Power plants usually have several synchronous generators installed in parallel. Thus, the total capacity of power plants increases. One of the typical modes of operation of a synchronous generator installed in power plants is its parallel connection to a powerful network. Precise or self-synchronization methods are used to connect the generator in parallel to the network.
The self-synchronization method is applied in case of system crashes.
To connect a synchronous generator to the network in parallel, the following conditions must be met: at the moment of parallel connection, the electric driving force of the generator and the mains voltage must be equal to each other; the electric driving force must be in the opposite direction to the phase mains voltage. The frequency of the generator electric driving force must be equal to the frequency of the mains voltage. The phase sequence of the generator and the network must be the same.
Failure to comply with any of these conditions may result in an accident.
The set of conditions that occur when a synchronous generator is connected in parallel to the network is called synchronization. During synchronization, the synchronous rotation frequency of the rotor is first obtained. In this case, an approximate equality of frequencies is obtained. Then the impact current is regulated and the electric driving force of the generator is equated with the mains voltage. The presence of voltage and electric force vectors in the opposite phase is monitored by a clockwise synchronoscope. When this condition is met, the lamps go out for a short time. Thus, the lamps are affected by the voltage
△U = Un - Ug. The phase sequence is also determined by the flashing of the lamps. If the lamps flash at the same time, it means that the phase sequence is correct, and if they flash alternately, the phase sequence is incorrect.
Once these conditions are met, the generator is connected to the network.
Image 67. Vector diagrams of a generator operating in parallel with the network
To increase the active power of a generator connected in parallel to the network, it is necessary to increase the external torque applied to its shaft.
In this case, the angle between the mains voltage vector Un and the electric driving force vectors changes. To increase the reactive power of a synchronous generator operating in parallel with the network, it is necessary to increase the exposure currently. The value of electric driving force increases due to the increase of the impact current. Since this increase is determined by the inductive resistance of the machine, the current becomes reactive and the voltage drops 900 times to phase (Image 67 b).
Comments