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Active Harmonic Filter Vs Reliable Passive Installation

Active Harmonic Filter

Read this case study of the advantages and disadvantages of the active harmonic filter and how passive filter installation removes harmonics, voltage surges and improves PF. Besides, the active harmonic filter needs the support of a stable external power source for injecting phase opposite current harmonics to downstream loads. Its efficacy depends upon the stability of the connected external power source.

AHF design needs passive components like a capacitor and a resistor, but it can either do harmonic control or power factor correction to its 100% rating. In the case of both PF improvement and harmonic reduction, its capacity needs a derating to 50%. The active harmonic filter is a load in an electrical power system that generates anti harmonics at 180degree phase opposite. AHF has energy losses. Most OEM pdf catalogues declare the kWh losses at 3% under laboratory measurement.

Active Harmonic Filter does not eliminate downstream harmonic, electronic failure, equipment and relay tripping.

By design, it doesn't remove harmonics from downstream power line but by injecting anti-harmonic cancels it to prevent it from flowing into the upstream utility supply. Its application is to limit upstream grid harmonics within IEEE-519 norm. Whereas passive harmonic filter being a harmonic absorption type sucks up harmonics by short-circuiting it from the downstream load as well as upstream power system within its range. By doing so, it cleans up the circulating-harmonic from downstream loads which otherwise get absorbed in the downstream equipment and In turn, increase voltage harmonic distortion within the supply transformer. In a chain reaction, that otherwise would magnify the current harmonics extent of which depends upon the fault level of the load bus PCC. Thus, by design passive harmonic filter relieves all downstream loads by removing the circulating-harmonics that eliminate equipment failure, break-down and nuisance tripping on voltage fluctuation. It improves Protection Relay functioning - read it in another case study at Solar Power Inverter with Harmonic Filter.    

Active Harmonic Filter has energy losses. Series impedance causes VFD tripping. Why a drive-wise harmonic correction is not a good idea.

It requires real-power in kW for injecting phase-opposite harmonic current coming from the downstream non-linear load. That causes a minimum of 3% real energy losses in kWh term. Though OEM catalogue mention only about 3% energy loss, that's measured under an ideal condition. Energy-intensive industries employ hundreds of VFD drives within one transformer say 2000 KVA and operate in between 70 to 90% load factor. It requires higher impedance typically over 3% in series with VFD drive which injects further kW losses. Thus the 3% energy loss data may be valid for low-intensity load, but for higher load-factor and THDv, the total losses including in the high-value series impedance may go up to beyond 3%.

Some consultants prefer to have a drive-wise harmonic filter which is not a wise thing to do though in particular when the supply transformer has too many VFD drives. Active front end harmonic filters use high impedance upfront with its connected VFD drive.  Summarily, it magnifies power system impedance which in turn increases THDv, disturbs VFD operation making it susceptible to tripping for even a minor grid voltage fluctuation.

It has a known problem connecting with backup diesel generator (DG) if plant loads are high and need variable reactive power compensation. The active harmonic filter can't deliver that as it inherits only a fixed and limited design capacitor.  An extra Power Factor control panel is required.  A STATCOM to work in conjunction with it or the SATCOM to be inbuilt within it. Some AHF manufacturers use an additional external APFC capacitor bank or a detuned harmonic filter which they refer to as a hybrid harmonic filter. A detuned filter does not control harmonics. It uses a detuned reactor in series for the protection of capacitors and not for eliminating the load harmonics.    

Active Harmonic Filter - advantages

The active harmonic filter does not require to be custom built since it is mostly impedance independence except the designed capacitors and resistors.  It does not need any load specific frequency tuning.  Active harmonic filter manufacturers claim it can handle wideband harmonic frequencies. On the other hand, the passive harmonic filter needs extensive engineering efforts and are custom built with load specific design. However, it is also true that the actual-load never generates beyond a few harmonic frequency bands.  For example, computer, server and switch mode power supply (SMPS) loads produce 3rd and 9th harmonic currents to the extent of 75% and 15% respectively.  Six pulse drive loads produce 5th (60%), 7th (20%) and balance in 11th and 13th harmonic currents. 12-Pulse inverter loads generate 11th (50%), 13th (20%), 5th (20%) and balance in other frequency harmonic currents.

