Travelling Waves on Transmission Systems

Introduction

Travelling waves play a crucial role in the operation and performance of transmission systems in EHV A.C. and D.C. Transmission. Understanding the fundamentals of travelling waves is essential for engineers and technicians working in the field of power transmission. This topic explores the shape, attenuation, and distortion of travelling waves, as well as the effects of junctions and terminations on their propagation.

Key Concepts and Principles

Shape of Travelling Waves on Transmission Systems

Travelling waves on transmission systems can have different shapes depending on the type of transmission line and the characteristics of the wave. The shape of the wave is determined by factors such as the line impedance, the frequency of the wave, and the termination conditions.

Attenuation and Distortion of Travelling Waves

Travelling waves on transmission systems experience attenuation and distortion as they propagate along the line. Attenuation refers to the decrease in the amplitude of the wave over distance, while distortion refers to the changes in the waveform caused by the line characteristics.

Effect of Junctions on Propagation of Travelling Waves

Junctions in transmission systems can have a significant impact on the propagation of travelling waves. When a wave encounters a junction, such as a branching point or a transformer, it can be reflected, transmitted, or partially absorbed. The behavior of the wave at the junction depends on the impedance matching and the characteristics of the junction.

Effect of Terminations on Propagation of Travelling Waves

Terminations, such as open circuits or short circuits, can also affect the propagation of travelling waves. When a wave reaches the end of a transmission line, it can be reflected back or absorbed depending on the termination conditions. The reflection coefficient and the standing wave ratio are used to quantify the effects of terminations on the wave propagation.

Over Voltages in Transmission Systems

Over voltages can occur in transmission systems due to various reasons, including lightning, switching operations, and temporary disturbances. These over voltages can pose a threat to the equipment and the stability of the system. Therefore, it is important to implement appropriate control measures to mitigate the effects of over voltages.

Causes of Over Voltages

Lightning

Lightning strikes near transmission lines can induce high voltages and currents in the system. These lightning over voltages can cause insulation breakdown and damage to the equipment. Lightning is a natural phenomenon that cannot be prevented, but its effects can be controlled.

Switching

Switching operations, such as the opening or closing of circuit breakers, can also generate over voltages in transmission systems. These switching over voltages are caused by the sudden change in the current flow and can lead to insulation failure and equipment damage. Switching over voltages can be controlled through the use of surge arresters and circuit breakers.

Temporary Over Voltages

Temporary disturbances, such as load switching or faults in the system, can result in temporary over voltages. These over voltages are transient in nature and can cause equipment malfunction and system instability. Temporary over voltages can be controlled by using capacitor banks and voltage regulators.

Control of Lightning Over Voltages

To control lightning over voltages, several measures can be implemented:

1. Lightning Arresters: Lightning arresters are devices that provide a low-impedance path for the lightning current to flow into the ground. They are installed at regular intervals along the transmission line to protect the equipment from lightning-induced over voltages.

2. Grounding Systems: Proper grounding of the transmission system is essential to ensure the safe dissipation of lightning currents. Grounding systems consist of grounding electrodes, conductors, and connections that provide a low-resistance path for the lightning current to flow into the earth.

Control of Switching Over Voltages

Switching over voltages can be controlled through the following measures:

1. Surge Arresters: Surge arresters are devices that provide a low-impedance path for the switching over voltages to flow into the ground. They are connected in parallel with the equipment to be protected and divert the over voltages away from the equipment.

2. Circuit Breakers: Circuit breakers are devices that interrupt the current flow in the event of a fault or abnormal condition. They are used to isolate the faulty section of the system and prevent the propagation of switching over voltages.

Control of Temporary Over Voltages

Temporary over voltages can be controlled through the following measures:

1. Capacitor Banks: Capacitor banks are used to improve the power factor of the system and stabilize the voltage during transient conditions. They absorb and release reactive power to maintain a stable voltage profile and mitigate the effects of temporary over voltages.

2. Voltage Regulators: Voltage regulators are devices that automatically adjust the voltage level of the system to maintain it within acceptable limits. They continuously monitor the voltage and control the tap settings of the transformers to compensate for voltage fluctuations and regulate the system voltage.

