Previous in Forum: Voltage Drops   Next in Forum: best protection for power transformer
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
13 comments
Rate Comments: Nested
hussam
Active Contributor

Join Date: May 2009
Posts: 16

hipot dc test

01/08/2010 11:36 PM

I was conducting a Hipot test on a 3 phase circuit consisting of 3 single core cables, 15kv ,120sqmm (250mcm) XLPE/PVC, with concentric neutral, 600m long , I was going to apply 64KV dc for 15 min ,I started with the red phase the other two cables Yphase and B phase are beside the red phase not grounded but the concentric neutral of the three cable are connected to each other and also to the ground from both ends, the 3 cables are in a trench are bonded together trofile formation ( NOT flat with a distance between them) when the tester reached 64 kv dc after 3 min suddenly the voltage started to increase by it self till 75 kv dc I have to stop the test .

I don't know why this happen! What was wrong?

The hipot tester is faulty?

Or I should connect the other two cables together and to the ground?

Can you help and advice please
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".
2
electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#1

Re: hipot dc test

01/09/2010 9:33 PM

It could be due to capacitive coupling. Also, it is general practice that when you apply Hi-pot test to one core/phase, the other cores/phases should be connected together and then connected to ground.
Register to Reply Good Answer (Score 2)
No more Good Answers.
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#3
In reply to #1

Re: hipot dc test

01/10/2010 2:08 AM

thanks electricalexpert65

when you say the other two phases should be connected together and to ground is this true for 1 core cable and 3 core cables
Register to Reply
electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#5
In reply to #3

Re: hipot dc test

01/10/2010 5:50 AM

It is also true for single-core cables if the cables are laid together (in trefoil). Trefoil only avoids inductive coupling but not capacitive coupling.
Register to Reply
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#6
In reply to #5

Re: hipot dc test

01/10/2010 9:27 AM

thanks electricalexpert65

i will let you know the result of my test
Register to Reply
Anonymous Poster
#7
In reply to #6

Re: hipot dc test

01/12/2010 12:53 AM

Dear Hussan,

Just one question. You mentioned that you were using 64kV dc to perform the test in this cable, why are you using 64kV test voltage? As far as i understand, this test should be made 1.6 times your rated voltage.

Regarding Electricalexpert65's answer is ok you soulhd put them toguether and then to ground, not the one under test, then you make the same to the second and the third and finally all toguether against earth.

Which equipment are you using?

Best regards,

Robert
Register to Reply
electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#8
In reply to #7

Re: hipot dc test

01/12/2010 8:55 AM

As per IEEE, the AC Hi-Pot test voltage is 1.25 to 1.5E, where 'E' is the R.M.S.Phase-to-Phase Voltage of the equipmet under test. And, the DC Hi-Pot test voltage shall be 1.7 times the AC Hi-Pot test voltage.

So, for the above 15kV cable, the DC Hi-Pot test voltage can be between 32kV to 38.25kV.

As Hi-Pot Tests are destructive tests, stressing the insulation every time the test voltage is applied, it is also suggested that during every subsequent High Voltage test on an equipment only 75% of the previous test voltage shall be applied.
Register to Reply
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#9
In reply to #8

Re: hipot dc test

01/13/2010 11:29 PM

High voltage field acceptance test
prior to being placed in service

Rated Voltage
Phase to
Phase

dc Hi-Pot Test

dc Hi-Pot Test

(15 Minutes)

Wall - mils

Kv

Wall - mils

kV

5000
8000
15000
25000
28000
35000
46000
69000		90
115
175
260
280
345
445
650		25
35
55
80
85
100
130
195		115
140
220
320
345
420
580
650		35
45
65
95
100
125
170
195
Note: If the leakage current quickly stabilizes,
the duration may be reduced to 10 minutes.

Thank you MR electricalexpert65 and MR Robert

My cable is Uo/U (Um) KV =12/20(24)KV IEC definitions

Uo=12KV which is rated phase to ground voltage for which the cable is designed

U=20kv which is rated phase to phase voltage for which the cable is designed

Um=24KV which is the highest system voltage for which the cable may be used (IEC 60038)

the cable is 120sq-mm ,copper XLPE/PVC with concentric neutral.

