minor subject ktu

1. Module 2
Economics of Power Generation

2. SYLLABUS
Types of loads, Load curve, terms and factors, peak load and
base load -Cost of electrical energy – numerical problems
Power factor improvement – causes of low power factor,
disadvantages - methods of power factor improvement,
calculations of power factor correction, economics of power
factor improvement

3. • A power station is required to deliver power to a large number of
consumers to meet their requirements.
• While de-signing and building a power station, efforts should be made to
achieve overall economy so that the per unit cost of production is as low
as possible.
• This will enable the electric supply company to sell electrical energy at a
profit and ensure reliable service.
• There are several factors which influence the production cost such as cost
of land and equipment, depreciation of equipment, inter- est on capital
investment etc

4. • The art of determining the per unit (i.e., one kWh) cost of production of
electrical energy is known as economics of power generation.
The following terms much used in the economics of power generation :
(a) Interest- The cost of use of money is known as interest.
 The interest payable on the capital investment must be included in pricing
the energy.
The rate of interest depends upon market position and other factors, and
may vary from 4% to 8% per annum.
(b) Depreciation- The decrease in the value of the power plant equipment and
building due to constant use is known as depreciation.
 Every power station has a useful life ranging from fifty to sixty years.
From the time the power station is installed, its equipment steadily
deteriorates due to wear and tear .
 This reduction in the value of plant every year is known as annual
depreciation

5. Cost of Electrical Energy
• The total cost of electrical energy generated can be divided into three
parts, namely ;

6. Power Factor Improvement
 The capacitor draws a leading current and partly or completely
neutralises the lagging reactive component of load current.
 This raises the power factor of the load.

7. • The capacitor draws current IC which leads the supply voltage by 90o. The
resulting line current I is the phasor sum of I and I and its angle of lag is
φ2 .
• It is clear that φ2 is less than φ1, so that cosφ2 is greater than cos φ1.
Hence, the power factor of the load is improved.

8. Power Factor Improvement Equipment
1. Static capacitors. 2. Synchronous condenser. 3. Phase advancers.

9. Static capacitor
The power factor can be improved by connecting capacitors in parallel with the
equipment operating at lagging power factor.
The capacitor (generally known as static capacitor) draws a leading current and
partly or completely neutralises the lagging reactive component of load current.
Advantages
(i)They have low losses.
(ii)They require little maintenance as there are no rotating parts.
(iii)They can be easily installed as they are light and require no foundation.
(iv)They can work under ordinary atmospheric conditions.
Disadvantages
(i)They have short service life ranging from 8 to 10 years.
(ii)They are easily damaged if the voltage exceeds the rated value.
(iii)Once the capacitors are damaged, their repair is uneconomical.

10. Synchronous condenser
• A synchronous motor takes a leading current when over-excited and,
therefore, behaves as a capacitor.
• An over-excited synchronous motor running on no load is known as
synchronous condenser.
• When such a machine is connected in parallel with the supply, it takes a
leading current which partly neutralises the lagging reactive component
of the load.

11. Advantages
(i) By varying the field excitation, the magnitude of current drawn by the
motor can be changed by any amount. This helps in achieving stepless
control of power factor
(ii)The motor windings have high thermal stability to short circuit currents.
(iii)The faults can be removed easily.
Disadvantages
(i)There are considerable losses in the motor.
(ii)The maintenance cost is high.
(iii)It produces noise.
(iv)Except in sizes above 500 kVA, the cost is greater than that of static
capacitors of the same rating.
(v) As a synchronous motor has no self-starting torque, therefore, an
auxiliary equipment has to be provided for this purpose.

12. Phase advancers
• Phase advancers are used to improve the power factor of induction
motors.
• The low power factor of an induction motor is due to the fact that its
stator winding draws exciting current which lags behind the supply
voltage by 90o
• If the exciting ampere turns can be provided from some other a.c.
source, then the stator winding will be relieved of exciting current and
the power factor of the motor can be improved.
• Phase advancer which is simply an a.c. exciter is mounted on the same
shaft as the main motor and is connected in the rotor circuit of the
motor.
• Major disadvantage of phase advancers is that they are not economical
for motors below 200 H.P

13. Calcula tions of Power Factor Corr ection