Short Answer:

The generated voltage at power plants is the voltage produced by alternators or generators before it is transmitted through power lines. Usually, the voltage generated at power stations ranges from 11 kV to 33 kV, depending on the size and type of the plant.

This voltage is not suitable for long-distance transmission because of high current losses, so it is stepped up to a higher level (132 kV, 220 kV, 400 kV, or more) using step-up transformers before being transmitted to the grid. The generated voltage level depends on generator design, plant capacity, and economic considerations.

Detailed Explanation :

Generated Voltage at Power Plants

The generated voltage at power plants refers to the voltage level at which electric power is produced by the alternators (AC generators) of the station. When mechanical energy from turbines (steam, water, gas, or wind) is converted into electrical energy, the resulting voltage is known as generated or generation voltage.

This generated voltage is determined by the generator’s design and is chosen based on technical, economic, and safety considerations. It must be high enough to minimize current for a given power output but not so high that insulation, cost, and size of equipment become uneconomical.

1. Typical Range of Generated Voltage:
   In most power plants, the generated voltage is kept in the range of 11 kV to 33 kV(kilovolts). This range is considered practical and economical for the following reasons:

• It keeps the generator insulation within safe and affordable limits.
• It avoids excessive current, which would otherwise increase copper losses and heating.
• It allows the use of standard generator sizes and transformer ratings.

The generated voltage varies according to the type and capacity of the power plant:

• Thermal Power Plants: 11 kV to 25 kV
• Hydroelectric Power Plants: 11 kV to 33 kV
• Nuclear Power Plants: 11 kV to 30 kV
• Gas Turbine Plants: 11 kV to 15 kV

For large generating units, 33 kV is often used because higher voltage improves efficiency by reducing current and losses.

2. Principle of Generation:
   The voltage generated in a power plant is based on Faraday’s Law of Electromagnetic Induction, which states that when a conductor moves in a magnetic field, an electromotive force (EMF) is induced. In a generator, the rotor (field winding) produces a magnetic field, and as it rotates inside the stator (armature winding), alternating voltage is induced.

The generated voltage (E) depends on:

Where:

•  = frequency (Hz)
•  = number of turns in the stator winding
•  = magnetic flux per pole (Weber)

From this equation, it is clear that voltage can be controlled by changing the magnetic flux or speed of the generator.

3. Factors Determining Generated Voltage:
   Several factors influence the selection and design of generated voltage at power plants:

• a) Generator Size and Rating:
  Large generators can handle higher voltage because they have better insulation and cooling arrangements.
• b) Insulation Requirements:
  As voltage increases, insulation thickness and cost increase rapidly. Hence, an optimum voltage is selected to balance efficiency and cost.
• c) Efficiency of Generation and Transmission:
  Higher generated voltage reduces current for the same power, minimizing copper losses (I²R losses) and improving efficiency.
• d) Type of Power Plant:
  Hydroelectric plants usually generate higher voltages (up to 33 kV) because they can accommodate larger generator sizes, while thermal plants typically generate around 11 kV.
• e) Economic Considerations:
  Very high generation voltages increase the cost of alternators and switchgear. Thus, moderate voltage levels (11–33 kV) are chosen for cost-effectiveness.
• f) Safety and Reliability:
  Extremely high voltage generation increases the risk of insulation breakdown. Therefore, safe limits are maintained to ensure stable and reliable operation.

4. Step-up Transformation for Transmission:
   The voltage generated in a power plant is not suitable for direct transmission over long distances because it would cause large current flow and significant power losses in the form of heat. To overcome this, step-up transformersare used to increase the generated voltage to a much higher level.

Typical transmission voltages after stepping up are:

• 132 kV
• 220 kV
• 400 kV
• 765 kV (in some modern systems)

For example, if a generator produces 11 kV, a step-up transformer raises it to 220 kV or higher for transmission to distant substations. The reason for stepping up the voltage is based on the formula:

For a constant power , increasing voltage  reduces current , which minimizes power losses () and allows thinner conductors, reducing transmission cost.

5. Voltage in Different Power Stations:

• Thermal Power Station:
  Steam turbines drive alternators that usually generate power at 11 kV to 25 kV.
• Hydroelectric Power Station:
  Large water turbines drive alternators that can produce 11 kV to 33 kV due to their large physical size and low rotational speed.
• Nuclear Power Station:
  Similar to thermal stations but may operate at 11 kV to 30 kV, depending on reactor output.
• Gas Turbine or Diesel Power Plants:
  Generally produce lower voltages, around 11 kV to 15 kV, suitable for small or medium power generation systems.

Thus, the type and size of the generating unit determine the generation voltage range.

6. Advantages of Choosing Optimum Generated Voltage:
   Choosing the correct voltage level at generation offers several benefits:

• Reduces power losses and improves efficiency.
• Keeps insulation and equipment cost within reasonable limits.
• Ensures reliable and safe operation.
• Simplifies synchronization and system interconnection.
• Reduces total power generation cost.

Hence, a balance between technical and economic aspects is always maintained while selecting the generated voltage.

7. Importance in Power System Operation:
   The generated voltage plays a crucial role in the overall power system. It determines the design of generators, transformers, switchgear, and transmission systems. Maintaining the correct generated voltage ensures stable frequency, efficient transmission, and proper power quality for consumers.

Any deviation from the rated generated voltage can cause overheating, inefficiency, and system instability. Therefore, voltage regulation systems like Automatic Voltage Regulators (AVRs) are used to maintain voltage within safe limits.

Conclusion:

The generated voltage at power plants is the voltage produced by the alternators before it is transmitted. It typically lies between 11 kV and 33 kV, depending on plant type, size, and economic considerations. This voltage is stepped up using transformers for efficient transmission over long distances. The selection of generated voltage is based on balancing efficiency, insulation cost, and reliability, ensuring economical and stable operation of the entire power system.