The Synchroscope is a device used for determining the phase angle differences between two or more machines at the time of the synchronization. The synchronization is essential for sharing the load on the bus bar of the power system. The following are the essentials conditions for synchronization.
- The magnitude of the incoming voltage becomes equal.
- The machines are in phase with each other.
- The frequency of the machines remains same.
For the parallel operation of the three-phase machines, it is essential that they are in phase with each other. The phase sequence of the device is correct at the time of the installation.
The Synchroscope compares the incoming voltage of the machines concerning the three-phase system. The figure of synchroscope shown below. It has a dial places on the circular calibrated scale on the motor. The position of the dial shows the phase difference between the incoming voltage and the infinite machines.
The scale of the Synchroscope marks with two arrows which indicate the direction of rotation of the pointer. The arrow indicates the clockwise and the anti-clockwise direction of the pointer. The clockwise arrows show too fast movement and the anti-clockwise direction show slow rotation of the incoming machine.
The arrow shows the movement of the machine concerning the bus bar. If the frequency of the incoming machine is more than that of the generator, the pointer deflects towards the fast mark. And if the frequency of the incoming machine is less then the pointer deflects towards the slow mark.
When the frequency of the incoming machine voltage and the infinite machine becomes equal, the pointer becomes stationary. When their frequency differs then the pointer deflects in one direction.
The deflection of pointer shows the speed of the incoming machines, i.e., the frequency of the incoming machine is higher or lower than that of the infinite bus or not. The frequency and phase position are controlled by the input of the prime mover.
When the pointer moves slowly and passes through the zero phase point, the circuit breaker is closed, and the incoming alternator connects to the bus. The Synchroscope does not give any information about the phase sequence. It shows relation only on one phase.
Note: The large synchronous motor can also be Synchronize through these methods. The synchronous machine is started, and when the machines gain synchronous speed, the direct current supplied to the field winding. If the load torque is not excessive, then the motor synchronized with the system.