Unbalance and Power Loss 1

[SMB1]

Hi,
my question is: Does unbalance current increase the power losses? and how?

Thank you very much

 

[magoo2]

Consider a 3-wire circuit. With the same current in each phase, the total losses is equal to 3 * I^2.

If they are not equal, then the resulting sum of I^2 will be greater than 3 * I^2 computed from the balanced case.

You can show if mathematically by setting one phase equal to I; the next equal to I + a and the last equal to I - a. This gives you the same average current. Now compute the sum of I^2 and you'll get 3 * I^2 plus the term 2 * a^2.

It's a bit more complicated if you add a neutral, but the same result applies.

 

[ScottyUK]

Yes, it does: imbalance causes negative phase sequence currents to flow which cause heating in rotating machines. In accordance with those pesky laws of thermodynamics that heat energy has to be supplied from somewhere, with 'somewhere' typically being an increased fuel burn in the power plant.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[slavag]

Hi.
When synchronous machines are unsymmetrically loaded, the symmetry of the stator currents is disturbed and a counter-rotating negative phase-sequence current is set up. This current results in double-frequency eddy currents being induced in the rotor, causing additional heat losses and local overheating of the rotor as well as mechanical vibrations.
Regards.
Slava

 

[SMB1]

thank you all for your answers