. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . eturn to the center of the delta until the three phases are closed. This sudden shifting of the static neutral is the cause of an unnecessary strain on the insulation of the system. Many failures of apparatus are recorded due to this cause. Not so with the star-connected system as a transmission line of any length may be charged at full voltage without shifting the position of the static neutral. In four-w
. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . eturn to the center of the delta until the three phases are closed. This sudden shifting of the static neutral is the cause of an unnecessary strain on the insulation of the system. Many failures of apparatus are recorded due to this cause. Not so with the star-connected system as a transmission line of any length may be charged at full voltage without shifting the position of the static neutral. In four-wire three-phase systems, where the emf. is stepped up throughdelta-star transformers, and three-phase power is supplied through star-delta step-down transformers, the latter system of connections, if theirneutral be connected to the neutral wire, serve as balancers for loads takenoff between neutral wires and lines, as indicated in the accompanyingdiagram Fig. 157. If the neutral point of the primary of the step-up star-star transformersbe connected to the neutral point of the generators, the secondary neutralpoint on the star-connected high-voltage side will be stable. The loads may. 282 HYDROELECTRIC PRACTICE be supplied between the neutral point and the Hnes but, since the genera-tors may have a third-harmonic component in the emf. between the neutraland terminals it is not advisable to ground the neutral point of the secondarywindings. If, however, the high-voltage secondary windings be an inter-connected-star, the neutral point may be grounded without causing theleast trouble. The reason why the interconnected-star eliminates the third-harmonic is that there is an interchange of the third-harmonic mmf. dueto the primary and secondary interactions of the interconnected trans-former windings. On account of their exposed position, transmission Hnes are the weakestUnk in the high-voltage transmission system. Even the failure of a singleinsulator may cause a complete shut-down
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