- Load Curve Definition: A load curve is defined as a graph showing energy demand changes over time.
- Daily Load Curve: The daily load curve represents the energy demand over a 24-hour period.
- Load Duration Curve: This curve shows the duration of specific load demands over a period.
- Industrial and Residential Loads: Industrial and residential load curves have different patterns, with industrial peaks during work hours and residential peaks in the evening.
- Power Plant Operations: Load curves help determine the capacity and operational schedule of power plants, ensuring efficient energy production.
Load Curve
A load curve is defined as a graph that shows how energy demand varies over time from a power source.
If the curve covers 24 hours, it is called a daily load curve. For a week, month, or year, it is called the weekly, monthly, or yearly load curve.
The load duration curve reflects the activity of a population quite accurately with respect to electrical power consumption over a given period of time. To understand the concept better its important that we take the real life example of load distribution for an industrial load and a residential load, and have a case study on them, to be able to appreciate its utility from the perspective of an electrical engineer.
Case Study on Daily Industrial Load Curve.
The load duration curve for an industrial load over 24 hours shows that demand rises after 5 AM as machinery starts warming up. By 8 AM, the entire load is active and remains steady until just before noon when it drops slightly for lunch. The demand returns to its morning level around 2 PM and stays steady until 6 PM. In the evening, machinery shuts down, and demand falls to a minimum by 9 or 10 PM, staying low until 5 AM the next day. This pattern repeats every 24 hours.
Case study on Daily Residential Load Curve.
In case of a residential load, as we can see from the diagram below, the minimum load is reached at about 2 to 3 hours at morning, when most people are asleep and during 12 noon, when most people are out at work. Whereas, the peak of the residential load demand starts at around 17 hrs and lasts upto 21 to 22 hrs at night, after which again the load drops rapidly, as most people retire to bed. Since, this residential load curve, is taken in a sub-continental continental country like India, we see that the load demand in summer is a bit higher in summer (shown in bold line) compared to a similar pattern of lower values during the winter season (shown in dotted line).
These examples show that the load duration curve provides a visual representation of the demand that supply stations must meet throughout the day. This helps determine the plant’s total capacity needed to handle peak demand and the most economical size of generating units. It also helps decide the power plant operating schedule, including how, when, and in what order units should be started, run, and shut down. During low demand periods, decisions about shutting down or restarting generator sets are based on economic considerations.
Shutting down and restarting generator sets leads to losses, and running them at partial loads also causes efficiency losses. The decision to shut down or continue running at reduced load depends on minimizing these losses. Power sector engineers analyze the load duration curve to make these decisions. Therefore, it is crucial to use load curve data to optimize power generation units efficiently.
