Single phasing a delta-wye(gnd) TFR 2

[Plinko]

Hello Fellow Engineers,

I'm looking for an exact reference to the situation of blowing a high side fuse on a delta-wye(gnd) connected power transformer(single phasing). From experience I know that when this occurs, the result is about a 1/3 voltage drop on the low side phase-neutral voltage...(i.e. on a 120V base, I measure about 80V when I lose a high side fuse at the sub).
I don't think the calculation is that simple. I've tried about every source I can think of to find an example calculation for when this problem occurs.
The reason I need this info is for breaker low voltage trip settings at the substations to avoid single phasing claims on motors and such.

Thanks in advance,
Plinko

 

[jbartos]

Suggestion: Please, would you elaborate. The delta - wye transformers have some voltage angle between the primary and secondary voltages, e.g. 30deg leading, lagging, 90deg, etc. Also, there will be different values of voltages in the secondary wye because of voltage asymmetries.

 

[busbar]

J Horak and G F Johnson—Basler Electric Company, A Practical Guide for Detecting Single-Phasing on a Three-Phase Power System, Western Protective Relay Conference, October 2002, Washington State University

 

[jbartos]

Suggestion: Visit

http://www.basler.com/downloads/practical.pdf

for the referenced paper.
However, the 80V appears to be somewhat high for the loss of one phase on the delta-wye transformer primary.