economics of power utilization.ppt
TRANSCRIPT
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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
2. Factors influencing Costs & Tariffs
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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
2. Factors influencing Costs & Tariffs
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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
2. Factors influencing Costs & Tariffs
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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
2. Factors influencing Costs & Tariffs
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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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6. Power Factor Correction
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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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6. Power Factor Correction
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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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6. Power Factor Correction
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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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6. Power Factor Correction
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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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6. Power Factor Correction