480 208/120 Delta Wye with Neutral

[glane]

I'm performing a redundant failover audit in our data center and need assistance in understanding how line current is determined in an unbalanced delta wye 480/208y transformer.

My known values are as follows:

Primary line currents (taken from metered UPS): A=67.7, B=81.4, C=72.1
Primary power @ UPS: 59.7KW with a 0.96PF
Primary voltage: 480V

Secondary line currents (clamp meter at main breaker after transformer): a=168.6, b=167.2, c=162.3
Wye neutral line current: 15.3A

I'm attempting to mathematically prove how the secondary line currents become the lower primary line currents, so that I can apply the same technique and determine what the currents would look like in a simulated redundant failover situation at the UPS.

Any help is appreciated. Thank you.

 

[Ingenieur]

Using averages (need more info to do it by phase)
Prim = 59700/(0.96 sqrt3 480) = 74.8 A based on power
math avg = 73.7 A

Prim current = secondary current x 120/480 x sqrt3
= sec current x 0.433

check
secondary avg = 166
primary = 166 x 0.433 = 71.9 A
the difference is the imbalance
Within 5%
should be good for your use

the sec is well balanced, the prim not so much

 

[Phil Corso]

Glane,

Can you provide the primary ph-ph and secondary ph-neutral voltage measurements?

Regards, Phli Corso