What are harmonics?
Harmonics are currents or voltages with frequencies that are integer multiples of the fundamental power frequency e.g. if fundamental frequency is 50Hz, then the 2nd harmonic is 100Hz, the 3rd is 150Hz etc.
Non-linear loads that draw current in abrupt pulses rather than in smooth sinusoidal manner create harmonics. Non-linear loads consist of inductive or capacitive loads. These pulses cause distorted wave shapes, which in turn cause harmonic currents to flow back into other parts of the power system..
Harmonics are measured in terms a parameter called Total Harmonic Distortion (THD). It takes into account all the harmonics and is expressed as percentage value of fundamental.
Harmonics are having adverse effects such as overloading of transformers (de-rating) and rotating equipment, tripping of circuit breakers and fuses, neutral overloading etc.
Ballasts are non-linear loads. Low power factor and harmonics generation are problems that evidence themselves on the lamp side. One of these is the lamp current crest factor, which is the ratio of the peak lamp current to the rms lamp current. A sine wave has a crest factor of 1.41. The service life of a fluorescent lamp is significantly shortened when the crest factor exceeds the lamp manufacturer's recommendation, usually 1.7 for most lamps