Conventional ways of Harmonic Mitigation

 We live in a world today where Electrical equipments are driven by Electronic controllers.  Although this has made systems more reliable and operations smoother, the devil of has also made a entry through these non-linear loads . Harmonic mitigation remains a major challenge for Electrical Engineers .

Whenever we consult any manufacturer for Harmonic mitigation, most  of them suggest methods like Active Filters, Tuned Filters, RTPFC etc. However, I am a firm believer in ' Prevention is better than Cure ' . I believe integrating conventional harmonic mitigation methods in the system architecture is the best solution for this case .

I would like to present the case of such methods implemented across many facilities in the world.

1) Distribution transformers can be selected to achieve a loading of 50% on full load. 

2) For HT VFDs, multi-winding transformers can be used to feed it . LT VFDs can be fed through separate Delta-Delta or Delta-star isolation transformers

3) HT Detuned filters can used to mitigate harmonics at the common bus in addition to Reactive Power Compensation for all distribution transformers .

These simple methods do need high capital investments but it pays back quickly through intangible benefits like below :

a) Long running hours with little maintenance.

b) Compliance to all requirements of Power Quality . (Unity PF with THD & TDD < 1.5%)

c) No resonance as detuned filters are used .

d) Balance capacity of TRFs can be used to feed critical loads as standby .

Most of the customers do not implement such suggestions to reduce initial investments.However, as the problems due to harmonic rise , half-cooked efforts are made to mitigate through methods suggested by manufacturers without giving a thought to system architecture .This results in complicated systems with partial compliance .

With increasing percentage of non linear loads, the issue of harmonics needs to be considered at design stage and solutions should be implemented in a planned way. The importance of restricting and / or limiting the harmonics at their source – which is non-linear load should be understood and practised to help maintaining required level of power quality.

The above case is a representation of methods implemented by leading electrical engineers across their clients . Selection of the methods must be done by a competent electrical engineer after a complete system study .