Can u plz help me to solve following problems:1.After an AC generator has been paralleled explain how the following are achieved for the incoming generator(i)Correct kW load sharing(ii)Correct load current when the generator has a different power factor to the other generators2. the cumulative damage that may be caused when the alternators are incorrectly synchronized3.For alternators operating in parallel the consequences of:(i)reduced torque from the prime mover of one machine(ii)reduced excitation on one machine
1. (i). Each engine should carry the SAME LOAD PERCENTAGE-wise, eg. 80%, to minimize the load change burden on the rest. (Smaller engines may run at full load, since their contribution may go unnoticed.) Since the overall kW bus load is constant, each generator will pickup a percentage of it, by controlling the torque on each prime mover. If it is a steam turbine, by throttling steam flow. If it is a diesel engine, by throttling fuel, and so. (ii). Each alternator should be adjusted to carry the SAME POWER FACTOR, by adjusting excitation accordingly, eg, .85, to avoid stability issues. Running alternators at leading power factors may turn the system unstable and force loss of synchronism 2. Considerable mechanical damage will be caused by incorrect synchronization to windings, shaft and keyways. 3. (i) reducing torque on one a prime mover is done when preparing to take it out of service. This has to be done gradually, so that other machines can pickup the load slowly. When close to unloaded, the generator can be taken off the grid. Power should never be reduced to the point of allowing the generator to be motored, i.e., reverse power flow, which can cause unpredictable damage to the turbine and system instability. (ii) reduced excitation is a very dangerous condition which will cause the power factor to turn leading, i.e., capacitive, weakening the synchronizing torque with possible loss of synchronism and forcing the bus voltage up. .
1 by adjusting governor setting load can be increased load limit can be increased on some goivernor adjusting exciation great danger if incorrectly synchronized,Turbine thrown out of base by huge magnetic shock or shearing of coup;ling with generaot reduced torque load will decrease kva will decrease
