How to work out real and reactive power losses in transformers & cable
How to work out real and reactive power losses in transformers & cable
(OP)
Hi, I'm trying to work out the real & reactive power losses through transformers and MV cables. However, I'm having trouble finding anything that deals with anything other than (I^2)(R) which only gives real losses and not reactive, nor does it take into account skin effect factor or proximity effect factor. Any help gladly aappreciated.






RE: How to work out real and reactive power losses in transformers & cable
That is, a reactive current of 10 Amps and 100 Volts will result in 1000 VA or 1 KVA. This is not a loss. However, the 10 Amps will result in a I2R loss in the conductor supplying the reactive load.
That's great for the classroom but in the real world, given a load that draws a reactive current of 3 Amps and a real current of 4 Amps the total current will be 5 Amps and the I2R losses in the cable will be based this current of 5 Amps.
Bill
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"Why not the best?"
Jimmy Carter
RE: How to work out real and reactive power losses in transformers & cable
Skin effect and resistance of a cable have little effect on the losses.
RE: How to work out real and reactive power losses in transformers & cable
Losses are always real and I2R. As Bill said reactive current will cause real losses and so will real load current. If both real and reactive components are present, the resultant current = square root of (square of real current + square of reactive current) will decide the I of the I2R. The cable's R and skin effect has impact on effective R and hence the losses. Similarly R of windings of the transformer affects copper losses.
In transformers there are also no-load or core losses, which again is real. They are caused by the resistance of the core encountered by the eddy currents in the magnetized core plus I2R due to the magnetizing current. These losses are independent of the load and are always present as long as the transformer is energized. This data you need to get from the manufacturer.
Rafiq Bulsara
http://www.srengineersct.com
RE: How to work out real and reactive power losses in transformers & cable
I would recommend a grate document from PML ( OK from Schneider Electric
http:
Best Regards.
Slava
RE: How to work out real and reactive power losses in transformers & cable
But many times I have had client's and project managers wonder where all of the MVArs went in their power plant. They can't reconcile the generator output meter with the high voltage utility meter and aux load metering. The generator puts out 0.85 power factor but the utility interconnect is operating at 0.92. Where did the VARS go?
Example:
Generator 400 MW @ 0.85 pf.
Aux load 8 MW at 0.8 pf.
300/400/500 MVA GSU with 10% X at 300 MVA.
Power to GSU is 392 MW, 241 MVAR = 460MVA @ 0.85 pf. The MVAr's used in the GSU will be =300 MVA x 10% x(460/300)^2= 70 MVAr.
Output to utility will be 392 MW and 171 MVAr (neglecting GSU kW loss) = 427 MVA @ 0.92 pf.
Managers treat the VArs like the Watts, comparing how much they produce with how much they deliver and consider the difference to be their auxiliary load + losses.
RE: How to work out real and reactive power losses in transformers & cable
RE: How to work out real and reactive power losses in transformers & cable
Neil
RE: How to work out real and reactive power losses in transformers & cable
In the absence of voltage, there won't be much current.
David Castor
www.cvoes.com
RE: How to work out real and reactive power losses in transformers & cable
Rafiq Bulsara
http://www.srengineersct.com
RE: How to work out real and reactive power losses in transformers & cable
Neil
RE: How to work out real and reactive power losses in transformers & cable
For instance: