The driving power from the prime-mover driving the alternator is lost ...
In case of failure of the prime mover of the generator and the excitation is present then the generator draws power from the other parallel generator and starts working as a synchronous motor with the same direction and for this motor, the turbine is working as a load.
Because of the huge mass of the turbine the motor draws a huge amount of current which damages the winding. It will absorb power from the bus bar.
The driving power from the prime-mover driving the alternator is lost ...
When the driving power from the prime-mover driving the alternator is lost, but the alternator remains connected to the supply network and the field supply remains on, the alternator will behave as a synchronous motor and rotate in the same direction as it would during generator action.
Here is a detailed explanation of why the correct answer is option 'C':
1. Alternator Operation:
An alternator is a synchronous generator that converts mechanical energy into electrical energy. It consists of a rotating magnetic field (created by the rotor or field winding) and a stationary armature winding. When the alternator is driven by a prime-mover (such as a turbine or an engine), it generates electrical power.
2. Prime-Mover Failure:
If the driving power from the prime-mover is lost, the mechanical energy required to rotate the alternator is no longer supplied. As a result, the alternator's rotor will gradually slow down and eventually come to a stop.
3. Connection to the Supply Network:
However, if the alternator remains connected to the supply network, the armature winding will still receive electrical power from the network. This power will create a magnetic field in the stator windings.
4. Field Supply:
In addition, the field supply to the rotor winding remains on. The field winding creates a rotating magnetic field. The direction of this rotating field is determined by the design of the alternator.
5. Synchronous Motor Operation:
In this scenario, the stationary armature winding acts as the stator and the rotating magnetic field (created by the field winding) acts as the rotor. When the armature winding receives electrical power from the supply network, it interacts with the rotating magnetic field and generates a torque.
6. Same Direction Rotation:
Since the rotating magnetic field from the field winding and the electrical power from the supply network are in sync, the alternator will behave as a synchronous motor and rotate in the same direction as it would during generator action.
7. Reverse Direction:
The given options do not indicate that the alternator will rotate in a reverse direction to that corresponding to generator action. Hence, option 'D' is incorrect.
In conclusion, when the driving power is lost but the alternator remains connected to the supply network and the field supply remains on, the alternator will behave as a synchronous motor and rotate in the same direction as it would during generator action.
To make sure you are not studying endlessly, EduRev has designed Electrical Engineering (EE) study material, with Structured Courses, Videos, & Test Series. Plus get personalized analysis, doubt solving and improvement plans to achieve a great score in Electrical Engineering (EE).