No. 95 · OCTOBER 2022

SUMITOMO ELECTRIC TECHNICAL REVIEWNew Products and Techniques

Environmentally Friendly
Non-crosslinked Insulated Power Cable
1. Outline

Currently, most power cables are XLPE cables, which
use crosslinked polyethylene (XLPE) for insulation. XLPE
has excellent heat resistance due to its crosslinks, but itshows no fluidity with heat and its material recovery isdifficult. In addition, the longer the cable to be produced,
the longer the lead time may be, because manufacturing
XLPE cables requires a crosslinking reaction process toform a network structure and a drying process to exhaustby-product gases from the reaction.
Against this backdrop, we have developed environmentally friendly non-crosslinked insulated power cables(Photo 1) that can contribute to improving productivity.

Recently, people around the world have become
intensely aware of the problem of global warming and theissue is seriously being discussed in various countries,
especially in Europe. For example, the EuropeanCommission gives top priority to climate change strategy
and aims to reduce greenhouse gas (GHG) emissions by
55% compared to 1990 levels by 2030. The Paris
Agreement was adopted at COP21 in 2015 and Japandeclared that it aims to achieve a decarbonized society(carbon neutrality) by 2050.
There is ever-increasing demand for power cables
because the market has been expanding with a combinationof the expansion of the renewable energy business, such as
offshore wind and solar photovoltaic power generation, andthe need for renewal of power cables laid in the highgrowth period.

2. Features
Features of the non-crosslinked insulated power
cables are shown in Table 1.
2-1 Excellent environmental friendliness
Since the insulation is non-crosslinked, the insulation
can be remelted and remolded, enabling material recovery(Fig. 1). The developed non-crosslinked material also has
higher dielectric withstanding voltage than XLPE, technically enabling the production of thinner insulation. This

Conductor
Insulation(non-crosslinked)

Shieldinglayer
Raw material

Sheathlayer

Processing

To recycledresin market

Photo 1. 22 kV class non-crosslinked insulated power cable

Product (Cable)

Material recovery of insulation

LayingCollecting(remoldable for non-crosslinked)

Fig. 1. Recycle flow of non-crosslinked insulated power cable

Table 1. Features of non-crosslinked insulated power cable
Item

Structure image

XLPE

Non-crosslinked material

XLPE insulation

Non-crosslinked
insulation

Conductor

Conductor(Larger size)

Samesize

Thinner
insulation

Manufacturing Precess
Recycling

Extruding, crosslinking, drying

Only extruding (shorter leadtime)

Mainly thermal recovery

Matrial recovery

GHG emissions

1.0

Allowable temperature

1.0

Bending property

1.0

1.0 (Samepart number and size)

Transmission cabacity

1.0

1.1 (When continuous allowable temper-atureis increased)

Withstanding voltage

1.0

1.1～1.2 (Initialelectric preperty)

Transmission loss

1.0

0.8 (When the insulation is thinned, the cable diameter
does not change, and the conductor is enlarged)

0.7 (Same part number and size)>1.1 (Continuous, overload, instantaneous)

Environmentally Friendly Non-crosslinked Insulated Power Cable

54（1）SUMITOMO ELECTRIC TECHNICAL REVIEW

No. 95 · OCTOBER 2022

can prevent the enlargement of the diameters of cables
based on the environmental and economical conductor size
optimization (ECSO*1) approach, which has been vigorously standardized by International ElectrotechnicalCommission, Japanese Industrial Standards, and otherorganizations in recent years.
2-2 High productivity
There is no necessity for crosslinking and drying
processes in the manufacture of the cables, thereby shortening the lead time. Moreover, since the manufacturing
process uses less electric power, GHG emissions will be
reduced by 10 to 30% compared to those for XLPE.
2-3 Excellent heat resisting property and flexibility
This product uses material with a non-crosslinked
structure but with excellent heat resisting property andflexibility for insulation by applying our originalcompounding technique. The developed non-crosslinked
material suggests that the cables can be used at higher
temperatures than conventional XLPE cables. Theshort-circuit cable tests (Photos 2 and 3) revealed that evenwhen the temperature of the conductor at a short circuit
was raised to 110% of Japanese standard for XLPE cables,
the insulation was not deformed.

(Test method)(1) Heat the conductor to the continuous allowable temperatureby pre-energization.
(2) Obtain the instantaneous allowable temperature by large current.

Photo 2. Short-circuit test of non-crosslinked insulated power cable(a)Fig. 2. Bending stiffness of each insulating material(66 kV class cable, at room temperature)

3. Future Developments
Offshore wind power generation, a pillar of the renewableenergy business, has a limited capacity to manually control theoutput power. The use of the non-crosslinked insulated
power cables, which are operable at higher temperatures,will allow more flexibility for operational conditions ofpower transmission lines against output fluctuations. We
will search for applications of the non-crosslinked insulated
cables through communication with customers and build
wider recognition of the non-crosslinked insulated cables
through the replacement of conventional cables and otheractivities.

＊ 1	
Environmental and Economical Conductor Size
Optimization (ECSO): An approach to selecting themost appropriate conductor size to make the life
cycle cost as low as possible, taking into accountthe cable’s running costs as well as initial costs.

(b)

Photo 3. Cross-section of non-crosslinked insulated power cable(a) Before short-circuit test, (b) After test

The elasticity of the cables is the same as that ofXLPE cables at room temperature and the bending stiffness
is also the same as that of XLPE at room temperature,
thereby achieving good wiring (Fig. 2).

Environmentally Friendly Non-crosslinked Insulated Power Cable

55（2）