It is 133% insulation level( not 100%), nominal insulation thickness is 5.5 mm( 220 mils)

So the DC test voltage should be 64 KV dc see Okonite cable co table above also my client specifications call for this
Register to Reply
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#10
In reply to #7

Re: hipot dc test

01/13/2010 11:30 PM

Thank you

High voltage field acceptance test
prior to being placed in service

Rated Voltage
Phase to
Phase

dc Hi-Pot Test

dc Hi-Pot Test

(15 Minutes)

Wall - mils

Kv

Wall - mils

kV

5000
8000
15000
25000
28000
35000
46000
69000		90
115
175
260
280
345
445
650		25
35
55
80
85
100
130
195		115
140
220
320
345
420
580
650		35
45
65
95
100
125
170
195
Note: If the leakage current quickly stabilizes,
the duration may be reduced to 10 minutes.

Thank you MR electricalexpert65 and MR Robert

My cable is Uo/U (Um) KV =12/20(24)KV IEC definitions

Uo=12KV which is rated phase to ground voltage for which the cable is designed

U=20kv which is rated phase to phase voltage for which the cable is designed

Um=24KV which is the highest system voltage for which the cable may be used (IEC 60038)

the cable is 120sq-mm ,copper XLPE/PVC with concentric neutral.

It is 133% insulation level( not 100%), nominal insulation thickness is 5.5 mm( 220 mils)

So the DC test voltage should be 64 KV dc see Okonite cable co table above also my client specifications call for this
Register to Reply
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#13
In reply to #5

Re: hipot dc test

02/06/2010 11:18 PM

I did the hipot DC test on the 15 kv cable 3-1/c 120mm sq all conductors were grounded except the core under the test , 64 kv d/c was applied for 15 min test was very good results were excellent

Thank you
Register to Reply
Anonymous Poster
#2

Re: hipot dc test

01/10/2010 1:19 AM

Hi base on what you inject 64kv for 15kv cable , it is standar to inject only 27kv

then check the arrangment of the Cable in trench , first check the sheat test by appling 10kv for one min, then check your connection for the hipot tester where you connect the groung,
Register to Reply Off Topic (Score 6)
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#4
In reply to #2

Re: hipot dc test

01/10/2010 2:16 AM

thanks guest

the standerds call for 64KV DC for 15 min the cable is raited for 20KV,the concentric neutral for the 3 sigle cores were connected together and to the ground,also the hipot tester was grounded, i tested the concentric neutral it was ok,the 3 1 cores are in the trnech bonded to each others in trofile formation, like a triangle
Register to Reply Off Topic (Score 5)
Dickson
Power-User
Engineering Fields - Power Engineering - New Member

Join Date: Nov 2009
Location: Abuja, Nigeria.
Posts: 126
#11

Re: hipot dc test

01/20/2010 6:25 AM

The testing procedure is very wrong for high voltage test. The bonding wires should be disconnected and every cable on its own separeted fron the concentric neutral.

A capacitive effect have taken place latching the meter to accept total discharg from the the cables.

Pls. observe all safty precautions.

Dickson Abuja Nigeria

__________________
 There is peace in silence and achievement in plans.
Register to Reply
hussam
Active Contributor

Join Date: May 2009
Posts: 16
#12

Re: hipot dc test

01/20/2010 6:52 AM

thank you for your reply please explain to me what was wrong and what i have to do exactly i didn't understand ?
Register to Reply
Register to Reply
Have a Different Question?
13 comments

Good Answers:

These comments received enough positive votes to make them "good answers".
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); Dickson (1); electricalexpert65 (3); hussam (7)

Previous in Forum: Voltage Drops   Next in Forum: best protection for power transformer
You might be interested in: Hipot Testers, Patch Cables and Cords, Computer Cables

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (63 right now)
Show Members
Advertisement