OTHER ELECTRICAL MEASURING DEVICESTest Instruments & Measuring DevicesSynchroscopeFigure 16 Ground Detector Lamp CircuitA synchroscope indicates when two AC generators are in the correct phase relation forconnecting in parallel and shows whether the incoming generator is running faster or slower thanthe on-line generator. The synchroscope consists of a two-phase stator. The two stator windingsare at right angles to one another, and by means of a phase-splitting network, the current in onephase leads the current of the other phase by 90°, thereby generating a rotating magnetic field.The stator windings are connected to the incoming generator, and a polarizing coil is connectedto the running generator.The rotating element is unrestrained and is free to rotate through 360°. It consists of two ironvanes mounted in opposite directions on a shaft, one at the top and one at the bottom, andmagnetized by the polarizing coil.If the frequencies of the incoming and running generators are different, the synchroscope willrotate at a speed corresponding to the difference. It is designed so that if incoming frequencyis higher than running frequency, it will rotate in the clockwise direction; if incoming frequencyis less than running frequency, it will rotate in the counterclockwise direction. When thesynchroscope indicates 0o phase difference, the pointer is at the "12 o’clock" position and the twoAC generators are in phase.ES-14 Page 26 Rev. 0
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