I understand that the 3 criterion below needed to be fulfilled in order to do syncronisation:

1)terminal voltage
2)frequency
3) phase

but, i don't understand how to control all these criterion, means the theory behind them.

please help me to understand them

 

paein,

1) When an AC (Alternating Current) generator is at or very near rated speed, generator terminal voltage is controlled by varying the excitation applied to the generator's DC field(s). There are many, many types of exciters so it would be extremely difficult to detail all of them.

The act of making the generator terminal voltage equal to or slightly greater than the voltage of other generators when synchronizing a generator with other generators is called "voltage matching."

2) Frequency is one of the most important attributes of an alternating current system. When synchronizing a generator to other generators the frequency of the "incoming" generator must be very nearly equal to the frequency of the other generators with which it is being synchronized. The frequency of a generator is a function of the speed of rotation of the generator's DC field(s) which is controlled by the speed of the machine providing the torque to the generator rotor (a steam turbine, or a gas turbine, or a hydro turbine, or a reciprocating engine). Varying the speed of the machine driving the generator will change the frequency of the generator.

Since the frequency of a generator is a function of the speed of the machine driving the generator (also called a "prime mover"), changing the frequency during synchronization of a generator with other generators is also called "speed matching."

3) Most AC generators have three phases, sometimes called A, B and C; or R, S, and T; or Red, Yellow, and Blue; or even 1, 2, and 3. It's extremely important when synchronizing a generator with other generators that the alternating current sine wave of the generator's Phase A be connected to the Phase A be connected to the Phase A alternating current sine wave of the other generators. And that the alternating current sine wave of the generator's Phase B be connected to the alternating current sine wave of Phase B of the other generators; similarly with Phase C's alternating current sine wave. This check is usually performed during the initial (very first) synchronization of a generator with other generators, and because the conductors of both the generator output and the "bus" of the other generators is made using bars of metal, or tubes of metal and they are not usually ever disassembled it usually only has to be checked once during initial synchronization of the generator.

So during subsequent synchronizations of an AC generator, the operator is usually only responsible for matching the voltage and matching the speed (frequency), since the phases were verified during initial synchronization and the conductors (bars or tubes) don't ever usually get disassembled in such a way that they might get reassembled incorrectly (though I'm sure it has happened somewhere in the world at some time since AC systems have been in use). Many generators have automatic "relays" that will perform voltage- and speed matching for the generator operator.

These are all <b>very</b> brief answers to complicated questions and principles; as such the answers are general and do not cover some other really important principles of alternating current generators and alternating current systems. You should use your preferred Internet search engine to do more research on synchronous generators (more correctly called alternators) and the principles of AC machines, and three-phase AC machines in particular (since the overwhelming majority of the AC generators in the world are three-phase generators). In this case, pictures of ac generators and their construction and of alternating current sine waves are worth thousands of words. Unfortunately, we can't provide pictures in this forum, but even if we could there are whole textbooks and reference books on AC machines and principles and we couldn't cover all of them in any detail.

Hopefully this will get you started on your search for answers. One great place for information about AC generators and AC principles and AC systems is candu.canteach.org. They have some really great basic information about AC systems and AC generators, and even synchronization of AC generators with each other (on an electrical grid).

 

Although the voltage remains the same when the generators are synchronized because they have to be "voltage matched", is the current (amperage) stepped up. For example: if two 400V generators are synchronized then the voltage is not step up the voltage to 800V because the voltages have to be "voltage matched". What is the advantage then? That there is an increase in current (amperage)?