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.