Principles of Power System Notes

1. INTRODUCTION


Energy is the basic necessity for the economic
development of a country.
Many functions necessary to present-day
living grind to halt when the supply of energy
stops. It is practically impossible to estimate the
actual magnitude of the part that energy has
played in the building up of present-day
civilisation. The availability of huge amount of
energy in the modern times has resulted in a
shorter working day, higher agricultural and industrial
production, a healthier and more balanced
diet and better transportation facilities. As a
matter of fact, there is a close relationship between
the energy used per person and his standard
of living. The greater the per capita consumption
of energy in a country, the higher is the
standard of living of its people.
Energy exists in different forms in nature but
the most important form is the electrical energy.
The modern society is so much dependent upon
the use of electrical energy that it has become a
part and parcel of our life. In this chapter, we shall
focus our attention on the general aspects of electrical
energy.
Introduction

1.1. Importance of electrical energy

Energy may be needed as heat, as light, as motive power etc. The present-day advancement in science
and technology has made it possible to convert electrical energy into any desired form. This has
given electrical energy a place of pride in the modern world. The survival of industrial undertakings
and our social structures depends primarily upon low cost and uninterrupted supply of electrical
energy. In fact, the advancement of a country is measured in terms of per capita consumption of
electrical energy.
Electrical energy is superior to all other forms of energy due to the following reasons :
(i) Convenient form. Electrical energy is a very convenient form of energy. It can be easily
converted into other forms of energy. For example, if we want to convert electrical energy into heat,
the only thing to be done is to pass electrical current through a wire of high resistance e.g., a heater.
Similarly, electrical energy can be converted into light (e.g. electric bulb), mechanical energy (e.g.
electric motors) etc.
(ii) Easy control. The electrically operated machines have simple and convenient starting, control
and operation. For instance, an electric motor can be started or stopped by turning on or off a switch.
Similarly, with simple arrangements, the speed of electric motors can be easily varied over the desired
range.
(iii) Greater flexibility. One important reason for preferring electrical energy is the flexibility
that it offers. It can be easily transported from one place to another with the help of conductors.
(iv) Cheapness. Electrical energy is much cheaper than other forms of energy. Thus it is overall
economical to use this form of energy for domestic, commercial and industrial purposes.
(v) Cleanliness. Electrical energy is not associated with smoke, fumes or poisonous gases.
Therefore, its use ensures cleanliness and healthy conditions.
(vi) High transmission efficiency. The consumers of electrical energy are generally situated
quite away from the centres of its production. The electrical energy can be transmitted conveniently
and efficiently from the centres of generation to the consumers with the help of overhead conductors
known as transmission lines.

1.2. Generation of electrical energy

The conversion of energy available in different forms in nature into electrical energy is known as
generation of electrical energy.
Electrical energy is a manufactured commodity like clothing, furniture or tools. Just as the
manufacture of a commodity involves the conversion of raw materials available in nature into the
desired form, similarly electrical energy is produced from the forms of energy available in nature.
However, electrical energy differs in one important respect. Whereas other commodities may be
produced at will and consumed as needed, the electrical energy must be produced and transmitted to
the point of use at the instant it is needed. The entire process takes only a fraction of a second. This
instantaneous production of electrical energy introduces technical and economical considerations
unique to the electrical power industry.
Energy is available in various forms from different
natural sources such as pressure head of water, chemical
energy of fuels, nuclear energy of radioactive substances
etc. All these forms of energy can be converted into
electrical energy by the use of suitable arrangements. The
arrangement essentially employs  an
alternator coupled to a prime mover. The prime mover
is driven by the energy obtaimed from various sources

1.3. Units of energy

The capacity of an agent to do work is known as its energy. The most important forms of energy are
mechanical energy, electrical energy and thermal energy. Different units have been assigned to various
forms of energy. However, it must be realised that since mechanical, electrical and thermal energies
are interchangeable, it is possible to assign the same unit to them. This point is clarified in Art 1.6.
(i) Mechanical energy. The unit of mechanical energy is newton-metre or joule on the M.K.S.
or SI system.
The work done on a body is one newton-metre (or joule) if a force of one newton moves it
through a distance of one metre i.e.,
Mechanical energy in joules = Force in newton × distance in metres
(ii) Electrical energy. The unit of electrical energy is watt-sec or joule and is defined as follows:
One watt-second (or joule) energy is transferred between two points if a p.d. of 1 volt exists
between them and 1 ampere current passes between them for 1 second i.e.,
Coal
Crude oil
Natural gas
Hydro-electric power
Nuclear power
Renewables
   5
Electrical energy in watt-sec (or joules)
= voltage in volts × current in amperes × time in seconds
Joule or watt-sec is a very small unit of electrical energy for practical purposes. In practice, for
the measurement of electrical energy, bigger units viz., watt-hour and kilowatt hour are used.
1 watt-hour = 1 watt × 1 hr
= 1 watt × 3600 sec = 3600 watt-sec
1 kilowatt hour (kWh) = 1 kW × 1 hr = 1000 watt × 3600 sec = 36 x 105 watt-sec.
(iii) Heat. Heat is a form of energy which produces the sensation of warmth. The unit* of heat
is calorie, British thermal unit (B.Th.U.) and centigrade heat units (C.H.U.) on the various systems.
Calorie. It is the amount of heat required to raise the temperature of 1 gm of water through 1ºC
i.e.,
1 calorie = 1 gm of water × 1ºC
Sometimes a bigger unit namely kilocalorie is used. A kilocalorie is the amount of heat required
to raise the temperature of 1 kg of water through 1ºC i.e.,
1 kilocalorie = 1 kg × 1ºC = 1000 gm × 1ºC = 1000 calories
B.Th.U. It is the amount of heat required to raise the temperature of 1 lb of water through 1ºF i.e.,
1 B.Th.U. = 1 lb × 1ºF
C.H.U. It is the amount of heat required to raise the temperature of 1 lb of water through 1ºC i.e.,
1 C.H.U. = 1 lb × 1ºC

The energy whether possessed by an electrical system or mechanical