Overcurrent relay and inrush current

[mabdeltawab]

Dear All,
I'm electronics engineer working on design on an overcurrent relay
as per my understanding, the overcurrent relay calculation is based on fundamental harmonics RMS
my questions are:-

- Why do we need to care about inrush as long as it affects only 2nd Harmonic which is not used in calculation?
- Does the inrush affect the 1st Harmonic, and how?

Thanks

 

[waross]

What is the intended application of the relay? Motor? Feeder? Transformer? Other?

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

 

[mabdeltawab]

Bill

it will be installed in RMU operating on around 13kv

Regards
Mohamed

 

[jghrist]

There is a significant amount of 2nd harmonic in inrush current, but mostly it is fundamental. Example plot from transformer energization:

Maximum fundamental 498 A rms. Max 2nd harmonic 235 A rms

 

[stevenal]

1) 2nd harmonic current can be used to restrain or block tripping during conditions of transformer inrush.
2) Yes. That is why you may wish to restrain or block during transformer inrush.