SYSTEM LOAD VARIATION – Electrical Engineering

The variation of load on the power station with respect to time.

SYSTEM LOAD

• From system‟s point of view, there are 5 broad category of loads:

1. Domestic

2. Commercial

3. Industrial

4. Agriculture

5. Others – street lights, traction.

Domestic:

· Lights,

· fans,

domestic appliances like heaters,

· refrigerators, air conditioners,

· mixers,

· ovens,

· small motors etc.

1. Demand factor = 0.7 to 1.0;

2. Diversity factor = 1.2 to 1.3;

3. Load factor = 0.1 to 0.15

Commercial:

Lightings for shops, advertising hoardings, fans, AC etc.

1. Demand factor = 0.9 to 1.0;

2. Diversity factor = 1.1 to 1.2;

3. Load factor = 0.25 to 0.3

Industrial:

Small scale industries: 0-20kW

Medium scale industries: 20-100kW

Large scale industries: above 100kW

Industrial loads need power over a longer period which remains fairly uniform throughout the day.

For heavy industries:

1. Demand factor = 0.85 to 0.9;

2. Load factor = 0.7 to 0.8

Agriculture:

Supplying water for irrigation using pumps driven by motors

1. Demand factor = 0.9 to 1;

2. Diversity factor = 1.0 to 1.5;

3. Load factor = 0.15 to 0.25

Other Loads:

a) Bulk supplies,

b) street lights,

c) traction,

d) government loads

which have their own peculiar characteristics

System Load Characteristics

a) Connected Load

b) Maximum Demand

c) Average Load

d) Load Factor

e) Diversity Factor

f) Plant Capacity Factor

g) Plant Use Factor

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 Use Factor:

It is the ratio of kWh generated to the product of plant capacity and the number of hours for which the plant was in operation.

Plant use factor = Station output in kWh / Plant capacity * Hours of use

When the elements of a load curve are arranged in the order of descending magnitudes.