Download - Economics of Power Utilization.ppt

7/28/2019 Economics of Power Utilization.ppt

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EE 2850 Applied Electricity

Economics of Power Utilization


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Contents

1.Cost of electric power

2.Factors influencing costs & tariffs

3.Load curve4.Tariff

5.Reduction of energy costs

6.Power factor correction


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1. Cost of Electric Power

It is necessary to properly account for the various

direct and indirect costs involved, before fixing

the final kWh charges for the consumers.

Fixed cost

Running / Operating cost


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Fixed Cost Operating Cost

Do not vary with the

operation of the plant

Vary with the operation of the

plant

Interest on capital investment Most of the fuel cost

Allowance for depreciation Small portion of salaries &

wages

Taxes & insurance Repair & maintenance

Most of the salaries & wages

Small portion of the fuel cost


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2. Factors influencing Costs & Tariffs1. Demand

- Load requirement averaged over a specified

interval of time of short duration

2. Average Demand

- Average power demand during a specified

period of time of considerable duration

(a day, month or year)


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3. Maximum Demand

- Greatest of all the demands which have

occurred during a given period

- Not the greatest instantaneous demand but

the greatest average demand

2. Factors influencing Costs & Tariffs


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4. Demand Factor- Ratio of actual maximum demand made by the

load to the rating of the connected load

Maximum demand < Connected load Electrical apparatus are usually selected

somewhat greater than the requirement In a group of electrical devices, all are not

imposing their maximum demand at the sametime



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5. Diversity of Demand- Maximum demand of various consumers occur

at different times during the day and notsimultaneously

- This results in lower costs of electric energy

6. Diversity Factor

- Usually > 1

- Higher diversity factor

- More consumers can be supplied

- Lower prices can be offered toconsumers



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7. Load Factor- Ratio of the average power to the maximum

demand

- Per year, per month or per day

- Equipments are selecting for maximum demand

- If fully occupied or not, there are fixed charges

- Poor load factors -> charge per kWh high

- To improve load factor -> accepting off-peak

loads at reduced rates



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8. Plant Factor / Capacity Factor

- Relates to a generator station

9. Utilization Factor

10. Connected Load Factor

- Relates to the receiving equipment



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3. Load Curve

1. Load Curve

Y-axis - Load in kW

X-axis - Time

Area under the curve - Total energy consumed

Following information can be obtained

Maximum load

Size of generator unit required

Daily operating schedule


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3. Load Curve

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4. Tariff Generating equipment has to be ready to meet

consumers full requirement at all hours of the day

Consumer should pay the

Fixed charges

for the portion of the plant that have been

allocated to him

Variable charges

- for the units used by him


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CEB Tariff - Domestic

Fixed Charge

(Rs/month)

Unit Charge

(Rs/kWh)

Up to 30 units 60.00 3.00

30 ~ 60 units 90.00 4.7060 ~ 90 units 120.00 7.50

90 ~ 180 units 180.00 16.00

180 ~ 600 units 240.00 25.00

Above 600 units 240.00 30.00


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CEB Tariff - Industry

Fixed Charge(Rs/month)

Unit Charge(Rs/kWh)

DemandCharge

(Rs/kWh)

I-1 240.00 10.50

I-2 3000.00 9.30 675.00I-3 3000.00 9.10 650.00

I-2 (TD) Peak 3000.00 24.60 650.00

Off peak 8.40

I-3 (TD) Peal 3000.00 23.00 650.00

Off peak 8.00


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3 part Time of Day tariff

Peak - 1830 hrs 2230 hrs

Day - 0430 hrs 1830 hrs

Off peak - rest of the time

CEB Tariff Industry / Hotel


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5. Reduction of Energy Cost Reducing energy consumption makes;

Reduce energy cost

Reduce pollution and make their communities

greener

Tips:

Monitor energy consumption

Choose energy efficient appliances

Replace incandescent bulbs with compact

fluorescent lights

Use less water

Use window treatments to control heat loss & heat

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6. Power Factor Correction

p.f. of all AC motors and transformers is < 1, lagging

Majority of industrial motors are induction motors High p.f. at full load

Low p.f. at light loads

For a 3-phase balanced system supplying a load W ata voltage V and p.f. cos;

Low p.f. -> high current

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Disadvantages of low power factor

Line losses (I2R) is high

Ratings of generators and transformers etc, are

proportional to I

- large equipment are required high capital cost

High capital cost for switch gears and cables

Low lagging p.f. causes a large voltage drop

- extra regulation equipment is required to

maintain voltage drop

Low efficiency

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Power factor improvement

Inject a leading current into the circuit

1. Installation of static capacitors

2. Installation of synchronous motors

3. Phase advancers

For a factory having no. of induction motors; Individual or centralized improvement

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1. Static Capacitors

p.f. is varying with load

Capacitor may result in over-correction

To overcome automatic p.f. correction (control

a no. of capacitors)

No moving parts installation & maintenance is

simple

Little or no floor space is requires

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2. Synchronous Motors

May be employed instead of a 3-phase IM

By increasing the DC exciting current, the p.f.

can be made to lead

More expensive

Synchronous capacitors

Only as a method of correcting the p.f. ofother apparatus

Not used to drive any machinery

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3. Phase Advancer

Method of manipulating the phase angle

Applied to large IMs

A form of AC exciter, mounted on the motor

shaft

Inject current in the IM rotor circuit

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Download - Economics of Power Utilization.ppt

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