Most Important Formulas on Variable Loads Every Power Engineer Should Know


Formulas on Variable Loads Every Power Engineer

  1. Average load (A.L)

  2. Load factor (LF)

  3. Generated units

  4. Diversity factor (DF)

  5. Plant capacity factor

  6. Reserve Capacity

  7. Plant use factor


Average load (A.L)

It is defined as the average of all loads that occur on a power station for a given period of time. Mathematically Average load formula can be linked by the following

Average load (AL) = No of units generated/Time Interval (in hours)

  • 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)

It is the ratio of total energy (KWh) used in the billing period divided by the possible total energy used within the period if used at the peak demand (KW) during the entire period. Demand Load Factor is useful in qualifying the benefits of demand control and battery energy storage strategies.

Load factor = Average Load/Maximum demand

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

Generated units

Each generating unit comprises a generator, a turbine, and its ancillary equipment. Turbines are made of a series of blades connected to an axis, which is in turn connected to the generator.
Units generated = LF * Maximum demand * time

Units generated = Average load * time

Diversity factor (DF)

Diversity factor is defined as the ratio of the sum of the maximum demands of the various part of a system to the coincident maximum demand of the whole system

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

 The diversity factor can be equal or greater than 1.

Plant capacity factor

It is the ratio of actual energy produced to the maximum possible energy that could have been produced during a given period.

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

Reserve capacity is a backup energy generation capacity that is used by the electric grid in the occurrence of unexpected fault such as the unavailability of a power plant. Energy storage systems have the ability to provide this service and are used to offset or reduce costs incurred for generation of reserve capacity.

Reserve capacity = Plant capacity – Maximum demand

Plant use factor

It is defined as “the ratio of actual energy produced (in kWh) in a given time period to the product of plant capacity and the number of hours the plant was in operation.”

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


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