The system consists of a lightweight non magnetic aluminium disc, which is mounted on a spindle having low friction bearings. This disc is placed between two electromagnets made up of soft laminated iron core. The upper electromagnet contains a voltage coil which is connected through a transformer between one phase and an artificial neutral of alternator output. The lower electromagnet also contains a current coil which is supplied from the same phase with the help of a transformer.
The voltage coil is particularly designed with a high inductance so that it can lag current in the coil by an angle approaching 90 degrees. Due to this lag, the magnetic field produced by the current also lags the magnetic field in lower electromagnet. When both these field passes through the aluminium disc, production of eddy currents take place, which results in a torque that tries to rotate the disc.
Under normal power flow, the trip contacts on the disc spindle are open and the disc bears against a stop.When reverse power occurs , the disc rotates in other direction and moves away from the stop and moves towards the trip relay. A time delay of 5 seconds is also provided so as to prevent tripping during synchronizing process. The general reverse power settings are 2 to 6% for turbine power movers and 8 to 15% for diesel engines.
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