Load Characteristics of Electrical Power System
Electric Load: It is component of a circuit that consumes Electrical energy in the form of the Electric current and transforms it into other forms like heat, light, work, etc. The electrical load may be resistive, inductive, capacitive or some combination between them. The term load is used in the number of ways.
- To indicate power required for a given circuit.
- To indicate the power or current passing through a line or machine.
Connected Load: It is sum of ratings of all the loads connected to the system or the connected load is the sum of all the nameplate ratings of the equipments within the consumer installation.
Maximum Demand or Peak Load: It is the greatest of all demands which have occurred on the system or power station during specific period. Maximum demand helps in determining the capacity of the power station or generating station. The power station or generating station must be capable of meeting the maximum demand. The maximum demand is always less than the connected load.
Demand factor: It is the ratio of Maximum demand to the connected load. It is always less than 1\\\;\\\textrm{Demand Factor} = \frac{\textrm{Maximum Demand}}{Connected Load}\\It helps us to determine the capacity of power station.
Average Load or Average Demand: It is the average load on the power station or average power generated by the generating station or average power consumed by the load in given period. It is the ratio of energy consumed or generated in given period of time. \\\;\\ Average Load or Average Demand = (Energy consumed or generated in given period of Time) / Time
Load Factor: It is the ratio of average load over a given period of time to the maximum demand (or Peak load) occurring in that period. it determines the efficiency of a power plant
Load Factor = Average Load / Maximum Load
Load Factor = Energy Generated in a Given Period / (Maximum Load X Hours of Operation)
Diversity factor: It is the ratio of sum of the Maximum demands of the various parts of the system to the Maximum demand of whole system. It is always equal or greater than 1. It is expressed in percentage or in ratio. If the diversity factor is expressed in percentage then it should be multiplied by load or it is expressed in numerical value then it is divided by load.
Diversity Factor = (Sum of Maximum demands of the various parts of the system) / Maximum demand of the whole system.
Diversity can be defined for loads, feeders, substations and generating stations.
If the diversity factor is greater than 1, then it is good diversity factor. The diversity factor of various loads as per IEC 60439 are given below.
| Loads (Circuits) | Diversity Factor |
| lighting | 90% |
| Heating and Air condition | 80% |
| Socket – Outlets | 70% |
| For Motors | 80% |
Diversity factor in distribution Network
| Elements of System | Residential | Commercial | General Power | Large Industrial |
| Between individual consumers | 2 | 1.46 | 1.45 | |
| Between Transformers | 1.30 | 1.30 | 1.35 | 1.05 |
| Between feeders | 1.15 | 1.15 | 1.15 | 1.05 |
| Between Substations | 1.10 | 1.10 | 1.10 | 1.10 |
| From Users to transformers | 2 | 1.46 | 1.44 | |
| From Users to feeder | 2.60 | 1.90 | 1.95 | 1.15 |
| From Users to Substation | 3 | 2.18 | 2.24 | 1.32 |
| From User to Generating Stations | 3.29 | 2.40 | 2.46 | 1.45 |
Plant Capacity Factor: It is the ratio of the energy generated or supplied by plant (or Generating Station) in a given period of time to the maximum amount energy that would have been generated if the plant is operated at the its installed capacity (or maximum capacity) during the same period.
According to the Department of Energy’s Energy Information Administration, in 2009, the plant capacity factor of various generating stations or plants are
- Coal plants was 63.8%
- Nuclear Plant was 90.3%
- Hydropower plant was 39.8%
- Other renewable plants was 33.9%
Plant Capacity Factor = (Actual energy produced in a specified time “T”) / (Maximum Plant rating x time (T))
Plant Capacity Factor = {Average Energy produced x Time (T)} / { Maximum plant Rating (or Plant capacity ) x Time}
Plant capacity Factor = Average Energy demand / Maximum plant capacity (or Plant Capacity)
The power plants have some reserve capacity to consider future expansion, increase in load & Maintenance
Reserve capacity of plant = Plant Capacity – Maximum Demand
Plant Use Factor: It is ratio of kWh generated to the product installed capacity of plant and time of operation.
Plant use factor = (Station output in kWh) / (Plant capacity x Hours of use)
Suppose a plant having installed capacity of 20 MW produces annual output of 7·35 × 106 kWh and remains in operation for 2190 hours in a year. Then,
Plant Use Factor = 7·35 × 106 / (20 x 103 ) x 2190 = 0.167 = 16.7 %
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