Uninterruptible Power Supplies and Harmonics

Harmonic pollution is a growing problem in Europe and one that designers of power continuity programmes and manufacturers of Ups (uninterruptible power supplies) cannot ignore. Typical harmonic problems consist of the distortion of mains power supply voltage, overheating of wiring, neutral conductors, supply transformers and switchgear and nuisance tripping of breakers. Harmonics can also cause disruption to equipment on the same supply and lead to random failures.

Harmonics are caused by voltage or current waveforms with frequencies that are multiples of the basal frequency - in Europe, 50Hz (50 cycles per second). The multiples are all the time ordered in a specific sequence: for example, the 2nd harmonic is 100Hz (2x50Hz), the third 150Hz and the fourth 200Hz and so on.

High Voltage Power Supply

The particular problem of Triplens (third order) harmonics. Harmonics are a particular issue for power continuity management due to the large estimate of switch mode power supply (Smps) loads being connected to modern electrical distribution networks - and their connected Ups systems. These are the most coarse form of power supply unit (Psu) in use today. As a non-linear load, they draw their power in quarterly modulated pulses of current from a mains power supply rather than as a continuous linear supply. This can lead to Smpss generating high levels of harmonics, especially when many are being supplied from a particular three-phase mains power supply.

In particular, ideas designers must be aware of the potentially damaging Triple-Ns (or Triplens) whose harmonic order numbers are multiples of three and consist of the notorious third-harmonics as well as ninths and fifteenths. Thirds are probably the most interesting harmonic in terms of neutral conductor loading within a three-phase system. Whereas other harmonics cancel each other out, third-harmonics are in phase with each other and exhibit a summing succeed which greatly increases the current - potentially overloading conductors and switchgear.

Harmonics and total power factor - implications for Ups sizing. Harmonics are also intimately connected to power factor management - and other key aspect of uninterruptible power supply ideas fabricate and implementation. The displacement power factor is only applicable to the basal frequency (50Hz in Europe) and therefore does not take into account the power factor generated by any harmonics induced into the mains power supply by the load itself (referred to as the distortion power factor and produced by the harmonics produced by non-linear loads). The blend of the displacement power factor and the distortion power factor gives what is known to Ups systems experts as the true power factor. When correctly sizing a Ups, an understanding of this is critical.

Mitigation of total harmonics distortion. Harmonics issues need to be addressed at the fabricate stage of any power continuity plan. Not least, because consumers are responsible for the harmonic levels introduced into their three-phase mains power supply.

A Ups can sometimes be fitted with a harmonic filter (post installation) but this can be a precious and inelegant solution as broad internal wiring changes may be required. For a transformer-based Ups, using a 12-pulse rectifier in place of a 6-pulse set will cut the levels of Thdi (total harmonic distortion). Coupling this with a passive filter will supply added discount to colse to 4%.

For a transformerless uninterruptible power supply, Thdi levels of less than 4% can be achieved by installing an active harmonic filter. However, levels as low as 3% can now be achieved by some designs whose rectifiers are Igbt (Insulated Gate Bipolar Transistor) based. This can take off the need for an added active harmonic filter and simplify the Ups fabricate process. Such designs are startling to come to be the norm: not only do they cut initial costs, but they allow a smaller Ups ideas footprint whilst increasing input power factors.

Active harmonic filters cut the impact of prominent power factors. When designing a power continuity plan and Ups system, various methods can be applied to cut the impact of prominent power factors (where the current waveform leads the voltage waveform): ensuring that prominent power factors characterize a smaller division of the Ups load, installing power factor correction between the Ups and the load, increasing Ups size (and that of any standby generation capacity) and specifying a Ups with prominent power factor capabilities.

A beloved arrival to cut the succeed of prominent power factors on a Ups factory is to use an active harmonic filter with power factor correction on the Ups output. This presents the Ups with a more suitable load, but results in higher capital and factory costs, lower efficiency and a greater footprint.

Familiar territory for Ups manufacturers. Although many aspects of harmonics must be considered when specifying a Ups system, reassurance can be gained from the fact that this is well-known territory for Ups manufacturers such as Riello Ups. End users and their expert advisers can assuredly be confident that this specialized aspect of Ups application will be wholly addressed while the modern consultative sales and specification process.

Uninterruptible Power Supplies and Harmonics

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Uninterruptible Power furnish - Power Conditioning

Power conditioning is one of the lesser-known but equally foremost functions of an uninterruptible power supply (Ups). Its primary purpose, of course, is to supply a source of electrical vigor to vocalize continuity of company throughout an interruption in mains electricity or until an alternative source of vigor (such as a generator) starts up.

