About the value of inrush current when energizing two transformer at the same time 1

[Bronzeado]

Hi folks,

In a simulation of energizing two similar transformers at the same time, the inrush current is not twice the value of the inrush current of just one transformer (in the same conditions).

I wonder if the experts could give a explanation on that "phenomenon". Thank you!

Cheers,

Herivelto S. Bronzeado
Brasília, Brazil

https://www.linkedin.com/in/heriveltobronzeado/

https://www.researchgate.net/profile/Herivelto_Bronzeado

 

[davidbeach]

If the two transformers were deenergized at the same time, the inrush should be similar to what it would be for one the size of the sum of the individuals. That based on observing raw relay event files and seeing a very clean single transformer inrush waveform. I haven't actually summed up the individual transformers and tried to calculate the inrush as a percentage of the equivalent total.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[waross]

If your simulation includes the voltage drop of the supply and of the supply conductors, then the inrush of two transformers will be less than twice.
In the real world, the magnitude of the inrush depends on both the point-on-wave when a transformer is energized and on the residual magnetism.
The residual magnetism, in turn, depends on the point on wave when the transformer was de-energised.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[crshears]

Will it not also depend upon the device used to place the pair of transformers on potential?

My former employing utility commonly and normally used motorized air break switches [ usually with arcing horns ] to energize banks; it was reported to me that the resistance of the closing air gap served to energize transformers with a sloping wave instead of a steep-front wave, supposedly extending transformer service life.

Of course they may have been string along a gullible individual . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[cranky108]

Are you by chance energizing both with the same breaker? If so, are they protected with there own differential, or just one differential?
The reason I ask is, protecting two transformers with a single differential, normally doesn't work. I've seen this not work, but most relay instruction manuals either don't say this, or explain why.

 

[bacon4life]

Waross's explanation makes sense to me. Expanding the question out to when we energize hundreds of service transformer using a substation breaker, the combined inrush for the whole feeder/circuit is far less than the sum of the individual transformer's inrush. In fact, on many of our circuits, the sum of individual transformer's inrush would far exceed the available short circuit current from the substation breaker.