Parallel operation of transformer

Parallel operation of transformer

1. PARALLEL OPERATION OF SINGLE-PHASE TRANSFORMER Pawan Kumar(EEB17033) Manish Kumar(EEB17036) Vishvas Kumar(EEB16022) Group-1

2. What is parallel operation of transformer ? The transformer is said to be in parallel operation when their primary winding is connected to common voltage supply and secondary winding are connected to common load. E a E b

3. Why parallel operation of transformers is needed ? Load Sharing (increase power transmission capacity) Continue flow of power during fault inside in transformer. Transportation is easier for small transformers. The cost of spare unit is less when two or more transformer is installed.. Flexibilty Availablity

4. The per unit impedance of each transformer on its own base must be the same. Necessary Conditions :- The transformers must have the same polarities. The transformers should have equal turn ratios and voltage ratio. Desirable conditions:- The ratios of their winding reactance to resistance should be equal for both transformers. This condition ensures that both transformers operate at the same power factor, thus sharing active power and reactive voltamperes according to their ratings.

5.   No-load operation:- Applying KVL on secondary side Figure:1   Where:- = Circulating current = No-load voltage of transformer ‘A’ = No-load voltage of transformer ‘B’ = Equivalent leakage impedance referred to secondary side of transformer ‘A’ = Equivalent leakage impedance referred to secondary side of transformer ‘B’   E b E a

6. Then E a – E b = 0 (No Circulating current) Then E a – E b < 0 (The effect of circulating current ‘ I c ’ is to boost the lower voltage to V and to reduce the higher voltage to V across output terminal). Then E a – E b > 0 (The effect of circulating current ‘ I c ’ is to boost the lower voltage to V and to reduce the higher voltage to V across output terminal).

7.   The angle by which lags is given by   Phasor diagram of no-load operation:-

8. On-load operation:- Fig 2 -Equivalent circuit diagram Therefore the load shared by first transformer is   V E a   Appling KCL at node A   A

9.   Therefore the load shared by second transformer is   From the above it is seen that the transformer with higher impedance supplies lesser load current and vice versa. In other word the load share by transformer is proportion to their KVA ratings.

10. Then the output KVA is less then the sum of KVA rating of individual transformer.

11. Then the output KVA is less then the sum of KVA rating of individual transformer

12. THANKYOU