ÿþUnit 2: Circuit elements  

Current moves from a point of high potential energy to one of low potential. It can only do so if there is a path for it to follow. This path is called an electric circuit. All circuits contain for elements: a source, a load, a transmission system and a control.  

The source provides the electromotive force. This establishes the difference in potential, which makes current flow possible. The source can be any device, which supplies electrical energy. For example, it may be a generator or a battery.  

The load converts the electrical energy from the source into some other form of energy. For instance, a lamp changes electrical energy into light and heat. The load can be any electrical device.  

The transmisson system conducts the current round the circuit. Any conductor can be part of a transmision system. Most system consist of wires. It is often possible, however, for the metal frame of a unit to be one section of its transmission system. For example, the metal chassis of many electrical devices are used to conduct current. Similarly the body of a car is part of its electrical transmission system.  

The control regulates the current flow in the circuit. It may control the current by limiting it, as does a rheostat, or by interrupting it, as does a switch.  

>>> Magneto Hydrodynamic MHD Genetation<<<  

In conventional power generation, fuel such as oil or coal is burned. The burning fuel heats boilers to produce steam. The steam is used to drive turbo-alternators. The MHD process generates electricity without requiring a boiler or turbine.  

MHD generation works on the principle that when a conductor cuts a magnetic field, a current flows through the conductor. In MHD generation the conductor is an ionzed gas. Small amount of metal are added to the gas to improve its conductivity. This is call seeding the gas. The seeded gas is the pumed at a high temprature and pressure through a strong magnetic field. The electrons in the gas are collected at an electrode. This movement of electrons constitutes a current flow.  

Two methods of MHD generation can be used: The open-cycle and the closed-cycle. In the open-cycle method the hot gas is discharged. In the closed-cycle method it is recirculated.  

The open-cycle method uses gas from burning coal or oil. The gas is seeded and then passed through a magnetic field to generate current. The seeding elemets are recovered and the gas can then be used to drive a turbine before being allowed to escape.  

The closed-cycle method uses an inert gas, such as helium, which is heated indirectly. The gas is circulated continually through the MHD generator.  

MHD generation is still in its early stages but already an efficiency rate of 60% has been reached. This compares with a maximum of 40% from conventional power stations.