Calculating VD due to starting inrush current of motor

[VTer]

Hi, I am working on a small project where I would like to verify if the inrush current of a motor could possibly cause me some potential problems because of voltage sag. Due to my lack of experience, I could not find nor remember of any good reference for calculating the voltage drop(sag) due to the inrush current of a motor. I have the following known scenario info with some assumed values because of lack of info at this point. I would appreciate if someone with experience could provide me some useful info and feedback if there are other ways of doing this calc to get the ballpark number or to see if this approach is accurate at all. Any info on the subject topic would be appreciated.

Scenario:
750KVA XFMR
480Y/277V Secondary
Assume 6% leakage reactance
50HP Induction Motor
60A @ 460VAC
600A peak Asymm. current @ 1st half of the cycle due to inrush (assumed)

FLA of XFMR at 480V = 750/.831=900A approx.
VD due to starting inrush = .06*600/(900*SQRT(2))= 2.82%

Based on this my voltage on the secondary of XFMR at 1st half cycle on motor inrush would only drop down to approx 466V which shouldn’t be a problem for non of the loads? FYI: this is the only VD I care about right now, I am not concerned of feeder and other VD’s at this time.


"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[EddyWirbelstrom]

I have used PTW DAPPER software and also manual calcs to determine voltdrop for FLC and also LRC.
DOL starting a 50hp ( 37kW ) induction motor supplied by a 750kVA transformer does not cause voltage drop problems for the motor or other equipment supplied by the transformer.
My assumptions are listed in the attached study resutlts.
More accurate data, such as cable impedance would give more accurate results.

 

[lansford]

Unless there is some very unusual source impedance (such as a high side transformer voltage of 480 volts), starting a 50HP across the line with a 750 KVA transformer, has minimal drop in starting.
JIM