What steps to be taken before synchronising two ac generators?

Answer 1

The basic run up checks should be made, and then the generator coming onto the grid that the first generator is on is brought up to speed. The operator runs up the rpm's of the generator coming online so it turns just a bit faster than the line frequency. Then, with the generator coming online running a bit faster than the line, the operator watches the phase relationship of the generator with the line. The indicator on the meter will be moving like a second hand on a clock, only faster. Maybe one cycle every half dozen seconds or so. As the phase indicator is coming up on 0 degrees (or 360 degrees, or "straight up" on the indicator), the operator actuates the breaker lever to close the breaker and parallel the machines. One rule of thumb is to shut the tie at "5 'til the hour" on the indicator. The idea is to get the machine coming online up to speed an running a tad faster than the line, and then shutting the tie when the oncoming machine is amost but not quite in phase with the line, but is a bit "ahead" of the line by a small margin. That gives the tie a second or so to close, and the machines will be "pretty close" to being in phase when the tie goes shut. The machines will then lock as soon as the connection is made, and the operator will then run up the field voltage in the oncoming generator to get it to assume more of the load on the line. He will balance the loads, or otherwise shift them, perhaps with the idea of taking the first generator off line.