Active Harmonic Filter- disadvantages

Active Harmonic Filter has a known issue in handing high-intensity loads wherein THDv is above 10% and without a linear-load mix for which many OEM recommend not to use it. It also creates energy losses which vary from 3% for low-intensity loads and goes up to 7% for high-intensity loads and voltage distortions. Whereas passive filter being harmonic absorption type saves 3 to 5% real energy in kWh for moderately polluted harmonic loads.  When it comes to massively polluted harmonic load like in rolling mill drive with a fourth quadrant regeneration operation, induction furnace etc., it delivers an even higher percentage of energy saving. The same higher percentage energy saving is possible when the transformer or DG operates at a higher load factor typically in between 80 to 90% and with a very high THDv.

Active Harmonic Filter malfunctions when THDv is high and is used without a linear-load mix

It malfunctions while handling high-intensity power and harmonic pollution wherein the total voltage harmonic distortion (THDv) is above 10%. Many OEM recommends not to use it when THDv is more than 10%. While the higher THDv problem is universal, it has another issue when the load doesn’t mix with some linear-load like full speed induction motor and the current harmonic percentage is high. We have independently verified these features in the following two case studies which are detailed below.

Active Harmonic Filter

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Harmonic Distortion is a crammed Harmonic Energy Surge

Harmonic Distortion

When a plant with high NLL runs at full load, it crams harmonics and active power in the power system, causing unacceptable energy surge wherein harmonic distortion is the ratio of harmonics to fundamental-power.  Total harmonic distortion (THD) and distortion factor are related terms defined by the ratio of square root sum of all high-frequency harmonic components to the fundamental frequency power.   Wherein the fundamental-frequency power (50Hz) is the active power which does all the useful work and drives the plant machinery. The high-frequency harmonics are the integer multiples of fundamental-frequency which do no useful-work and get wasted by heating-up plant equipment.

The Harmonic Distortion Filter is not a mass manufacturing process. It's a custom design engineering process for the manufacturers of power quality filter.

1.    Limit both THDv (Total Voltage Harmonic Distortions) and THDi (Total Current Harmonic distortions) and reconstruct distorted waveform back into Sine Wave, as shown in the caption picture above, a technology that improves and transforms the fuel guzzling, bad power quality dirty power into Clean Quality Power.

2.    Enhance quality of finished products since torque vibrations across plant and machineries get eliminated. Slash quality check rejections for final products. Eliminate equipment tripping and failures, slashing down mean time between failures (MTBF). Enhance plant's 3P, Power, Productivity, and Profitability.

3.    Debottleneck equipment capacity limitation with Non-Linear-Loads, allowing increased Load Factor up to rated capacity, sustainably for all equipment from captive power plants (TG or DG), transformers, switchgears, ac/dc drives, ac motors-SQIM/SRIM, dc motors to cables and terminations. Reduce equipment sizing substantially, slashing both project investment costs and running energy bills.  

4.    Eliminate equipment maloperation across all industrial, commercial and building operations. For example, it eliminates building elevator uneven floor landing with the landing floor, and in-addition its erratic operations.

5.    Eliminate tripping in plant equipment, drives, and process loads due to voltage fluctuations/ sags that originate from either external grid source or internal power system.

6.    Eliminate building's electrical fire risk due to excessive third harmonic current (also called zero sequence harmonic current) which add up to neutral, and any infirmness in neutral is a very serious fire hazard.  

7.    Eliminate overheating in equipment, drives, process loads, cables, and terminations.

8.    Eliminate failures with plant and machineries.      

9.    Automatically maintain unity PF eliminating the need for a separate capacitor panel, which with nonlinear loads magnify harmonics and further complicate the harmonic problem.

