Introduction
In power system operation, electrical load is never constant. It changes throughout the day depending on consumer usage. To understand these variations and to plan electricity generation efficiently, engineers use load curves. Load curves play a vital role in power generation economics, system planning, and cost optimization.
1. Load Curve
A load curve shows how the electrical load on a power station varies with time. The load is usually recorded at hourly or half-hourly intervals over a full day.
When these values are plotted on a graph with:
- Time on X-axis
- Load (kW or MW) on Y-axis
the resulting graph is called a Daily Load Curve.
🔹 From the load curve, we can easily identify the peak load and the time at which it occurs.
Importance of Load Curve
The load curve is extremely important because:
- It shows load variation throughout the day
- The area under the load curve gives total electrical energy generated in a day
Energy Generated (kWh/day) = Area under daily load curve
- The highest point on the curve indicates the maximum demand
- Average load can be calculated as:
Average Load = Total Energy Generated / 24 hours
Advantages
1.Helps in deciding:
- Number of generating units
- Size of power station
2.Used to calculate Load Factor
Load Factor = Average Load / Maximum Load
3.Assists in operation scheduling of generators
2. Load Duration Curve
A load duration curve is derived from the daily load curve. In this curve:
- Loads are arranged in descending order
- The highest load is placed on the left
- The lowest load is placed on the right
- Time duration is shown on the horizontal axis
This curve shows how long a particular load level persists, rather than when it occurs.
The area under the load duration curve is equal to the area under the daily load curve and gives total energy generated.
Types of Load Duration Curves
- Daily Load Duration Curve – for 24 hours
- Annual Load Duration Curve – for one year
Average Demand = Energy consumed (kWh or MWh) / Time period (hours)
Average Demand = Area under the load duration curve / Base of the load duration curve
Steps to Draw a Load Duration Curve
- Identify maximum load from the load curve and its duration
- Arrange loads in decreasing order
- Plot load magnitude versus total duration
3. Integrated Load Duration Curve
This curve shows to fulfill a given load (kW), how much energy (kwh) is required to be produced.
An integrated load duration curve shows the relationship between:
- Load demand (kW or MW) on Y-axis
- Total energy generated (kWh) on X-axis
It is obtained from the load duration curve by multiplying each load level with its corresponding time duration and plotting cumulative energy.
Advantages
- Helps estimate energy requirement for different load levels
- Useful in:Generation planning
- Economic analysis
- Tariff calculation
- Shows how much energy is produced up to a particular load level.
4. Mass Curve (Energy Curve)
A mass curve represents the cumulative electrical energy consumed by a load up to a certain time of the day.
Advantages
- Studying energy consumption patterns
- Planning storage systems
- Load management analysis
