Harmonic Filters – Which One Should You Use?

To comply with IEEE519-1992—the standard that a utility or an engineer may specify to limit the maximum current and voltage distortion in a facility—there are several strategies that can be employed.   They all accomplish a similar end result, so how do you make a decision about which strategy to use?   The answer—like so many problems that have more than one answer—is “that it depends”.  So, this blog is a discussion on those “depends” factors.

First, a disclaimer:  Sloan is the distributor and integrator of the three harmonic filter technologies presented, therefore this analysis is based upon product specifications, experience in their application and servicing.  We do not advocate for any particular technology or manufacturer until we have a comprehensive understanding of the site and application conditions, including some familiarity with site personnel and client internal policies or preferences – you guessed it, this is “Depends” factor #1.

“Depends” factor #2:  An analysis of the site conditions to determine current and voltage distortion limitation requirement per IEEE519-1992.

The others are “sub-depends” as policy (read politics) and technology preference will usually trump the “sub-depends”.

What follows is a review of the harmonic filter technologies, my own numerical scores based on my experience and knowledge (1=NG, 3 = GOOD, 5 = BEST) of the following “sub-depends” criteria of:

  1. long term reliability
  2. Maintenance requirements: service skill level, and is the VFD down if the filter is down?
  3. Efficiency:  heat losses and required cooling requirements.
  4. physical size:  will it fit in the available area?
  5. cost.

Harmonic Filter Technology Summary:

A. Active Filters – these are analogous to a VFD that is designed to generate opposing harmonics to cancel the harmonics from the motor VFD.  There are two installation types available:

  1. Integral to the VFD:  These are technically the most alluring in that the filter is electrically and mechanically integrated with the VFD.  Hence the VFD-Filter package becomes the most “real estate” efficient.  Efficiencies are slightly less (94-95%) than the VFD (96-97%).  Complex service skills are required if a repair is needed.  Reliability is less than the VFD due to the higher switching speeds required of the transistors and the higher component count.  Cost is on the high side, but as it’s already “installed”, the total cost may be lower.  If the filter section is down, the VFD is down.

Scoring:   Reliability:  3

Maintenance:  1

Efficiency:  3

Physical size: 5

Cost:  3

Total score:  14

  1. Separate component:  The standout feature in a separate active filter is a stand-alone component that can be added onto the AC bus that feeds multiple circuits with multiple VFDs.  It is the highest initial cost, but may be total lower cost in an application when several VFDs of various sizes are used.  A high impedance input reactor must be added to each VFD.  Should the filter fail, the VFDs will not know it and keep running.  Installation requires an additional power circuit (or circuits for paralleled active filters to achieve required filtering capacity) and associated real estate.  The rest of the previously mentioned comments apply.

Scoring:   Reliability: 3

Maintenance:  5

Efficiency:  3

Physical size (depending if space available if retrofit):  3

Cost:  1

Total score:  15

B. 18 Pulse Filters – this is the original harmonic filter technology.  12 pulse is not often discussed as it is rarely seen.  A special transformer takes the incoming 480 volts, and creates three each phase shifted, three phase secondary circuits with voltages of 160 phase-to-phase volts.  These are then connected to additional fusing, then diodes for rectification, then connected to the VFD DC bus.  Efficiency is the lowest due to multiple circuit losses in transformer and diode rectification losses.  Cost is high.  Physical space requirement is high.  Reliability is good – but if the filter is down the VFD is down.  Excessive long term heat has been the primary cause of filter failure and then VFD failure.

Scoring:   Reliability:  5

Maintenance:  1

Efficiency:  1

Physical size: 1

Cost:  1

Total score:  9

C. Passive Filters – passive means there are no electronic components required for harmonic mitigation.  The components used are special reactors, capacitors and power resistors (small scale).  They are the most efficient filters at 99%, reliability expectation is similar to that of a transformer – very high.  Should there be a filter problem, it can be bypassed to keep the VFD running.  Cost is the lowest.

    Scoring:   Reliability:  5

Maintenance:  5

Efficiency:  5

Physical size:  1

Cost: 5

Total score:  21


So, now you can analyze the pros and cons of each technology that will fit your application. To speak with one of our trained technicians, give us a call for assistance.

Harmonic Filters – Which One Should You Use? was last modified: July 20th, 2017 by admin

About admin

Jerry is the owner of Sloan Electromechanical and is active in all aspects of the company. He is passionate about doing the work RIGHT and proposing the best product solution, hence the Sloan team is focused on aligning company values with client values. Please post your questions or comments and Jerry will respond. For a faster or confidential response, please contact Jerry directly 619-515-9691 or LinkedIn www.linkedin.com/pub/jerry-gray/17/332/5a1
This entry was posted in Electric Motors. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *