Magnetisation Current Calculation 1

[McManaman]

Hi all,

I have a transformer with the following information:
3150kVA, 3.3kV/0.415kV, Yd11, Z=6.5p.u.

The maximum magnetisation current at 0.02 seconds is 67420Ampere. How can I calculate this value as I have no idea about this.

 

[bass1mj]

The current that you gave is the infinite bus Fault Current calculated by I = (VA/(Sq3 * Vp))/Z

The Magnetising Current is the current to overcome the No-Load losses in the Transformer.

 

[cuky2000]

Applying a rule of thumb of 8 to 10 times the full load current of the transformer at 0.02 sec. provides satisfactory results in many applications.

This magnetizing phenomenon occurs during energization of transformer and other apparatus. In the worst-case scenario, a value of flux approaching 300 per cent of nominal can be attained, thus causing appreciable saturation of the magnetic core and a massive inrush magnetizing current. The transient component decays rapidly during the first few cycles and more slowly thereafter. The damping is caused by the R/L factor, which is initially high due to the core saturation (L low) and decreases as the core becomes less saturated.
Suggestion: search in this site and the Internet. There are plenty publications similar to the enclose samples:

thread238-10885

http://www.sandc.com/webzine/111102_1.asp

http://www.sandc.com/webzine/012003_1.asp

http://pm.geindustrial.com/FAQ/Documents/T60/GER-4001.pdf

 

[Sett]

you are talking about Inrush Currents or Magnetizing Currents?

 

[electricpete]

I think it's fair to say that cuky was referring to inrush current, also sometimes called magnetizing inrush. His comments on that topic were accurate.

I believe that steady state magnetizing current is typically in the range of 10% of full load current. It can of course be determined by measuring the primary current when there is no load on the secondary. Also can be determined from factory test data