You've described a fairly common, albeit older, MV transformer configuration. Having the lightning arrestors and HV terminals directly mounted on top of the transformer with connections to open bus/conductor is not unusual, especially in outdoor substations.Here's a breakdown of potential solutions and considerations, focusing on the code (NEC) aspects and best practices

Considerations and Challenges:
Clearances (NEC 110.26, IEEE C2)

Maintaining proper phase-to-phase and phase-to-ground clearances is critical. 22" between points is tight. You must adhere to the requirements of the National Electrical Code (NEC) and, ideally, consult IEEE C2 (National Electrical Safety Code - NESC) which provides more detailed guidance on clearances for substations. These clearances are voltage-dependent, so 35kV class equipment requires careful attention.

Environmental Exposure

Being outdoors, the connections are exposed to weather, UV, and potential contaminants. Corrosion is a concern.

Safety

The primary reason for shielded cable is safety. In your case, being behind a locked fence provides some safety, but doesn't eliminate the risk of accidental contact (maintenance personnel, etc.).

Mechanical Stress

The conductors must be able to withstand mechanical forces (wind, ice, vibration) and the weight of connections.

Corona

High voltage gradients on sharp points or improperly installed terminations can lead to corona discharge, causing insulation degradation and radio interference.

Possible Solutions


Bare Copper Buswork



Pros

Simplest and potentially most cost-effective. Good current carrying capacity.

Cons

Highest risk of flashover if clearances are not meticulously maintained. Requires careful engineering for mechanical support. NEC compliance will be extremely difficult. The NEC generally requires insulation at these voltage levels unless you can meet the requirements for exposed live parts operating at over 600V (and those requirements are extremely stringent).

Code Issues

NEC 310.15 specifically requires conductors operating at over 600V to be insulated unless specifically permitted otherwise (e.g., in switchgear). The exposed conductors are very likely to violate 110.26 (Working Space and Guarding) and 225 (Outside Branch Circuits and Feeders).

Implementation

If using bare copper, consider: Use heavy-duty copper bar (busbar) for rigidity. Ensure rounded edges to minimize corona. Thoroughly clean and treat the copper to prevent corrosion. Use insulating spacers between phases and to ground. Choose the right material for 35kV service. The busbar design must address expansion and contraction due to temperature variations. Very careful engineering analysis is required to prove compliance with the NEC, IEEE C2, and other applicable standards.2.

Insulated, Non-Shielded Cable (35kV Rated)



Pros

Offers some insulation protection against accidental contact and environmental factors. Easier to route than bare copper.

Cons

Shielding is very desireable for MV and HV system to help contrain the electric field. Non-shielded cable may create issues with leakage current.

Code Issues

Less problematic than bare copper but still subject to NEC scrutiny. You must verify that the cable is rated for the specific application (outdoor, wet location, etc.) and that the clearances meet code. The insulation still has to meet the voltage rating.

Implementation

Select a cable specifically designed for 35kV applications, outdoor exposure, and your operating temperature. Use cable lugs and terminations rated for the cable and voltage. Properly support the cable to prevent stress on the terminations. Use a high grade mastic tape and sealant on the crimped connector to protect the connection. Maintain adequate clearances to grounded objects.3.

Shielded MV Cable with Modified Terminations



Pros

Offers the highest level of safety, reliability, and performance. Minimizes electrical stress on insulation. Reduces the risk of corona and radio interference. Complies better with NEC intent.

Cons

More complex and expensive to install, especially with short runs. Stress cones are bulky.

Implementation



Challenge

You're right; standard stress cones are likely too large for the 22" span.

Solution

Look for manufacturers that offer "short" or "compact" stress cones specifically designed for limited space applications. These are designed to be smaller and easier to install in tight quarters. 3M, ABB, Elastimold, and others make such terminations. Call their technical support. Another possible option is using heat shrink terminations. These can sometimes be a bit more compact. Ensure proper cable grounding (shield grounding) is done according to manufacturer instructions and NEC requirements. Use proper crimping tools for the cable lugs and connectors. Pay meticulous attention to detail during installation to avoid damaging the cable insulation or shield.4.

Prefabricated MV Bus Duct



Pros

Engineered solution, offering excellent reliability and safety. May be easier to install than custom solutions.

Cons

Potentially the most expensive option. May require long lead times. May not be readily available for such short runs.

Implementation

Contact manufacturers of MV bus duct (e.g., Siemens, Eaton, Schneider Electric) to see if they offer a suitable solution. Ensure the bus duct is rated for your voltage, current, and environmental conditions.

Recommendations

Consult with a qualified electrical engineer with experience in substation design. They can perform a thorough engineering analysis, select the appropriate solution, and ensure compliance with all applicable codes and standards. This is essential for safety and liability reasons.2. Prioritize Safety

Shielded cable, even with short terminations, offers the best level of safety and long-term reliability.3.

Consider Long-Term Costs

While bare copper might be cheaper initially, the potential for failure, increased maintenance, and liability risks can far outweigh the initial savings.4.

Documentation

Meticulously document all design decisions, materials used, and installation procedures. This is crucial for future maintenance and troubleshooting.5.

Contact Manufacturers

Talk to the technical support teams of cable, termination, and bus duct manufacturers. They can provide valuable guidance and recommendations for your specific application.

In Summary:

While bare copper might seem like a simple solution, it is likely to violate code, poses significant safety risks, and is generally not recommended. Exploring compact stress cones for shielded cable is the best starting point. A qualified engineer is vital for this project. Good luck! Flag for review