PI Test on cable 1

[wauld]

Can a PI test be carried out on a 3.3kv motor supply cable, or can this type of test be carried out on the motor windings only?
The motor was removed recently,and the cable may have sustained damage during this time and will need to be checked before reconnection.

 

[Zogzog]

DC hipot test will only give you essentially a pass/fail result, the cable may pass and still be bad. A VLF, TD, or PD test is a much better indicator.

 

[wauld]

DC hipot test will only give you essentially a pass/fail result, the cable may pass and still be bad. A VLF, TD, or PD test is a much better indicator.
Hi Zogzog
Could you explain what the above tests are?
Thanks

 

[hlrl]

Hi,
Do you have the test voltage(DC) for 3.3kV cable?

I read in some articles which recommended the follow:
Test voltage (DC) = [(3.3kV * 2)+ 1kV] * 1.4

Cheers.

Yeo

 

[hottip]

@wauld

VLF = Very Low Frequency
PD = Partial discharge
TD = Dissipation factor measurement (tan delta)

The TD and PD diagnostic methods complement each other ideally

Dissipation factor measurement (tan delta)
A reliable diagnostic method for determining the general condition of a cable section.

Partial discharge level measurement (PD)
Using this diagnostic method, PD level measurement as well as the localisation of partial discharge sources can be performed.

VLF cable testing
The test using VLF on plastic insulated medium voltage cable systems has gained acceptance over the last few years and is rightly displacing the rather uninformative and damaging DC test.

For more informations I strongly suggest Google.

 

[Zogzog]

Thanks hottip, well stated, you saved me the effort.

Wauld, the March NETA conference will be focusing on cable testing.

http://www.netaworld.org

rlyeo, new or existing cable? What is the insulation level?

 

[wauld]

Thanks everyone for replying. Looks like Tan-Delta would be the appropriate test.

 

[aolalde]

My personal opinion; for a cable at operating voltage 3.3 kV, a megger test at 2500 VDC for 1 minute and IR>5 Mega-Ohms at 40°C is enough.
PD and Tan delta are more applicable for higher operating voltages and they make sense when you have previous test references. If you want to invest for the future, make these last tests and save the results for a future reference, the trend will show you the aging rate of the insulation.

 

[Zogzog]

NETA and the IEEE disagree with your opinion.

 

[aolalde]

We are discussing here how to evaluate medium voltage cables already in service may be for several years. This is not a manufacturing or new installation evaluation of the cable.
I do not think a regular industry can afford neither a PD test nor even a VLF high pot test (destructive) every time a motor is reconnected after service to a 3.3 kV line.
I do not know the IEEE std neither who are leading that IEEE 400?, but it should distinguish between a factory test, new installation test and maintenance evaluation test, a shielded cable and non shielded ,kV, etc.

 

[powerjunx]

aolalde, i agree with your opinion although zogzog posted such testing standard as NETA and IEEE but the one you suggested would approximnately within the limits as standard imposes.
We called it as a RULE OF THUMB - i meant a shortcut of a long procedure from testing standard eventually a result is close to standard test result. Such test would only practical if you have substantial experience, i neither recommend to Newbies.

Zogzog, i hope you got my point as aolalde suggested.

 

[Zogzog]

Wauld stated "The motor was removed recently,and the cable may have sustained damage during this time and will need to be checked before reconnection."

He has some reason to believe his cable may be damaged, putting 1000VDC will not show minor damage such as water trees. Is it a good test to do every time before reconnecting a motor, yes, and probally sufficent, but that is not the case here, he suspects the cable is damaged.