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25 / 03 / 2020 1107 Views
  • Product news

Those who work with Variable Speed or Frequency drives (VFDs or VSDs) know that one of the biggest problems (not seen at a first look) is distortions that a drive produces in a supply grid. A standard 3-phase drive can produce harmonic distortions in supply voltage and current up to 30%. This impact called Total Harmonic Distortion (THD) and is regulated by the standard IEEE-519. Than more drives powered from the same grid than more summary distortions will be there.

These harmonics are lead to negative currents and losses in power equipment (lines, transformers, generators). High distortions causing energy loss in supply elements. That means that quite a lot of money is lost because of losses of energy. Plus such distortions can cause damages in electronic devices, power from the same grid. As an addition, a lifetime of supply equipment reduces due to the negative impact of the THD.

There are several typical solutions to reduce THD level produced by drives:

VSDs with multiphase rectifiers and with phase-shift transformers Such a VSD has a more complicated rectifier (12, 18, or even 24-pulses), bigger junction box (6, 9, or 12 input phases comparing to 3 for standard 6-puls drive). This solution requires additional supply phase shift transformer – additional spends. That means that you need an additional piece of power equipment and a place for it at a well-side. But note that only 24-pulses drives can meet requirements of the IEEE-519 standard.

Input harmonic filters (passive or active). Passive harmonic filter probably is the cheapest solution…but… The efficiency of a passive filter depends on a load of a VSD: the higher load of a VSD means lower THD level. It means that if VSD is loaded less than 70% then THD level would be above 5% (not comply with IEEE-519).

Active filters can give you a much better result. Such filters can filter negative harmonics, nevertheless a load level. On another side, this solution is complicated and quite expensive.

Active front end (AFE). Probably the most expensive and complicated solution. Here you won't get a standard VSD, but about two times bigger one. Such drives have good and, some times, really useful features, but a price usually doesn't worst a result.

Triol has all these solutions, as different countries have different requirements or habits.

But today I want to talk about the new drives with passive input harmonic filters that can adapt to a load level – VSD CP (clean power)

Triol AK06-CP drives are equipped with input and output harmonic filters and provide THD level less than 5%, meeting requirements of the IEEE-519 standard. CP VSDs are designed as a single cabinet drives, thus they have less footprint and require less installation and commissioning time, comparing to the other solutions.

Our AK06-CP VSDs can operate with a load down to 25% from its rated power range and maintain 5 % (or less) of THD due to the patented twin filter design, two parallel rectifiers, and software solutions.

Thus, simple and not so effective solution became a still simple but the one that exceeds expectations.

Installation

Without Triol drive the level of THDu is enormous: 11.7-12.2%. It means that there is a high "background noise" from the other drives, supplied from the same grid.

When Triol drive was on and loaded about 60%, the THDu level didn't increase but it even lowered to 10.7-11%. Thus Triol VSD doesn't add voltage distortions in the supply grid but filters all harmonics produced by itself. As an addition, it removes some part of distortions that exist in the grid.

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