Therefore the single phase loads can be balanced on three phase if required, and banks may be paralleled if required. When different rating transformers are used then the maximum safe transformer bank rating is three times the capacity of the smallest transformer.
-do- If one transformer becomes damaged or removed from the service ,the transformer bank may become inoperative. Conditions for paralleling distribution transformers 1. All transformers have identical frequency rating. 2. All transformers have identical voltage rating. 3. All transformers have identical tap settings. 4. Per unit impedance of one transformer is between 0.925 and 1.075 of the other.
Three Phase Transformers Advantages: The three phase transformers takes less space than does the three single phase transformers having same capacity. Three phase transformers are more efficient and less expensive than equivalent single phase transformer banks. Disadvantages: If one phase winding is damaged then entire three phase transformer has to be removed from the service.
The T or Scott connection This connection is used to transform a three phase to two phase transformation. T connection is used to get three phase transformation. Scott connection is used to get a two phase transformation. The T or Scott connection change the number of phases but not the power factor.
The Auto transformer Auto transformer has only one winding part of which is used as primary and part of which is used as secondary. It is rated on the base of output KVA rather than the transformer’s KVA. It has lower reactance, lower losses, smaller excitation current requirement.
The Booster Transformer Booster transformers are also called as Buck and boost transformers. They provides fixed buck or boost voltage to the primary of a distribution system when the line voltage drop is excessive. The transformer connection is made in such a way that the secondary is in series and in phase with the main line. Boosters are often used in distribution feeders where the cost of the tap changing transformer is not justified.
Amorphous Metal distribution transformers This is highly efficient transformer because amorphous metal provides low magnetic losses and provides the opportunity to reduce core losses by approximately 60%. It reduces the operating cost. It is quieter(38 db) than its equivalent silicon steel transformer (with 48 db). It reduces the utility operating cost and defer generating capacity addition.
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- Fall '19
- v.k mehta
- transformer bank, Symbols, Transformer sizes