Load

Important Terms and Factors

(i) Connected load. It is the sum of continuous ratings of all the equipment connected to supply system. Unit : Watt (W).

(ii) Maximum demand. It is the greatest demand of load on the power station during a given period. The knowledge of maximum demand is very important as it helps in determining the installed capacity of the station. Unit: Watt (W).

(iii) Demand factor. It is the ratio of maximum demand on the power station to its connected load. The knowledge of demand factor is vital in determining the capacity of the plant equipment.

(iv)Average load. The average loads occurring on the power station in a given period (day or month or year) is known as average load or average demand.

(v) Load factor. The ratio of average load to the maximum demand during a given period.

Example 1.1

The maximum demand on a power station is 100 MW. If the annual load factor is 40%, calculate the total energy consumed in a year.

Solution:

Energy consumed in a year = Max. demand x hours in a year x L.F.

Example 1.2

A generating station has a connected load of 43 MW and a maximum demand of 20 MW and the unit generated being 61.5 x 106 kWh per annum. Calculate:(i) the demand factor(ii) load factor

Solution:

(i)

(ii)

Example 1.3

A 100 MW power station delivers 100 MW for 2 hours, 50 MW for 6 hours and is shut down for the rest of each day. It is also shut down for maintenance for 45 days each year. Calculate the annual load factor.

Solution:

The generated unit on working hour:

Operation days in a year = 365 – 45 = 320 days in a year

The unit generated in a year: = 500 MWh x 320 = 160000 MWh

Annual load factor

Examples 1.4

A diesel station supplies the following load to the various consumers:

Industrial consumer : 1500 kWCommercial establishment : 750 kWDomestic power : 100 kWDomestic light : 450 kW

If the maximum demand of the station is 2500 kW and the number of kWh being supplied per year is 45 x 105, determine:(i) Average load in a year(ii) Annual load factor

Solution:

(i) Annual average load

(ii) Annual load factor

Example 1.5

A power station has the following daily load cycle:

Time in hours

6-8 8 - 12 12 - 16 16 - 20 20 - 24 24 - 6

Load in MW

20 40 60 20 50 20

(i) Plot the load curves(ii) Plot the load duration curves(iii) Calculate the total energy being supplied in a day(iv)Calculate the daily load factor

Solution:

1. The load curves

time (hrs) 2 4 6 8 10 12 14 16 18 20 22 24

70

60

50

40

30

20

10

Loa

d in

MW

2. The load duration curves

3. Total energy supplied

4. Daily load factor

2 4 6 8 10 12 14 16 18 20 22 24

60

50

40

30

20

10

Hours duration

Loa

d in

MW

Tutorial 1

1. Give the advantages and disadvantages of the electrical power generation station which using the following energy sources:

a. Sunb. Water c. Windd. Nuclear

2. Discuss the difference between base load, intermediate load and peak load.

3. State the advantages of National Grid System.

4. Explain the significance of daily load curves.

5. Discuss the difference between load duration curves and load curves.

6. A generating station has a connected load of 40 MW and a maximum demand of 20 MW. The units generated to supply the consumer are 60 x 106 kWh. Calculate (i) the demand factor and (ii) the load factor

[Ans: (i) 0.5 (ii) 34.52% ]

7. A generation station has the following daily load cycle:

Time (hours)

0-6 6-10 10-12 12-16 16-20 20-24

Load (MW)

20 25 30 25 35 20

Draw the load curve and fond:(i) maximum demand(ii) Total unit generated per day(iii) average load(iv)load factor

[Ans: (i) 35 MW (ii) 560 x 103 kWh (iii) 23333 kW (iv) 66.67%]

8. A power station has to meet the following load demand:

Load A 50 kW 10 am till 6 pmLoad B 30 kW 6 pm till 10 pmLoad C 20 kW 4 pm till 10 am

Plot the daily load curve and determine:(i) Unit generated per day(ii) load factor

[Ans: (i) 880 kWh (ii) 52.38%]

9. A generating station supplies the following consumer’s loads:

Industrial consumer : 1500 kWCommercial establishment : 750 kWDomestic power : 100 kWDomestic light : 450 kW

If the maximum demand on the station is 2500 kW and the number of kWh generated per year is 60 x 105, determine the annual load factor.

[ Ans: 27.43% ]

10. The annual load of a substation is given in the following table. During each month, the power is assumed constant at an average value.

(i) Obtain the plot of the annual load curve. (ii) Calculate the average load(iii) Determine the annual load factor

Annual Load SystemMonth Load (MW)January 8February 6March 4April 2May 6June 12July 16

August 14September 10

October 4November 6December 8

[ Ans: (ii) 8.02 MW (iii) 50.14% ]