offers significant benefits, it also poses
several challenges. These include increased costs associated with constructing and
maintaining high-voltage infrastructure, as well as technical challenges such as corona
discharge, capacitance effects, and electromagnetic interference. Additionally, EHV AC
systems require careful planning and coordination to mitigate environmental impacts and
ensure compatibility with existing infrastructure and land use.

7. **Advancements**: Over time, advancements in technology have improved the

efficiency and reliability of EHV AC transmission systems. For example, the development of
high-temperature superconducting materials may enable the construction of more efficient
transmission lines with lower losses. Additionally, advancements in power electronics have
led to the adoption of voltage source converter (VSC) based HVDC (High Voltage Direct
Current) transmission systems, which offer certain advantages over traditional EHV AC
systems in specific applications.

Overall, EHV AC transmission plays a crucial role in modern electrical power systems,
enabling the efficient and reliable transport of electricity over long distances to meet the
needs of consumers and industries.
An EHVAC Transmission line stands for Extra High Voltage Alternating Current
Transmission line. EHV lines are able to move large power across a single line so
the overall conductor requirement is decreased.

Constitution of EHV d.c (what is EHV dc)-

EHV DC stands for Extra High Voltage Direct Current. It refers to the transmission of
electrical power at voltages significantly higher than those used in conventional high-voltage
direct current (HVDC) systems. EHV DC systems operate at voltages typically exceeding 800
kV and can extend up to several million volts (MV), depending on the specific application
and technological capabilities.

Here's a detailed overview of EHV DC:

1. **Voltage Range**: EHV DC systems operate at extremely high voltages compared to

conventional HVDC systems. While there's no universally agreed-upon threshold, voltages
above 800 kV are generally considered EHV DC. These voltages can range from several
hundred kilovolts (kV) to several megavolts (MV).
2. **Purpose**: The primary purpose of EHV DC transmission is similar to that of
conventional HVDC transmission: to efficiently transport large amounts of electrical power
over long distances with minimal losses. By transmitting power at higher voltages, EHV DC
systems can achieve lower losses compared to equivalent AC systems, especially over very
long distances or when transmitting large amounts of power.

3. **Transmission Technology**: EHV DC transmission systems utilize high-voltage

converters to convert alternating current (AC) power from the grid into direct current (DC)
for transmission, and vice versa at the receiving end. These converters, often based on
voltage source converter (VSC) or line-commutated converter (LCC) technologies, are
capable of handling the extremely high voltages and power levels associated with EHV DC
transmission.

4. **Transmission Lines**: EHV DC transmission lines consist of conductors supported by

towers or poles, similar to EHV AC transmission lines. However, the conductors used in DC
transmission lines are typically arranged in pairs (positive and negative) to carry the DC
current, rather than in three-phase configurations used in AC transmission lines. The
conductors are often made of high-strength materials such as aluminum or aluminum alloy.

5. **Substations**: Like AC transmission systems, EHV DC transmission requires substations

at various points along the transmission route to regulate voltage levels, switch power
flows, and facilitate interconnections with other transmission systems. These substations
incorporate converter stations, where AC/DC conversion takes place.

6. **Insulation and Environmental Considerations**: Insulation and environmental

considerations are critical in EHV DC systems to prevent electrical breakdown and ensure
the safe and reliable operation of the transmission lines and equipment. Insulators and
other components must be designed to withstand the high voltages and environmental
conditions encountered in EHV DC transmission.

7. **Challenges and Advancements**: EHV DC transmission presents unique challenges

related to converter technology, insulation, and system control. However, advancements in
converter technology, materials science, and control systems continue to improve the
efficiency, reliability, and cost-effectiveness of EHV DC transmission systems, enabling their
use in an increasing number of applications, including long-distance power transmission,
interconnections between asynchronous AC grids, and integration of renewable energy
resources.
Overall, EHV DC transmission plays a crucial role in modern electrical power systems,
offering advantages in efficiency, reliability, and scalability for long-distance power
transmission and other applications.
The control of power in a DC link can be achieved through the control of current or
voltage. From minimization of loss considerations, we need to maintain constant
voltage in the link and adjust the current to meet the required power.

Principle of hvdc system

Kind of dc links
Limitation and advantage of ehv ac

EHVAC (Extra High Voltage Alternating Current) systems refer to the transmission of
electrical power at voltages significantly higher than those used in conventional high-voltage
AC systems. Let's explore the advantages and disadvantages of EHVAC systems:

**Advantages of EHVAC:**

1. **Lower Transmission Losses:** EHVAC transmission lines experience lower resistive

losses compared to lower voltage AC lines. By transmitting power at higher voltages, the
current required for a given amount of power is reduced, leading to lower resistive losses in
the transmission lines. This results in increased efficiency, especially over long distances.

2. **Increased Power Transfer Capability:** EHVAC systems can transmit more power than
equivalent lower voltage AC systems using the same transmission infrastructure. This
increased power transfer capability is particularly beneficial for transporting large amounts
of electrical energy over long distances without significant losses.

