Electrical noise from classical electrical loads: 

The classical systems used bridge rectifiers for operation, and the resultant noise was predominant in the first lower order frequency spectrum. The switching noise from the bridge rectifiers has predominant 3rd, 5th, 7th, 9th, and 11th order. The noise decay over the higher-order frequencies from its 11th order. 

noise from classical system

Noise spectrum from the classical electrical load

Electrical noise from modern digital equipment:

However, the modern system uses SMPS topologies with high-frequency switching components such as MOSFETs, IGBT’s, etc., at 50-300kHz range. The resultant switching noise from the SMPS is in the higher-order harmonics spectrum, as shown in the graph below. 

noise from modern load

Noise spectrum from the modern digital load

The other factors that contribute to an increase in high-frequency frequency/oscillations in the system are:

  1. Increasing use of low-loss distribution transformers, which reduces the network damping substantially.
  2. Increasing use of power electronics with minimal ohmic loads such as electrical heaters – causing a reduction in the network damping. 

Are harmonics filters good enough for the system? 

May not be. Harmonics filters are an excellent solution for the classical system, removing the electrical noise in the lower order frequencies. However, the harmonic filters may not effectively remove the electrical noise generated in the higher-order harmonics from modern digital equipment. They are not tuned to remove the higher-order frequencies

To remove the higher-order harmonics and the switching noise, the facility must need specifically custom-tuned powerful electrical filters to remove the higher-order frequency noise. A well-designed low pass filter with surge suppression capabilities can attenuate the higher-order frequency, as shown in the following picture. 

Noise before filtration

Noise before adding high-frequency noise filters

Noise after filtration

Noise removal after adding high-frequency noise filters