World Energy Transmission System

"HV, EHV and UHV electrical long links by AC and DC insulated power cables: Availability of strategic power links"

Was held within the scope of JICABLE'15 in Paris on June 25th 2015

Session 1 - How to ensure the quality of a cable High Voltage system at commissioning?

Chairman : Ken Barber, Nan Electric Cable Australia Pty Ltd, Australia
Rapporteur : Christian Rémy, Prysmian, France

What is the relative impact of the production, transportation, civil engineering, laying and  installation. How to globally optimize the actions of these project components
Which are the after laying tests recommended for dielectric system. What is the stake?
Which are the after laying tests recommended for current transmission (conductor and screen). What is the stake?

Introduction – Current World Wide Experience with Long Length AC Cable Links (Ken Barber)
( WETS 15 1.1 Ken Barber)

Introduction – HVDC Projects (Paul Penserini)
(WETS 15 1.2 Paul Penserini)

Existing HVDC
(WETS 15 1.3 Paul Penserini)

Planned projects HVDC
( WETS 15 1.4.Paul Penserini)

Quality at Commissioning – Right Tools for Right Purpose (Marc Jeroense)
( WETS 15 1.5 Marc Jeroense).

A review of each type of test is made: development tests (PQ and TT), production tests (Routine, sample, FAT) and after laying tests (commissioning test) and their purpose in respect with the quality of the cable. Monitoring of cables during the cable operation live is also considered. This test are required also because people are more trusting overhead line which are fully visible than buried and invisible underground lines. It is clear that the commissioning cannot replace a good Quality Control, good workmanship, and good equipment, and good materials.

The Japanese practice is performing a "soak test" but having strong technical ties the utility sites for keeping a high level of trust.

V.L.F. testing presents least limitations on maximum lengths, but either a higher voltage (2 or 3 times usual one, and this could be an issue for the interfaces with the accessories) or longer testing time.

Note IEC has issued standards on VLF testing of MV cables. A CIGRE WG is dealing also with VLF.

Session 2 - Localization of a failure on a submarine link (HVAC , HVDC)

Chairman : Ken Barber, Nan Electric Cable Australia Pty Ltd, Australia
Rapporteur : Christian Rémy, Prysmian, France

What are the standard techniques
What is the sequence of techniques for improved efficiency (optimum time and location accuracy, the impact of the weather)
Coordination of experts and of intervention resources

Introduction – Reliability of Supply (Ken Barber)
(WETS 15 2.1 Ken Barber).

Introductory presentation on the reliability of supply and the works of the CIGRE WG B1-47.

Localisation of a Failure on a Submarine Link (Jean Charvet on behalf of Antoine Naud)
(WETS 15 2.2 Antoine Naud)

Pre-location by improved TDR:

It is clarified that the improvement is on the data analysis and not on the TDR technique. The TDR wave is damped in the case of MI insulation, not for XLPE. Cable construction could also have an impact on the propagation.

Fault pin pointing by magnetic field survey:

The current injected for the test is only a few A. The feasibility of the test is linked to the frequency of the testing signal.

The use of an optical cable is also proposed for localising the hot spot corresponding to the faulty point.

The use of R.O.V. is limited to cases where the cable is fully uncovered (e.g. no rock berm, etc.)

The use of a potential measurement technique from a ship going along the cable route is also reminded.

Fault Location in Submarine Cables (Seung-Ik Jeon)
( WETS 15 2.3 Seung lk Jeon).

The acoustic method used is based on the injection of a current in the cable and sounds record by hydro microphones.

The AIS system is used for a precise positioning of the testing ships.

The use of an optical cables and stimulated Brillouin backscattering, sensitive to strain, is proposed.

The localisation duration of 6 weeks is reported. The mobilisation time can be reduced strongly if repair/assistance ships are made permanently available near the target link.

Session 3 - Repairing a submarine link (HVAC, HVDC):

Chairman : Ray Awad, Ray Awad Inc., Canada
Rapporteur :  Jean Charvet, RTE, France

Availability of equipment - stock of spare parts
Mobilization of resources for intervention
Coordination of experts and of intervention resources

Vincent Moindrot (RTE, France)
( WETS 15 3.1 Vincent Moindrot)

presented the different maintenance strategies concerning vessels mobilization : one shot contract, or framework contract and compared pros and cons. Better conditions for maintenance could be obtained if TSO find a joint solution with shared ressources, similar to what is done in telecom area.

During the following discussions, comparison was made with onshore actions plans in order to obtain mobilization of dedicated team to locate and excavate on the location of the fault. It was raised for offshore cable that there was generally no dedicated vessels for these operations but it might change in the future. Question were adressed regarding qualification of jointers. Benefit for standardization of cables and accessories was discussed, although not easy because every project is specific, and qualification of transition repair joint is not an easy subject. A dedicated vessel is also tricky because different vessels might be needed depending on water depth, etc..

Session 4 - Preventive maintenance:

Chairman: Ray Awad, Ray Awad Inc., Canada
Rapporteur:  Jean Charvet, RTE, France

Monitoring by temperature measurements
Partial discharges, sheaths testing .
Monitoring diagnosis by measuring partial discharges

Jean Charvet (RTE, France)
(WETS 15 4.1 Jean Charvet)

presented the status of temperature measurement at RTE and showed a compelling example of a hot spot detected in a link in Paris and corrective maintenance  performed.

During the following discussions, limitations of this technique and location of optic fibers was addressed.

Ken Barber (Nan Electric Cable, Australia)
(WETS 15 4.2.Ken Barber)

presented what are the problems associated with integrating Optic Fibers into power cables. Different generations of cables integrating Optic Fibers were presented : historical design with simple steel tube next to sheath wires, improved low profile unit without steel and less risk of damage. Issues regarding water tree and jointing procedures were addressed. A concept concerning corrugated aluminium sheath cables was also presented.

Hideo Tanaka (VISCAS, Japan) (WETS 15 4.3 Hideo Tanaka)

presented the partial discharge measurement effectiveness for preventive cable maintenance. PD gives useful information for specific kind of insulation defects. Limitation of PD monitoring was addressed, track records of on-site measurement was presented. Currently on-site measurements are mainly carried out as "spot measurements" but not for on-line and permanent monitoring.

Experience among participants was shared. No clear consensus exists on the subject.

Fernando Garnacho (LCOE, Spain)
( WETS 15 4.4 Fernando Garnacho)

An additional presentation on PD measurements from Fernando Garnacho (LCOE, Spain)
has been given but not presented because of travel constraint.