10.    Lower equipment footprint allows space savings. Lower carbon footprint reduces global warming effect. Slash down both with equipment maintenance and AMC costs.

Harmonic Distortion

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Passive Harmonic Filter proven valuable When Equipment Fails

Passive Harmonic Filter

With a passive harmonic filter, the harmonics reduce by absorbing it from the downstream load. It relieves harmonic stress on load end equipment and solves its failure and tripping problem. It permits the plant to achieve a full load run with reduced energy consumption. Encon facilitates the best harmonic solutions. Engineers worldwide depend on passive harmonic filters when the electric-load is sizeable, harmonic distortions alarming and yet there's a need to slash equipment footprint by designing a full load plant operation.

Unlike the ineffective series type passive harmonic filter, the highly effective passive harmonic filters are always parallel type harmonic filters. It eliminates load generated harmonics by drawing them towards it creating a short circuit path, and then absorbing harmonic within it. It thus eliminates the need for any equipment derating even with extreme harmonic distortions and allows plant operation at a hundred percentage loading for all plant machinery.

Unlike active filter, a high-power shunt passive harmonic filter is highly flexible for any input voltage design which covers the complete working voltage range of plant equipment from as low as 120 volts to 36 kV. It enhances the plant's 3P, power, productivity and profitability by manifold. We manufacture the most valued passive harmonic filter - type Super Tuned which is a top-end custom-built product.

When you have problems - repetitive failure in process drives, electronics, servers and in electrical equipment or unwanted tripping and high neutral current and neutral voltage; it will solve all your problem. Needless to say that it will mitigate harmonics (both voltage and current) to tolerable limits as defined by IEEE-519 standard. A super tuned harmonic filter is of high power capacity which reduces extremely high harmonic distortions in both voltage and current waveform within a safe working limit, thus identifying it as harmonic distortion filter.  

There are few other variants of passive harmonic filter though, series type passive harmonic filter, detuned harmonic filter and triplen harmonic filter. The series passive harmonic filter introduces an impedance before an individual load that reduces a little current harmonics, by the principle of ohm's law. It seems to work without causing equipment tripping problem when a transformer has very few non-linear-loads. Series harmonic filter finds its application connected in series, with a smaller non-linear-load, within a much bigger transformer wherein harmonics remain within IEEE-519 limits, thus indicating it as IEEE harmonic filter. But by doing so, it increases voltage harmonics which could cause tripping in sensitive electronics and VFD drives, with little voltage fluctuation, if there are sizeable series harmonic filters within a transformer.  

De-Tuned filters do not mitigate harmonics but improve power-factor (PF). When its added to an electrical power system, it creates two paths. One path is into the filter, and another is toward the source. The harmonic current does not flow into the detuned-filter as it offers a high impedance path and diverts into the low impedance source, as per the current divider rule of ohm's law.

Data center servers, electronic gadgets and large LED light installations generate high neutral harmonic current wherein neutral current equals the phase current. Besides, that increases the neutral voltage. It's triplen harmonic filter which suppresses neutral harmonics and mitigates high neutral voltage across UPS loads. It has many names being a neutral current eliminator - zero-sequence harmonic filter, third harmonic filter and 3rd harmonic filter.

Passive harmonic filter - why Super Tuned?

1. It Eliminates equipment Failure and voltage fluctuation Tripping.

2. It Prevents Arc Flash and Electrical Blasting. Refer to the case study.

3. It Reduces the running temperature of equipment. We have achieved up to 10-deg.C.

4. It Reduces CAPEX and footprint by eliminating the need for that costly de-rating.

5. It Reduces OPEX, first by reducing footprint and then by enhancing energy efficiency.

6. It Reduces end product quality rejection. We have achieved up to 50% on six-sigma scale.  

How Power and Harmonics Flow?

1. Being a Current Source, it flows in the opposite direction from downstream load to all branches in the upstream power system.

