13 Most Important Formulas on Variable Loads Every Power Engineer Should Know

The electrical power station provides electricity to a large number of the consumer loads. While the consumer demand varies time by time, this variation in load is referred as the variable loads. Keeping this load variation in mind, a power engineer has to deal with various factors involving the installation and maintenance of additional equipment, production costs and usage of electricity. Of this, here are 13 Most important formulae which you should remember.

Average load (A.L)

The average of units generated at a power station for a certain interval of time is referred as average loads. We can contemplate the average load for a day, for a week, for a month, for a year or for a decade. Practically daily, monthly and yearly average loads are common.

Daily average load = Units generated in a day / 24 hours

Monthly average load = Units generated in month / 720 hours (hours in month)

Yearly average load = Units generated in year / 8760 hours (hours in year)

Load factor (LF)

Load factor = Average Load/Maximum demand

The average load is an average of all loads that occur on a power station for any specific period of time. Whereas the maximum demand is the highest demand for the load which occurs for that specific time. The load factor is the ratio of average load to the maximum demand for a specific time. Like average load, the load factor is also time dependent we could have daily LF, monthly LF or yearly LF. We can multiply average load with time for manipulation of generated units.

LF = (AL * t) / (Max demand * t) = Units generated / (Max demand * t)

Generated units

It is often desired to calculate the units that are generated at a station. We can achieve this from LF and Maximum demand by manipulating the previous formula.

Units generated = LF * Maximum demand * time

Since the average load is Load factor * Maximum demand we achieve:

Units generated = Average load * time

Diversity factor (DF)

DF is the ratio between the sum of individual maximum demand occurring at the power station to the maximum demand on the power station.

DF = Sum of individual max demand / Max. demand on the power station

Since the sum of individual demands is always greater than the max demand of station, the diversity factor is always greater than 1.

Plant capacity factor

The ratio of actual energy produced to the maximum energy that could have been produced from the plant.

Plant capacity factor (PCF) = Actual energy produced / Max energy that could have been produced

PCF = (Average demand * time)/(Plant capacity / time)

PCF = Average demand / Plant capacity

Reserve Capacity

The additional capacity which is not needed but is reserved for future requirements.

Reserve capacity = Plant capacity – Maximum demand

Plant use factor

It is the ratio of actual units generated by the plant to the overall capacity of plant multiplied by hours of operation.


Plant use factor = Plant Output Units in kWh / (Plant capacity * Hours of use)

Let’s take a summarize review of formulas:


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