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Comparing Transformer-based and Transformerless Uninterruptible Power Supplies
Choosing between transformer-based or transformerless uninterruptible power supplies may not be a simple ‘either/or’ decision, particularly above 10kVA. Both technologies have their place in today’s power protection scenarios but the key differences between them are: physical size, efficiency, noise output and the levels of input harmonic distortion that they generate.
Both uninterruptible power supply designs produce a tightly regulated source of uninterrupted power but they differ in the way they generate the dc voltage required by their inverters and their output stages.
Transformer-based Uninterruptible Power Supplies: until the early 1990s, the only design of online uninterruptible power supply was transformer-based. Nowadays, the design is still available but generally in larger sizes for UPS from eight to 800kVA. The most common applications for this are large industrial sites.
This type of UPS has a robust transformer-isolated inverter output, which makes it more suitable for the type of application where there is a likelihood of electrical noise; spikes, transients, and potentially, a high degree of short-circuit currents.
The inverter generates an ac supply from its dc power source, which is fed into a step-up transformer. The primary function of the transformer is to increase the inverter ac voltage to that required by the load. The transformer also protects the inverter from load disruption, whilst also providing Galvanic isolation (a method of isolating input and output).
Modern inverter designs use IGBTs (Insulated Gate Bipolar Transistors) in place of more traditional switching components (such as power transistors and thyristors). IGBTs combine the fast-acting and high power capability of the Bipolar Transistor with the voltage control features of a MOSFET gate to form a versatile, high frequency switching device. This in turn has given rise to more powerful, efficient and reliable inverters.
Transformer-based UPS are also supplied with a dual input option as standard, which can be selected at installation by simply removing a linking connector from its input terminal. This allows it to be powered from two separate ac supply sources thus adding further resilience. A transformerless UPS can be installed with dual input capability, with supplies derived from the same source, but this is typically a factory-fit option.
Transformerless Uninterruptible Power Systems
Transformerless UPS is a newer design, commonly available from 700VA to 120kVA. The primary purpose behind the introduction of transformerless units was to reduce the overall physical size and weight thus making an uninterruptible power supply unit more suitable for smaller installations and/or computer room/office type environments, where space may be limited. It also generates far less noise and heat than its transformer-based cousin and has far lower input harmonic distortion levels making it compatible with environments where electronic equipment (such as computers) may be more sensitive to this type of distortion.
In place of the step-up transformer, a transformerless UPS uses a staged process of voltage conversion. The first stage combines a rectifier and booster-converter to generate a dc supply for the inverter. An uncontrolled, three-phase bridge rectifier converts the ac supply into a dc voltage. This is passed through a mid-point booster circuit to step the dc voltage up to typically 700-800Vdc from which a battery charger and inverter are powered. In the second stage, the inverter takes the supply from the booster-converter and inverts it back to an ac voltage to supply the load.
An added benefit of this method is that the rectifier can operate from either a three or single-phase input supply. This can be configured at installation for systems up to 20kVA. A control system ensures a stable, regulated dc voltage is supplied to the inverter at all times and the inverter can operate regardless of UPS output load variations or mains power supply fluctuations or disturbances.
Choosing between Transformer-based or Transformerless Uninterruptible Power Supplies
In many applications the choice between the two may be clear. It is where the two ranges overlap, in terms of power rating, that the decision is more complicated. Consideration needs to be given then to: initial purchase cost, physical size, running costs, the installation environment, and in particular, the levels of input harmonic distortion they generate. Both designs can be operated in parallel to achieve higher levels of availability and resilience.
Over the last decade, the gap between these two uninterruptible power supply technologies has reduced as manufacturers have applied common techniques and research & development efforts to both designs. The driving force behind this has been cost and size, alongside demands to improve operating efficiency and reduce harmonic generation. In terms of online performance, both designs provide the same level of performance and are classified as VFI systems (voltage and frequency independent - in accordance with EN/IEC 62040-3). Their principal differences are their effects on upstream supplies and the operating environment.
Transformerless UPS are generally recognised as more efficient and having a higher power factor than an equivalent transformer-based design, therefore operating costs can be lower.
Below 10kVA, the transformerless UPS design dominates the online uninterruptible power supply market and has become the standard within data centre environments as they offer a more compact footprint, higher operating efficiencies and lower noise output. However, the strengths of the transformer-based design come into play in the industrial environment.
About the Author
Robin Koffler is the General Manager for Riello UPS Ltd the UK subsidiary of Riello UPS (RPS S.p.A) a leading European manufacturer of Uninterruptible Power Supplies and a co-author of The Power Protection Guide(ISBN 978-0-9554428-0-3)- available from Amazon.com
Troubleshooting And Repairing Power Supply The Simple Way - Basic Solution To Repair Power Supplies
The working principle of switch mode power supply is various from the linear sort. Initial the AC voltage will flow to a full wave rectifier (bridge rectifier) which produces an uneven DC output {after which} filtered by a big capacitor (generally 220 micro farad and {as much as} 450 volts). The clean DC voltage will then flows {to begin} up resistors and {towards the} input of switch mode power transformer. When the voltage passed via the high ohms resistor (get started up resistors) the voltage would drop to a value where it then flows {towards the} VCC supply pin of Pulse width modulation IC.
When the PWM IC received the voltage it's going to output a signal to drive the transistor (or FET) and produces a {altering} in magnetic field within the transformer {main} winding. The {altering} magnetic field induces voltage inside the secondary windings. Every of these AC voltage produced by the secondary windings is then rectified, filtered, and regulated to create a clean DC voltage. {1} of the major DC output voltage may be the B+ that supply to flyback transformer (for {Television} and Monitor Circuit)
The output from the B+ voltage supply is then connected, by means of a “feedback” loop (which consist of optocoupler ic and an error amplifier TL431 IC), back {towards the} PWM IC. When the voltage from the B+ supply rises or drop a bit, the PWM IC will act to {right} the output.
In case you {nonetheless} {don't} fully grasp the above explanation, please {don't} be discourage since you are able to often invest in technical books and schematic diagrams and read it till you get the complete notion of how a SMPS {function}. It is possible to ask a repair friend or even surf the web for a superior and simple explanation.
Here I would like you to download a totally free SMPS write-up by Sencore and I discovered it to be a fantastic aid for you {who're} {nonetheless} struggle on how SMPS {function} and tips on how to troubleshoot when it fails. You should ask your self what's the purpose and its function of the components inside the SMPS circuit and the best way to check them if they fail. Come across out on your own the function of these components in SMPS circuit:
How do you get a 30V output from the HP E3631A power supply?
Here's a diagram of the supply:
http://www.ese.upenn.edu/rca/instruments/HPpower/psfig4.gif
All I know is that you have to connect the voltage outputs at the bottom in series. What exactly gets connected to what?
How about setting the voltage on the 6V side to 5V, and then connecting the positive terminal from the 6V side to the common ground on the 25V side, and connecting the + terminal on the 25V side to the - terminal on the 6V side?
you have two 0 to ±25 volts supplies. That means that between the ends, you have from 0 to 50 volts. So connect between the terminals marked ±25 volts, and you will be able to adjust the total between 0 and 50 volts, negative on the right red terminal and positive on the left red terminal.
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#254 - Q&A: What does maximum output mean on a power supply?
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