Synchronous Operation of UPS and Mains

What do you mean by "synchronous"?

Actually, you don't need to worry about synchronizing since you're supposed to connect your load to the UPS. Your mains feeds the UPS and charges its batteries. If the mains power should fail, the UPS will allow your load to continue running for a limited time (depending on how much battery capacity you have).

regards,

Vulcan

I mean you have a critical load and you connect both a ups output and mains output at the sametime so that even mains is gone UPS is feeding the load with no interruption it is just a scenario or perhaps such a situtation exists i dunno, is it possible or such an application is possible in practical life?

question 2 : a ups takes a vaveform rectifies it and inverts it again and have a new vaveform almost same with the first one, so is there a phase difference between these two ? if not it means a ups and an utility mains is connected in parallel easily because no phase difference exists? if so again and connect them in parallel what happens? it is a bit paradoxal:)

While both can be done technically it would not be too reliable and not cost effective if you tried to make it reliable.

Yes most of the UPS in industries are being used like this only. I mean, UPS output and another mains are in sync always. If the battery also fails (discharged) after certain peroid of time, load will switch over to the other mains (which normally called bypass supply).

This condition also comes if any fault in Inverter, even mains and battery are healthy, load will then get transferred to bypass (another mains) with out interruption.

To achieve this, both UPS and bypass mains will be in sync. That is, UPS output will follow the mains waveform as UPS cannot control mains. They will be in sync always.

The sync is also required for any intentional load transferrs to carry maintenance on UPS.

Rate it if find good.

Cheers

so what I understood is this, Ups and bypass mains will work parallel true?

İf they work parallel so how is load sharing? also what do u mean saying "ups will follow mains since the reverse is impossible"? what happens if the output of ups is not in phase with mains? pls make me get rid of this tricky questions..also i will rate u after giving answer to these two questions....thank u in advance...

Imandi007 is absolutely right. Let me explain it little elaborately:

The UPS supplies the power to the critical loads but what happens when

(1) UPS itself fails,

(2) UPS needs maintenance (nothing is maintenance free) and

(3) The loads exceed the UPS capacity (by some reason)

To resolve this, there must have the alternate supply (generally called bypass supply) to feed the loads. This alternate supply is generally supplied from main bus by a transformer called 'Bypass transformer'. The output voltage of UPS and Bypass transformer should be same and in sync. They are not connected in parallel though, rather connected to the inputs of the transfer switch (described below).

There are two transfer switches used to transfer the loads:

(a) One is static transfer switch which automatically transfers the load to the bypass source with 'make before break' logic for the case (1) and (3) above (the bypass circuit generally have more than 20% load capacity than the UPS for case 3). Most of the UPS, this switch is integrated within the inverter component.

(b) The other switch is 'manual maintenance bypass switch' which is a manual switch and it is used to transfer the load for the maintenance of the UPS. It is also a 'make before break' switch. This switch should never be operated without the synchronous condition of the two supplies (generally a warning sign is written with this switch). If the two supplies are not in synchronous condition and this switch is operated, there will be short circuit between the two supplies. The UPS has a signaling light which turns on when the 'out of sync' occurs. It is the responsibility of UPS to keep its output in sync with the bypass source.

All I described here are related to relatively larger size UPS system for industrial use.

These links may have additional help:

http://www.solidstatecontrolsinc-chn.com/pdf/data_se.pdf

http://www.chloridepower.com/upload/USA/Custom%20Power/Documents/APPGUIDE.pdf

http://www.custom-power.com/UPS_Series%20IV.pdf

- MS

okey it is clear that ups and grid can be in in synchronisation no problem but what i ask is this:

when we feed the load with both bypass and ups output at the same time with a sync. achieved so what happens ??? WHİCH source loaded with which percantage ??? if this is not possible why?? is it clear now?? if it is possible can ups follow the output of grid automatically ??? if it is possible has it an application such that a criticial load is feed through this two source and whenever one of them is gone the other goes on without interruption??

There is no feed from the UPS-output and the UPS-bypass simultaneously. In the event of a failure of the UPS, weather it be that the load capacity of the UPS was exceeded, the technician switched the UPS offline for maintenance, or the inverter took a dump, the UPS will bypass itself and connect the load to the line-side of the UPS. The synchronization of the UPS is required so that when this "switch" does occur, the load will not see any discontinuity of the power source. For instance, one would not switch generators without synchronization and the same is true for the UPS/Line Bypass situation.

Your Ques: when we feed the load with both bypass and ups output at the same time with a sync. achieved so what happens ???

Answer: MSAMAD explained very well about the static switch. To simply the question raised by you...the sync condition of UPS and Bypass is just like the sync condition of two generators (one loaded and another coming in line) just before breaker closing. That means, both are ready to operate in parallel but still load is on UPS only. When ever condtions explained by MSAMAD comes, the static switch will transfer the entire load on to bypass. Normally entire load will be on UPS only.

Your Question: if it is possible can ups follow the output of grid automatically ??? if it is possible has it an application such that a criticial load is feed through this two source and whenever one of them is gone the other goes on without interruption??

Answer: UPS circuits (inverter) will take the reference signal from Bypass and inline with it , it maintain its ouptut so that the sync conditions always exist. If the load is very critical, general practice is to go for redundant UPS systems.

I think its clear.

Hi, the company I work for uses double PSU's for every switch (Cisco 4500, Cisco 3400), one connected to grid and the other to UPS. The UPS is not in sync with grid. But for telecom/fiber solutions its OK. The PSU's converts to DC internally in the switches, so sync is not needed. And the supply security is high and maintenance can be carried out without disconnection of the switch. The PSU's are "hot swapable".

regards, moe