Can the harmonic protector really remove the harmonic? Is the ground removing the harmonic?

release time:2022-03-17Author source:SlkorBrowse:2183

What are harmonics?

Harmonic is not a strange word in the power industry. The interference of higher harmonics is a major "public hazard" affecting the power quality in the current power system, and it is urgent to take countermeasures.

Harmonic is a steady power quality index parameter, which must be distinguished from transient phenomenon. Many people hope that harmonic protectors can filter harmonic waves to reduce losses, so are harmonic protectors really that magical and useful? Can it improve the power quality to some extent?

1 Definition of harmonics

Internationally recognized harmonics are defined as:

Harmonic refers to the components of voltage and current whose frequency is an integral multiple of the fundamental wave. Generally, it refers to the components of voltage and current whose periodic sinusoidal voltage and current are decomposed by Fourier series and whose frequency is an integral multiple of the fundamental wave.

Harmonic is a steady power quality index parameter, which must be distinguished from transient phenomenon. Generally speaking, the waveform of harmonics repeats periodically, while the transient phenomena such as high-frequency noise, pulse spikes, power surges, etc. change or attenuate in the waveform every week, so they are not considered as harmonics, but only as a transient phenomenon.

2 Introduction of harmonic protector

Basic principle and structure of HPD

ANHPD is a new type of protection device used to filter out higher harmonics and protect precision instruments and equipment. It adopts ultra-microcrystalline alloy materials and innovative special circuits. It is mainly composed of voltage clamp, low-pass filter and absorber. It can not only suppress and absorb the random high-order harmonics generated by users' electrical equipment, including page 2, page 8, and the interference of high-frequency noise, pulse spikes and surges, but also track the voltage waveform at any time, instantly filter out the spikes, surges and clutter in the power supply, correct the high-order harmonics caused by harmonic influences, eliminate harmonic pollution from the source, and provide protection for electrical equipment.

ANHPD reference standard

GB/T14549-1993 power quality: harmonics of public power grid GB/T15945-2008 power quality: allowable deviation of power system frequency

GB17625.1-2012 Electromagnetic Compatibility Limits Harmonic Current Emission Limits

IEEE 519-1992 International Harmonic Control Standard Q31/Q31/0114000129C026-2017《ANHPD Harmonic Protector

Model description

technical parameter

3 About the energy density of the filter

Commonly used filtering devices include LC tuned filter and active power filter.
The filtering principle is to form an active or passive low-resistance path for harmonic current source, so that harmonic current can flow into the low-resistance path, thus realizing the purpose of filtering.

Definition of energy density:The amount of energy contained in a unit volume.For the passive filter, the energy exchange between the harmonic source and the passive filter, when p(t)>0, the harmonic source releases harmonic energy and flows into the filter device.
The energy is stored in the capacitor, and the stored energy is. When p(t)<0, the energy flows out of the filter and is absorbed by the harmonic source. For the passive filter device, not only the harmonic energy should be stored, but also the fundamental reactive energy should be exchanged, so the capacitor installation capacity should be large enough to store these energies.For active power filter, there are two paths to realize the energy exchange between the DC side storage capacitor and the power grid.

First, directly exchange energy with harmonic source; Secondly, when the voltage of the DC side energy storage capacitor changes, the IGBT is controlled to charge and discharge the DC side energy storage capacitor to ensure its voltage stability, so the capacity of the active filter device is smaller than that of the passive filter device.Regardless of the active or passive filter device, the exchange energy between the filter device and the harmonic source determines the capacity of the filter, which requires the filter to have a certain energy density.

4 Harmonic protector does not have harmonic filtering function.

To sum up, the harmonic protector does not have the function of harmonic filtering from 350 Hz to 20 MHz:

(1) high-frequency noise, pulse spikes, surges and other disturbances generated by electrical equipment do not belong to the category of harmonics, and filtering these transient harmonics is not harmonic filtering;

(2) The filter device should have a certain energy density to meet the demand of energy exchange with the harmonic source. The harmonic protector is a passive device. If the harmonic can be filtered, there must be energy storage elements inside, but the size of the harmonic protector is very small (145mm*120mm*70mm). Such a small size can only exchange energy with the harmonic source with a large energy density, which is impossible for ultra-microcrystalline alloy materials.

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