Electrical interference by 132 KV underground cable crossing a 16" pipeline 1

[brpillai]

Dear experts,

In one of our current projects, two 132 KV buried cable is proposed to be running parallel for about 50 meters to a16” buried pipeline with a gap of about 5 to 6 meters. These cables will be crossing the pipeline again after some distance, the cable will be the HT cable will be crossing about a meter below the pipeline.

The pipeline will be cathodically protected with impressed current system. I have read about interference in the case of overhead lines, which are of bare conductor.

I would like to seek your advice on the following:

1 Whether the 132 KV electric cable will have any adverse effect on the pipeline, due to possible electromagnetic inductance.
2. Is there any minimum distance ( for parallel running and for crossing)required for laying the cable from the pipeline.
3. Is there any mitigation/ required?
4. any other precaution to be taken during installation?
5. Is there any literature/ study on this fro refrence?

With warm regards

Bhaskaran R Pillai
Head of Engineering- Pipelines
S/B: + +971 2 494 0700 / D: +971 2 494 0830 / F: +971 2 494 0701
Mob: +971 50 2662185 / Email: brpillai@ccel.ae Web:

http://www.ccel.ae

CHIYODA CCC ENGINEERING LIMITED (CCEL)
P.O. Box: 6195, Global Tower, Floor No. 8,
Sheikh Zayed The First Street, Abu Dhabi, U.A.E.

 

[Power0020]

I have carried out a similar study with a transmission line crossing a crude oil pipeline in Indonesia.

Strictly speaking, the fault conditions on cables will cause some voltage on the pipelines. How much is this voltage? computer simulation and calculations needed.

How dangerous this voltage can be? depends on the construction of the pipeline and how long the transferred voltage can go.

You mentioned the pipe has cathodic protection. Is it completely electrically isolated from soil? or in partial contact with soil?. As far as I know, the CP system will ensure an electrically continuous system but if the induced voltage is high enough, it can cause malfunction to CP DC system.

A good read in

http://ro.uow.edu.au/cgi/viewcontent.cgi?filename=0&article=1638&context=theses&type=additional

with a TL.

 

[brpillai]

Power0020, Thanks for the reply. The attached literature speakes about overhead power lines crossing pipelines ( both above ground and underground). In the case I am referring is interference of UG cable with a UG pipeline, crossing and also running parrelel for about 50 meters.

You have also mentioned above that cables will induce some voltage during fault conditions. I am looking for exactly this scenerio.

The pipeline is electrically is having corrosion coating for the 50 m underground portion and also at road crossing, where it is going underground. It has an isolation joint at the tie in with offshore line , which is sacrificially (CP) protected. 1600m shore section is only about 300 m underground with remaining portion on elevated supports, where the pipeline is resting on teflon pads on steel supports. No Iso flange or iso joint at road crossings.

Please go through the article i have found and attached herewith "section C. Electric & Magnetic Fields and Figure 5: Comparison of underground cable and overhead line magnetic field levels". Considering this request whether the 132 KV UG cable crossing the 16”MOL needs to be examined for any impact on the CP.

Warm regards

 

[Power0020]

Usually, 90 degrees crossing will cause minimal effect, you get much voltage by running in parallel to the cable.

There is no quick answer for the spacing as the induction needs to be modeled, cable layout and sheath bonding schemes, amount of available fault current and cable construction.

A very helpful software named CDEGS available from SES & Tech will accurately model the case.

I personally think that, 5 m from the pipeline for a 132 kV cable and for some 50 m parallel run means that some high voltage will appear during line-to-ground faults if these cables are single point bonded or cross bonded. Detailed assessment needed though.

 

[7anoter4]

In my opinion, if the single-core cables are completely crossbonded and if the currents are equilibrated no induction built-up voltage in the pipe is expected.
In a phase-to-ground short-circuit [fault] case the inducted voltage in the pipe may be appreciated in the same way as in overhead line case.
In the case of cables crossing under the pipe NESC Rule 353 B states:
1. Where a cable crosses under another underground structure, the structure shall be suitably supported to limit the likelihood of transferring of a detrimental load onto the cable system.

 

[brpillai]

Power0020 and 7anoter4, thanke for your valuable opinion. I am taking up with the cable laying contractor to study the impact on the inductance effect on the pipeline for parrallelism and for crossings.

Thank one again.