Primary is 13,200 V, secondary is 240 VWhat are the nominal primary and secondary voltages?
Primary is 13,200 V, secondary is 240 VWhat are the nominal primary and secondary voltages?
But wouldn't no-load losses be the core losses [I-core squared x R-core] plus the "copper losses" of the entire "core current" (I-core + I-magnetizing) flowing through the primary winding [I-o squared x R-primary]?What they call no load losses, I would call core loss. What they call full load losses, I would call copper loss, or I squared R loss.
Because the magnetizing current (more properly the exciting current) is so small compared to normal load current, we usually ignore the copper losses caused by the exciting current. This is determined by the "open circuit test".But wouldn't no-load losses be the core losses [I-core squared x R-core] plus the "copper losses" of the entire "core current" (I-core + I-magnetizing) flowing through the primary winding [I-o squared x R-primary]?
The ratio for impedances is as the square of the turns ratio, not directly as the turns ratio.Also, do you know if, since we are talking about about a 13.2 kV primary, 240 V secondary transformer, I can assume that the R and X, and thus Z, values of the windings are in the same ratio (55 to 1) as the coils?
But in my real example of a 10 kVA transformer, the core loss is more than 1/2 the amount of copper loss. This does not seem to be negligible! I am missing something here?Likewise, when the "short circuit test" is performed, the core loss is assumed to be negligible compared to the copper loss.
Have a look at the "Short circuit test" section of this page:But in my real example of a 10 kVA transformer, the core loss is more than 1/2 the amount of copper loss. This does not seem to be negligible! I am missing something here?
Even in a 500 kVA transformer they give the core loss as ~17% the size of the copper loss.
Don't forget that it's the impedance referred to the secondary; at the primary it would be 353.7 ohms. The transformer specs you gave in post #15 show an impedance of 1.46%--where did 2.03% come from?On another note, can I calculate the total impedance of the transformer from the % impedance given in the data thus?
full load current in the secondary (41.667 amps) divided by the % impedance = 2.03% gives short circuit current of 2,052.5 amps across the secondary. Secondary voltage of 240 V divided by this gives the total actual impedance of the transformer: 0.11693 ohms.
In post #15 I copied that value wrong (1.46% is for a 5 kVA), it should have been 2.03%, sorry about that.Don't forget that it's the impedance referred to the secondary; at the primary it would be 353.7 ohms. The transformer specs you gave in post #15 show an impedance of 1.46%--where did 2.03% come from?
no load loss should be 47, full load loss should be 155, total power losses 202. The rest are accurate.Are all the values in post #15 for a 5 KVA transformer?
So do you think this is accurate?So should we assume then that this % impedance value takes into account both core losses and copper losses?
Lets forget about the % regulation values given by the manufacturer for a minute, would you say this is an accurate way to calculate the voltage coming out of the secondary under a 10-amp load?If I'm trying to figure out the total voltage drop of the transformer, then, can I just refer it all to the secondary? So let's say the secondary current is 10 amps, will total voltage coming out of the secondary be 240 - 1.1693 V, or 238.8307 V? This seems low, especially given the values for % regulation given by the manufacturer...
You should be aware that you need to take the word "accurate" with a grain of salt when it comes to grid frequency transformers. Let's say that it is reasonably accurate.Lets forget about the % regulation values given by the manufacturer for a minute, would you say this is an accurate way to calculate the voltage coming out of the secondary under a 10-amp load?
So finally, if I want to get the best approximation for voltage drop given the values I have from the manufacturer, then instead of using % impedance or the no-load and full-load losses, do you recommend I use the % voltage regulation numbers ? Since 1.0 PF regulation is 1.57% (output voltage is 236.29 V at full load), then I can increase voltage up to 240 at no load in a linear relationship as current decreases?You should be aware that you need to take the word "accurate" with a grain of salt when it comes to grid frequency transformers. Let's say that it is reasonably accurate.
This transformer will be used in a power distribution circuit, so applied voltage will be regulated by the generator to remain at or near a setpoint. Current will vary as the load varies. My understanding is the core loss is constant as the load current changes but voltage stays the same, that is why the no-load power loss given as a separate value.The way the impedance measurement is made, core loss is near zero, and doesn't figure into the measurement.
The measurement of regulation is made with full rated voltage applied to the primary, so core loss is near maximum. As load is applied, the core loss decreases slightly, so the drop in output voltage is slightly compensated for by the decrease in core loss.
You have suggested that you might linearly vary certain parameters with applied load. Be aware that core loss does not decrease linearly with applied voltage. If you decrease the applied voltage by one half, core loss will not decrease by half. It will decrease much more than that; the variation with applied voltage is highly non-linear.
Probably the best thing for you is to use the regulation parameter, adjusted for your load PF.
Core loss is not perfectly constant with changes in load current. The flux in the core depends of the voltage seen by the core. The resistance of the primary wire causes a slight decrease in the voltage seen by the core as the load current in the primary increases. The core loss decreases more rapidly for small decreases in primary voltage than a linear relation would suggest, because transformers are operated somewhat into saturation, which leads to a non-linear relation between voltage seen by the core, and the flux in the core.This transformer will be used in a power distribution circuit, so applied voltage will be regulated by the generator to remain at or near a setpoint. Current will vary as the load varies. My understanding is the core loss is constant as the load current changes but voltage stays the same, that is why the no-load power loss given as a separate value.
Does this change your recommendation at all?
Also power loss in the core is equal to V squared / R, so its proportional to V squared rather than V, right?Core loss is not perfectly constant with changes in load current. The flux in the core depends of the voltage seen by the core. The resistance of the primary wire causes a slight decrease in the voltage seen by the core as the load current in the primary increases. The core loss decreases more rapidly for small decreases in primary voltage than a linear relation would suggest, because transformers are operated somewhat into saturation, which leads to a non-linear relation between voltage seen by the core, and the flux in the core.
Core loss is non-linear with respect to applied voltage because the core is operated somewhat into saturation, but it's more nearly V^2/R than V/R.Also power loss in the core is equal to V squared / R, so its proportional to V squared rather than V, right?
by Duane Benson
by Aaron Carman
by Jake Hertz