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Which is the lowest order harmonic present in the source current of 12 pulse converter?
5th order
7th order
11th order
13th order
11th order
In a p-pulse converter, the characteristic harmonics present on the AC side are given by the formula n=kp┬▒1, where k is any positive integer. For a 12-pulse converter, p=12, resulting in harmonics of the order 12k┬▒1 (i.e., 11th, 13th, 23rd, 25th, etc.), making the 11th order harmonic the lowest.
In a p-pulse converter, the characteristic harmonics present on the AC side are given by the formula n=kp┬▒1, where k is any positive integer. For a 12-pulse converter, p=12, resulting in harmonics of the order 12k┬▒1 (i.e., 11th, 13th, 23rd, 25th, etc.), making the 11th order harmonic the lowest.
n=kp┬▒1 тАФ Generalized harmonic order formula for a p-pulse converter
h=12k┬▒1 тАФ Specific harmonic order formula for a 12-pulse converter where k=1,2,3...
The 12-pulse converter is achieved by connecting two 6-pulse bridges in series/parallel with a 30-degree phase shift between their supply voltages, typically using a Y-Y and Y-Delta transformer configuration. This phase shift causes the 5th, 7th, 17th, and 19th harmonics generated by the individual 6-pulse bridges to cancel out. Consequently, only the harmonics defined by n=12k┬▒1 remain in the resultant source current.
Characteristic harmonics are those inherent to the commutation process in power converters.
The cancellation of 5th and 7th harmonics in 12-pulse systems significantly reduces Total Harmonic Distortion (THD).
Higher pulse numbers result in lower amplitude and higher frequency harmonics, which are easier to filter.
Lower THD in current and voltage waveforms compared to 6-pulse converters.
Reduced requirement for large and expensive AC harmonic filters.
Requires more complex transformer arrangements (phase shifting).
Higher total component count increases converter footprint.
High Voltage Direct Current (HVDC) transmission links.
Large industrial VFDs (Variable Frequency Drives) to meet IEEE 519 standards.
| Feature | 6-Pulse Converter | 12-Pulse Converter |
|---|---|---|
Lowest Harmonic | 5th (n=6k┬▒1) | 11th (n=12k┬▒1) |
The 5th and 7th harmonics are characteristic of 6-pulse converters. In a 12-pulse system, these are suppressed due to the 30┬░ phase shift between the two bridge inputs.
Option A and B represent harmonics of a 6-pulse bridge, while D is the next higher harmonic after the 11th in a 12-pulse system.
C is correct тАФ The lowest order harmonic in a 12-pulse converter is defined by n=12(1)тИТ1=11.
Always remember the simple rule: if the number of pulses p increases, the lowest harmonic n also increases, which simplifies power quality improvement.