Machine Parts

  The use of shunt generator is somewhat restricted. It is used to supply power to equipment located within the immediate vicinity of the generator. Its use is not satisfactory for supplying power to remotely located points because not only does the terminal voltage of the generator drop as load increases, but there is also a voltage drop in the line. The greater the load the greater the greater the voltage drop in line. The combined effect of the reduction in generator voltage plus the line drop makes the shunt generator unsatisfactory for the transmission of power over long distances. Diverter resistor: A resistance shunting the series field of a compound generator to adjust the degree of compounding to produce a desired voltage regulation is called diverter resistor. Why a self excited shunt generator will not build up voltage?     How can the voltage, current and power ratings of a generator be adjusted?     ...

Reasons for not building up voltage of a self excited shunt generator: ·          No residual magnetism: The start of the build up process requires some residual magnetism in the magnetic circuit of a generator. If there is little or no residual magnetism, because of inactivity or jarring in shipment, no voltage will be generated that can produce field current. ·          Field connection reversed: The voltage generated due to residual magnetism is applied to the field and current flows in such a direction as to produce lines of flux in the same direction as the residual flux. If the field connections are reversed, the lines of flux produced by the current flow will oppose the residual flux so that the generated voltage will decrease rather than increase. ·          Field circuit resistance too high: If the field circuit resistance is greate...

Justify the statement: Stability of operation is an important factor in the parallel operation of generators. Shunt generators share the load proportionately. Should anything to occur to upset this proportionate division of load, it would be desirable for the generators to restore automatically the division of load. Assuming that the speed governor of one of the motors driving the generators is such that it will not hold the speed constant and because of this condition the speed of generator 2 will increase. The increase in speed will produce a large r induced voltage in generator 2,which in turn will cause generator 2 to deliver more load. Of course ,if generator 2 delivers more of the load, generator 1 delivers less. This larger load upon generator 2 will cause more current to flow in the armature of generator 2,producing a larger I a R a drop, a larger drop due to armature reaction, and a larger reduction in armature current, all of which tends to oppose the increas...

Critical resistance :   The resistance of field-circuit for which around value build up process is possible is known as critical resistance .(After the value build up process is possible)    The significance of critical resistance in a self excited shunt generator:-   Due to residual magnetism in poles, some emf and hence current would be generated .When this current flow through the field coils will strengthen the magnetism of the poles.This will increases the pole flux which will further increase the generated emf that means further increase current which further increase the flux and so on. This phenomena will be happening till the generate voltage equal to terminal voltage. This phenomena also depends on the resistance of the field circuit. If field resistance is increased, then slope of the resistance line will   be increased, and hence the maximum voltage in which the generator will build up at a given speed decreases. If the field circuit...