In the case of series operation the motors shafts of the two machines are connected to the same load and also the two armatures are series connected. This forces a common armature current through both the machines and the torques developed by the machines are proportional to the flux in each machine. Series operation of series motors is adopted during starting to improve the energy efficiency. This method is ideally suited for shunt and compound machines with nearly flat torque speed characteristics. Such machines can go through high amount of dynamics without the fear of becoming unstable. This configuration is used in steel mills. Having two smaller machines connected to the shaft is preferred over there in place of one large machine as the moment of inertia of the motors is much reduced, thus improving the dynamics.
Auto Transformer Tap Changing: Working Principle, Switching Sequence and Applications Auto transformer tap changing is a practical method of adjusting transformer output voltage without unnecessarily interrupting the electrical supply. In power transmission and distribution networks, the load does not remain constant throughout the day. As load current changes, voltage drops across transformers, cables, feeders, and transmission lines also change. A tap-changing arrangement compensates for these variations by modifying the effective number of turns in the transformer winding. A reactor-type on-load tap changer uses a center-tapped reactor, selector switches, and a bypass or short-circuiting switch to transfer the load from one tap to the next. The reactor limits the circulating current during the transition, allowing the tap position to change while the transformer continues supplying the connected load. This article explains the auto transformer tap-changing working principle , switch...
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