Harmonic Filters

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Enspec Power design and manufacture the VArComp® range of Harmonic Filters at distribution levels from 400V up to and including 36kV.

Harmonic Filters are designed to attenuate troublesome harmonics to within defined parameters or dampen system resonances to prevent harmonic amplification. Our highly qualified and experienced chartered engineers have been designing Harmonic Filters since the proliferation of non-linear harmonic producing loads began back in the 1980’s.

  • What is harmonic distortion and what causes it?

    Modern power-electronic power converters such as rectifiers, variable speed drives, soft-starters, inverters, UPS’s and switch-mode power supplies are typical examples of non-linear loads. These ubiquitous devices utilise semiconductor switching technology to accurately control output, speed, torque and electrical energy efficiency. They operate quite differently to linear loads (resistors, inductors, capacitors) that draw continuous current from the electricity supply. Instead, non-linear loads can draw short, rapid bursts of current.

    Apply a sinusoidal voltage to a linear device and the current that flows will be sinusoidal.

    Apply a sinusoidal voltage to a non-linear device and the output will be non-sinusoidal.

    The resultant non-sinusoidal waveform, (said to be distorted by harmonics), can be broken down into various components that comprise a fundamental waveform of the same shape and frequency as the applied voltage plus multiple integers of this fundamental known as the harmonic components.

    Various factors contribute to the level and severity of harmonic distortion to the supply voltage of an electrical system: The amount and type of non-linear load installed, amplitude and frequency of harmonic currents generated, and strength of supply (fault level) or system impedance of the electrical network in question.

  • What are the effects of harmonic distortion?

    The detrimental effects of harmonic distortion can be manifested in many ways. Increased heating effects can lead to insulation breakdown and even premature failure of expensive capital plant such as distribution transformers, switchgear and associated conductors.

    Capacitor banks that are typically used for Power Factor Correction or voltage control are particularly susceptible to damage by harmonics due to their inherently low impedance at increased harmonic frequencies. (Caution should always be applied when installing capacitor banks to the modern electrical system to ensure system resonances at critical frequencies and amplification of harmonics are avoided).

    Nuisance tripping of protective devices or fuse operations, mis-timings of sensitive electronic equipment and interference of IT and telecommunications equipment are all possible unwanted effects of harmonic distortion.

    The VArComp® range of Harmonic Filters can help to prevent such unwanted effects.

  • What harmonic filtering technologies can Enspec offer?

    Enspec will always offer the best engineered solution to a particular problem from a number of technologies.

    The latest LV filtering technology is the active Harmonic Filter: A power-electronic device that certainly has its benefits including its ease of implementation. This particular feature has today led to many companies with little or no engineering expertise promoting active filters as a one-stop magical cure to all power quality problems. Unfortunately, electrical engineering is seldom a case of one cap fits all and this is certainly not the Enspec approach.

    We are first and foremost an electrical engineering company. We know that every client is different which is why we treat each case individually. Only after listening closely to a client’s problems, careful consideration and diligent engineering analysis, will we offer the best possible engineered solution to that individual’s needs. This may include any one or a combination of Enspec’s harmonic filtering technologies that include:

  • Passive Harmonic Filters

    Passive Harmonic Filters are constructed from a combination of power components that may include resistors, inductors and capacitors. In power systems, simple passive filters are usually constructed from capacitors and inductors, and are tuned for a specific frequency of interest.

    Multiple filters may be used if more than one frequency needs to be removed, or at higher voltages, double tuned filters may be used to minimise the number of components required.

    Passive filters should never be applied without considering their effect on the whole network – incorrect application can cause many problems including premature failure of the filter, but designed and applied correctly, passive filters provide an extremely cost effective solution to harmonic problems at all voltage levels. Passive Harmonic Filters are applied extensively at distribution and transmission voltages across the world.

  • Damped Harmonic Filters

    Passive Harmonic Filters are often tuned to absorb a single harmonic, although they will invariably affect the magnitudes of other harmonics on the electrical network – the level to which other harmonics will be damped is determined to a large extent by the filter’s resistor and its location of connection within the filter. Enspec’s Damped Harmonic Filters incorporate resistance into filter circuits to provide a damped response across a broad range of frequencies.

    Depending on the filter’s power rating and tuning frequency, these damped filters may be configured as 2nd Order, 3rd Order or C-Type filters to minimise fundamental frequency losses.

  • Active Harmonic Filters

    Active Harmonic Filters are power-electronic devices that cancel out unwanted harmonic currents from electrical networks by generating harmonic currents in anti-phase with the harmonics to be removed.

    Active filters offer varying degrees of selectivity, enabling specific harmonics to be targeted and can be used in Hybrid Harmonic Filters, where they can be used to target higher order harmonics and allow more cost effective Passive Harmonic Filters to remove the lower order harmonics.

  • Hybrid Harmonic Filters

    Passive filters generate leading VArs that may be undesirable above a certain level making it more difficult, (but not impossible), to filter multiple harmonic orders.

    Active filters, dependant on their control logic, can use most of their available output to filter out the single largest harmonic on the network. Fifth harmonic tends to be the most prominent harmonic on distribution networks due to the prolific use of 6-pulse inverter technology, so in an all-active solution, the size of an Active Harmonic Filter may need to be increased to deal not only with the 5th harmonic but with any higher order harmonics that may require filtering also.

    Enter the hybrid filter – a combination of passive and active technology where the passive section is used to filter low order harmonics, usually fifth and seventh, thus keeping the VAr output minimised, and the active filter is targeted at higher order harmonics only, thereby minimising the size and cost of the overall solution.

  • I may have a harmonic problem but how can Enspec help me?

    Enspec provides turnkey engineering solutions to all manner of clients. Following initial consultation, our friendly field engineers can gather accurate harmonic spectrum information and system details from on-site measurements to provide the basis for accurate VArComp® Harmonic Filter design.

    Using sophisticated engineering techniques and the latest in power systems analysis software to model your particular network, our chartered electrical engineers will design a solution specific to your needs. Upon completion of the electrical design, our highly skilled workforce will manufacture and test your bespoke solution at our manufacturing facility in Washington, Tyne & Wear.

    Our field engineers can then install and commission equipment into service at a time convenient to you and can further offer ongoing planned preventative maintenance contracts to ensure the continued safe operation and longevity of your investment.

    All of our field engineers are highly trained in Health & Safety issues; each carries a Safety Passport and CSCS card for your added peace of mind.

We can help you to reduce harmonic distortion, clean up your electricity supply and ensure the longevity and integrity of your electrical network. For more information, please contact us. We will be pleased to help, whatever your requirements.