3. **Grid Stability and Reliability:** EHVAC systems contribute to grid stability and reliability
by reducing voltage drops and power losses during transmission. This helps maintain voltage
stability and ensures reliable power supply to consumers, especially in areas located far
from power generation sources.

4. **Integration of Renewable Energy:** EHVAC transmission facilitates the integration of

renewable energy sources, such as large-scale wind farms or solar installations located in
remote areas, by enabling the transmission of power over long distances to population
centers where demand is high.

5. **Optimized Land Use:** EHVAC transmission lines can transmit large amounts of power
over relatively narrow corridors, optimizing land use and reducing environmental impact
compared to lower voltage transmission lines that require wider rights-of-way.

**Disadvantages of EHVAC:**

1. **Higher Initial Investment:** The initial capital investment required for constructing
EHVAC transmission infrastructure, including substations and transmission lines, can be
higher compared to lower voltage AC systems. This is due to the increased complexity and
specialized equipment required for EHVAC transmission.

2. **Technical Challenges:** EHVAC systems present technical challenges such as corona

discharge, capacitance effects, and electromagnetic interference. These challenges require
careful engineering and design considerations to ensure the safe and reliable operation of
the transmission infrastructure.

3. **Environmental Impact:** While EHVAC transmission lines may require narrower rights-
of-way compared to lower voltage lines, they can still have environmental impacts, including
habitat fragmentation, visual intrusion, and electromagnetic field exposure. Proper
environmental planning and mitigation measures are necessary to minimize these impacts.

4. **Grid Interconnection Complexity:** Interconnecting EHVAC transmission systems with

existing AC grids or other EHVAC systems can be complex and require careful coordination
to ensure compatibility and grid stability. This may involve the implementation of advanced
control and protection systems to manage power flows and voltage levels effectively.

Overall, EHVAC systems offer significant advantages in terms of efficiency, power transfer
capability, and grid stability, especially for long-distance transmission of electrical power.
However, they also pose challenges related to initial investment, technical complexity,
environmental impact, and grid interconnection, which must be carefully addressed to
realize their full potential.
Limitation and advantage of ehv dc

Extra High Voltage Direct Current (EHV DC) systems refer to the transmission of electrical
power at voltages significantly higher than those used in conventional High Voltage Direct
Current (HVDC) systems. Let's explore the limitations and advantages of EHV DC systems:

**Advantages of EHV DC:**

1. **Lower Transmission Losses:** EHV DC transmission lines experience lower resistive

losses compared to EHV AC lines, especially over very long distances. This is because DC
transmission lines have lower electrical losses due to absence of skin effect and reduced
reactive power requirements.

2. **Increased Power Transfer Capability:** EHV DC systems can transmit more power than
equivalent EHV AC systems using the same transmission infrastructure. This increased
power transfer capability is particularly beneficial for transporting large amounts of
electrical energy over ultra-long distances with minimal losses.

3. **Interconnection of Asynchronous Grids:** EHV DC systems enable the interconnection

of asynchronous AC grids operating at different frequencies or phases. This allows for
efficient power exchange between regions with incompatible grids, promoting grid stability
and reliability.

4. **Integration of Renewable Energy:** EHV DC transmission facilitates the integration of

renewable energy sources, such as offshore wind farms or remote solar installations, by
enabling the transmission of power over long distances to population centers where
demand is high. This helps to mitigate the variability and intermittency of renewable energy
generation.
5. **Reduced Environmental Impact:** EHV DC transmission lines require narrower rights-
of-way compared to equivalent EHV AC lines, reducing land use and environmental impact.
Additionally, DC transmission lines can be buried underground or submerged underwater,
further minimizing visual intrusion and habitat disruption.

**Limitations of EHV DC:**

1. **Higher Initial Investment:** The initial capital investment required for constructing EHV
DC transmission infrastructure, including converter stations and transmission lines, can be
higher compared to equivalent EHV AC systems. This is due to the complexity and
specialized equipment required for EHV DC transmission.

2. **Converter Complexity and Cost:** EHV DC systems require complex converter

technology for rectification and inversion of AC to DC and DC to AC, respectively. These
converters are expensive and require sophisticated control systems, adding to the overall
cost of the transmission system.

3. **Grid Synchronization Challenges:** Maintaining precise synchronization between

interconnected EHV DC systems or AC grids can be challenging, especially when dealing with
grids operating at different frequencies or phases. This requires advanced control and
protection systems to ensure stable and reliable operation of the interconnected grids.

4. **Limited Converter Availability:** Availability of high-power, high-voltage DC converters

may be limited compared to AC transformers, which are widely available and standardized.
This can lead to longer lead times and higher costs for procuring EHV DC converter
equipment.