Power & Harmonics Flow diagram

2. By Ohm’s Law, it flows across all paths in the power system based on each path’s relative impedance. Along its flow path, two-events happen.

3. Firstly, the downstream equipment and cables, designed for 50/ 60Hz absorbs these high-frequency harmonics causing excessive stress to themselves. It causes equipment failure, high running temp, tripping and malfunction. The super tuned passive harmonic filter by creating a short-circuit path diverts the harmonics and troubleshoots the problem.

4. Secondly, the grid being relatively a lower impedance path absorbs the remaining harmonics leftover by the downstream plant and machinery. The active harmonic filter prevents these harmonics from going over to the upstream grid.

Passive Harmonic Filter - why a reliable troubleshooter?

1. It alters the dynamics of the harmonic flow by creating a Short-Circuit path for the flow of harmonic frequencies like 250hz for 5th harmonic etc.

Passive Harmonic Filter - Working Principle

2. The load harmonics now, instead of getting absorbed in the downstream loads, are diverted as soon as it’s produced through this short-circuit path into the filter, thus solving equipment failures, tripping, and malfunctions. It allows only a small harmonics within a limit over to the grid, meeting the IEEE 519 harmonic standard, for both voltage and current harmonics.

3. Besides, it's a stored energy LC power bank which will oppose any momentary change in voltage fluctuation, either sag or swell and power surge which may originate either within the plant or outside in the grid. A passive harmonic filter is an indispensable tool in eliminating nuisance tripping of critical plant equipment - process drives, control system, computers, server to name a few.

4. By relieving the downstream equipment from the burden of harmonic absorption, it eliminates that need for costly de-rating saving CAPEX and equipment footprint cost.  

5. It saves OPEX cost in the manifold. Firstly, it eliminates harmonics naturally and allows full load plant operation sustainably. Secondly, it troubleshoots failures and thirdly it enhances energy efficiency.

6. The harmonious operation with the optimum power quality results in lesser end-product quality rejections which we have tracked up to 50% savings on Six-Sigma Scale.

Passive Harmonic Filter - why direct corporate clients select us?

1. There's no-one like it before and someone that you like has arrived. We pride in manufacturing the most Beautiful passive harmonic filter - super tuned type.

2. Its beauty is a deception. It's a monster. It mercilessly Slashes down harmonics as no-one did before.

3. It's Rough and Tough (IP55) to withstand a harsh environment. Unlike active harmonic filter, it does not need an air-conditioned room installation.

4. It's 50kA, 1sec Short-Circuit proof, and Basic Insulation Level (BIL) compatible for 12kV/ 4kV. That withhold Arc-Flash hazard.  

5. This beauty is for ever. Its design life is over 40-years.

6. It's Fully Automatic, Variable and adjusts with process load variations and harmonic distortions in the power system.  

7. Thanks to you, our 350+ corporate clients, for believing in it and every time designing your projects with it. Your trust on us, over three decades, has catapulted Encon's passive harmonic filter as the most valued brand in today's world market.

Passive Harmonic Filter

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Solar String Inverter with Harmonic Filter

An automobile industry was facing high incident of harmonic failure in SCADA, motor drive & electrical equipment after installing 1MW solar power inverter. The rated capacity of 1.0MW DC solar power is evacuated through 16Nos, 50kW, 3Phase, 415Volts, 50Hz solar string inverter which itself got affected with the harmonic problem. While designing the solar string inverter a 20% power loss is considered by the solar panel manufacturer for conversion from DC solar panel power to AC power delivered in the 3Ph, 415V, 50Hz electrical power grid.

Every day during the peak solar power generation when the sun is at the top of the sky, randomly one inverter trips and remains switched off for several hours. It causes a loss of 3 to 5% in the solar power generation by considering that the inverter trips at the most productive time. The solar power inverters diagnose it as over voltage tripping. But during the root cause analysis carried out before installing harmonic filter, we did not find any over voltage problem in the factory's electrical power system. We designed the harmonic filter for troubleshooting the factory's electrical and electronic equipment failure as well as providing a photo voltaic solar string inverter solution by mitigating its over voltage tripping condition.   

