Transformers 2

[garciaf]

I have to transformers each one of 2500 KVA, working 50% of capacity, so in other words both are supplying energy to the plant. Supposedly by desing one is for reserve in case of failure.

Right now the total consumption is low, that one transformer can assume this charge.

My question is the following:

If only one transfomer works, would be saving energy?

Heat losses for Eddy currents/Creating the magnetic field of the bobine (reactive power),create in both transformers the magnetic field in order to work and heat losses for eddy currents.

Please help. Exceuse If I made a mistake. Thank you all.

 

[mparenteau]

If you used only one, then you would save the losses on the backup assuming it was de-energized. You lose reliability in power delivery though...

Mike


IRStuff: Great point! Thanks for keeping me honest.

 

[IRstuff]

Losses would ostensibly go up. Power loss is I^2 * R, but currently, you're running (I/2) on each transformer. New situation is all the current on one transformer

Current sit: 2 * (I/2)^2 * R
New sit: I^2 * R

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[davidbeach]

Running one instead of two would halve the no-load losses and double the load losses. That may or may not increase the total losses.

 

[crshears]

mparenteau: You lose reliability in power delivery though...

Excellent point!

Routinely running with two transformers in parallel to increase reliability, although safely done all the time, is nevertheless something that has to be done with the concurrence of and in collaboration with BOTH the AHJ and the supplying utility, as both real-time power flows and available fault current values can do otherwise unexpected things...

The nature of the reliability sought is also of great importance; the customer can...

[1] Tolerate brief interruptions in supply, but wish to have a high certainty of having power restored within five minutes [or other time interval]

[2] Not tolerate even brief interruptions in supply, but can, with appropriate notice, take a complete interruption of all supply with four hours' notice [or other time interval]

[3] have any number of supply conditions...or none at all [ and yes, some customers do indeed operate to the latter scenario, believe it or not ]

Depending on cost, complexity, etc., grid connections can be configured in various ways to accommodate such requirements, and in every instance it is important that all stakeholders be on the same page.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[IRstuff]

The reliability gets worse than just losing the redundancy. The increased power dissipation increases the temperature, which degrades the reliability.

TTFN (ta ta for now)
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[che12345]

Dear Mr.garciaf

There are numerous proposals with advantage and disadvantage, in brief :
a) Use one load up to near full load instead of two in parallel, each half-loaded. Advantage, higher efficiency. Disadvantage, lower reliability.
b) Use one and dispose of the other [immediately]. Advantage, immediate cash in hand. No depreciation cost for the stand-by unit. Half the maintenance cost. Disadvantage, lower reliability, no spare standby.
Etc.

Che Kuan Yau (Singapore)

 

[waross]

Dear Mr. che12345.

a) Use one load up to near full load instead of two in parallel, each half-loaded. Advantage, higher efficiency. Disadvantage, lower reliability.

I[sup]2[/sup]R losses may cause lower efficiency rather than higher efficiency.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[IRstuff]

I think he meant that the two transformer configuration was more efficient than the single.

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[prc]

If you already have two transformers of identical ratings, better to put both of them in service in parallel.
1) Total losses will be less with two units in parallel.
Let no-load loss of one unit be X kW. Load loss will be generally 4X
Condition 1- one unit meeting total load -Total loss =X+4X =5X
Condition 2 -two unis in parallel -Total loss =2X + 2x 4X/4 =4X
2) An un-energised transformer is more liable to accumulate moisture in insulation than an energized unit under partial load,

3) Since hot spot temperature is less with two in parallel, ageing of insulation is avoided

The only disadvantage is with two units in parallel, short circuit level on secondary goes up.

 

[mparenteau]

Let's not forget arc flash considerations for paralleled transformers as well.

 

[Parchie]

mparenteau (Electrical)
Let's not forget arc flash considerations for paralleled transformers as well.

@prc already stated that the available fault current at the secondary will double when you parallel transformers. Naturally, the arcflash energy increases with it.

 

[7anoter4]

Following davidbeach idea, for a standard 2500 kVA transformer cast resin insulated and aluminum strips conductors [Siemens catalogue for instance] the no-load losses could be 3100 to 4400 W and load losses 19000 to 20000 W.
That means, if you use one transformer the total losses for full load will be 19000 to 20000 W but if you'll use 2 transformers and ½ full load the total losses will be
14150 to 16100 W[18-34% less]

 

[waross]

The voltage regulation will be twice as good with two transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SilverfoxUK]

Things to consider:
if your single transformer failed would that mess your process up. Would a messed up process be expensive. Would you have safety issues if you plunged the place into darkness. How long would it take you to recover. Would you still have a job?

Lets say you go onto a single transformer and isolate the other. How long would you leave it be re-energizing it with confidence. 1 day, 1 month how about 5 years. At what point would it not be an available spare transformer and you would need to get involved in safety checks before re-energizing.

My advice would be keep it connected and in service.