lecture2 load curves 2015

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Power Generation & System Planning (EN 302/642) 2014-15 Santanu Bandyopadhyay

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Understanding Electrical Load

Lecture 2


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Outline

Topics Number of lectures (approx)

Load curve and load duration curvePower system planning

2 (8, 12 Jan)


System Load

• Time intervals– daily, weekly, seasonal, annual, etc.

• Usage– Residential, industrial, commercial,

agricultural, etc.• End-usage

– Lighting, air conditioning, pumping, etc.

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4

Load Curve• Graphical representation of electrical load

(i.e., power) as a function of time• Area under the curve represents energy

requirement• Important for plant

operation (preparation, take-off, shut down coordination, etc.)

0

5

10

15

20

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (hour of the day)

Dem

and

(kW

)

2


Annual Load Curve

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Typical Load Curves

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Industrial plant with single shift Commercial shops

Street lighting Urban load curve


Understand Load Curves

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Off-peak

Morning peak

Partial peak

Evening peak

Off-peak


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Load curve of a typical day –MSEB(8/11/2000 source: WREB annual report-2001)

10260 MW9892 MW

6000

7000

8000

9000

10000

11000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Time hours

Dem

and,

MW

morning peak

Evening peak

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Load Duration Curve• Graphical representation of electrical load

as a duration of time• Area under the curve represents energy

requirement• Important for

system designingand planning

0

5

10

15

20

0 2 4 6 8 10 12 14 16 18 20 22 24

Time (hour)

Dem

and

(kW

)


Few Definitions-1

• Peak load– maximum demand– Growth of peak load

• capacity addition• Capital cost investment

• Average load– total energy/time duration– Operating cost, as it is related to energy

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Few Definitions-2

• Load factor (System load factor)– Defined as: average load/peak load– Pertaining to the demand– Represents the variation in the demand

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Few Definitions-3

• Capacity factor (Plant load factor, PLF)– average load/plant capacity– Total energy produced/maximum energy

production possible– Pertaining to the generating plant– Represents the part load operation– Efficient utilization of the plant– Recovery potential of invested capital

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4


Few Definitions-4

• Plant use factor– Energy generated/(capacity × operating hour)– Always higher than PLF– For uninterrupted operation, same as PLF.– Actual part load operation of the plant– Operating cost

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Load & Capacity Factors-1

• Load factor and capacity factor ≤ 1• Inadequate utilization of installed capacity• Part load operation of the plant• Reduction in efficiency (as part load

efficiency is poor) implying more fuel consumption (and higher operating cost)

• Rapid rate of increase of load may cause system instability

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Load & Capacity Factors-2

• Load curve and load duration curve, normalized with respect to the peak load and total duration, represent load factor when integrated

• Load curve and load duration curve, normalized with respect to the plant capacity and total duration, represent capacity factor when integrated

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Few Definitions-5

• Utilization factor– Peak load/plant capacity– Extent up to which plant capacity is utilized to

satisfy the peak demand– Related to the reliability of the power system– Helps in planning capacity addition

• Reserve factor– Load factor/capacity factor– Inverse of utilization factor

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5


Few Definitions-6• Connected Load

– sum of the continuous (or nameplate) ratings of equipment.

• Demand factor– Peak load/connected load

• Diversity factor– Sum of individual peak load/actual peak load– Helps in improving load factor and economic

operation– Inverse of diversity factor is coincidence factor

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Diverse Load Curves

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Total

Industry

Residential

Shop


Problem• A 120 MW power plant supplies following

power to the consumers:

• Draw load curve and load duration curve• Determine:

– Average load, load factor, capacity factor, and utilization factor.

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Time (h) 0-6 6-10 10-12 12-16 16-20 20-22 22-24Load (MW) 30 70 90 60 100 80 60


Answer

• Energy generated– 30*6+70*4+90*2+60*4+100*4+80*2+60*2 =

1560 MWh• Average load = 1560/24 = 65MW• Load factor = 65/100 = 0.65• Capacity factor = 65/120 = 0.54• Utilization factor = 100/120 = 0.83

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Peak Load Variation

• week-end, weather, season, festival, etc.• Typically

– Daily peak/monthly peak ~ 0.87– Monthly peak/annual peak ~ 0.83

• Therefore,– Annual load factor ≈ daily load factor × 0.87 ×

0.83

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LDC Variation

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daily

monthly

annual

15% 90%

Bas

e lo

adP

eak

load


Power Plants-1

• Peak load power plant– Plants used for small fraction of time– Operating cost is not very important– Capital investment should be minimum– Low start up time– Response time should be very fast– Gas turbine, small hydro, etc.

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Power Plants-2

• Base load power plant– Runs almost through out the year– Operating cost should be minimum– Capital investment may be high– Coal plants, nuclear plant, etc.

• Intermediate power plant– Both capital and operating costs are important– Combined cycle, cogeneration, etc.

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Power Plants-3a

• Incidental power plant– Solar, wind based renewable plants– Production varies with resource variations– high variability (low reliability)– low capacity factor– high capital cost– Do not match with load curves– Storage is an option, cost increases

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Power Plants-3b

• Incidental power plant– Low carbon footprints– Ramp up with polluting peak plant– Transmission line construction– Good for distributed generation

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Load Management• Objective is to improve load factor (i.e., to

make load curve flat)

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Planning• A scheme, program, or method worked out

beforehand to achieve optimum balance of needs or demands with the available resources

• The planning process:– identifies the goals/objectives to be achieved– formulates strategies to achieve them– arranges or creates the means required– implements, directs, and monitors all steps in

their proper sequence.28

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Need for Power System Planning

• Appropriate matching between generation and demand, as large storage is not possible

• Variable and seasonal loads• Investments for power plant, transmission

line, distribution system• Very high gestation period

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Power System Planning

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Planning: Short Term

• Up to 5 years• Short term forecasting• Economics is the most important objective• Existing constraints

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Planning: Medium Term

• Up to 5-10 years• Planning for thermal plants• Economics is the preferred objective• Existing constraints• Renewables

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Planning: Long Term

• Up to 10-20 years• Long term forecasting• Renewable energy• Policy development• Understanding risk

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Major Parameters for New PlantParameters Alternatives

Energy Source/Fuel Fossil fuelsNuclearHydroRenewables

Generation system Steam-cycleGas turbineCombined cycleHydroelectricIC engineothers

Plant type BaseIntermediatePeakIncidental

Site Site requirements 34


Further Readings• W.D. Marsh, Economics of electric utility power generation,

Clarendon Press, 1980• P.K. Nag, Power Plant Engineering, Tata McGraw-Hill Education,

2002• S Kennedy, Wind power planning: assessing long-term costs and

benefits, Energy Policy 33 (2005) 1661–1675• The combined load duration curve and its derivation, IEEE

Transactions on Power Apparatus and Systems, Vol. PAS-96, no. 3, May/June 1977

• Modeling of the Load Duration Curve Using the Asymmetric Generalized Gaussian Distribution: Case of the Tunisian Power System, 2008 IEEE Power Engineering Society General Meeting

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lecture2 load curves 2015

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