Overall, EHV DC systems offer significant advantages in terms of lower transmission losses,
increased power transfer capability, grid interconnection flexibility, and environmental
impact reduction. However, they also present challenges related to higher initial
investment, converter complexity, grid synchronization, and converter availability, which
must be carefully addressed to realize their full potential.
Power control in ehv ac and dc
Gartez circuit hvdc ( write the full story and diagram of hvdc …..ekk image aur hai jho
neeche hai)
Firing angle control
Firing angle control, also known as phase angle control or angle control, is a method used in
power electronic converters to regulate the amount of power transferred to the load. It is
commonly used in both Extra High Voltage Alternating Current (EHV AC) and Extra High
Voltage Direct Current (EHV DC) transmission systems, albeit with different implementations
due to the distinct characteristics of AC and DC.

**Firing Angle Control in EHV AC Systems:**

In EHV AC systems, firing angle control is typically associated with voltage source converters
(VSCs), which are used in HVDC (High Voltage Direct Current) transmission systems. VSC-
based HVDC systems use insulated-gate bipolar transistors (IGBTs) to control the conversion
of AC to DC and vice versa. The firing angle control technique involves adjusting the timing
of the IGBT switches to control the magnitude and polarity of the DC voltage output.

By varying the firing angle, the converter can control the amount of real power transferred
between AC and DC systems. This allows for precise control of active power flow, reactive
power compensation, and voltage regulation. Firing angle control in VSC-based HVDC
systems enables smooth and continuous power modulation, making it suitable for grid
stabilization and integration of renewable energy sources.

**Firing Angle Control in EHV DC Systems:**

In EHV DC systems, firing angle control is not directly applicable, as DC transmission does
not involve periodic switching like AC transmission. Instead, EHV DC systems primarily use
voltage and current control techniques to regulate power flow and voltage levels.

One common method used in EHV DC systems is the control of converter firing angle in
rectifier bridges. In a rectifier bridge, the firing angle determines the point in each cycle of
the AC input waveform at which the thyristors or other semiconductor devices are turned
on. By adjusting the firing angle, the converter can control the average DC output voltage,
thereby regulating the power flow from the AC system to the DC system.

Overall, while firing angle control is a crucial technique in EHV AC systems, particularly in
VSC-based HVDC transmission, it is not directly applicable in EHV DC systems. Instead,
voltage and current control methods are employed to regulate power flow and ensure
stable operation.

In detail –

https://www.studocu.com/in/document/vardhaman-mahaveer-open-university/electronic-
media/ee8017-unit-3-firing-angle-control/58391709

overlapping
In the context of Extra High Voltage (EHV) AC and DC transmission systems, "overlapping"
typically refers to the synchronization or coordination of operations between different
elements of the transmission network. Let's explore the concept of overlapping in EHV AC
and EHV DC systems:

**Overlapping in EHV AC Systems:**

In EHV AC systems, overlapping may occur in various aspects of the transmission network,
including:

1. **Grid Interconnection:** When interconnecting different AC grids or power systems,

overlapping involves ensuring that the frequency, phase angle, and voltage levels are
synchronized between the interconnected grids. This ensures smooth and reliable power
exchange between the grids without disruptions or instability.
2. **Substation Operation:** Overlapping in EHV AC substations involves coordinating the
operation of various elements such as transformers, circuit breakers, and protective devices
to ensure the safe and efficient transfer of power within the transmission network. This
includes synchronization of voltage levels, switching operations, and fault protection.

3. **Control and Protection Systems:** Overlapping in EHV AC control and protection

systems involves redundancy and backup mechanisms to ensure reliable operation and fault
tolerance. This may include redundant control systems, multiple communication links, and
backup protection schemes to detect and isolate faults in the transmission network.

**Overlapping in EHV DC Systems:**

In EHV DC systems, overlapping may occur in similar aspects as EHV AC systems, but with
specific considerations for DC transmission:

1. **Converter Operation:** Overlapping in EHV DC converter stations involves coordinating

the operation of multiple converter modules or arms within the station to ensure smooth
and efficient conversion of AC to DC and vice versa. This includes synchronization of firing
angles, current sharing, and voltage regulation.

2. **Multi-Terminal HVDC Systems:** In multi-terminal HVDC systems, overlapping involves

coordinating the operation of multiple converter stations and transmission lines to enable
power exchange between different AC grids or renewable energy sources. This includes
synchronization of voltage levels, power flow control, and fault management.

3. **Control and Protection Systems:** Similar to EHV AC systems, overlapping in EHV DC

control and protection systems involves redundancy and backup mechanisms to ensure
reliable operation and fault tolerance. This may include redundant control processors,
communication links, and protection schemes to detect and mitigate faults in the DC
transmission network.

Overall, overlapping in EHV AC and DC systems is essential for ensuring the reliable and
efficient operation of the transmission network, including grid interconnection, substation
operation, and control/protection systems. Coordination and synchronization of operations
between different elements of the network are crucial for maintaining grid stability, power
quality, and system reliability.