Underground Cables - Enabler & Facilitator to achieve long term EU Energy Goals

Transcript from the Q&A session

1. Sigrid Jacobs:What do you mean with XLPE cables are environmentally friendly ? Do you mean they are shielded so no electro-magnetic fields escape to the level above where the people are walking ?

The magnetic field at 1 metre distance on top of the cable is higher than directly under an equivalent OHL. But the field falls rapidly to the side of the cable and at just 2 metres from the centreline of the cable, the field is reduced to below 1 microtesla whereas for an overhead line a distance of more than 40 metres from the centreline is necessary to achieve the same level at ground level. Moreover the cable does not emit an electric field unlike the OHL.

2 .Ian Nakashima:Are there any additional considerations that have to be taken into account in earthquake areas?

EHV cables at voltages up to 500kV have been laid in Japan. The installation of a cable will have to take account of seismic activity but it is considered that cables are more likely to withstand an earthquake than an OHL.

3. Kees Kokee:When including the converter cost, would this DC technology still be comparable with current AC overhead lines?

Independent studies have shown that HVDC systems can be considered as a cost efficient alternative when fully undergrounding point-to-point connections over 100km.

4. Mayur:How this experience can be transferred to middle east region?

EHV cables have been installed in several countries within the Middle East including Abu Dhabi, Bahrain,Dubai, Oman & Saudi Arabia. Europacable would be interested in sharing their European experience with stakeholders in the Middle East.

5. Ahmet Tepiroglu 2:How would the copper consumption be effected?

Most EHV cables use copper so any significant increase in demand for EHV cables should be beneficial to the copper industry. As a general rule one km of 2500mm2 copper cable including screening uses around 25 tonnes of copper.

6. Dome:do we have a global figure regarding disturbances overhead/underground

Since their introduction, EHV XLPE cables have an excellent track record with hardly any outages. Given that the majority of recent installations have only a small service track record, long term service reliability cannot yet be established but all indications from extensive testing of the cable systems and their history to date are that underground cable systems can achieve service reliability that matches OHLs. Unfortunately there is no global figure available for disturbances of OHL versus UGC..

7. john o'reilly Mainstream RP :Regarding HVDC you gave a value of 700MW for single core and 1400MW for bi-polar. What do you mean by single core is it ground return?

Single core is one pole with a ground return. Bi polar is two poles

8. john o'reilly:You gave an U?G spacing for 4 AC circuits, what is the spacing for the same HVDC circuit?

Assuming a bi-polar arrangement. HVDC cables can be placed less than 0.5m apart.

9. Mayur:What are the drivers for the regulators to limit distance of 200 m & 400 m from house?

In general the public do not want to have transmission lines close to their homes/schools. The main driver in limiting distance from properties is the magnetic field.

10. kisholoy gupta: Impact of cable life if it is use for laying underground near the sea bed for wind power machine.

Depending on depth and surrounding conditions cables can be either laid on the sea bed (e.g when depth is a natural protection from anchors and fishing equipment) or buried and/or protected when the area where the cable is laid is critical for sea traffic or other activities.

11. eduardo mariscal-hay:what about meteorological discharges (lightning) on disturbances, and on damaged cables ?

Unlike OHL, cables are not susceptible to the impacts of severe weather. In recent years there have been several severe weather related events that led to widespread damage to electricity pylons and conductors. This includes France in December 1999, North East USA in August 2003, Italy in September 2003 and Germany in November 2005. Most of these incidents were due to either trees falling onto conductors or damage caused by heavy winds/snow storms. In the 2005 incident in Germany, 83 pylons were damaged and three months after the event, half of the damaged pylons were still not replaced. Events such as these have led to a series of investigations and demands to place more OHLs underground.

12. john o'reilly:Given the present technology, what is the maximum load that can be transferred from an off-shore windfarm with one HVDC circuit?

The maximum load which can be transferred from a windfarm using HVDC technology is not different from the powers stated in your question 7. Please note that depending on the power and distance from shore, HVAC or HVDC conditions may be considered.

13. john o'reilly:Do you consider cable factories are capable of meeting the demand for HVDC cable given the long distances being planned for off-shore windfarms? John O'Reilly Mainstream RP & Manuel Hernandez:where will the major investment be for xlpe cables, will it be renewables, transmission or distribution networks. do you have any data in terms of quantities or expenditure

The increase in market demand for EHV cables is expected to continue into the foreseeable future due to several factors - Transmission interconnection needs in Europe; Connection of offshore and onshore wind parks and other renewable energy facilities to the transmission network; Increased demands for partial undergrounding of proposed new overhead lines passing through sensitive areas such as outstanding natural beauty or environmental heritage; Refurbishment/replacement of aging transmission infrastructure in Europe, including replacement of overhead lines with cables, particularly in urban areas and Increased demand in markets outside of Europe, particularly Asia and the Middle East.

Much of the future demand is expected to be for XLPE EHV cables and these are currently manufactured at 15 facilities across Europe, with an additional 5 new production lines under construction. As each production line has the capacity to produce 100-140km of EHV cable per year, supply can be expected to exceed 2,500km of cable/year.

14. Mayur:Would it be fair to say that the main argument in favor of EHV undergrounding remains improved visuals and other arguments are secondary ?

Apart from creating less visual and environmental impact that generates large opposition from local communities, underground cables have several other unique benefits, in particular, they have lower transmission losses; can absorb emergency power loads; have lower maintenance costs; emit no electric field and can be engineered to emit a lower magnetic field than an overhead line; require a narrower band of land to install, and are less susceptible to the impacts of severe weather.

Reply