UPS Questions 2

[NickParker]

I have some questions on UPS.
1. Why there is a transformer at the input & output side of the UPS module? Are these called as "Isolation transformers"? What advantage it brings? how does galvanic isolation helps?
2. Why some UPS require 3 phase 4 Wire input power and some UPS require 3 phase 3 wire input power?
3. What is common mode noise attenuation in laymen terms?
4. Why does battery recharge time has to be considered as 10 hours to a 80% state of charge in industrial applications? What is the basis for this 10 hours and 80%?

 

[Gr8blu]

NickParker Let's see if I can answer at least a couple of your questions.
1) First - no guarantee that the internal voltages used in the IPS scheme are anywhere near the input (line side) and output (load side) voltages. Second - isolation is a possibility, depending on the UPS type and circuitry.
NOTE: not all UPS schemes use transformers - some use both in-and-out, some only in OR out, and some none.
2) Because the specific UPS designs are created for specific system configurations. If everyone used 3-PH 3 WIRE, then there wouldn't be any 3-PH 4-WIRE versions.
3) Design to reduce the effect one line lead signal on the other leads, or between a line lead and the common ground plane, or between the actual ground plane and the UPS common neutral. Remember that all power electronics switch - and the switching sequence means that there are times when more than one device is passing current. Doing so creates a disturbance where the internal neutral "moves" relative to the external ground plane. Also the high-frequency noise associated with the switching action can introduce transients on other line (or neutral) leads.
4) As far as I can tell, the 10-hour criteria is related to the use of lead-acid batteries. When these are charged, they tend to heat up - the quicker the charge time, the more heat gets generated. Likewise 80% is the "minimum" recharge level to produce a battery worth using (because at 80%, the battery voltage is likely to be lower than the "rated" output).

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[waross]

If the inverted battery voltage does not match the required output voltage a transformer is needed.
Think:
12 Volt battery, 120 Volts AC out. Needs both input and output transformer.


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Ohm's law
Not just a good idea;
It's the LAW!