Harmonic Filter

An electrical Harmonic Filter is a multitasker. It eliminates harmonic, maintains grid stability by mitigating power surge, voltage fluctuation and resonance. A harmonic filter is an engineering tool in preventing power plant blackout by stabilizing power system parameters for successful de-synchronization and islanding on a grid failure. Besides, it relives station generator from momentary fluctuations and surges over a grid or internal power disturbances which helps in preventing its premature winding insulation failure.

A quality harmonic filter 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 election if the transformer has many variable speed drives.

4. The myth is the series passive harmonic filter wherein current goes through it, reduces 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.

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 a top-end custom made filter

The custom made Passive harmonic filter, super tuned type, is the top-end fit-for-purpose harmonic filter. Its application is diverse across all industry, datacentre, utility company, co-generation power-plant, renewable energy, grid-tied solar power plant and commercial facilities. It's scaleable - built for any size, 10A to 5000A for low voltage, 575V to 2000V for mill-duty and induction-furnaces, 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

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. 

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