Double Star Stator Connection of Hydrogenerators

In some hydro generator designs, there may be a number of circuits per phase and each circuit may consist of a number of multi-turn coils connected in series. In these machines, the parallel-connected circuits may be formed into two groups that are paralleled with only two leads being brought out to external connections. There may be an equal or unequal number of circuits in each group. In this design, current transformers can be provided in each phase group and in the leads to the external connections.

The star-connected double-winding construction sometimes used in large steam-turbine generators. Each phase has two separate windings that are connected externally to form two star connections. The high-voltage terminals of each phase are connected in parallel to form a single three-phase output. Separate star connections are formed on the neutral end of each winding. These neutrals may be physically at opposite ends of the machine. This arrangement is sometimes referred to as the double-ended, twelve-bushing machine and is used where the total full-load phase current exceeds the current carrying capability of a single bushing. The bushings at each end of the winding can accommodate three current transformers.

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