Using AC to test power cable

[relayman1000]

thread238-248906
What are test times for shielded and nonshielded cable using AC at 60HZ? What are 60HZ AC test voltages for 5KV and 15KV cable?

 

[collies99]

The recommended practice is for AC Very Low Frequency testing. Test voltage levels and test times are in IEEE 200.2-2013 standard.

 

[iceworm]

The recommended practice is for AC Very Low Frequency testing. ...

I definitely agree. (minor typo - look in ieee 400.2)

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[collies99]

Iceworm thank you for the correction, much appreciated.

 

[iceworm]

You're welcome.

I am hoping someone will respond with a spec (and reference). I'd like to know. Truely, the only power line frequency testing I have done is to "Power - ON". That would be ieee 4 (as I recall). Not much of a predictive nature there. And maybe at that stage it doesn't matter. If the cable is broke (precise engineering term) it is of little use until replaced. Except one might have less glowing slag to clean up if one could show, "Yes, the cable is bad - do not energize"

As you asy, AC VLF is preferable.

ice

Harmless flakes working together can unleash an avalanche of destruction

 

[VLFit]

To answer your question, the IEEE 400.2-2013 standard for VLF testing MV and HV cable specifies the following for 5 kV and 15 kV shielded power cable of any solid dielectric material:

5 kV cable: Installation test voltage = 13 kV peak - phase to ground, Acceptance = 14 kV peak, Maintenance = 10 kV peak.

15 kV cable: Installation test voltage = 27 kV peak - phase to ground, Acceptance = 30 kV peak, Maintenance = 22 kV peak.

The above numbers assume the use of a sine wave producing VLF power supply operating at 0.1 Hz. This is a Voltage Withstand, pass/fail test. The test duration should be a minimum of 30 minutes with 60 minutes preferred. This standard also defines the test methods for performing a Tan Delta diagnostic test on the cable, where the VLF applies an over voltage of 1.5 - 2.0 times normal voltage and the TD, or loss factor, of the cable is measured, which provides an indication of the extent of insulation degradation. 50/60 Hz test voltage levels are lower and for shorter duration. Depending on the capacitance (length and size) of the cables to be tested, the current/power required from the test set may be prohibitively high, which is why power frequency is rarely used in the field and why VLF technology was developed and now used worldwide.

Hope this helps.

 

[ausphil]

IEC standards 60502 (cables systems from 6 - 30 kV rating)and 60840 (cable systems from 33 - 150 kV rating) do specify power frequency ac tests after laying.

There are 2 methods, either a HV test or a 24 hour system soak.

IEC 60502 applies the phase to phase rated voltage magnitude to each phase to earth (ie 1.414 times the normal operating electrical stress). The test duration is 5 minutes. The only frequency guidance is "power frequency".
IEC 80640 applies the phase to phase rated voltage magnitude (give or take within a certain rated voltage range) to each phase to earth (essentially the same as IEC 60502). The test duration however is 1 hour. This also states that the test frequency has a range from 20-300 Hz, which takes into account the use of resonant test sets at these higher voltages.

Ausphil

 

[VLFit]

The above post showing the IEC standards may be correct (I haven't verified them but the info is basically true) but this is America and the IEEE standards cite the above letter's info but IEEE 400 and IEEE 400.2 also permit VLF testing, which is a lot easier and cheaper to do in the field.IEEE 433 is for using VLF for testing rotating machinery. There are other countries, including Germany and the VDE Standards, that also have VLF testing standards. Of course no one will deny that testing with power frequency is best and is mandatory in factory certification testing and some installation/acceptance testing in the field. However, it is not a practical method for the thousands of field test requirements for cable from 5 - 138 kV or for testing large rotating machinery. Every method has its place.

 

[ausphil]

VLFit,

I apologise for citing standards that answered Relayman1000's original post, ie testing with power frequency.

I thought that the VLF test requirements had been covered well by others, and I wanted to give Relayman1000 a reference for his initial line of questioning.

Ausphil

 

[VLFit]

Hello ausphil,

You are correct, he did ask about power frequency. The subject quickly was turned to VLF by others and that subject took over. He now should have all that he needs.

Good day