Average Demand
- The average demand on a station is always referred in particular period i.e. a day, a month or a year. Depending upon this period the average demand is either daily, monthly or yearly.
In case of daily average demand = kWH delivered by the station in 24 hrs of the day / (24 hours in a day)
Similarly, Monthly average demand = kWH delivered in a month / 24 x days in a month kWH delivered in a year
Annual average demand = kWH delivered in a year / 24 x 365 (days in a year)
Maximum Demand
- The maximum demand of the power station is equal to maximum load on the station considered in a given period of time. Consider Figure, the load curve Is drawn on taking average load against time in hours. Hence, the maximum demand on hourly basis is represented by M.D. in Figure
- The practical use of M.D. is made in deciding the capacity of the generating units.
Demand Factor
- For understanding the meaning of demand factor, we will consider the following example of a building having different types of loads as follows :
Lighting load = 200 Nos, each of 40 W – 8000 W
Fan and coolers = 100 Nos. each of 60 watts = 6000 W
Lift load = 2 x 4000 watts 8000 W
Total = 22 kW
- The total connected load is 22 kW or the maximum demand of the building is 22 kw .i.e. maximum demand is equal to connected load of the building. The building will not use all the light points, fan points or lifts at the same time. Let us assume that only 100 lamps, 50 fans and one lift is in use at a time . Hence average load of lamps , fans and lift
= 40 x 100 + 60 x 50 + 4000 – 11000 W – 11 kW
The ratio of this average demand to maximum demand at a time is called as maximum demand factor.
In our case it is equal to 11 kW 22 / kW = 0.5
Maximum demand = Average demand / factor Maximum demand
Hence the maximum demand factor may be defined as the ratio of the average load to maximum load.
Plant Capacity Factor
- At the time of deciding capacity of the power plant , we take into account the present maximum demand in that area and consider a fixed rate of growth so that future demand in a particular period of time can be decided. The plant capacity factor is the ratio of average demand on the station divided by the installed capacity.
i.e. Plant capacity factor =Average demand on the station / Maximum installed capacity of the station Hence, the reserve capacity of power reflects the reserve capacity of the power station.
In a different way,
Plant capacity factor = Actual energy produced / Maximum possible energy that could have been produced
Plant Use Factor (Utilization Factor)
- It is similar to the load factor, but the load factor refers to the total load on the station and the total capacity of the station, while plant use factor relates only to one particular plant or plants where it is generating system or distribution system.
- The plant use factor is the ratio of average demand to the rated capacity, i.e.
Plant use factor = Station output in kWH / (kW1) x H1 + (kW2) x H2 + (kw3) x H3
- Plant use factor indicates how much is the plant capacity utilized , but it does not indicate the time for which the plant remained idle.
- The load factor and plant use factor will be equal if the installed capacity of the plant is equal to maximum demand on the station.
- In other way, Plant use factor = Actual energy produced / Plant capacity x Time (Hours)
Diversity Factor
- Generally, the supply agency try to provide supply to different consumers in such a way that they will have their maximum demand at different times of the day, so that station M.D. is always less than the sum of maximum demands of different consumers. This reduces the Installed capacity of the generating plant.
- For this purpose the supply agency may offer different tariffs to consumers so that they will diverse their demand and maximum demands. The diversity factor is defined as the ratio of the sum of maximum demand of the individual category to the maximum demand of the power station.
i.e . Diversity factor = Sum of maximum demand of each category / Maximum demand of the station
Diversity factor = Maximum demand of station / Maximum demand of station
In this case its value is less than 1.
Load Factor
- The load factor of a station can be determined from its load curve. The area under the load curve gives the number of units generated. The total area of the rectangle in which the load curve is contained represents the total number of units which could have been generated had the maximum demand remained at the highest value constant throughout this period.
- The ratio of number of units actually generated in a given period to number of units which could have been generated with the same maximum demand is called as load factor for the station
Load factor = Average demand / Maximum demand = Energy generated in a given period / (Maximum demand) (Hours of operation in the given period)
- When the period under consideration is a day, the load factor is termed as daily load factor.
- If the period is a month, it is a monthly load factor, OR it is a yearly load factor when the time period is considered a year.
Plant Load Factor
- The plant load factor is similar to that of load factor , but it is different from it in the following respects.
- The load factor refers to the total load on the station and the total capacity of the station. But the plant factor relates only to one particular plant.
- The plant load factor is the ratio of average demand to the rated capacity i.e.
Plant load factor = Station output in kWh /(kW1) x H1+ (kW2) x H2 + (kW3) x H3