It can be seen that the previous method is not accurate since it requires correct sense of judgement of the operator. Hence to avoid the personal judgement, the machines are synchronized by accurate device known as synchroscope.
It consists of a rotating pointer which indicates the exact moment of closing the synchronizing switch. If the pointer rotates in anticlockwise direction, it indicates that incoming machine is running slow whereas clockwise rotation of pointer indicates that incoming machine is running faster. The rotation of pointer is proportional to the difference in the two frequencies. The pointer should rotate at a very low speed in the direction of arrow marked fast as shown in the Fig. 1.
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| Fig. 1 |
When the rotating pointer reaches the vertical position at slow speed, the switch must be closed. The pointer will oscillate about some mean position instead of rotating if difference in frequencies is large. In such cases the speed of incoming machine is adjusted properly.
The connections for synchroscope are shown in Fig. 1. Any two bus bars lines are connected to its terminals while its other terminals are connected to corresponding lines of incoming machine. The phase sequence from bus bars and from machine must be same. It can be checked with the help of phase sequence indicator. The voltmeter is used to check the equality of voltage of bus bars and incoming machine. The synchronization procedure is already explained before.
Note : The use of lamps and synchroscope together is a best method of synchronization.
Now a days automatic synchronizing devices are also available which will perform the entire process of synchronization automatically without the help of shift engineer. But such schemes are more complicated and may take larger time than required by a shift engineer.
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