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The consequences of electrical insulation failures in ageing umbilicals: copper loss and hydrogen generation.

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Earthing Arrangements

IEC has standardised on three families of earthing – TN, TT, IT

1st Letter is connection between earth and supply

2nd Letter is connection between earth and device being supplied

TN TT IT

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Monitoring of IT Systems

IEC 60364 is the international harmonised standard that details requirements for low voltage electrical installations.

•Part 4-41 (Protection for safety – Protection against electric shock) specifies that an IT (floating earth) system shall always be equipped with a suitable protective or monitoring device.

•For high system availability, an IMD should be used, to indicate the first fault, with suitable automatic disconnection of the supply

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Cable Insulation Integrity Measurement

Leakage current 𝑓() of 3 sub-currents

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Experimental Set-Up

Viper

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The IMD two-week effect

Single point damage to insulation equivalent to an insulation resistance of 30kΩ

Day 1 Day 14

Copper Corrosion

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The IMD Electrochemical Cell

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IMD Experimentation

At the positive surface:

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AC Power Experimentation

At the negative surface:

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The two conductors after AC power applied

Tarnishing of copper: 2 Cu(s) + O2(g) → 2 CuO(s)

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Copper Corrosion after AC power applied

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V-LIM Changes to Reduce Copper Loss

IMD current is a minimum at High IR and a maximum at low IR

The output voltage from the IMD can be reduced as the IR reduces without loss of accuracy.