Unit-Substation Transformers Efficiency
Unit-Substation Transformers Efficiency
(OP)
Does anyone has a graph showing the efficiency vs. loading for unit-substation transformers rated 1500-2500 kVA? In double-ended unit-substations these trafnsformers are usually loaded at 50%, and I am interested in seeing what penalty one pays for this.
Thanks
Thanks






RE: Unit-Substation Transformers Efficiency
Click on the above download within this link: http://
RE: Unit-Substation Transformers Efficiency
Scott Peterson
Training Manager
Power Plus Engineering
www.epowerplus.com
RE: Unit-Substation Transformers Efficiency
So with two transformer at 50% load versus one at 100% load, the load losses are reduced, but the core losses double.
RE: Unit-Substation Transformers Efficiency
no-load(iron), and load (copper) losses are equal. I want to know where that point is? Is it at 100%, 90%, 50% or what?
RE: Unit-Substation Transformers Efficiency
As an estimation a 2.5 MVA 11/0.433kV transformer will have approximately 2.8 kW no-load loss & 21 kW load loss.
Assuming these figues the maximum efficiency will be approximately 99.4% at unity power factor and will be obtained between 30% and 50% loading.
To be honest there is only a small a variation in efficiency over a wide loading. Between 10% and 100% load the efficiency variation approximately 98.8% to 99.4%
You should also note that the power factor of the load will also reduce the efficiency.
Maybe you should also consider the loss capitalisation costs to help you decide at what sort of level to operate your transformer at.
RE: Unit-Substation Transformers Efficiency
Also, check out this Guide for the Evaluation of Large Power Transformer Losses
http://www.usda.gov/rus/regs/bulls/1724e301.pdf.
RE: Unit-Substation Transformers Efficiency
I hope this help.
RE: Unit-Substation Transformers Efficiency
There is somebody with me about this?
RE: Unit-Substation Transformers Efficiency
I think IEEE requires that all parasitic loads, such as cooling fans and pumps be included in the input power, while IEC does not include these. But this difference has nothing to do with the subject at hand.
RE: Unit-Substation Transformers Efficiency
The graph above (Good graph Cuky) shows the effeciency well, at very light loads the no-load losses (iron) bring down the effeciency drastically.
The load losses are I2R losses therefore load dependant, iron losses are considered constant losses and are typically 0.5%.
For a 2.5MVA transformer, you could expect thye manufacturer to quote load losses of 25-28kW at 75C
You dont mention the transformer type, if you have an indoor compact substation with AN/AF cast resin transformers then you could load the transformers up to 70% of their nominal rating, that way you can support the full substation load from one transformer by force cooling the unit, otherwise if you have ONAN or AN type without forced cooling then you can load to 50% as you noted.
RE: Unit-Substation Transformers Efficiency
Thanks for the sanity check. However,the simplified formula gives sufficient accurate values for practical purposes.
For instance, in the example above for loading factor range up to full load and PF=1, the worst deviation between the two formulas is less than 2x10-5%.
Therefore, the term n2Psc can be neglected.
NOTE: If an accurate formula is required, the efficiency may be calculate with more precision as follow:
n= {1 - (Poc +n^2Psc)/[n.S.PF(1-Uφ/100)+Poc+n^2.Psc]}100%
Where: Uφ = The voltage regulation determined as the difference between the rated voltage of a winding and the voltage which occurs at particular values of load and power factor when rated voltage is applied to the other winding or windings.