Harmonic Reactors

Harmonics - Introduction:

There has been much discussion and interest in recent years on the subject of power quality. Where as in the past, power received and utilized by an industrial plant was generally a pure sinusoidal wave form – i.e. clean power – most frequently to-day industrial plants have deal with problems of “Dirty Power”. Harmonic distortion is a specific type of Dirty Power that is usually associated with an industrial plants increased use of adjustable speed drives, power supplies and other devices using solid-state switching. Harmonic distortion can cause series operating problems in plant environments.

  Consequences of Dirty Power:

Just as high blood pressure can create stress and serious problems in the human body, high levels of harmonic distortion can create stress and resultant problems for the utility’s distribution system, the plant’s distribution system, as well as all of the equipment that is serviced by that distribution system. Equipment shutdown can be caused by a number of events. As an example, the higher voltage peaks that are created by harmonic distortion put extra stress on motor and wire insulation which ultimately can result in insulation breakdown and failure. In addition, harmonics increase RMS current resulting in increased operating temperatures for many pieces of equipment resulting in greatly reduced equipment life.

Harmonic distortion disrupts plants. Of greatest importance is the loss of productivity, throughput and possibly sales. These occur because of process shutdowns due to the unexpected failure of motors, drives, power supplies or just the spurious tripping of breakers. Plant engineers realize how costly downtime can be and pride themselves in maintaining low levels of plant downtime. In addition, maintenance and repair budgets can be severely stretched. For example, every 10°C rise in the operating temperatures of motors or capacitors can cut equipment life by 50%.

  IEEE Standard:

Electric utilities, consulting engineers and major production or process facilities throughout the world are readily adopting IEEE-519 harmonic distortion standards. The point at which the harmonic limits are applied is typically referred to as the Point of Common Coupling (PCC). If harmonic distortion appears at this PCC, then it will also be experienced by the other loads which are supplied by this bus. The standards recommend THD for Current less than 8% & THD for Voltage less than 5% at PCC for industrial environment.

  The Power Quality Products:
  • Harmonic Reactors - For each VFD inputs, typically reduce current distortion less than 25%
  • Harmonic Tuned Filter – For each VFD inputs, typically reduce current distortion less than 12%
  • Harmonic Broad Band Filter – For each VFD inputs, typically reduce current distortion less than 8%
  • Conversion P.F. Capacitor Bank to Harmonic Filter bank – For PF correction with harmonic attenuation, typically reduce current distortion less than 10% at PCC
harmonic reactor

When non-linear loads make up more than 20% and less than 30% of the electrical load on a distribution system, some type of harmonic filtering is required to maintain harmonic distortion within the limits. The least complicated filter is a series Reactor, often called “harmonic Reactor”.

The input harmonic current distortion can be reduced significantly by the simple addition of input line reactance. The inductive reactance of harmonic reactor allows 50 Hz current to pass easily but presents considerably higher impedance to all of the harmonic frequencies. Harmonic currents are thus attenuated by the inductive reactance of the harmonic reactor. Reactors are by far, the most economical means of reducing input current distortion on a drive system. Harmonic reactors offer very consistent results and will have no invasive effect on the electrical power system.

  Reactors at Partial Load:

Since the nameplate impedance rating of a reactor is based on its full load rating, whenever the load current is less than reactor FLA, the effective percent impedance will be lower than the nameplate impedance. This means that harmonic current distortion, as a percentage of fundamental current, will be lowest when the load current is nearest to the maximum rating of the line reactor. A 6% impedance line reactor will only act like a 3% line reactor when the load current is 50% of the line reactor’s full load current rating. From the table below, the harmonic level at full load is 32.5% for 6% reactor rating and harmonic level at 50% load is 44%. The load decreases, the harmonic level increases. GR has addressed this issue in larger. We introduced swinging effect to the reactor inductance.

harmonic reactor

It is important to recognize that the effective impedance is also an indication of the full load voltage drop across this series reactance. One should avoid excessive voltage drop. It is possible however to achieve a high effective impedance, without a severe AC voltage drop when line reactance is combined with dc bus reactance. For example, 1% effective transformer impedance + 5% line reactance = 6% total effective percent impedance and the estimated harmonic distortion is 32.5% at full load.

  What is a Harmonic Swinging Reactor (HSR)?

To get effective harmonic filtering we have developed an innovative harmonic reactor called as Swinging Reactor, and we are the first manufacturer in India for this novel Swinging Reactor. We are adapting special manufacturing techniques with specially processed reactor core laminations to achieve swinging actions. Swinging Reactor is an inductor that has an inductance value that is inversely proportional to its operating currents. Over a substantial portion of the normal operating current range, the inductance decrease as the current in the choke increases. A conventional or linear Reactor has a fixed inductance value that changes very little as operating current varies in the normal operating range.

  What does Swinging Reactor do?

Used as a Harmonic Reactor in a VFD, the Swinging Reactor reduces harmonic currents just as a linear Reactor does. The main objective of using swinging Reactor is to provide further harmonic reduction when the drive is operating below its rated horse power. This further reduction is provided with no increase in physical size or weight compared to a similar conventional Reactor.

  Special Design Features:

As reactors and their required air-gaps gets bigger, flux fringing and eddy currents can cause heating and insulation breakdown. The stray losses increase considerably due to flux fringing. GR has addressed this issue in larger. GR reactors by utilizing Distributed Gap technology - a construction technique that subdivides a large gap into two or more smaller gaps. A GR reactor built with this technique will run cooler and more efficient and last longer than the competitions cheaper single gap products. We are the first manufacturer in India to introduce distributed air gap technology in reactors.

  Model selection:
harmonic reactor

Broad Band harmonic filter capacity selection is based on the VFD or non-linear load KW rating. Choose model based on the VFD HP rating or Non-linear load 1KVA = 1HP rating. The expected harmonic reduction at filter input will be 50%

harmonic reactor
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