Load Duration Curve

1.1. LOAD-DURATION CURVES

When planning a power plant…

Two basic parameters to be decided are :

1. Total Power output to be installed (kWinst)

2. Size of the generating unit

1. Total Power output to be installed (kWinst)

1. First demand (kW ) estimated.


2. Size of the generating units.

Variation of load (load curve) during 24 hours.


12 6 1212 6

am pm

kW

12 6 1212 6

am pm

kW

Industrial Load Urban Load


12 6 1212 6

am pm

kW

12 6 1212 6

am pm

kW

Residential Load Street lighting


12 6 1212 6

am pm

kW

6 1212 6

am pm

Metropolitan Area Load

6 1212 6

am pm

SundaySaturdayWeek day



m = -----------------------------------------------------Average load over a given time interval

Peak load during the same time interval

Load Factor :

m = ----------------------------kW-h (ave.) in a year

kWmax x 8760 (one year = 8760 hr)

Average Load = ----------------------------------------Area under load curve (kW-h)

24 (h)


n = -------------------------------------Average load

Rated capacity of the plant

Capacity Factor : (or plant factor)

n = ----------------------------------kW-h generated in a year

kWinst x 24 x 365

If rated capacity of the plant is equal to the peak load,

Then, Load Factor (m) = Capacity Factor (n)

(numerically)

= ----------------------kW-hgen (year)

kWinst x 8760


Reserve Factor :

The difference between load factor and capacity

factor is an indication of the reserve factor

r = --------kWinst

kWmax

= --------------------------Load Factor (m)

Capacity Factor (n)


Demand Factor :

Connected Load = sum of the continuous

ratings of all the equipment and outlets on

the consumer’s circuits.

Maximum Demand = is the maximum load

which a consumer uses at any time.

It is always less than, or equal to,

the connected load.


Diversity Factor :

div = ----------------------------------------------Sum of individual consumer group

Actual peak load of the system

The time distribution of maximum demands

for similar types of consumers.

div = -------------a + b + c

d


Diversity Factor :

Diversity helps to improve the load factor and economic operation of the

power plant.

6 1212 126AM PM

Total Load (d)

Shopping area

offices and

workshops (b) Industry (c )

Residence (a)

kW


Diversity Factor :

Load curves of an industrialized country

6 1212 126AM PM

winter

summer

Residence (a)

kW


Diversity Factor :

A high load factor is, in general, an indication of

balanced load curve with relatively small load

changes.

High value of demand factor, load factor, diversity

factor and capacity factor are desired for

economic operation of the plant and to produce

electricity at less cost.

•••


Plant Use Factor :

It is the ratio of energy produced in a given time to

the maximum possible energy that could have

been produced during the same time of operation.

••• Plant use factor (u) = --------------------------------kW-hgen

kWinst x operating hours

If the operating time is 1 year or 8,760 hrs, the

plant use factor is equal to the capacity factor

(i.e., u = n)

•••


Plant Use Factor :

Larger the unit size,

LESS COST to PRODUCED ELECTRICITY

••• Plant use factor (u) = --------------------------------kW-hgen

kWinst x operating hours

If the operating time is 1 year or 8,760 hrs, the

plant use factor is equal to the capacity factor

(i.e., u = n)

•••


MW

126 1212 6AM PM

MW

126 240 18

2.6h6h 8.6h

Nmax

Day

Load curve Load-duration curve

Load-duration curve indicates how many hours a certain load

has been required in the course of the day.


MW

126 1212 6AM PM

MW

126 240 18

2.6h6h 8.6h

Nmax

Day


Rearrange the load elements of a chronological curve in the

descending order of magnitude. (see load curve)

1 Load-Duration curves.xls


MW

126 1212 6AM PM

MW

126 24-day0 18

2.6h6h 8.6h

Nmax


By compiling the load hours on various days the load duration

curves for one month or for year can be obtained.

Day

Month

Year

720-month8760-month


Pow

er

Dem

ands

Time

Load-duration curve

The area under the annual load duration curve represents the

total energy supplied by the utitlity’s generating system

during the year.

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

The variable load problem affects power plant design and

operation as well as the cost of operation.

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

Base load plant should be run at high LOAD FACTOR

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

Peak load plant should smaller capacity to reduce cost

of operation.

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

Peak load plant could be,

* gas turbine

* pumped-hydro system

* diesel engine

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

Prime movers and generators should act

quickly and take up or shed load without

variation of voltage or frequency of system.

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load


Pow

er

Dem

ands

Time

Load-duration curve

The function of governor is to control the

supply of fuel (or steam) to the prime mover

according to load.

Load-curve

Base Load (100%)

Intermediate load

Peak Load (15%)

Base Load

Intermediate load

Peak Load

Load Duration Curve

Documents

Transcript of Load Duration Curve