Why High Voltage is Used in Power Transmission – Explained with Advantages

⚡ Advantages of High Transmission Voltage

In electrical power systems, the voltage level used for transmission plays a crucial role in determining efficiency and cost. Transmitting power at high voltage offers multiple technical and economic advantages. Here are the key benefits:

1️⃣ Reduces Line Current

For a given amount of power, increasing the transmission voltage decreases the current flowing through the line:

I = P / (√3 × V)

• Lower current leads to reduced losses and smaller conductor size.

2️⃣ Minimizes Power Losses (I²R Losses)

Since power loss is proportional to the square of the current (I²R), reducing current significantly lowers transmission losses:

Power Loss ∝ I² × R

• This improves the overall efficiency of the system.

3️⃣ Reduces Conductor Size and Cost

• Smaller current allows the use of thinner and lighter conductors, reducing the cost of transmission lines and towers.

4️⃣ Increases Transmission Efficiency

• With reduced losses and optimized conductor use, the efficiency of the transmission system increases, especially over long distances.

5️⃣ Better Voltage Regulation

• High-voltage transmission systems maintain better voltage levels at the receiving end with minimal voltage drop.

6️⃣ Suitable for Long-Distance Transmission

• To transmit large power over long distances economically, high voltage is essential. It allows for centralized generation and wide-area distribution.

7️⃣ Reduces Number of Substations

• Due to efficient long-distance power flow, fewer intermediate substations are needed, reducing infrastructure and maintenance costs.

8️⃣ Economic Benefits

• Although initial insulation and equipment costs are high, the long-term savings from lower losses, smaller conductors, and reduced infrastructure make high-voltage transmission more economical.

📌 Summary Table

Advantage	Explanation
Lower Current	For same power, current decreases with higher voltage
Less I²R Loss	Reduces power loss in the line
Smaller Conductor Size	Lower current requires thinner wires
Improved Efficiency	Less loss = higher transmission efficiency
Better Voltage Regulation	Voltage drop is minimized at high voltage
Long-Distance Suitability	Ideal for power transmission over large areas
Fewer Substations	Reduced infrastructure cost
Cost Effective	Lower operating cost over time

💡 Quick Tip for Exams:

• Remember: High Voltage → Low Current → Low Loss
• Formula: Power Loss = I²R, and I = P / V → So higher V → lower I → lower loss

📌 Example:

Suppose we need to transmit 100 MW power through a line of resistance $10 \, \Omega$.

• At 10 kV:

  $$I = \frac{P}{V} = \frac{100 \times 10^6}{10 \times 10^3} = 10,000 \, A$$

  Power loss:

  $$P_{loss} = I^2 R = (10,000)^2 \times 10 = 1000 \, \text{MW}$$

  👉 Loss is greater than the transmitted power.

• At 100 kV:

  $$I = \frac{100 \times 10^6}{100 \times 10^3} = 1000 \, A$$

  Power loss:

  $$P_{loss} = (1000)^2 \times 10 = 10 \, \text{MW}$$

  👉 Loss is only 10% of transmitted power.

🔢 Why Transmission Voltages Are Multiples of 11kV (11, 33, 66, 132, 220...)?

You might have noticed transmission voltages like 11kV, 33kV, 66kV, 132kV, 220kV etc., are usually multiples of 11. Here's why:

Standardization with Loss Margin:

• The originally designed voltage may be 10kV, 30kV etc., but due to line losses and voltage drops, about 10% extra voltage is added for compensation. This is why voltage levels are designed as 11kV, 33kV, 66kV, and so on.

Manufacturing & System Standards:

• Power systems globally adopted 11kV multiples as a standard for ease of manufacturing transformers, breakers, and insulation levels. It avoids mismatch and ensures compatibility.

Economic Design of Equipment:

• Most electrical equipment (transformers, switchgear) is optimized for standardized voltage levels, keeping cost, reliability, and efficiency in mind.

✅ Fun Fact:

Modern EHV systems use voltages like 400kV, 765kV (not multiples of 11) because at very high levels, losses and insulation factors are separately optimized, and exact multiples are no longer necessary.

❓ Frequently Asked Questions – High Transmission Voltage

Q1. Why is power transmitted at high voltage?

To reduce current, which minimizes I²R losses and improves overall transmission efficiency.

Q2. Why are voltage levels in multiples of 11 like 11kV, 33kV, 132kV used?

Due to voltage drop compensation and system standardization. About 10% is added for design margin, so 10kV becomes 11kV, and so on.

Q3. What is the typical transmission voltage in India?

Common voltage levels in India include 11kV, 33kV, 66kV, 132kV, 220kV, 400kV, and 765kV for EHV transmission.

Q4. Is high voltage transmission dangerous?

Yes, it requires proper insulation, clearance, and safety measures. That’s why it's used only in controlled infrastructure like substations and towers.

Q5. What is the role of a step-up transformer in high voltage transmission?

It increases the generator voltage (usually 11kV) to high voltage (like 132kV or 220kV) to enable efficient long-distance transmission.

Q6. Does high voltage affect power quality?

No, in fact, it improves voltage regulation and stability over long distances when properly designed.