A 1407A Encon Harmonic Filter is installed during Nov. 2017 at the 415V main incomer PCC of 2500KVA transformer. It's designed for the full transformer load including the 1.0 MW solar power harmonic at the downstream of transformer. Passive harmonic filter being a harmonic absorption type, engulfs harmonics from both downstream as well as upstream within its range.

Read the full case study at:  https://enconengineers.in/solar-power-inverter-harmonic-filter

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Harmonic Filter Powerful with Super Tuned Specification

Harmonic Filter

When super tuned, the electrical harmonic filter turns a multitasker that eliminates harmonics, maintains power system stability by mitigating power surge, voltage fluctuation and resonance. A super tuned harmonic filter is an engineering tool that prevents power plant blackout by stabilizing power system parameters for a successful grid de-synchronization, and islanding power generators on utility power failure. Besides, it relives station generators from momentary voltage fluctuations and power surges over a grid or internal power disturbance which helps in eliminating premature winding insulation failure of the generator.

A quality harmonic filter panel is custom-built for the project needs with incremental costs and complexities. In its basic specification, it provides a low impedance parallel path which enables current harmonics from its source at downstream loads to flow into it and allows a tolerable level of current harmonics, within IEEE-519 norm, to flow into the upstream utility grid. However, basic harmonic filters can't control high harmonic levels. Whereas, a top-end harmonic filter mitigates both current and voltage harmonic distortion from any higher level to within limits.

Harmonic Filter - a fact check on common misconceptions

There are misconceptions in the minds of even expert consultants and engineers which result in their hyping-up not only fancy specification but installing unsuitable harmonic filter type.

1. The myth is higher current harmonic 80% is dangerous. The fact is if the power of that load is small compare with its supply transformer, it does not need a harmonic filtering solution. It's important to note the total current harmonics at the transformer-end and history of equipment failures and tripping within the transformer.  If transformer-end harmonics are near 8% and no-failure history, a de-tuned filter does the job of achieving power factor correction though it does not mitigate harmonic distortions.

2. The myth is high voltage harmonics 40% can't be corrected. The fact is any higher voltage harmonic is controllable with a correctly designed harmonic filter type.

3. The myth is, a harmonic filter at each variable frequency drive end is the best solution. The fact is it's the worst selection if the transformer has many variable speed drives.

4. The myth is the series passive harmonic filter wherein current goes through it, reduces current harmonics within norms. The fact is it can't do beyond a few percentages. It increases impedance in the harmonic flow path that impedes little harmonic. But by doing so, it increases voltage harmonic though.

5. The myth is it's required to eliminate all 2nd to 51st harmonics. The fact is the elimination of a handful of harmonic numbers is enough to limit the total harmonic distortion within IEEE-519 limits.

6. The myth is an active harmonic filter does three-phase load balancing. The fact is AHF injects anti-harmonic current to cancel downstream load harmonics within its rated capacity. But it can't compensate for unbalance load.

Harmonic Filter - hallmarks of top-end custom made design

The custom made Passive harmonic filter, super tuned type, is the top-end fit-for-purpose harmonic filter in an electric power system. Its application is diverse across all industry, data center, utility company, co-generation power-plant, renewable energy, grid-tied solar power plant and commercial facilities. It's scale-able, built for any size 10A to 5000A for low voltages- 120volts to 480volts, 525V to 2100V for mill-duty motors-ac vsd or dc and induction-furnaces, and 3.3kv to 36kv for medium to high voltage applications.

It's flexible in installation - suitable for connection at a point-of-common-coupling for a large group of linear and non-linear-loads. OEM recommends to connect it at transformer PCC for the whole group of harmonic and other loads. Besides, if a transformer has a few VFD/VSD drives, it is suitable for individual drive-end connection.

