Transformer Grounding

much of the logic for such an array of equipment depends on the remainder of the distribution system you don't show.

Typically the serving utility would have a solidly grounded source, to be sure you can detect system faults, and stabilize transient voltages generated by distributed line capacitance. In the case of a single grounded leg that couldn't be fixed quickly, I suppose you could shut down the system and open the ground switch connection.

The balance of the equipment could be used to protect the transformer primary winding insulation, while allowing operation with one grounded leg. An intermittent arcing fault can generate transient overvoltages that stress transformer insulation.

I think that, like most of our colleges, this neutral ground connection is not linked to NEC even directly in IEEE. So I will try to explain this in simple words.

A step-up transformer it is a very expensive part of a power station. Insulation of the high voltage winding is a very expensive part of the transformer so the turns insulation is reduced gradually from terminals to neutral. In this case the system has to be solid grounded. Sometime the high voltage system short-circuit ground fault current is higher than permissible so neutral of transformer has to be disconnected from the grounding and the surge arrester has to protect the transformer neutral for the transients as a lightning phenomenon.

Since the arrestor could be damaged by a very high lightning strike a discharge gap is provided as back-up protection.

Because this drawing is not describing a grounding scheme, but an improperly drawn call-out box for an impulse counter installation. The line drawn to the neutral should have been drawn with an arrowhead pointing to the transformer, which would indicate that the "stuff" in the box was part of a surge counter installation, and is not to be taken literally.

Surge counters are typically installed at the bottom of LAs on transformers when there is a history of equipment failure traceable to high/repeated TOVs (Transient Over Voltage). The spark gap (aka Arcing Horn/Ring) is there to protect the equipment from TOVs that would cause insulator flashovers and carry any subsequent powerline frequency follow-through currents. The two counters give a relative indication of the "normal" LA operations vs. the number of "severe" TOV flashovers across the spark gap.

Notice that there are two dual-core CTs in the grounding conductor of the spark gap, one often goes to the protective-relaying system, the other to a TDR (Transient Data Recorder) and/or SCADA/DAQ system.

The disconnect switch is mislabeled, it is a safety grounding switch that ensures that the lines are de-energized and provides a drain for any random charge buildup on the transmission lines, all for personnel safety.

There is one circumstance where such a setup IS connected to the neutral, that would be if it were installed as part of a high voltage test lab for type-testing of different winding insulation systems. The 30MVA generator makes this an unlikely scenario as presented, especially since no impulse generating equipment and additional testing circuitry is shown.

This information is hardly trivial so I'm glad some people on the forum take the time to answer for those of us that are not simply incompetent but perhaps not versed in that specific area of engineering. Very interesting information

This forum is a wonderful resource but the bickering and rudeness is rivaled only by a kindergarten playground. It truly is a shame