Construction & Working of Electrodynamometer (Weston) Synchroscope

Construction & Working of Electrodynamometer (Weston) Synchroscope Points : Construction & Working of Electrodynamometer (Weston) Synchroscope Electrodynamometer synchroscope has mainly two parts; one static and another dynamic. Static part consists of mainly one three-limbed transformer and a lamp. Outer limbs of the transformer have two windings, one on each limb. One of these windings is excited from bus-bar and the other from the incoming machine. A lamp is connected to the winding on the central limb. Phasor sum of the two fluxes produced by the out limb windings passes through the central limb and are so connected that phasor sum of fluxes produced by these windings and add each other in central limb.

Now when phases of incoming machine voltage and buss-bar voltage are same then flux phasing through the central limb is maximum and voltage induced in the central limb winding is maximum. In this condition, lamp connected to central limb winding flows with maximum brightness. When these two voltages are out of phase with angle 1800 then flux passing through the central limb is zero and lamp remains dark. In the case when frequencies of incoming machine and bus-bar voltages are different then lamp glows becomes dark alternately (flickers). This frequency of flickering of lamp becomes equal to the difference of frequencies of the incoming machine and bus bar.

For synchronisation of incoming machine with bus bar, the speed of machine is so adjusted that frequency of flickering of lamp becomes very low. Then incoming machine is connected to bus bar when lamp flows with maximum brightness.

A dynamic part is also introduced in this system of synchronisation to get indication, whether the incoming machine is slow or fast. Flickering of lamp also shows the difference in frequencies of income machine and bus bar. A fixed coil, divided into two parts is connected to incoming machine in series with resistance and inductance. Moving coil is connected with bus bar in series with the capacitor.

Inductance in series with fixed coil and capacitor in series with moving coil are used to make current of these coils exact in quadrature when voltage of the incoming machine and bus bar are in phase.

In the condition, when these two voltages are in phase then current in these two coils will be in quadrature, as shown, So these will be no deflecting torque on the moving coil and pointer will remain stationary to indicate synchronisation of the incoming machine with bus bar. Control springs, which supply current to the moving coil are so adjusted that the pointer remains vertical in this condition.

When two voltages are out of phase by 1800 then in as shown and so there will be no deflecting torque on the moving coil and the pointer will remain stationary and in vertical position. But the main difference in these two conditions is that in the latter condition lamp glows with maximum brightness and in the former condition the lamp remains dark. So the correct instant of synchronisation is that when the pointer is stationary and the lamp glows with maximum brightness. But in practice, adjustment of speed of incoming machine is not possible to this extent that pointer takes stationary position. So pointer oscillates across its centre zero position on the scale.