Advantages Of Stationary Armature Winding In Alternator

The field winding of an alternator is placed on the rotor and is connected to DC supply for producing the magnetic flux through slip rings/ brush-less excitation.The 3Ø armature winding is placed in the stator. This have following advantages:

1.    will increase.

     

      Because in 210 MW unit the excitation current(2600 A) is very small the the alternator full load current(9050 A).  I=210 x 10^6  /  √3 x 15750 x .85

                              =9056 A

      

   This much current will not possible to come out through slip ring/ brush

2. More no of brush will required for 3Ø four wire STAR-CONNECTIONS.

3. The Output Voltage will reduced by the reduce of no of turns of conductor or Area.

4. Due to simple and robust construction of the rotor , Higher speed of rotating rotor is possible  

5. The stationary 3-Phase armature can be directly connected to load without large  unreliable slip ring and brushes.

INDUCTION GEMERATOR

The induction Generator not a self-generator. It is necessary to exite the stator an external  source to rated voltage and frequency.it will genwrate only whenit is connected to a source to fixed voltage and frequency and if is then driven at a speed above the synchronous speed.
thus the induction or asynchronous generator has very short uses. It's application of the principle of induction generator lies in automatic breaking in dynamic.

application:

1. breaking Induction or magnetic
2. use in wind power plant for generating electricity.

PERCENTAGE DIFFFERENTIAL PROTECTION(MERZ-PRICE PROTECTION) FOR TRANSFORMER

The percentage differential protection or Merz-Price protection based on the circulating current principle can also be used for the transformer. This system gives protection against pass to phase faults to the power transformers.
The principle of such a protection scheme is the comparison of the currents entering and leaving the ends of transformer, two currents at the two ends of ends of the transformer are equal and balance is maintenance . So no current flows through the operating coil of the relay is inoperative .But when there is phase to phase fault , this balance gets disturbed. The difference current flows through the operating coil due to which relay operates, tripping the circuit breaker.

Compared to the differential protection used in generators, there are certain important points which must be taken care of while using such protection for the power transformer. These points are.

1. In a power transformer, the voltage rating of the two winding is different. The high voltage winding is low current winding while low voltage winding is high current winding. Thus there always exists difference in current on the primary and secondary sides of then relay may get operated through there is no fault existing.

To compensate for this difficulty, the current ratios of CT s. on each side are different. These ratios depend on the line current of the power transformer and the connection of CT s. Due to different turns ratio, the currents fed into the pilot wire from each end are same under normal conditions so that the relay remains inoperative