Question

What is a meaning of load duration curve.

Answer 1

What is a Load Duration Curve?

A Load Duration Curve (LDC) is a graph used in electrical power engineering to illustrate the relationship between power demand (load) and the amount of time that load is required.

In simple terms, it answers the question: "For how many hours in a given period (e.g., a day, a month, a year) is the electricity demand at or above a certain level?"

Key Differences from a Standard Load Curve

A standard (or chronological) load curve shows the power demand as it changes over time (e.g., 8 AM, 1 PM, 10 PM). A Load Duration Curve takes all the load values from that period and rearranges them in descending order, from the highest load to the lowest.

How to Read the Curve in Your Image

Let's break down the specific Load Duration Curve you provided, which covers a 24-hour period:

• Y-Axis (Vertical): This is the Load in Megawatts (MW). It represents the amount of power being demanded.
• X-Axis (Horizontal): This is the Time in hours. It represents the duration, not the time of day.
  
  Here's what the graph tells us:

1. Peak Load (80 MW): The highest demand is 80 MW. Looking at the x-axis, this peak load lasts for 3 hours (from hour 0 to 3).
2. Intermediate Load (35 MW): The load drops to 35 MW. This level of demand lasts for the next 4 hours (from hour 3 to 7).
3. Intermediate Load (20 MW): The load then drops to 20 MW and stays at this level for the next 5 hours (from hour 7 to 12).
4. Base Load (5 MW): The lowest demand is 5 MW. This is called the "base load" because it's the minimum power required continuously. It lasts for the remaining 12 hours of the day (from hour 12 to 24).

Important Note: The curve shows that a load of at least 5 MW is needed for the entire 24 hours. A load of at least 20 MW is needed for 12 hours, and so on.

Why is the Load Duration Curve So Important?

The LDC is a fundamental tool for power utility companies for several reasons:

1. Power Plant Planning: It helps decide what types of power plants are needed.
   Base Load Plants: The steady, low-level demand on the right side of the curve (the 5 MW load) is best supplied by base load power plants. These plants (like nuclear, large coal, or geothermal) are highly efficient and cheap to run, but are slow to start and stop. They are designed to run continuously.
   Peaking Power Plants (Peakers): The high, short-duration demand on the left side of the curve (the 80 MW load) is best supplied by peaking plants. These plants (like gas turbines) can be started and stopped very quickly to meet sudden demand spikes, but they are more expensive to run.
   * Intermediate Load Plants: The demand in the middle is met by plants that are more flexible than base load plants but cheaper than peakers (like combined-cycle power plants).

2. Economic Dispatch: It helps the utility decide which power plants to turn on and in what order to meet the demand at the lowest possible cost.

3. Energy Calculation: The area under the Load Duration Curve represents the total energy (in Megawatt-hours, MWh) consumed during that period.

In summary, the Load Duration Curve is a rearranged view of electricity demand that is essential for economically and reliably planning and operating a power grid.