Harmonics has effect on transmission line in various ways.
1. Skin effect and Proximity effect: these effects depend on frequency. Harmonics increase these effects. As a result effective ac resistance increases in presence of harmonics.
2. Loss: Additional harmonic current increases copper loss of transmission system and reduce power transmitting capacity. Copper loss is given by
Where In is the nth harmonic current and Rn is the system resistance at that harmonic frequency.
3. Voltage drop: Harmonic current produces harmonic voltage drops across various circuit impedances. As a result a weak system of large impedance has low fault level and greater voltage disturbances where as a stiff system of low impedance has high fault level and lower voltage disturbance.
4. Dielectric stress: Harmonic voltage increases dielectric stress of cables used in transmission line. The dielectric stress is proportional to their crest voltages. This reduces dielectric strength. This results in shortening of the useful life of the cable and probability of the number of faults and hence, the cost of repairs.
5. Corona: Corona starting and extinction levels depend on peak to peak voltage. The peak voltage depends on the phase relationship between the harmonics and the fundamental. Harmonic voltage increases peak to peak voltage. It may happen that the peak voltage is above the rating while the RMS. voltage is well within this limit. In this matter the IEEE 519 standard provides typical capacity derating curves for cables feeding six pulse converters.
1. Skin effect and Proximity effect: these effects depend on frequency. Harmonics increase these effects. As a result effective ac resistance increases in presence of harmonics.
2. Loss: Additional harmonic current increases copper loss of transmission system and reduce power transmitting capacity. Copper loss is given by
Where In is the nth harmonic current and Rn is the system resistance at that harmonic frequency.
3. Voltage drop: Harmonic current produces harmonic voltage drops across various circuit impedances. As a result a weak system of large impedance has low fault level and greater voltage disturbances where as a stiff system of low impedance has high fault level and lower voltage disturbance.
4. Dielectric stress: Harmonic voltage increases dielectric stress of cables used in transmission line. The dielectric stress is proportional to their crest voltages. This reduces dielectric strength. This results in shortening of the useful life of the cable and probability of the number of faults and hence, the cost of repairs.
5. Corona: Corona starting and extinction levels depend on peak to peak voltage. The peak voltage depends on the phase relationship between the harmonics and the fundamental. Harmonic voltage increases peak to peak voltage. It may happen that the peak voltage is above the rating while the RMS. voltage is well within this limit. In this matter the IEEE 519 standard provides typical capacity derating curves for cables feeding six pulse converters.