Background

Electrical energy needs to be transmitted and distributed from the point of generation to the point of use in the most cost-effective way, taking into account the geographical, topographical and political barriers between those two points. By and large, electrical energy cannot be stored except on a very local and usually low power basis (for example, using batteries).  As a result, electricity is normally generated in “real-time” and transmitted directly from the point of generation to the point of use, taking into account fluctuating demand.  In recent years billions of pounds have been committed globally to a renewal and expansion of the electrical grid system and the development of ‘smart grids’ which will distribute electrical power more efficiently. Smart grid initiatives seek to improve operations, maintenance and planning by ensuring that each component of the electric grid can effectively both ‘talk and listen’. This leads to increased efficiencies through demand-side management and improved up-time by automatically communicating potential faults to control centres. In the UK alone, National Grid is expected to invest £22.5 billion between 2013 and 2021[1]. In the US, the commitment to grid renewal is £11 – 16 billion per year over the next twenty years. The overall cost of all the up-grades to the US grid including new cabling, smart meters and the software and infrastructure to run them will be circa $606 billion but is hoped to deliver savings of $1.3 trillion[2].

Existing high voltage wire and cable systems of the type used in present-day grids and foreseen for use in smart grids lose on average circa 10.6% (globally) of the power transmitted as system losses. In Western Europe the average figure for system losses is 7.2% and in the United States of America and Canada is 8.7%[3].

In the power industry, the term “cable” has a particular meaning referring only to encased conductors that are placed sub-surface, either in a trench or conduit on land or on or beneath the seabed when submarine. While CTS is named as a “cable” it could also be suspended from pylons, albeit potentially requiring much smaller ones than current technology, to replace existing overhead lines (“OHL”). Suitable mechanical reinforcement of the CTS will be required for such an application.

Conductor length is distinct from grid length as there are multiple lengths of overhead line strung from pylons. For example, the grid length in the US is 450,000 miles (724,200 kilometres) but contains 10 million kilometres of OHL and cable. [4]

Problems with conventional cables and OHL:

  • System losses of more than 8% (OECD average)
    • Wasteful in terms of cost
    • Wasteful in terms of resource
    • Increased CO2 emissions
  • Potentially harmful electro-magnetic emissions and electrostatic fields
    • Necessitating location of HV cables a safe distance from people
    • Generally requires pylons for overland transmission
  • Require additional expensive step-up/down transformers and boosting substations
    • Costly and require maintenance
  • Potentially valuable real estate with high opportunity cost used
    • ‘Strip width’ of up to 60 metres with restricted usage demanded by conventional OHL pylons

Strip width of conventional transmission line

  • Heating
    • Heating of wires whilst under electrical load is a major issue for under-grounding of conventional cables

The T & D market is perceived to be conservative in its uptake of new technologies. There are several factors which the Enertechnos Board believes should increase the likelihood of adoption of CTS technology.

  • Substantial investment in ‘smart grid’ is already committed utilising new methods and devices to increase efficiency and versatility of the T & D network. CTS has the potential to be a key component of smart grids because of its expected resilience to varying load factors and its ability to incorporate data communication links for demand-side management.
  • Feeding in to main grids from renewable generation such as wind, geothermal, wave and tidal generation assets is identified as a key potential market for CTS. This is because of its characteristics that enable efficient transmission of electrical energy over greater distances with lower losses.
  • Latest design of CTS can incorporate hybrid cable design, where some elements of the cable are configured as conventional cable and others are configured as capacitive cable. This enables the advantages of CTS to be leveraged to their most effective implementation irrespective of the length of the cable run and for adjustment of capacitance to tune reactance post-installation according to variations in load factors. Future testing will directly compare CTS configured as conventional cable with outcomes for similarly-sized conventional cable.
  • Possible adoption of CTS as alternative to HVDC transmission for certain length ranges would be attractive as it eliminates costly inverters at each end of the transmission line. This is particularly advantageous for subsea applications and offshore wind generation.
  • Possible reduction in need for large power transformers (LPTs) by adoption of CTS is very attractive on grounds of cost and security. LPTs are a potential point of failure in the grid and so having fewer of them decreases risk.

[1] Ofgem , 2013

[2] Electric Power Research Institute [EPRI], 2011

[3] Frost & Sullivan report, March 2014

[4] United States of America Department of Energy https://energy.gov/articles/top-9-things-you-didnt-know-about-americas-power-grid