RHF – Harmonic filter for drives
Harmonic mitigation of variable frequency drives – VFDs
Harmonics – Ideally all loads and sources have a pure sinusoidal current waveform. But unfortunately the true waveform of most equipment is very different. Nonlinear loads like for example the diode input bridge of a 6 pulse drive, are causing a distortion of the mains voltage…
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This distortion evaluated by the Total Harmonic Distortion THD, typically evaluates frequencies from the 2nd up to the 40th or 50th harmonic. In a 50Hz Network this is the area between 100Hz and 2.5kHz.
The impact of the harmonic distortion is diverse, and the most typical effects are:
- Transformer overload
- Capacitor bank (PFC) overload
- Increased energy costs
- Decreased equipment lifetime
- Prone to failure equipment
- Vibration damage on rotating equipment
Learn more about the effects of harmonics in our Learning sector or visit our Webinar- Harmonic solutions for drives.
REVCON Harmonic Filter – RHF-5P and RHF-8P – are passive double stage filter. These Filter reduces the THDi of variable frequency drives (VFD) or other similar non-linear loads and sources to significantly below 5% THDI ( 8% THDi) even under realistic circumstances including imbalance and pre-distortion. This is necessary to reach various standards and recommendations, such as IEEE 519-2014…
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The Filter is simply connected in line with the load and can be used with any standard 6-Pulse VFD. The design is made with a forced air cooling in an IP20 enclosure (optional IP21). As a result, we can provide a significant smaller size than products based on natural convection. The internal filter circuit allows for a full DC bus inside the connected drive, therefore the connected drive will nor require any de-rating with the use of RHF-5P or RHF-8P and multiple drives can be paralleled up to one common Filter.
Simpler single stage passive harmonic filters are tuned to the 5th harmonic and therefore focus mainly on the frequency around 250Hz (300Hz for 60Hz). The patented double stage filter circuit used insde the RHF works like a bandwidth and and reduces the THDi from e.g. 35% to typically 3% THDi with a smooth damping of all harmonics up to 200th order. The RHF reaches an unique efficiency of up to 99.5% and therefore the produced power losses are up to 75% less than those produced by alternative solutions.
The RHF-5P and RHF-8P are available for all inverter size from 4kW up to 800kW and comes with the capacitor disconnect option as a standard. Please conisder the Datasheets for further information.
Double-Stage Filter Technology – Passive harmonic filter basically show significant difference in the internal setup. The following pictures describes the RHF-5P and 8P hardware configuration. Instead of using a simple drain circuit for the 5th Harmonic, both RHF-5P and 8P are using a double-stage filter and specifies the performance by changing the main inductance value…
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The 3 main advantages of this REVCON patented filter circuit are:
- Performance: The RHF is designed to reach its stated performance in the field and not defined for unique simulated conditions. Therefore, the double stage filter offers a smooth damping of all Harmonics up to 200th.
- Full Drive Power: The RHF allows for 100% DC-Bus voltage at 100% drive load. As a result, no further calculations and de-rating of the drive is require (Drives connected to Simple Harmonic Filter may have up to 7% less power ratings)!
- Efficiency: Simple Harmonic Filter may add RC circuits in order to reach specified 5% THDi which leads to lower efficiency .The RHF-5P harmonic filter cause up to 70% less power loss than comparable <5% THDi solutions.
Beside these technological advantages, the RHF-5P and RHF-8P are designed as enclosed solutions. One the one hand this results in smaller size which improves production and transport costs. On the other hand this also enables a significantly more reliable product. The main reason for this is the cooler core temperature of the capacitors. The typical life time of an RHF-5P or RHF-8P is 15 years and can be significantly higher in friendly environment.
Harmonic Filter required? The use of RHF-5P and RHF-8P is very simple and they can be combined with any VFD brand as long as it uses a 6 pulse rectifier at the input. Becasue harmonics harm over time especially in continuously running applications mitigation should be considered. Examples for frequent applications are: pumps, compressors and ventilations…
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Above all, particular caution is required when the sum of VFD power and other non-linear loads are high in relation to the total Load. In this case, harmonic compensation is always necessary.
Take a look at our references for further examples where RHF filters are already being used successfully. Here you will also find our test reports which shows the Filter in combination with the corresponding VFD.
If you have any questions, don’t hesitate to contact one of our colleagues!
RHF sizing – The first number in the type code of the RHF indicates the corresponding nominal motor power. Consequentely the RHF-5P 280-400-50-20-C is therefore designed for a 280kW Motor. The true input power of the Harmonic Filter is significantly higher due to the power losses inside the VFD and motor…
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The motor correlation is based on motors with an efficiency corresponding to IE3 with max 6 poles and is valid for VFD used in Heavy Duty (HD) or Normal Duty (ND). For Motors with lower efficiency higher rated harmonic filter may be necessary.
A de-rating of the VFD due to the voltage drop is not necessary using a REVCON RHF-5P or RHF-8P.
*Typically the VFD will show a higher nominal output current compared to the RHF input current. This is necessary, due to the fact that the drive need to provide the reactive power required for the motor to operate. Therefore dimensioning based on VFD current leads to an unnecessary and unfavourable oversizing of the filter.
Further information on individual sizes are listed in the datasheets. Please select your parameter.
If you can´t find your preferred filter above, please don´t hesitate to contact us. Due to our wide portfolio and long experience we are able to offer customized solutions for any application.
