TanDelta measurement is a non-destructive test that evaluates the condition of the insulating system of an entire cable route. The relation between the effective power and the reactive power of the cable is measured. This provides clear information on the condition of the cable insulation and its ageing condition. The values given in the test are checked against the evaluation criteria given in IEEE 400.2-2013

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The voltage is raised in steps from 0,5 to1,5*U0 and this allows for the following evaluation criteria:

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• VLF-TD time stability (VLF-TDTS) at U0

• Differential VLF-TD in mean TD between 0.5 and 1.5 U0

• Mean VLF-TD at U0

 

Typical reasons for dielectric losses

▪ Presence of water trees in XLPE insulation 

▪ Moisture in joints and terminations

▪ Presence of partial discharge (PD)corrosion of the metallic shield

▪ Corrosion of the metallic shield poor contact between metallic shield and insulation shield

▪ Poor contact between metallic shield and insulation shield

▪ Drying in the insulation of paper-insulated mass-impregnated cables 

▪ Damaged insulation in paper-insulated mass-impregnated cables due to moist 

 

 

The results of the test will be as follows:​​

▪ No action required

▪ Further investigation

▪ Action must be initiated

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Typical reasons for dielectric losses:

▪ Presence of water trees in XLPE insulation

▪ Moisture in joints and endings

▪ Corrosion in laminate with PD

▪ Poor contact between laminate and cable screen

▪ Drying in insulation of paper/oil insulated cables

▪ Damaged insulation in paper/oil insulated cables due to moisture

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Neka uses two different technologies for Tan Delta testing:

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TanDelta diagnosis with DAC reveals:

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​▪Dipole losses is represented by insulation ageing which is detectable with TD measurements above 10 Hz
​▪Interface losses is represented by problems between materials which is detectable with TD measurements at 50/60 HZ
​▪Localized high intensity discharging defects is represented by PD which is detectable with TD measurements above 10 Hz

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"DAC TD is especially useful for detecting degradation in paper/oil cables"

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TanDelta diagnosis with VLF reveals:

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​▪Conductive losses is represented by Water-treeing in xlpe cables which is detectable with TD measurements below 1 Hz