When are hi pot tests done? before or after installation? 1

[bdn2004]

When are high pot tests done and what is the specific reason they are done? We are going to install new multiple runs of medium voltage cables and one of the construction tasks are these hi pot tests. Are the tests done before or after the installation? How long does a typical test take?

 

[davidbeach]

After the terminations have been applied. Generally late in the lead up to initial energization, but before any arrestors or VTs are connected.

 

[DTR2011]

If you are using XLPE cable, please do not specify a DC Hypot test, as this can cause damage to the cables (treeing).
There is a modern solution to this, utilizing very low frequency AC, which can assess the cables, while avoiding cable damage. Often these modern test sets can also perform a tan delta (power factor) test, which gives more information about the quality of each cable / accessory tested. The test time can be based on various specifications, but in general is between 10-20 minutes per cable.

There is a member on this forum that may chime in that is an expert in this matter.

 

[bdn2004]

The cable to be used is as per attached. It is an armored cable, EPR insulation. I just talked to the Construction manager, their procedure is to do a hi pot test on these cables.
Is there a problem with these?

 

[dpc]

Regarding test method - follow manufacturer's recommendations. A large consulting firm I worked for decades ago required a high-pot test of the cable while still on the reel as soon as it arrived on the jobsite, then a second hi-pot after installation, prior to energization.

 

[bdn2004]

I worked at a chemical plant that did the same thing. They always used 3/C jacketed cable with a special build on everything cause they said it was easier to pull it through the cable trays without damage. They claimed the manufacturer would make the special cable with their existing 1/C cable and it would sometimes get damaged in the process. It was part of the reason for my question...if such is standard practice in industry. My job right now is to right up a scope of work for all tasks to be done.

 

[GroovyGuy]

Hi Bdn,
I generally only ask for hi-pot tests post installation. Occasionally I have asked for a test while the cable is still on the reel, but this is only if the installation is arduous and the cable is supplied by someone other than the installer (ie an Owner-supplied cable). If the cable is supplied, installed and terminated by the installer all I care about is the final test.
An 'arduous' installation may include the following;
- large and long cable (ie $$$)
- direct buried cable
- vertical installation (in a mine)
Also a reel test will usually be done without stress cones installed, and depending upon the test voltage, corona discharge might make the results difficult to interpret.

The time required to take the test can vary considerably depending upon the voltage and the length of the cable. For short runs in a typical industrial plant I have seen tests done as quickly as one phase per 1/2 hour. I have also tested a 11km cable to 125kV that took one day per phase, due to capacitance charge/discharge time constants of the cable. Of course the above times do not include travel and or set up time.
Regards,
GG

"Wish I didn't know now what I didn't know then." -- Bob Seger

 

[dpc]

if such is standard practice in industry

If you are referring to hi-pot testing of the cable on the reel prior to installation, no it is not an "industry standard" by any means. It is generally used when the cable is owner-furnished for installation by a contractor.