Inrush Currents in STEP UP Transformers
Inrush Currents in STEP UP Transformers
(OP)
HI all. I understand that the inrush would be greater if a step-down transformer is energized at the LV side.
However, if we have a STEP-UP transformer, is the inrush "seen" at its LV terminals and no inrush at its HV terminals. The reason I ask is that our contractor has set the relay of the HV side high enough to bypass the transformer inrush current.
If the inrush is at the HV side, is it going to be 12X as well? If not, how much inrush I would get at the LV side?
Thanks
However, if we have a STEP-UP transformer, is the inrush "seen" at its LV terminals and no inrush at its HV terminals. The reason I ask is that our contractor has set the relay of the HV side high enough to bypass the transformer inrush current.
If the inrush is at the HV side, is it going to be 12X as well? If not, how much inrush I would get at the LV side?
Thanks






RE: Inrush Currents in STEP UP Transformers
Inrush current will not be huge on HV side as the nominal current is not that big on GSU HV side.
In this case, and since no flux has built up in the yoke, no inrush current will be transferred to the LV side when energized from HV side.
RE: Inrush Currents in STEP UP Transformers
RE: Inrush Currents in STEP UP Transformers
If that is the case, then the inrush may be a higher percentage when the transformer is energized from the low voltage side.
Are you following this Electricpete?
Is it possible to estimate the high side resistance by looking at the transformer losses at different load levels? Once you have the high side resistance, can you use the impedance voltage the X/R ratio and the high side resistance to determine the low side resistance?
With the resistance of both the high side and the low side, can you see if the resistance ratio is similar to the turns ratio or if the low side has proportionally lower resistance?
Thanks friend.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Inrush Currents in STEP UP Transformers
RE: Inrush Currents in STEP UP Transformers
My question is that, if we energize the 4.16 kV side, the inrush would be seen at the 4.16 KV side and not on the 7.2 kV side. Our contractor was thinking that the inrush is also seen at the 7.2 kV but I argue and explain to him that it is not the 7.2 kV winding that is energized first but the 4.16 kV side. Since he insists on it..I want to make it sure I am not missing anything.
I will try asking the manufacturer the inrush data of this step-up transformer.
RE: Inrush Currents in STEP UP Transformers
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Inrush Currents in STEP UP Transformers
RE: Inrush Currents in STEP UP Transformers
RE: Inrush Currents in STEP UP Transformers
Even if residual flux is nil in the core,there will be inrush current and will be maximum when switching is done at the zero point on voltage wave.Then the flux in the core will be two times the rated flux density(normally 1.7 T),much more than the saturation flux density of core ie 2.0 T.Then air core inductance of winding decides the inrush current required to maintain such flux level inside the winding.
The latest tutorial on the subject is CIGRE technical brochure no.568 (125 pages),issued in Feb 2014,titled ' Transformer Energisation in Power systems: A study Guide' available at e-cigre.org
RE: Inrush Currents in STEP UP Transformers
prc give us a very good explanation on the difference between LV and HV transformer inrush currents.
Best Regards,
Herivelto S. Bronzeado
Brasflia, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...
RE: Inrush Currents in STEP UP Transformers
Do a voltage dip calculation if you want to energize from the LV side.