Theoritically 5th and 7th harmonics doesnt exist in 12 pulse rectifier. But when i observed practically, it exists in the range of 4-5%. Can someone give idea on how to eliminate those to make it NIL?
When you analyze theoretically, you assume all the three phase are balanced in magnitude and phase displacement. This is not true in practice, hence the observed deviation. It is very difficult to achieve the target but I recall there was one paper long time back in IEEE Xplore that presented a technique of unbalanced triggering angle for the three phases to achieve a closer goal.
When you analyze theoretically, you assume all the three phase are balanced in magnitude and phase displacement. This is not true in practice, hence the observed deviation. It is very difficult to achieve the target but I recall there was one paper long time back in IEEE Xplore that presented a technique of unbalanced triggering angle for the three phases to achieve a closer goal.
It would appear that any unbalance will create some harmonic somewhere down the line or back into the line.. A practical approach would be perhapsto try
1.increase/decrease the configuration to eliminate particular harmonics
2.Filters(expensive)
3.switched mode operation.plus 2 above.
Cheers
4-5% of 5th and 7th harmonics, that is abnormal for 12 pulse thyristor rectifier. if the ac voltages are symmetrical, there would something wrong or from ideal conditions. please let me know your ac voltage conditions, your converter transfor voltages on grid side and rectifier side, tranformer winding turns for each winding?
if we can create an physical model for the 12 pulse SCR rectifier, and by controlling the phase, the 5th and 7th harmonics can be get , then the filter and other methods can be used to ...
Make sure the connection of transformer has Y/Y/D (0/30), you may test the incoming transfomer.
The best method to create a 12-pulse rectifier is to use two separate transformers whose primaries are identical (usually Delta connected) and one secondary is Star while the other secondary is Delta connected. However, it is essential that the turns ratio of the two secondaries are as close to 1.732 (root of 3) as possible. It is possible to take transformers with reversed connections in primaries and secondaries. A single transformer with one primary and two sets of secondaries normally does not give good results since the leakage inductance of the two secondaries are different, yielding different voltage regulation upon load and hence different current sharing. However, special winding techniques for single transformers can reduce this problem.
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