Design and Operation Investigations for large Converter-Fed Synchronous Machines in Hydropower Applications

Abstract

The work presented in this thesis deals with design and operation investigations for large converter-fed synchronous machines in hydropower applications. It is shown that the optimal rated frequency that gives the lowest total cost is reached between 40 Hz and 50 Hz. Increasing the value of the synchronous reactance from 1.2 p.u. to 2.0 p.u. reduces the total cost of the generator. The reduction in cost can help offset parts of the cost of the converter that are associated with having a converter-fed synchronous hydrogenerator in pumpedstorage plants. This, in turn, can make variable-speed pumped storage plants more cost-competitive versus traditional fixed-speed solutions. The effect of converter operation on AC copper loss in large hydrogenerators is investigated. Current harmonics produced by the converters increase the AC copper losses in traditionally designed stator windings. These additional losses could cause intolerable heating and probably destroy the windings. If a generator is going to be built for converter operation using a two-level or a three-level topology, it is found that the strand thickness would have to be reduced. If this is not possible, a filter between the converter and the generator must be used. Including damperbars in a converter-fed synchronous hydropower generator increases the AC copper losses in the stator. In addition to this, the losses in the damperbars themselves increase substantially. It is advised against using damperbars, if possible, when two- or three-level converter topologies are used. Experimental work is been presented for a generator test setup. Losses have been measured at different levels of magnetization and at different rotational speeds. Mechanical losses and core losses are estimated from measurements. Experimental results have been used to verify the loss calculations used in this thesis.