With more reading, I've picked up a few things. Most available information I'm finding concentrates on HV
AC, rather than DC; power transmission as opposed to communication; and there's a lot of information for Medium (2-5kv+) and High (15-35kv+) cabling and little information for installations below 2kv.
It's common to include a semi-conducting coating/layer/wrap that exists over the conductor's insulation layer, with typical resistance of ~500 ohms/meter. This is not a shield in the sense I think of a "shield", but a method to reduce corona formation that can create ozone and accelerate deterioration of the insulation. I do not know the voltage threshold where this becomes a significant factor, nor do I know if it's a problem only with AC, or also with DC, but a
Wikipedia article seems to indicate that above 2kv this semi-conductive layer is requred.
Metallic shielding can be effective to reduce RFI/EMI but may not restrain/contain magnetic fields, or may only dampen/attenuate them.
During HV cable construction -- and especially when performing a splice -- there is a strong desire to maintain concentricity of the conductor, the semi-conductive layer, and the shield layer. Having a consistent radial dielectric strength (K) reduces flux imbalances that can lead to elevated insulation stress when a conductor is not centred in the insulation and has varying distance from the shield (or a nearby conductor of significant potential).
In addition to concentricity, it is vital (at elevated voltages) to eliminate ALL voids (air) between the conductor and the shield, as air can be ionized and create ozone as indicated above. Using a filler when needed (resin, flowable silicone, or in combination with vacuum degassing: epoxies or dielectric greases) is a common procedure when forming splices on HV cabling.
In power transmission, it's common to have multipoint grounding of the shield: at both/all ends of cables, as well as at splices, and even at intermediate drops. This is in contrast to shielded communication (data) cables, which commonly do
not ground a shield at multiple locations.
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What techniques are people in the DIY EV realm using when extending HV DC leads? Are shielded cables not used? Or, is there a generally accepted practice for splicing, keeping the shielding intact after repair?
