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Development and Delivery of an Easy-Assembly Rubber-Block
Joint for 66-kV XLPE-Insulated Cable

VISCAS announces that they have developed an easyassembly rubber-block joint (ERJ) for 66-kV XLPE-insulated cables, and have recently delivered units to Tokyo
Electric Power Company.
The rubber block joint (RBJ) using main insulation ofunitized structure--also known as one-piece structure,
can be field-assembled and offers extremely stable quality, currently constitutes the mainstream of joints for XLPEinsulated cable. Specifically the VISCAS RBJ is a coldshrinkable joint (CSJ), which is expanded at the factory
prior to delivery. It can then be fastened to the cable in thefield simply by loosening the expanded spiral core, earning it high marks for ease of assembly and minimal skill
requirement.
Here we announce the development of the ERJ whichapplies new technology to peripheral components of theRBJ, effecting even easier assembly.

1.

the cable sheath and tube, so that even if the joint itself
is immersed in water inside the manhole, there is noseepage into the internal insulation.
•	D ressing of the rubber block ends conventionallyrequired repeated wrap with several layers of conductive tape, but we have developed a roll (the C roll) thatis thick and in the shape of a rod, yet is still easy towrap, so that wrapping a few times is all that is needed
to complete the dressing.
•	When forming the shielding layer on the rubber block, it
was necessary in the past to wrap braided tape severaltimes, but we have fabricated a novel metal mesh insleeve form (a shield mesh sleeve), which only needs
to be fitted over.
•	In dressing the cable shielding layer, the wire shieldand flat-braided copper wire have conventionally beenpressure bonded, bound together and soldered, but byadopting a coil spring in the shape of a roll (roll spring)
and a clip in the shape of a key (sheath bond clip) wehave been able to eliminate the pressure bonding operation and achieve a solder-free process.
•	In dressing the insulating shield of the cable, conventionally glass shaving and sandpapering are followedby fitting and shrinking the tube for smoothing the surface (to make a simple mirror surface) but by use of aninsulating shield cutting tool an operation is performed
in which glass shaving is applied only to the electricallyimportant parts of the insulating shield followed bysandpapering.

ERJ CHARACTERISTICS

Figure 1 shows the structure of the easy-assembly rubber-block joint (ERJ), and its main features (advantages
over the conventional RBJ) may be summarized as follows:•	It is of a design that eliminates the metal protective tube
and waterproof compound, adopting a newly developed thick non-flammable water barrier tube (powertube), that is fitted over the rubber block and shielding,and shrunk. And since there is no metal tube, a protective cover has been adopted that can be mounted laterto protect against external damage.
•	When there is only the tube, water barrier performanceat the ground wire outlet presents a problem, but thedesign provides that the grounding wire is connectedto the outside via a ground holder (long holder) fitted to2.

PERFORMANCE EVALUATION

For the ERJ, for which assembly can be accomplished ina short time, the partial discharge characteristics immediately after assembly are important, and as shown in Table

1200 mm or lessRubber forked tube
Long holder

Sheath bond clipRoll spring

Shield mesh sleeve
Rubber block insulator

Flat braided copper wire

Figure 1

Power tube
Semiconductive tape
C rollWaterproof
tape

Insulating tape
Conductor connection tube

Structure of easy-assembly rubber-block joint (ERJ).

Furukawa Review, No. 32

200764

Development and Delivery of an Easy-Assembly Rubber-Block Joint for 66-kV XLPE-Insulated Cable

1, as a result of inspections of multiple samples within twohours after mounting, it was confirmed that partial discharge did not occur.
Also, with respect to thermal expansion due to energizing of the cable, offset tests simulating field assembly
conditions were carried out and no problems were found(Figure 2 and Table 2). In addition we also confirmed
water barrier performance at immersion to 10 m, cable

Table 1Result of voltage withstand tests.

Test item

Conditions

Results

85 kV for 10 min

No partial discharge

Partial discharge test*w
 ithin 2 hr of mounting rubber block(No partial discharge
confirmed even at 140 kV)

Commercial frequency withstand voltage

130 kV for 1 hr

Satisfactory

Lightning impulse withstand voltage±485 kV, 3 times

Satisfactory

Anti-corrosion layer lightning impulse
withstand voltage-40 kV, 3 times
with joint submergedin water

Satisfactory

Figure 2

restraining force, non-flammability, etc., and were able toobtain type certification by Tokyo Electric Power
Company.

3.

DELIVERY TO IN-SERVICE LINE

Delivery of a total of 24 ERJ units for 2 circuits for 600
mm2 use, which is the largest for 66-kV XLPE-insulated
PVC Sheathed Triplex cable, for conversion work on
Tokyo Electric Power’s Ohgami Line, began this year. At
present work on one circuit has been completed and it
has gone into commercial service. We have also fully
implemented separation of materials and construction(assembly done not by our company but by a construction company), and at the present point have received
orders for more than 120 units.
For more information, please contact:
Engineering Dept., Power Cable Div., VISCAS		 TEL: +81-3-5783-1851 FAX: +81-3-5783-1870

Testing set-up for offset section loading test.
Figure 3

Table 2

Results of offset section loading test.

Test item

Offsetsectionloadingtest

Residualperformance

View of assembled ERJ on site.

Conditions

Results2Sample
cable

66 kV 1 x 500 mm(insulation thickness 10 mm)

Amount ofstretch

Yearly: 42.6 mm, 30 cycles
Daily: 7.4 mm, 10,800 cycles

Offsetconfiguration

Length: 1350 mm
Width: 800 mm

Heat cycle

RT ~ 90°C: 25 cycles
RT ~ 105°C: 5 cycles

Satisfactory

Test voltage

65 kV for 30 days

AC withstand voltage

130 kV for 1 hr

Satisfactory

Lightning impulse
breakdown-20 kV in 3-times steps tobreakdown-960 kV

Check for internal slippage,
deformation or other abnormality

NoneStrip-down examination

Figure 4

View of assembled ERJ with protection cover.

Furukawa Review, No. 32

200765