Synchronizing the Generator to the Mains
How and with which method will you synchronize the generator?
physical method
After discussing the principles of synchronizing the generator to the grid, we will briefly look at the physical method of doing this. In theory, there are at least two simple measurements or indicators that can be used to synchronize a generator to a grid.
When two voltages are of equal magnitude, of the same frequency, and satisfy the conditions for having zero angles between them, they add up on sine waves so that they are zero around the voltage loop at every instant of time.
As a result, both voltmeters connected to each of the sync breaker contacts will read zero. Lights placed in the same location will also turn off completely when all synchronization conditions are met.
In practice, to synchronize a generator to the grid we need information that voltmeters and light will not give us. During the actual physical synchronization process, we want to know whether the generator or the grid is fast and how fast.
The instrument that will provide this information is the synchroscope. The image below shows a synchroscope connection between the synchronized generator and the mains.
We will still need to use two voltmeters to check that the generator and mains voltage are the same (note that these two voltmeters are not the ones mentioned above because they are placed on the sync breaker contacts).
“ The position of the synchroscope indicator shows the angle difference between the generator voltage and the mains voltage. When there is zero angle between the two voltages, the synchroscope indicator will be in the vertical or 12 o'clock position.
The speed of rotation of the indicator shows the difference in the frequency of the two voltages. The indicator will rotate slowly or counterclockwise when the generator frequency is below the mains frequency. The indicator will rotate Fast or clockwise when the generator frequency is greater than the mains frequency.
It should be noted that the synchroscope will rotate only for small differences in frequency up to 2 Hz. At larger frequency differences, the synchroscope is designed not to rotate.
The last two paragraphs state:
- Indicator in vertical or 12 o'clock position,
- The indicator is fixed, does not rotate. Then the two voltages are in phase and the frequencies of the generator and mains are equal.
In practice, the sync breakers are turned off when the generator is a little fast and moving towards 12 o'clock in the approximately 5 minutes to 12 position. This action allows time for the synchronous breakers to close and ensures that the generator does not act as a motor when the synchronous breaker is closed.
“ Before each synchronization, it is important to check whether the synchronization is working properly.
To do this, the generator is operated at below synchronous speed and the synchroscope must rotate in a slow direction. Similarly, when the generator is operated at a higher speed than synchronous, the synchroscope should rotate in the fast direction.