Before discussing the average value and rms value calculations for different curves, we discuss the elementary mathematics that would be required in the problems.

The electric circuit consists of basic elements resistor, inductor and capacitor. If the single phase voltage is applied to the circuit, the circuit is called single phase AC circuit.

When the current flows in a conductor a magnetic flux is generated around the conductor and therefore magnetic field is developed. The direction of the magnetic flux developed is given by the right hand thumb rule which states that if the conductor is grasped by the right hand thumb such that the direction of the thumb is in the direction of the current, the flux is established in the direction of the magnetic field in which the finger curl. The direction of the magnetic fields is tangential to the flux direction. We are familiar with the electrical circuits and electrical parameters like emf, current, electric field strength etc. In the same manner the magnetic circuit has their own parameters that we will discuss in this chapter.

The networks are studied to find the voltage drop across the circuit elements and to find the current through circuit elements. These theorems may be applied in AC as well as DC network. But we are discussing only DC network with resistances as a circuit element in this chapter. The circuit elements in the circuit are resistance, inductance and capacitance but in this chapter we are dealing with resistance as a circuit element. Similarly the sources that may be used in the circuit are voltage source and current source.

Electrical measuring instruments are used to measure the electrical quantity such as voltage, current, power, energy etc. The instruments may be divided into two categories. 1. Absolute instruments 2. Secondary instruments

For any electrical circuit, we require two paths. The first is called forward current flowing path while another one is called reverse current flowing path. In Forward current flowing path the current flows from supply to load and to complete the circuit

It is quite interesting fact that Electrical energy is the form which is neither available nor required for any application. The available form of energy at first stage is normally mechanical energy in the form of potential energy of water, energy released by the combustion of coal of fusion energy of heavy radioactive atom etc. Also the required form of energy at final stage is normally mechanical energy to rotate our fans, wheel of train, and movement of various parts in case of mills etc. But the problem with mechanical energy is that this is available at one place and required at another place and its transfer from available point to required point is almost impossible. Now the question may arise why conversion of this energy into electrical energy at first stage called generating point and further conversion of electrical energy into mechanical energy back. The fact is that electrical energy is the only form of energy that can be transferred for a very long distance easily and safely. The conversion of energy is possible through the electromechanical energy conversion devices that we will discuss in the next chapters.

We have discussed about the use and importance of transformer in chapter 7. The transformer comes in picture when we have electrical power but as we have discussed that, Electrical energy is the form which is neither available nor required for any application. The available form of energy at first stage is normally mechanical energy in the form of potential energy of water, energy released by the combustion of coal or fusion energy of heavy radioactive atom etc. Also the required form of energy at final stage is normally mechanical energy to rotate our fans, wheel of train, and movement of various parts in case of mills etc. But the problem with mechanical energy is that this is available at one place and required at another place and its transfer from available point to required point is almost impossible. And with the fact of electrical energy that it can be transferred for a very long distance easily and safely. The conversion of energy is required through the machines. These machines are called electromechanical energy conversion devices.

Three Phase induction motor is the most popular motor for industrial and domestic purposes. Almost all the motors used in daily life are induction motor.

As far as our domestic supply is concerned we use 230 V, 50 Hz ac supply. For this supply we require motors operating at this voltage and single phase operated. A single phase induction motor is used for the same. Washing machine, electric fan, cooler, mixer and grinder are the commonly used example for the single phase supply.

Synchronous machines come in a variety of different constructions and designs. The main application of Synchronous machines is electricity generation. They are used as generators in all the hydro, nuclear, coal-fired, gas-fired and oil-fired power plants. This means that a synchronous generator is a standard machine used for conversion of mechanical energy into electric energy in all the power plants. Rated powers ofsynchronous generators are typically from a few megawatts up to a few tens of megawatts, or even a several hundreds of megawatts. The generation through synchronous generator is of three phase AC supply generally; therefore it is also named as alternator commonly.

Large amount of power is generated at the generating stations. The present trend is to install bigger size of alternators to generate large amount of power to supply to require increasing demand. The centralized generation of electrical power is through the thermal power plant, hydro power plant and nuclear power plant whereas the 70% demand is fulfilled by thermal power plant in India. In spite of the high cost of the production of the power per KWHr, the DG set is a preferable way for decentralized generation of power by many industries and commercial places because of the high reliability and stability of power supply. Many renewable ways are also growing very fast to balance the demand of supply due to the swift increase in the cost of the fuel. The site of the power station depends upon the type of the power station. The new thermal stations are being construction at pit head near the coal mines because of the higher cost of the transportation of the coal. Hydro power plant is governed by the availability of the water resources. The nuclear plant are also situated remote from the centers of the consumption due to safety reason. Thus, the difficulty of the getting power station sites near the consuming centers make it inevitable to transfer bulk electrical energy through longer distances. Long distance bulk power transfer is only possible by high voltage transmission system. Extra high voltage and ultra high voltage system have been developed in various countries for transporting energy from remote power station.