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Start by
atul talati
08-23-2014 09:40 PM

Inrush current in transformer

We all know that heavy magnetizing inrush current is generated in the primary of transformer when it is energized ? ABB also has developed formula for this. I want to know that actually who measures and keeps record of this current ? Manufacturers or customers ? Is there any special test for this inrush measurement ?
08-23-2014 11:41 PM
Top #2
Filippo Guarda
08-23-2014 11:41 PM
Where can I find the ABB formula? Thanks
08-24-2014 01:57 AM
Top #3
carlo del carlo
08-24-2014 01:57 AM
Per i piccoli trasformatori le norme danno la corrente di inserzione tipica (I=f(t)) per i grandi trasformatori è meglio chiedere al costruttore del trasformatore. Ho lavorato per decenni in BBC/ABB e mi occupavo di studi di rete ed ho sempre chiesto ai costruttori del trafo.
Se vuoi scambiare informazioni su studi di rete etc volentieri
08-24-2014 04:54 AM
Top #4
08-24-2014 04:54 AM
Mr. Guarda, Kindly download the ABB Technical Application Paper No.2 "MV/LV transformer
substations: theory and examples of short-circuit calculation". In this Application paper, a detailed write-up is available on transformer inrush currents in the Annexure A.
08-24-2014 07:17 AM
Top #5
Gerbrand Ronsmans
08-24-2014 07:17 AM
Not only the primary, if you energize the transformer from the secondary side same inrush effect will take place.
The inrush currents can be measured by the fault recorder, some utilities use the close command of the breaker as trigger condition for a record. But do not mistake, inrush is an unwanted side effect not the aim!
So both have records, manufacturers and customers for various reasons. There is not really a special test for it. It is a phenomenon that takes place during energizing of a transformer and depends on the magnetic remanenz and size of the transformer. Think of it as a magnetic capacitor.
Since it is an unwanted effect transformer manufacturers try to limit it based on the design, core material and so on. The utilities they try to limit the inrush by closing the breaker at the best moment depending on the voltage sinusoide.
A similar phenomenon is called outrush or sympathetic inrush, same underlying magnetic physical effect.
08-24-2014 09:43 AM
Top #6
Ashok Toshniwal
08-24-2014 09:43 AM
It also depends on the impedance of the transformer.
08-24-2014 12:34 PM
Top #7
08-24-2014 12:34 PM
Worst case inrush happens when the primary winding is connected at an instant around the zero-crossing of the primary voltage, (which for a pure inductance would be the current maximum in the AC cycle) and if the polarity of the voltage half cycle has the same polarity as the remnance in the iron core has, ie, the magnetic remanence was left high from a preceding half cycle
08-24-2014 02:59 PM
Top #8
Jim Phipps, P.E.
08-24-2014 02:59 PM
Inrush current is a random variable that depends on many factors two of which are the magnetization of the core at the instant when the transformer was last de-energized and the magnetizing polarity of the voltage waveform at the instant when the transformer is energized. If these two factors match, the inrush will be small; if these two factors are opposite of each other, the inrush will approach a maximum value as Carl stated. Since inrush current is random, the need to keep records of such events does not provide a great benefit. It is necessary, however, to design the relay protection system to allow for transformer inrush without tripping.
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