Does a small dip in primary voltage of a step down transromer effect seconary voltage

[rfazeli55]

Hi All,

if there is a small dip in the utility (I am talking 2 volts in 1-2 seconds) voltage would this affect the secondary voltage and by how much? I give you an example, I have a 600V system feeding a UPS and the UPS has a step down transformer within it that gives our 480V. the tolerance of the UPS is plus/minus 10% (not that this matter for the question but as an FYI). I reviewed the voltage on my Eaton meter and saw from the graph that a 2 volts drop in Phase B as Phase A-B and B-C dropped but not A-C so I assumed phase B was the issue (hope that is right). Then the UPS went to battery back up, this is a 150kVA UPS with the step down transformer in it, so before I figure out with the UPS manufacturer in regards to the tolerance level I wanted to confirm if the small dip in voltage affects it or does that small dip turn into losses and makes no difference in the secondary.

hope this makes sense as I am not good with explaining things.

Thanks,

 

[mpoulton]

Transformers maintain a constant ratio of voltage from primary to secondary. They are not regulators. If the primary voltage drops by 1%, the secondary voltage will drop by 1%. So if it is a 480:240V transformer, a 2V drop on the primary would cause a 1V drop on the secondary. A UPS is not just a transformer though. If it is a "double conversion" UPS, then it will maintain constant regulated output voltage regardless of the input. If not, then the output will usually fluctuate proportionally with the input.

 

[rfazeli55]

Thanks, so I know UPS is not a transformer but there is a step down transformer in the same enclosure and so the voltage gets stepped down before getting converted to DC. The UPS is online so it is double conversion but it went to battery back up as the voltage dropped. so if I get 2V drop in primary I get 2V drop on secondary as you mentioned 1V drop on secondary but was this a typo. maybe I misunderstood you. Thanks for your response and time and I hope you message me back and explain it more to me please.

 

[iwire]

Thanks, so I know UPS is not a transformer but there is a step down transformer in the same enclosure and so the voltage gets stepped down before getting converted to DC. The UPS is online so it is double conversion but it went to battery back up as the voltage dropped. so if I get 2V drop in primary I get 2V drop on secondary as you mentioned 1V drop on secondary but was this a typo. maybe I misunderstood you. Thanks for your response and time and I hope you message me back and explain it more to me please.

If a UPS is going onto battery at just 2 volt drop it is not a double conversion unit or the settings are set too tight

 

[mpoulton]

Thanks, so I know UPS is not a transformer but there is a step down transformer in the same enclosure and so the voltage gets stepped down before getting converted to DC. The UPS is online so it is double conversion but it went to battery back up as the voltage dropped. so if I get 2V drop in primary I get 2V drop on secondary as you mentioned 1V drop on secondary but was this a typo. maybe I misunderstood you. Thanks for your response and time and I hope you message me back and explain it more to me please.

It was not a typo. The voltage RATIO from primary to secondary remains constant. If the primary has twice the voltage of the secondary, then the voltage drop on the secondary will be half the drop on the primary.

 

[GoldDigger]

It was not a typo. The voltage RATIO from primary to secondary remains constant. If the primary has twice the voltage of the secondary, then the voltage drop on the secondary will be half the drop on the primary.

But between 600V and 480V you do not have a ratio or 1:1 nor a ratio of 2:1.

 

[Smart $]

But between 600V and 480V you do not have a ratio or 1:1 nor a ratio of 2:1.

No, but the ratio is in between those at 5:4. Drop 5 volts on primary and the secondary drops 4.

 

[rfazeli55]

So my question then is when does an online double conversion UPS go to battery back up? what are the items for me to look at? the only thing I can think of is the tolerance to ensure a dip in the voltage does not affect it? does anybody agree with this?

 

[ron]

So my question then is when does an online double conversion UPS go to battery back up? what are the items for me to look at? the only thing I can think of is the tolerance to ensure a dip in the voltage does not affect it? does anybody agree with this?

Each UPS, depending on its design will have an acceptable input voltage threshold before it goes to battery.

You need to find the value for yours. It may be adjustable which means that you would have to look into the display to find it out or have a factory tech plug their computer into it for data

Sometimes it is 10% as you mentioned in your post.

 

[Jraef]

If a UPS is going onto battery at just 2 volt drop it is not a double conversion unit or the settings are set too tight

So my question then is when does an online double conversion UPS go to battery back up? what are the items for me to look at? the only thing I can think of is the tolerance to ensure a dip in the voltage does not affect it? does anybody agree with this?

Each UPS, depending on its design will have an acceptable input voltage threshold before it goes to battery.

You need to find the value for yours. It may be adjustable which means that you would have to look into the display to find it out or have a factory tech plug their computer into it for data

Sometimes it is 10% as you mentioned in your post.

So it actually depends on the tolerance of the EQUIPMENT on the load side of the UPS. If that equipment cannot handle a 2% fluctuation, then the UPS will be programmed to immediately go into battery mode if there is a 2% drop on the line side. In other words, the UPS might be used as a low tolerance voltage regulator, so do NOT make assumptions and start messing with the UPS programming until you know WHY it is programmed so tight. That may be absolutely deliberate!