INTRODUCTION : 80% of total electricity produced in the world, is hydral, while remaining 20% is produced from nuclear, thermal, geo-thermal energy and from magneto hydr o dynamic (MHD)generators. MHD is a device used for converting heat energy of fuel directly into electrical energy with out a conventional electric generator The thermal efficiency of an MHD convertor is increased by supplying the heat at the highest practical temperature It has no turbine and usage of copper winding

Principle of MHD: The principle of MHD power generation is “An Electric conductor moving through a magnetic field will induce emf and the electric flux is produced”. “Retarding force is converted to electric work by means of electro magnetic induction.” If the fluid is at the right angles to the magnetic field induction an emf is induced in the direction at right angles to the both flow and field directions

Construction and main parts: DUCT: It is a divergent channel made up of heat resistant alloy with water cooling MAGNETS: The o/p power delivered by an MHD generator is proportional to B 2. They are 3 types: a) Water cooled electro magnets b) Permanent magnets c) Super conduction magnets ELCTRODES: Electrodes are mainly used to collect the power generated. The hall current minimizes the generated current. The electrode pairs may be connected in various ways to minimize hall current.

How MHD works? In MHD generator, electrically conducting gas at a very high temperature is passed at high velocity through a strong magnetic field at right angles to the direction of flow, thereby generating electrical energy. The current so obtained is direct current which can be converted into a.c by an inverter. Air becomes highly ionized at temperatures of 5000°c- 6000°c. The induced current is collected by suitably placed electrodes and carry d.c current to the external load.

 Segmented electrode configuration.  Continuous electrode configuration.  Hall generator. Electrode configuration of MHD :

Open cycle MHD

Closed cycle MHD:

Closed cycle MHD with liquid metal:

Advantages: Since high temperatures are involved, operational efficiency is high. No moving part, so more reliable. Ability of reaching the full power level instantly. The size of the plant is considerably smaller than conventional fossil fuel plants. The closed cycle system produces power, free of pollution. The capital cost of the MHD plants are estimated to be competitive with those of coal fired steam power plants.

Problems encountered indesign of MHD The major problem forced by this generator is the economics. Although the overall thermal efficiency is 60% against 40% for conventional thermal plant, additional investment in the magnet, generator, duct and d.c to a.c converters may increase the plant cost. Seed materials potassium attacks insulating materials and make them conducting electrode materials are chemically eroded by combustion of gases. Most of the gases related to material problems caused by high temperature and highly corrosive and abrasive environment.

Conclusion: Really MHD is a boon to the growing world. Hence we conclude that MHD is one of the special and eco friendly techniques that cannot be depleted. Mainly it is usefull when we use it as a combined plant with the steam power plant. The efficiency of a thermal power plants can be improved to a great extent if they are used in retrofit with MHD power plants.