SOLUTIONS FOR MECHANICAL AND ELECTROMAGNETIC PROBLEMS IN BULB TYPE HYDROPOWER UNIT

摘要

The paper presents the results of studying the specificrnproblems that occurred during the exploitation of twornbulb type generators (42 MVA, power factor 0,95), andrnthe methods for solving them. The problems were eitherrnof purely mechanical type or those caused by therncombination of electromagnetic and mechanicalrnphenomena. The work focuses particularly on tworngroups of problems that were more pronounced on onlyrnone of the two hydropower units.rnThe first problem is increased vibration of thernhydropower unit. After extensive research andrnnumerous measurements it has been determined that therncause of the vibration is the increased wear of the spiderrnto shaft joint elements. The spider has been connected tornthe shaft by a number of keys. In time this joint hasrnloosened. This has caused the various relative shifts,rnboth axial and radial, at the contact surfaces of the keysrntowards the hub and the shaft. The weakening of thernjoints has been a cause for several repairs of the unitrnthat have not permanently solved the problem. Inrnaddition to mechanical problems the eccentricity of thernrotor causes the unbalanced magnetic force pull thatrnfurther emphasises the problem. The user has installedrnseveral sensors into the generator itself, thus enablingrnthe measuring of the otherwise, in other generators nonmeasurablernvalues (air gap width, flux density in airgap,rnetc.) and allowing easier and more accuraterninterpretation of phenomena, as well as repair of thernresulting problems during the operation of thernhydropower unit. The data acquired by measurementsrnhas been used for detailed calculations of flux densityrnand magnetic force. FEM based software has been usedrnto calculate the unbalanced magnetic pull.rnNon-standard solutions have been applied to alleviate orrneven eliminate the problem of vibrations by shortcircuitingrnthe excitation winding of one pole, in order torncompensate for geometric non-symmetry by magneticrnnon-symmetry.rnFinally, it has been decided to completely replace thernmachine rotor with the new one that will have the spiderrnwelded to the shaft, as opposed to original wedged joint.rnThe fact that the welded connection proved reliablernduring the operation of the similar power plant withrnbulb type generators indicates this would be the bestrnsolution for the problem.rnThe other problem is electromechanical oscillation inrnthe stationary and transient states, which significantlyrndepend on the operating point of the drive. Since thernexcitation regulator and protection devices do not allowrnthe generator to operate in the regimes that could causernthe resonance of electromagnetic oscillations, the reasonrnfor power oscillation is suspected to be of hydraulicrnnature. The problem is partly solved by individualrncontrol of the guide vane blade openings in order tornbalance the inflow to the runner. This has reducedrnoscillations 5 to 10 times in the 17 to 33 MW powerrnrange, but reduction of oscillations at full load is still tornbe tested.