Transformer based UPS vs Transformer less UPS

What is the main difference between Transformer based UPS and Transformer less UPS and its operation?

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Dheeraj Rai

  • May 22nd, 2016

Transformer Based UPS
Transformers in general are used for number application, the most obvious one is to stepping up or down the voltage. In UPS application they are also used:
To create galvanic or magnetic isolation from AC input and DC supply
To create local ground bonded neutral
To reduce harmonic current by employing delta-wye transformers
Impedance that limits fault current. Although these days fault current is mainly limited to 3-5 times the FLC using complex active means of fault managment
To eliminate ground loops with multiple generators or main sources. Ground loops are more pronounced when soil resistivity of your premises not adequate
To accommodate nonstandard output voltages by using taps on transformers
Transformer-less UPS
Transformer free systems are much more complex than the one with transformers where passive component (transformers, capacitors, inductors) are replaced with power circuit assemblies utilizing PWM power conversion techniques. This results in higher number of component which subsequently means lower reliability, lower MTBF and more maintenance.
choose transformer based one if you need:
Input and output voltage configuration flexibility
Neutral output
High resistance grounding implementation
Magnetic isolation on Input/DC/Output
And choose the transformer free option following criteria are more important to you:
Size and weight limitation
AC input waveform correction
Genset compatibility
Low initial system cost
Higher efficiency.
Reference:Faraz Mirzaagha - MIEAust CPEng NER
Power System Engineer at SMEC International

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