synchroscopes

synchroscopes

The armature of the synchroscope carries two windings at right angles to each other and is capable of rotation between field poles F F1

R is a non inductive resistance and XL is a highly inductive resistance both connected to one phase of the bus bars. This produces a field which rotates relative to the armature at the bus bar frequency. When the incoming machine is connected to the coils of the field poles a pulsating field is produced at the same frequency as the incoming machine.

If the two fields are not at the same frequency then the armature will rotate at a speed equal to the difference

In the modern rotary synchroscope there are no slip rings. The rotor has two soft iron pole pieces and with its shaft carrying the pointer it is magnetised by coil R from the bus bars. With this coil is fixed adjacent to the shaft, therefore, there are no moving coils, contacts or control springs.

Single Phase

Single phase synchronising with lamps Lamps Dark

Lamps bright

If using single phase synchronising it is considered better to use the lamp bright method as it is easier to judge the middle of the bright sequence rather than the middle of the dark sequence

Three phase synchronising

Synchroscope with two lamps (lamps dark)

The secondary windings of transformer T1 supplies field coil F of the synchroscope. The secondary windings of T2 supplies the rotating coils R of the synchroscope.
If the incoming machine is in antiphase with the bus bar the voltage difference between the output of the secondary of T1 and T2 is double the normal voltage giving normal volt drop across each lamp. When in phase there is no voltage difference between the outputs of T1 and T2 and therefore lamps are dark when synchronised.

Synchroscope with two lamps (Lamps bright)

Three phase synchronising with lamps (Lamps dark)

No1 Vector is stationary, if the incoming machine is running two slow then the No2 vector moves away from No1 vector in an anti clockwise direction. In the position shown as the No2 vector moves progressively anti clockwise then 'a' will brighten, 'b' will brighten shortly reaching maximum luminosity then darken, 'c' will darken .

When the machines are in phase, then 'R1' and 'R2' will be in align therefore 'a' will be dark, 'Y1' and 'B2' will be 120o apart and therefore 'b' will be approaching maximum luminosity, and the same will be for 'c' with 'Y2' and 'B1' 120o apart