Why the Need for Power Conditioning?

High Voltage Power Supply Circuit

There are issues related with raw mains electricity that can cause problems for electronic equipment. These include, but are not exiguous to: sags, surges, brownouts, spikes and transients, electrical noise, harmonics, frequency variations and, of course, complete blackouts. At best, power problems can cause equipment (particularly computer and telecommunications equipment) to lock or crash. At worst, they can consequent in a complete breakdown - thus entailing costly and disruptive fix and/or replacement. In the case of computers, they can also consequent in data being lost or corrupted, which for many industries that are heavily regulated (such as banking and finance) can be disruptive to business, damaging to prestige and credibility, and in extreme cases, can lead to heavy fines or financial penalties.

Power Conditioning, therefore, by uninterruptible power supplies and related equipment, is a process by which it monitors incoming mains electricity, cleanses it and significantly reduces the consequent of problems such as those highlighted already. Some Ups, fitted with special filters, can sell out the consequent of harmonics. All Ups vocalize frequencies to within prescribed limits thus correcting frequency fluctuations. Ultimately, this means protected loads upstream, receive a clean and regulated supply of electrical energy.

Power Conditioners

Power conditioners attenuate spikes, transients and electrical noise voltages to low levels. They can be solid state electronic or transformer-based. Where these types of problems predominate, and sensitive equipment is being protected, that's where power conditioners will be used, typically in commercial environments. Some power conditioners can also supply voltage stabilization over a wide input voltage window (typically minus 20 to plus 15%) and yield voltage regulation (typically plus or minus 5%). Models of this type can be referred to as Constant Voltage Transformers (Cvt) or Ferroresonant type design.

This type of transformer is more reliable than a solid-state electronic build and provides electric isolation (a means of preventing unwanted electrical currents from traveling between two separate units). It's history rest in uninterruptible power supply designs from the 1980s (known as Ferro Ups), which paired the Cvt with a Line Interactive Ups to accomplish a 'no-break' output. Though reliable and robust, this type of uninterruptible power supply was only practical for single-phase installations and couldn't compete on cost, noise, physical size and weight, with transformerless Ups designs that were beginning to emerge.

Automatic Voltage Stabilisers (Avs)

Avs supply security from sags, brownouts and surges. They can be electro-mechanical or solid-state electronic devices and are often referred to as self-operating Voltage Regulators (Avrs). Avs typically have wide input voltage windows (minus 40 to plus 20%) to enable them to do their job. When presented with a low or high mains power supply voltage, a control circuit selects a transformer tap setting to buck (step down) or boost (step up) the voltage to more accepted levels. The yield voltage tracks the input voltage window as there is, typically, no voltage regulation.

Some self-operating Voltage Stablisers consolidate a filter to supply both the load and Avs with security from spikes, transients and electrical noise. The primary application of an Avs is in remote areas where sags, surges and brownouts are coarse to safe equipment such as fridges, freezers and domestic electrical goods.

Filters and Filter Strips

Filters supply security from spikes, transients and electrical noise. Instead of attenuating problems like power conditioners, filters clamp peak voltages to pre-defined levels and prevent damaging electrical noise from passing through to related loads.

There are a whole of filters ready and execution varies considerably across the range. Filter (surge) strips, for example, are ordinarily used within Ict environments for power distribution. At the higher end, more expert filters can be acquired for expert environments, such as scientific laboratories. Filter performance, clamping level and speed of response, is dependent upon their circuit build and the size of the disturbance it is faced with.

Transient Voltage Surge Suppressors (Tvss)

Tvss supply security from transient voltages and high-energy spikes, particularly those induced into a building's electrical supply by local lightning strikes. They are rated in terms of the Amps (A) or Joules (J) they dissipate. They regularly sit parallel to the load and only react when presented with a transient or high-energy surge.

When installed within a building, a 'zoned approach' is recommended, which places high rated devices before distribution boards. A Tvss may be fitted upstream of a Ups or inside a bypass panel, generator Amf panel or distribution boards to supply security from around lightning strikes.

Tvss designs tend to be based around Metal Oxide Varistors (Movs) rather than Gas removal Tubes (Gdts) typically found in surge suppressors. Some manufacturers consolidate their Mov designs with a Silicon Avalanche Diode (Sad) front-end to speed up their response time.

Uninterruptible Power furnish - Power Conditioning

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