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Elimination with AccuSine+ Solutions

What is resonance? Resonance is a phenomenon that we see in everyday life. Soldiers marching on a bridge can lead to extreme vibrations at the bridge's natural that may break it apart. This is an example of mechanical resonance.

Electrical resonance occurs in an electrical circuit when impedances of the elements in the circuit cancel each other. This happens at a particular frequency called the 'resonant frequency' and it can result in excessively high currents and voltages. Understanding Resonance Parallel resonant curve in green => Create an increased impedance on a low voltage network that can potentially magnify Many electrical systems encounter resonance due to the installation, and then harmonic in current and voltage. interaction of independent, but inter-related electrical components. Resonance leads to equipment failure, shortened lifespan and other costs. Resonance |Z| without Cap bank |Z| with Cap bank problems are becoming much more frequent due to the massive installation of 70 60 semiconductor products (nonlinear loads), such as variable frequency drives, 50 UPSs, welders and battery chargers. 40

30 Resonance is a form of system instability. Typically, components of the overall 20 system interact with each other to cause results that are not intended. Interaction 10 usually involves passive components, such as and , or 0 control systems with crude control algorithms. Resonance involving passive 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 1250 components is relatively common when systems are modi ed or expanded Harmonic magni cation caused the parallel resonance in the incrementally when loads grow. The addition of capacitors to improve power above graph. factor or the addition of a bus-applied passive harmonic lter may spawn resonance. There is also a potential for resonance when the supplying utility adds or changes capacitors or transformers near the customer's facility.

Individual harmonic voltages The unintended result is voltage and current resonance. Resonance causes 12% voltage or current to exceed design limits for system components and causes 10%

components to be overworked. For example, capacitors will experience excessive 8% voltage and will be charged and discharged with excessive currents. This leads 6% to failure through voltage breakdown and heating. Depending upon the 4% magnitude of resonance, failures can occur immediately or over many months. 2% Sometimes system operators can not correlate failures to their real cause due to 0% the time lag until failure. U3 U5 U7 U9 U11 U13 U15 U17 U19 U21 U23 U25 Before capacitor bank connection After capacitor bank connection

The probability of system resonance is increased dramatically in the presence of semiconductor (nonlinear) loads which produce harmonics that excite the natural inherent in the electrical system. A variable frequency drive produces harmonics at many frequencies, including, for example, the 29th order. The addition of the drive (which contains capacitors) or a bank of power factor capacitors might create a 29th order natural resonant frequency. Note: capacitors would have been designed to be charged and discharged at a rate of 60 times per second, not a rate that is 29 times faster. In this case, they may overheat and fail.

Resonance Elimination has big benefits: Resonance Elimination reduces component failures due to heating and voltage breakdown and maximizes component lifetime. The system will operate the way intended - proper correction of power factor, attenuation of harmonics, and so on. It is not uncommon to nd electrical systems in industrial applications where power factor correction capacitors and tuned lters have been disconnected due to overheating or frequent failure, all caused by resonance.

Key Benefits of Resonance Elimination with AccuSine+

• Stabilization can be realized with little or no costly engineering. • Since AccuSine+ is installed in parallel to the load, it is easy and inexpensive to install. • AccuSine+ is scalable. Additional units can be added later and operated in parallel with each other if the load increases. • AccuSine+ is exible; it can be installed at the main distribution bus, a sub-distribution panel, local distribution panel or a single load, thus stabilizing the system at its optimal point. A Complete Solution AccuSine+ is a Power Correction System, that eliminates the potential for resonance. AccuSine+ attenuates current harmonics. It identi es the current oscillation from system resonance as a harmonic to be cancelled. AccuSine+ responds by injecting opposite current, thus dampening the resonance. Since most voltage resonance is simply the result of current resonance, both the current and voltage resonance end up being corrected.

How AccuSine+ Works Active Harmonic Filters (AHF) are static power electronic products that employ digital logic and IGBT semiconductors to synthesize a current waveform that is injected into the to cancel harmonic currents caused by nonlinear loads. AHF employ current transformers to measure the load current to determine the content of harmonic current present. By injecting the synthesized current, network harmonic currents are greatly mitigated, thus reducing the heating eects of harmonic current and reducing voltage to permit other equipment to operate properly and enjoy a long product life span.

AHF also have the ability to correct for poor displacement power factor (DPF) and for mains current balancing. DPF correction can be provided for either leading (capacitive) or lagging (inductive) loads that cause poor DPF. Mains current balancing is achieved by measuring the negative sequence current present and injecting the inverse negative sequence current to balance the current for the upstream network.

Comparing Alternatives You have a few choices when it comes to resonance elimination. Since it is the worst case result of installation of independent but inter-related equipment, your best option is to avoid it.

Eliminate, Add or Adjust System Components In many situations, capacitor banks are added in order to improve power factor and eliminate power factor penalty charges. Unfortunately, resonance situations are often resolved by simply 'turning o' system components, such as the capacitors. Resonance is prevented but the remedial bene ts of the capacitor banks are lost. A better choice would be to gain total power factor correction and avoid resonance. Customized Power Factor Control Systems A customized capacitor bank is often designed with protection against resonance in mind. However, since such systems are site speci c and are not scalable, customers have shied away from them. The AccuSine+ Power Correction System If sized correctly, a Power Conditioning System like AccuSine+ delivers complete resonance elimination in low voltage (to 600V) electrical systems. Sizing is simple, installation is inexpensive, performance is assured, and the system is scalable. AccuSine+ is often the low total cost solution.

Remember, Resonance Elimination is just one of the bene ts of a Power Correction System.

For additional information, refer to the AccuSine+ catalog at www.schneider-electric.us/powerquality.

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