MV insulation resistance test

[usamaegypt]

Hi;
I have a medium voltage cable 6/10 KV , 3x185 mm sq , CU/XLPE/PVC and I want to test the insulation resistance between phase to phase and phase to sheild , would you please inform the DC voltage level that could be used for such test. Could we use 10000V to test phase to phase and phase to shield insulation resistanc.
Best regards.

 

[electricpete]

It is certainly safe to apply IEEE43-2000 motor test voltages to cables and that is what we use.

500vdc for 480vac and below.
2.5kvdc for 4.16kv system (5kv cable)
5 - 10kvdc for 13.8kv system (15kv cable)

Hi-pot voltages under limited carefully evaluated circumstances may go much higher. For example 13.8 kv motors maintenance level hi-pot is ~ 28kvdc for motors but 40+kvdc for cables.

One thing to beward of is wet cables. Certain cables are susceptible to treeing when dc voltage is applied while wet.... could cause a failure during test or later of a cable that likely would not have caused any problem otherwise. Particularly XLPE and certain types of EPR.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[electricpete]

If you are reasonably confident the cable is dry it should be no problem to apply 10kvdc. 5kv would be even safer.


=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[busbar]

 
If the individual phase shields are grounded, there should not be any point to a phase-to-phase test.