# What are the main components reducing harmonic distortion?

I'm doing a study of harmonic distortion in a system. The system contain several large VSDs and other non-linear loads. There are no filters in the system, and all cables are relatively short.

Not surprisingly, the results show that the harmonic distortion is low close to large generators, while it is very high far from the stiff part of the network (given that there are non-linear loads in that part of the system).

My question is: What exactly is it that determine the level of distortion, except for the harmonic contributing equipment?

What influence does the different factors have:

1. Voltage level
3. Short circuit current capacity

I understand that if the non-linear loads are 1/1000th of the total load, the THD will be low, and if the load is completely non-linear the THD will be high, but is it the most important factor? And supposing the load level is the same at two buses, what other factors will determine the THD levels? Will the distortion level be different if the loads at the bus are passive linear loads, compared to for instance motors?

• It's a simple impedance-divider problem. The generator, transmission line, and load all have some impedance. The load is basically injecting noise (the harmonics) at its location with some voltage and impedance. The rest is a divider problem to determine how those harmonic signals are attenuated at various points in the network. Oct 20, 2013 at 13:18
• @OlinLathrop: I agree, harmonics must of course follow KCL / KVL, thus the distortion levels will be a function of impedances etc. But, assuming there exist a "typical motor", and typical "passive loads". If you turn off a motor and turn on a gigantic light bulb drawing the same power, will it affect the harmonics? (I'm aware of the fact that this depends on specific impedances etc., but is there a general "rule of thumb"?) Oct 20, 2013 at 13:37