Table of Contents
How third harmonics are generated?
As the harmonics are generated because of the above so called reasons, responsible for malfunction of circuit breaker, large neutral currents, skin effects, overheating of transformer, decrement in power factor, and distortion in voltages and extra losses in rotating machines.
What is third harmonic voltage?
Harmonics are voltages or currents that operate at a frequency that is an integer (whole-number) multiple of the fundamental frequency. So given a 50Hz fundamental waveform, this means a 2nd harmonic frequency would be 100Hz (2 x 50Hz), a 3rd harmonic would be 150Hz (3 x 50Hz), a 5th at 250Hz, a 7th at 350Hz and so on.
Why are even harmonics not considered?
In a power system, though we may have distortions in the current or voltage waveforms, but the waveform is mostly symmetrical. That is, negative half cycle is the mirror image of positive half cycle. Due to symmetry, even harmonics do not exist in majority of the cases. Hence they are considered insignificant.
Why is the third harmonic posses much concern than others?
The third harmonic causes a sharp increase in the current in the neutral conductor. Harmonics cause malfunctioning of electronic parts, transformer heating, and malfunctioning of power factor correction capacitors.
Are harmonics in phase?
Harmonics are AC voltages and currents with frequencies that are integer multiples of the fundamental frequency. Normally, only odd-order harmonics (3rd, 5th, 7th, 9th) occur on a 3-phase power system.
Why are harmonics only odd?
Most electrical loads (except half-wave rectifiers) produce symmetrical current waveforms, which means that the positive half of the waveform looks like a mirror image of the negative half. This results in only odd harmonic values being present.
Why even order harmonics are Cancelled?
So for odd harmonics, there is a positive half cycle still left which does not have a negative half cycle to cancel it. That does not happen for even harmonics. They have equal number of positive as well as negative half cycles. Actually of the cancellation they cease to exist in power systems.
Why do 3rd harmonic currents overload neutral conductors?
Due to the mathematical phase properties, third harmonic currents add instead of cancel out on the neutral wire (see Fig. 1). Therefore, in a building with a large number of Personal Computers installed, the neutral wire can carry much higher currents than it was designed for.