PT shielded cable close to capacitor banks

[ePOWEReng]

Does anybody know a type of PT cable that has a shield that will minimize transients due to magnetic coupling? This is for a sub with cap banks. We tried using a 4 conductor cable with a copper shield but it turns out that doesn't reduce magnetic coupling very well.

 

[scottf]

What about using sheilded twisted pair? The shielding needs to be ferrous to shield for magnetic field, I believe.

 

[peebee]

Scottf is right on, you need ferrous shielding for magnetic circuits.

Maybe you could run your wiring in steel conduit.

 

[busbar]

It may be worth investigating if indeed magnetically-coupled capacitor currents are introducing errors in the PT cabling. {As implied, non-ferrous shielding is primarily effective for electrostatic influence.}

If for instance, the PTs are used for capacitor-unbalance protection, some initial or quiescent voltage may be present from accepted capacitor-manufacturing tolerances, and somewhat influence what would be considered an otherwise near-zero secondary quantity, like on the order of a 0.05 per-unit value. The need for sensitivity in ground-overvoltage relaying makes accurate determination of ‘neutral-shift’ voltage quantities important, and otherwise not “buried in the mud.” [Reference IEEE Std C37.99-2000.]