INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

If you want to learn more, please visit our website Hengfeng.

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!

• Talk With Other Members
• Be Notified Of Responses
  To Your Posts
• Keyword Search
• One-Click Access To Your
  Favorite Forums
• Automated Signatures
  On Your Posts
• Best Of All, It's Free!

Join Us!

*Eng-Tips's functionality depends on members receiving . By joining you are opting in to receive .

Posting Guidelines

Students Click Here

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Eng-Tips Posting Policies

Contact US

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

thread238- Forum Search FAQs Links MVPs

• Forum

• Search

• FAQs

• Links

• MVPs

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

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

bdn

(Electrical)

(OP)

23 Aug 16 18:05

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?

Replies continue below

Recommended for you

RE: When are hi pot tests done? before or after installation?

davidbeach

(Electrical)

23 Aug 16 21:38

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

Recommended article:
5 Reasons Flexible Metal Conduit is the Ultimate Water Proof Solution
Is Flexible Metal Conduit the Safest Choice for EU Buildings?
10 Questions You Should Know about Electrical Flexible Conduit Square-lock
Category 6 cable
Which Flexible Metal Conduit Low Fire Hazard EU: The Ultimate Safe Solution for Electrical Wiring?
The Ultimate Guide to Metallic Fittings UL
Exploring the Benefits of Using Silicone Jacketed Tube

Contact us to discuss your requirements of DC Hipot Test Kit. Our experienced sales team can help you identify the options that best suit your needs.

RE: When are hi pot tests done? before or after installation?

DTR

(Electrical)

24 Aug 16 10:13

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.

RE: When are hi pot tests done? before or after installation?

bdn

(Electrical)

(OP)

24 Aug 16 15:44
Is there a problem with these?

• http://files.engineering.com/getfile.aspx?folder=5d0f-97f8-4ac6-b9cf-67

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?

RE: When are hi pot tests done? before or after installation?

dpc

(Electrical)

24 Aug 16 16:27

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.

RE: When are hi pot tests done? before or after installation?

bdn

(Electrical)

(OP)

24 Aug 16 18:16

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.

RE: When are hi pot tests done? before or after installation?

GroovyGuy

(Electrical)

25 Aug 16 01:59
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

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

RE: When are hi pot tests done? before or after installation?

dpc

(Electrical)

27 Aug 16 20:22

Quote:

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.

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

News

Hi,

High voltage test...
We test our products (power supplies) as follows.
Input to ground, output to ground, input to output if necessary, if there is galvanic isolation between the two.
Whereby ground means the housing(earthing point).
As a rule, we test this with DC voltage, which has the advantage that any capacitors against ground (EMC!) are charged once.*
If we were to test with AC, there would be a unwanted constant current flow.
The inputs/outputs are connected together to protect internal components in the event of a breakdown.
The polarity does not play a role in DC tests in the constellation, but generally minus is connected to ground, while plus is connected to the inputs or outputs.
However, we once had a case where a diode was connected in series in the input as reverse polarity protection.
In this case, minus was connected to the input, plus to ground.
Now there was a breakdown against ground and since the reverse voltage of the diode was lower than the test voltage, it broke due to the breakdown, which would not have happened if plus had been connected to the input.
Since then, plus has always been connected to the input and minus to ground.
What to do in the event of a high-voltage breakdown?
Possible causes:
- Test voltage accidentally set too high
- Tripping current set too low for DC, keyword charging of EMC capacitors against ground
- Insulation of installed cables damaged
- Insulation generally too low between the potentials
- Metal chip residue present in the housing
- Wire residues present in the housing/between the potentials due to incorrect insulation of cables.
- Humidity too high during test (creepage distance: 1mm/V)
- Rare: Defective components in the system itself

Repetitions after a failed high voltage test are best carried out with reduced test voltage, as long as this does not fall below the minimum requirement.
Reason:
The components experience a stress phase as a result of a high voltage test, which they should not be subjected to too often (shortening of service life).

The company is the world’s best vlf tester supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.