Power generation is of two types AC or DC
We prefer synchronous generation only. In the case of thermal plants or nuclear plants power generation is done using a Synchronous generator.
We have Star and the Delta connection.
In this, we prefer star connection in alternator as if there occurs any fault then-current needs to find a path for groundings (relays have been used to find a path for groundings).
If we use a delta connection it is difficult for us to use as there is no grounding when there is any fault.
We use star connection windings in the stator of the alternator. So that neutral grounding can be done. Also, the rotor winding of the alternator is excited with a separate DC source which produces the magnetic flux. When the rotor is rotated with some external mechanical input then the flux which is obtained due to the rotor winding excitation cuts the stator flux and the voltages will get induced. The voltages which get induced in three phases that are equal in magnitude and are displaced by 120 degrees.
It is preferred to transmit the power at an increased voltage level by using the step-up transformer at generating end.
The power which is generated in the voltage range is around 11KV to 33KV which is transmitted to the load point using a transmission network.
Why do we need power system protection?
If there is any fault in the transmission line then at that time we need power system protection.
There are two faults generally,
- Open circuit fault/ Series fault
- Short circuit fault/ Shunt fault
When there is any unwanted opening of the circuit breaker contact or when the fuse melts then it is due to the open circuit fault.
In the three phases, if any of the phases got disconnected then it is treated as an open circuit fault.
During an open circuit fault, one of the phase currents will be zero so that net power increases as there will be an overvoltage due to the decrease in the current which in turn damages the insulation.
Short circuit fault,
It is also called a shunt fault and they are of five types namely LG fault, LL fault, LLG fault, LLL fault, and LLLG fault.
The main reasons for the occurrence of the short circuit fault are the failure of an insulator or the falling of tree branches on power conductors.
During short circuit conditions, there will be a high current so that the voltage will be less and the energy stored in an inductor will be very high which in turn decreases the power factor.
Due to a short circuit fault, there will be thermal stress and mechanical stress. Thermal stress occurs due to excessive heat generation and due to the mechanical stress, there will be the breaking of the conductor.
Relay is nothing but the sensing device whereas the circuit breaker acts as isolation which isolates the faulty section and the normal section.
Relay and circuit breaker configuration:
The relay may be an electromechanical or electrothermal device that continuously senses or monitors the assigned electrical quantity. When the relay coil observes that the assigned quantity exceeds the set value then the relay coil initiates the trip circuit which in turn energizes the trip coil so that the circuit breaker will be isolated.