Q. What are the advantages of parallel operation of transformers?
2) To maximize electrical power system availability: If numbers of transformers run in parallel we can take shutdown any one of them for maintenance purpose. Other parallel transformers in system will serve the load without total interruption of power.
3) To maximize power system reliability. If any one of the transformers in a parallel system, is tripped due to fault other parallel transformers is the system will share the load hence power supply may not be interrupted.
4) To maximize electrical power system flexibility: Always there is a chance of increasing or decreasing future demand of power system. If it is predicted that power demand will be increased in future, there must be a provision of connecting transformers in system in parallel to fulfill the extra demand because it is not economical from business point of view to install a bigger rated single transformer by forecasting the increased future demand as it is unnecessary investment of money. Again if future demand is decreased, transformers running in parallel can be removed from system to balance the capital investment and its return.
Q. What are the Conditions for parallel operation of transformers?
b) Same percentage impedance: impedance of transformers running in parallel are inversely proportional to their MVA rating
c) Same polarity: Polarity of all transformers run in parallel should be same otherwise huge circulating current flows in the transformer but no load will be fed from these transformers.
d) Same phase sequence: If they are not in same phase sequence, during the cycle, each pair of phases will be short circuited.
Q. Explain about auto transformer?
It is used where transformation ratio differs little from unity.
As it contains only one winding, it uses less copper and hence cheaper.
Its efficiency is more when compared with the conventional one.
Its size is relatively very smaller.
Voltage regulation of autotransformer is much better.
Low requirements of excitation current.
Less copper is used in its design and construction
In conventional transformer the voltage step up or step down value is fixed while in autotransformer, we can vary the output voltage as per out requirements and can smoothly increase or decrease its value as per our requirement.
Q. How does a transformer contribute towards the widespread popularity of AC system over DC?
ii. Using a transformer, AC voltage can be increased or decreased without any power loss.