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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. Ea Eb
- 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. 𝐼𝑐 = 𝐸𝑎 − 𝐸𝑏 𝑍𝑒𝑎 + 𝑍𝑒𝑏 No-load operation:- Applying KVL on secondary side Figure:1 𝐸𝑎 − 𝐼𝑐𝑍𝑒𝑎 = 𝐸𝑏 + 𝐼𝑐𝑍𝑒𝑏 Where:- 𝑰𝒄= Circulating current 𝑬𝒂 =No-load voltage of transformer ‘A’ 𝑬𝒃=No-load voltage of transformer ‘B’ 𝒛𝒆𝒂= Equivalent leakage impedance referred to secondary side of transformer ‘A’ 𝒛𝒆𝒃= Equivalent leakage impedance referred to secondary side of transformer ‘B’ Eb Ea
- 6. 𝐼𝑐 = 𝐸𝑎 − 𝐸𝑏 𝑍𝑒𝑎 + 𝑍𝑒𝑏 If Ea = Eb If Ea > If Ea < Eb Then Ea – Eb = 0 (No Circulating current) Then Ea –Eb < 0 (The effect of circulating current ‘Ic’ is to boost the lower voltage to V and to reduce the higher voltage to V across output terminal). Then Ea –Eb > 0 (The effect of circulating current ‘Ic’ is to boost the lower voltage to V and to reduce the higher voltage to V across output terminal).
- 7. 𝛽 = tan−1 ( 𝑥𝑒𝑎 + 𝑥𝑒𝑏 𝑟𝑒𝑎 + 𝑟𝑒𝑏 ) The angle 𝜷 by which 𝑰𝒄 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 𝑰𝒂 = 𝑰𝑳 𝒛𝑩 𝒛𝑨 + 𝒛𝑩 V Ea 𝑆𝑎 = 𝑉𝐼𝑎 Appling KCL at node A 𝑰𝒂 + 𝐼𝑏 = 𝑰𝑳 A
- 9. 𝑰𝒃 = 𝑰𝑳 𝒛𝑨 𝒛𝑨 + 𝒛𝑩 Therefore the load shared by second transformer is 𝑆𝑏 = 𝑉𝐼𝑏 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. Advantage Maximize electrical system availability Maximize power system reliability Maximize electrical system flexibility Maximize electrical system efficiency
- 13. Disadvantage Increase short-circuit current that increase necessary breaker capacity Diminish load capacity and increase losses. The supply bus rating could be too high. Parallel transformer reduces the transformer impedance The control and protection of these unit in is more complex.
- 14. THANKYOU
Editor's Notes
- Load sharing. Power contributed by each transformer to load and according to their kva rating.. Maintainenace required …in availability … Substation in flexibility ..
- Polarality should b main1.Voltage induced in seconday side will not equal if voltage ratio will not equal..this leads to circulating current ..this current also flow in primary side ..and it leads to core loss…2.As load sharing is done according to their rating ..a transformer with higher rating will draw more current and vice versa ..and higher rating machine have lower impedence . And vice versa but we know that voltage drop across each transformer must be same . Thus per unit impedence of each transformer must be same .to maintaining the proper load sharing … 111…polarity should b maintain
- Always two transformers of equal voltage ratios are selected for working in parallel. This way one can avoid a circulating current between the transformers . The equivalent circuit diagram is shown is shown in figure 2 in this diagram Za is equivalent leakage impedance of transformer A and Zb is equivalent leakage impedance of transformer B. Ia is the load current shearing by the the Xmer A using current divider rule …… we can write like this
- Similarly ib is ……. Therefore the load sheared by second transformer is ………… this implies the transformer having lower value of KVA rating must have higher leakage impedance in other words the load share by transformer is proportion to their KVA ratings.
- If leakage impedance angle of transformer A is not equal to the leakage impedance angle of transformer Then the output KVA is less then the sum of KVA rating of individual transformer because the IL is the vector sum of Ia and Ib if Ia and Ib is not in same phase then IL is not equal to