I would scrap the entire installation and install a single, properly sized, listed ground clamp that has not been field-fabricated or field-modified like the two pictured. The top clamp has “stacked” washers/hex nuts that do not appear to be part of the original assembly, and the lower mess...
No one has cited this one yet…
From IEEE C57.13 7.7 Short-circuit capability
Voltage transformers shall be capable of withstanding for 1 s the mechanical and thermal stresses resulting from a short circuit on the secondary terminals with full voltage maintained on the primary terminals...
Do a Google search on transformer ferroresonance. At least it may be something to rule out.
IEEE std C57.105 §8 has some basic information on transformer susceptibility to ferroresonance.
You might consider something like a “Group-U” [440Δ - 220Y/127V 3ø, 50Hz] transformer listed at www.acmepowerdist.com/energy-efficient-transformers-three-phase.htm
Check out back issues of EC&M magazine. { www.ecmweb.com } There have been numerous articles on triplen and other power-system harmonics. One caveat—the online material is without charts, photos or illustrations. You have to purchase the articles to get those.
www.keybellevilles.com is one manufacturer, but beware of their healthy minimum quantities and setup fees.
www.sandc.com has, in times past, filled smaller orders for me.
A de facto document is ANSI standard IEEE C57.105-1978 IEEE Guide for Application of Transformer Connections in Three-Phase Distribution Systems §7, that be of some help.
An aside—from practical experience, voltage-mode imbalance [ANSI device 47] protection should only be applied to inhibit 3-phase motor starting—where current-mode relays [ANSI device 46] are needed to reliably interrupt motor running.
This doesn't directly answer your question, but here is a ~50-year-old account of the perils on LV ungrounded systems—as opposed to high-resistance grounded systems. This all-time classic description is detailed in a chapter on system grounding in Beeman’s Industrial Power Systems Handbook...
See http://www.tnb-canada.com/en/catalogues/online/industrial_MRO/pdf/c3/05en.pdf page 1 “Two-Hole Lugs – Standard Barrel Certified to 600V and Recommended up to 35 kV”. My understanding is that the >600V application is to facilitate taping; but otherwise identical.
I think, per the formula in C37.99, that your scheme should detect open fuse conditions. Just make sure that the 59N relay is restrained for third-harmonic conditions.
As referenced by waross, in this day and age there is no valid reason not to use hydraulic-compressed slices with heatshrink covers. Both have been around for decades with well-proven reliability.