Step-by-step Walkthrough of Typical Problems and Solutions

This section provides a step-by-step walkthrough of typical problems related to over voltages in transmission systems and their solutions. It covers the following scenarios:

Problem: Lightning Over Voltage

Solution: Installing Lightning Arresters

In this scenario, the problem is the occurrence of lightning over voltages in the transmission system. The solution is to install lightning arresters at regular intervals along the transmission line. The lightning arresters provide a low-impedance path for the lightning current to flow into the ground, protecting the equipment from over voltages.

Problem: Switching Over Voltage

Solution: Using Surge Arresters and Circuit Breakers

In this scenario, the problem is the occurrence of switching over voltages during the operation of circuit breakers. The solution is to use surge arresters and circuit breakers. The surge arresters provide a low-impedance path for the switching over voltages to flow into the ground, while the circuit breakers interrupt the current flow and isolate the faulty section of the system.

Problem: Temporary Over Voltage

Solution: Using Capacitor Banks and Voltage Regulators

In this scenario, the problem is the occurrence of temporary over voltages during transient conditions. The solution is to use capacitor banks and voltage regulators. The capacitor banks absorb and release reactive power to stabilize the voltage, while the voltage regulators automatically adjust the tap settings of the transformers to maintain a stable voltage profile.

Real-World Applications and Examples

This section provides real-world applications and examples of the concepts discussed in the previous sections:

Example: Lightning Protection Measures in a Power Transmission System

In this example, we explore the lightning protection measures implemented in a power transmission system. We discuss the installation of lightning arresters, grounding systems, and other protective devices to control lightning over voltages.

Example: Switching Over Voltage Control in a Substation

In this example, we examine the switching over voltage control measures implemented in a substation. We discuss the use of surge arresters and circuit breakers to mitigate the effects of switching over voltages.

Advantages and Disadvantages of Travelling Waves on Transmission Systems

Advantages

Travelling waves on transmission systems offer several advantages:

1. Efficient Power Transmission: Travelling waves allow for efficient power transmission over long distances. They minimize power losses and maximize the transfer of electrical energy.

2. Improved System Reliability: Travelling waves help in detecting faults and abnormalities in the transmission system. By analyzing the characteristics of the waves, engineers can identify potential issues and take corrective actions to improve the system reliability.

Disadvantages

Travelling waves on transmission systems also have some disadvantages:

1. Cost of Implementing Protection Measures: Implementing protection measures against over voltages can be costly. The installation and maintenance of lightning arresters, surge arresters, and other protective devices require significant investment.

2. Complexity of System Design and Maintenance: Travelling waves introduce complexity in the design and maintenance of transmission systems. Engineers need to consider the wave characteristics, impedance matching, and termination conditions to ensure proper wave propagation and protection against over voltages.

Conclusion

In conclusion, understanding travelling waves on transmission systems is crucial for engineers and technicians working in the field of EHV A.C. and D.C. Transmission. The shape, attenuation, and distortion of travelling waves, as well as the effects of junctions and terminations on their propagation, play a significant role in the performance and reliability of transmission systems. By implementing appropriate control measures and protection devices, the effects of over voltages can be mitigated, ensuring the safe and efficient operation of the system.

Summary

Travelling waves on transmission systems play a crucial role in EHV A.C. and D.C. Transmission. This topic explores the shape, attenuation, and distortion of travelling waves, as well as the effects of junctions and terminations on their propagation. It also covers the causes of over voltages in transmission systems and the control measures to mitigate their effects. Real-world applications and examples are provided to illustrate the concepts discussed. Travelling waves offer advantages such as efficient power transmission and improved system reliability, but they also introduce complexity and cost in system design and maintenance.

Analogy

Travelling waves on transmission systems can be compared to ripples on the surface of a pond. Just as ripples propagate outward from a disturbance in the water, travelling waves propagate along transmission lines. The shape of the ripples and the way they interact with obstacles in the pond can be compared to the shape and behavior of travelling waves on transmission systems. Understanding the principles of travelling waves is like understanding the physics of ripples in a pond, which helps us predict and control their behavior.