Short Answer:

Transmission efficiency is the ratio of the power received at the end of a transmission line to the power sent from the generating station. It shows how effectively electrical power is transmitted from the source to the load without major losses.

In simple words, transmission efficiency indicates how much power is successfully delivered to consumers compared to the total power generated. A high transmission efficiency means less power is lost in the transmission lines, while a low efficiency indicates higher energy losses due to resistance, heating, and other factors.

Detailed Explanation :

Transmission Efficiency

The transmission efficiency of a power system is an important factor that determines the performance and economy of electric power transmission. When electrical power is transmitted over long distances, some part of it is lost due to resistance and other losses in the transmission lines. Transmission efficiency is a measure that shows how much of the total power generated actually reaches the consumer end.

It is expressed as a ratio or percentage of power received at the load end to the power sent from the generating end. The goal of an efficient power transmission system is to minimize these losses and achieve maximum efficiency.

1. Definition and Formula:
   Transmission efficiency can be mathematically defined as:

Let:

•  = Power sent from the generating station (sending end)
•  = Power received at the consumer end (receiving end)

Then,

Since power losses () occur during transmission, we can also write:

Hence,

From this equation, it is clear that the smaller the losses (), the higher will be the transmission efficiency.

2. Meaning of Power Losses in Transmission:
   When electrical energy flows through transmission lines, it faces opposition due to the resistance of the conductors. This causes power loss in the form of heat.

The power loss in a transmission line is given by the formula:

Where:

•  = Current in the line
•  = Resistance of the line

This means that higher current and resistance result in greater power losses, which reduce transmission efficiency. Hence, efficient transmission aims to reduce both current and resistance.

3. Factors Affecting Transmission Efficiency:
   The efficiency of a power transmission system depends on several technical and design factors:

• a) Transmission Voltage:
  Increasing the transmission voltage reduces the current for the same amount of power, thereby reducing  losses and improving efficiency. That’s why power plants use step-up transformers to increase voltage for long-distance transmission.
• b) Length of Transmission Line:
  Longer transmission lines have higher resistance and cause more power losses. Therefore, efficiency decreases with distance.
• c) Cross-sectional Area of Conductors:
  Thicker conductors have lower resistance, which helps reduce line losses and increases efficiency. However, large conductors increase material cost.
• d) Power Factor:
  A low power factor increases current for the same power, leading to higher losses. Maintaining a high power factor using capacitors or synchronous condensers improves transmission efficiency.
• e) Type of Conductor Material:
  Materials with lower resistivity (like copper or aluminum) improve efficiency. Aluminum is commonly used because it offers a balance between conductivity, weight, and cost.
• f) Line Loading and Operating Conditions:
  Heavy load or overload conditions cause higher current flow and greater power loss, reducing efficiency.

4. Methods to Improve Transmission Efficiency:
   To maintain high efficiency in transmission lines, the following methods are used:

• a) Using High Transmission Voltage:
  By increasing voltage, current in the line decreases, reducing power loss. For example, increasing voltage from 11 kV to 220 kV can drastically reduce transmission losses.
• b) Reducing Line Resistance:
  Using conductors with larger cross-sectional area or lower resistivity helps minimize losses.
• c) Power Factor Improvement:
  Installing capacitors or synchronous condensers in the system helps maintain a power factor close to unity, which improves efficiency.
• d) Using Shorter Transmission Paths:
  Reducing the length of transmission lines where possible lowers resistance and loss.
• e) Maintaining Balanced Load Conditions:
  Equal loading of all phases in a three-phase system minimizes unbalanced current and losses.

These methods help achieve efficient, reliable, and economical power transmission.

5. Example Calculation:
   Suppose a power station sends 100 MW of power to a city through a transmission line, but 2 MW of power is lost due to resistance.
   Then:

 

This means that 98% of the generated power reaches the destination, and only 2% is lost during transmission.

6. Importance of Transmission Efficiency:
   Transmission efficiency plays a critical role in the performance of a power system for the following reasons:

• Ensures reliable delivery of power to consumers.
• Reduces energy wastage and improves overall system economy.
• Decreases operational cost by minimizing fuel consumption at generating stations.
• Improves voltage regulation and system stability.
• Supports sustainability by reducing losses and environmental impact.

A transmission efficiency above 95% is generally considered good for high-voltage systems.

7. Typical Values of Transmission Efficiency:

• For Low-Voltage Distribution: 85% – 90%
• For High-Voltage Transmission: 95% – 99%

High-voltage transmission systems are designed to keep losses below 5%, ensuring effective power delivery over long distances.

8. Relation Between Transmission Efficiency and Voltage Regulation:
   While high transmission efficiency means less power loss, voltage regulationrefers to the change in voltage between sending and receiving ends.
   Good transmission lines are designed to maintain both high efficiencyand good voltage regulation. However, increasing voltage improves efficiency but may slightly worsen voltage regulation. Therefore, an optimal design balance is necessary.

Conclusion:

Transmission efficiency is the measure of how effectively electrical energy is transferred from the generating station to the receiving end. It is the ratio of received power to sent power, expressed as a percentage. Efficiency mainly depends on voltage level, line resistance, and power factor. High-voltage transmission systems are used to reduce losses and improve efficiency. Maintaining high transmission efficiency is essential for economical, stable, and sustainable operation of electrical power systems.