Short Answer:

The purpose of guide vanes in turbines is to control the direction and flow of water before it strikes the runner blades. They help in adjusting the flow angle so that water enters the turbine efficiently and smoothly, improving the performance and power output of the turbine.

Guide vanes also regulate the quantity of water entering the turbine. By opening or closing these vanes, the flow rate can be controlled without disturbing the efficiency. This helps maintain steady operation under varying load conditions and protects the turbine from damage due to unbalanced water forces.

Detailed Explanation:

Purpose of Guide Vanes in Turbines

In hydraulic turbines, guide vanes are fixed or adjustable blades located just before the runner. Their primary role is to guide, control, and regulate the water entering the turbine runner. These vanes are particularly important in reaction turbines like Francis and Kaplan types, where water flow and pressure both contribute to energy conversion.

Guide vanes are placed inside the turbine casing in a circular arrangement around the runner. Their orientation and opening can be adjusted depending on the required flow rate and load demand. They are designed to direct the water at the correct angle to the runner blades so that the energy transfer is smooth and efficient.

1. Directing the Water Flow
   One of the main purposes of guide vanes is to direct the water towards the runner blades at an optimal angle.

• This reduces turbulence and shock losses.
• Ensures that water strikes the blades uniformly.
• Increases the efficiency of energy transfer.

Proper alignment of guide vanes leads to better hydraulic performance and minimizes energy losses due to uneven flow or pressure.

2. Controlling Flow Rate
   Guide vanes also serve as a flow control mechanism.

• They can be adjusted (opened or closed) to regulate the amount of water entering the turbine.
• This helps in matching the power output to the actual electricity demand.
• During low demand, vanes can be partially closed to reduce water usage.

This flexible control system avoids the need to stop the turbine completely and ensures smooth operation under varying load conditions.

3. Preventing Cavitation and Vibration
   By maintaining a uniform flow pattern, guide vanes also help reduce cavitation (formation of vapor bubbles that can damage the blades) and vibrations in the turbine.

• Properly guided water enters the runner smoothly, reducing uneven pressure.
• This leads to longer turbine life and lower maintenance needs.

Thus, guide vanes are essential for both performance and safety of hydraulic turbines.

4. Supporting Load Adjustment
   In large power stations, load on the turbines may vary depending on the power requirements.

• Guide vanes are controlled automatically using governors that adjust the vane angle.
• This helps the turbine adapt to changes in electricity demand without manual intervention.
• It also improves the stability of the power supply system.

Conclusion

The purpose of guide vanes in turbines is to direct and control the flow of water before it hits the runner blades. They ensure efficient energy transfer, regulate flow rate, reduce losses, and support stable turbine operation under varying conditions. Guide vanes are critical components in the smooth and safe performance of hydraulic turbines.