It's variable as per project need and automatic in operation. It eliminates harmonic distortions - both current and voltage, reconstructs distorted sine waveform to sinusoidal voltage and current waveform improving quality of power, improves power factor to near unity.

It eliminates failure and nuisance tripping in plant and machinery both in electrical equipment - generator, transformer, switchgear and in critical plant loads - variable frequency drive, dc drive, control system, computer, server. By providing an improved power quality, it minimises end-product-quality rejection.

  Harmonic Filter - a tool that prevents Arc Flash

A mandate that is increasingly becoming noticeable among electrical engineers and safety regulators is the NEPA 70E standard. Besides, the Occupational Safety and Health Administration (OSHA) issues citations based on the requirement NEPA 70E. It stipulates employers to protect employees from arc flash hazard while working in an electrical system by wearing Switching Arc-Flash Suit. We are using non-linear-loads (NLL) since the 1970s, but the arc flash issue came into prominence much later since the year 2005. What has changed since then? 

Arc flash and electrical blast - why it's happening now?

By now, we have expanded our use of variable frequency drive (VFD) also called variable speed drive (VSD). Then, we used speed control for critical process load that required matching speed variation. We then preferred DC drive over VFD drive which did not make use of high-frequency switching, the IGBTs. Today, we use variable-speed drives engaging high-frequency IGBT at every other motor load. We save energy using VFD drives for energy conservation projects. We achieve conditions for our comfort by utilising it in HVAC and air-conditioning projects.  

Arc flash - what's the Root Cause?

The switching frequency (also called carrier frequency) of a VFD drive is the rate at which it's DC bus voltage is switched on and off during pulse width modulation (PWM) process. VFD manufacturers increase switching frequency apparently to reduce audible noise from motor and harmonic generation. VFDs typically operate in between 4-20khz frequency range.

At higher switching frequency, the noise pitch from stator lamination moves higher beyond the human hearing range, so we hear a lower audible noise from the motor. Similarly, at the higher switching frequency, the measurable harmonic generation, typically up to 50th order are lesser, which matters for the sake of meeting regulatory harmonic-norms which do not measure higher and kilo Hz order harmonics.

Harmonics are high-frequency currents and voltages. All frequencies which are odd multiple of three (like 3x50hz, 9x50hz, 27x50hz etc.) are called triplen harmonic currents or voltages. Unlike the fundamental-frequency (50 or 60hz) and other harmonic frequencies; triplen harmonics don't cancel at three-phase neutral but add-up and grow three-fold. The lower order triplen frequencies add-up and increase the neutral current in the electrical power circuit. The arc-flash problem happens with the higher-order triplen-frequencies which add-up to a charged voltage forming an electrical field (potential gradient) around electrical conductors in its power system.

Arc flash - how encon harmonic filter eliminates it

Arc flash phenomenon is similar to the corona effect on high-voltage transmission power lines. It happens when the air around a high voltage electrical conductor ionise to a sufficient potential gradient (electrical field) to form a conductive region. It generates a bluish glow around the air of the current-carrying metal conductor. When the strength of the electrical field is high enough to cause an electrical breakdown, arcing happens to a nearby object at ground potential.  

Adding-up of high-frequency triplen-harmonics from the variable frequency drives and other IGBT-based NLL is the precursor of an arc flash. Once it attends sufficient field strength, it arcs to a nearby object at ground potential causing electrical blast involving electrical equipment.

We have troubleshot many dangerous arc flash blasts wherein we found the frequent arcing objects to be switchgear (air circuit breaker, MCCB, Fuse), the body of electrical panel, Bus Bar. The electrical bus bar affects in several ways. Pitting along the bus bar is a common effect. In one incident a portion of bus bar at the junction of horizontal and vertical joint evaporated and vanished in an arc with its body. We built our super tuned harmonic filters with special zero-sequence winding which provides a path to the high-frequency electric field which prevents arcing.

Harmonic Filter