Megger / Cable Insulation testing - Absorption Current?

[akyip]

Hi guys,

I'm running a second drill of Zach Stone's Electrical PE Review. One of the questions (question 64) regarding insulation testing mentions both Dielectric Absorption Current and Absorption Conduction Current... What is the specific difference between these two currents?

Thank you to anyone who answers this question!

 

[Orchid PE]

I haven't personally heard the term "Absorption Conduction Current."

I've heard of Dielectric Absorption Current (or polarization current) which is the current that is initially drawn by the insulation. That current gradually drops off after a few minutes as the insulation's dipoles are aligned with the magnetic field of the current.

I've also heard of Conduction Current (or leakage current, or resistive current) which is the current drawn by the resistance of the insulation. This shouldn't change with time.

There is also Capacitive Charging Current. This is present when DC is applied to a conductor to charge the capacitance that is apparent between the insulation and earth.

There is also Total Current which is the sum of the previous three currents. Note Dielectric Absorption, Capacitive, and Total currents all change with time. Conduction current does not.

There is a good amount of resources on the web that delve deeper into these currents that are present during insulation testing.

 

[Orchid PE]

A few resources:

Standard Handbook for Electrical Engineers (Santoso, Beaty) (page 149-164)

https://dam-assets.fluke.com/s3fs-public/1579160_b_w.pdf (page 3)

http://www.idc-online.com/technical_references/pdfs/electrical_engineering/Dielectric_Absorption_Test.pdf (page 1)

http://www.techni-tool.com/site/ARTICLE_LIBRARY/Megger - The Complete Guide to Electrical Insulation Testing.pdf (page 3)

 

[Dude99]

A good basic reference

https://www.instrumart.com/assets/Megger-Guide-to-Insulation-Testing.pdf

 

[Orchid PE]

Just an FYI, that reference contains the exact same text as one I posted above. Both are not needed.

 

[Zach Stone P.E.]

Hi guys,

I'm running a second drill of Zach Stone's Electrical PE Review. One of the questions (question 64) regarding insulation testing mentions both Dielectric Absorption Current and Absorption Conduction Current... What is the specific difference between these two currents?

Thank you to anyone who answers this question!

Hi @akyip, looks like I missed this. There is no such thing as absorption conduction current, it was included as just a trick answer however I can see how this could be confusing. I updated the solution to expand on this, and to also label and describe the other insulation current curves shown on the graph. 

Here is the updated solution if you'd like to save it for your records. You can click the image to open it in full size:

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