Raychem Heat Shrink Straight Through Joints

Raychem Heat Shrink Straight Through Joints: The design of a single-core joint for a polymeric insulated cable is described here. The same design principles are used for 3-core cables. For transition joints, special oil barrier tubing are used to transform a draining oil (MI) as well as non draining oil (MIND) paper insulated cable into a quasi polymeric insulated cable with a radial field.

• Electrical stress control: The stress control tubing and the patch have a precisely defined impedance characteristic which smoothes the electrical field over the connector and cable screen ends. During the installation of 12 kV and 24 kV joints, the special void filling yellow tape will be compressed by the two stress control tubing. The patch over the connector will be compressed by the high shrink force of the triple extruded joint body. For the design of a 42 kV joint only the special yellow void filling tape is used, which is compressed by one stress control tubing. It is not necessary to chamber the cable insulation or to use a connector with specially profiled shape.
• Insulation and screen: The triple extruded joint body provides the correct thickness of insulation (red) in one installation step. The insulation screen is provided by the outer wall of the tubing, which is of heat-shrinkable conductive polymer (black). This technique saves installation time and ensures a flawless bond between joint insulation and screen, even up to 42 kV.
• Metallic shielding: Copper mesh and roll springs ensure the correct screen connection across the joint area and make electrical contact with the outer screen of the joint. The design passed tests up to 11 kA short circuit and up to 400 A currents simulating ground fault situation.
• Outer sealing and protection: The heat used to shrink the outer tubing causes the pre-coated adhesive to melt and flow, resulting in a lasting moisture and corrosion barrier on the cable oversheath. The outer tubing provides mechanical impact and chemical resistance as expected from cable oversheaths. For armoured cables, Raychem joints incorporate either a quick to install galvanised steel joint case or steel tape or fibre glass reinforced heat-shrink wraparound.

Installation Procedure
The elastomeric joint component and the outer sealing tubing are slid over the prepared cable end. The screen ends are electrically smoothed with void filling compound and stress control tubing are shrunk over the cable ends. By simply tightening the bolts of the mechanical connector, the conductors are jointed and then covered with a stress control patch. The elastomeric component is quickly shrunk over the connection area. Roll springs and copper mesh rebuild the cable shield and the oversheath is replaced by an adhesive coated sealing tubing. All kits are supplied with illustrated step by step instructions.

Triple Extruded Elastomeric Technology
The triple extruded joint body, supplied in an expanded form, consists of 3 bonded layers. The two heat-shrinkable outer layers (1. black conductive, 2. red insulating) hold the inner elastomeric layer (3. red insulating) at full diameter. Application of the heat causes the outer layers to shrink, allowing the elastomeric, insulating layer to contract at the same time and closely fit on the jointing cable. Elastomers typically experience a reduction of the contraction force after storage and at cold temperatures. By applying heat this effect is overcome thus allowing an unlimited storage time and installations at low temperatures. The rubber-like characteristics of the insulation material combined with the rigid outer heat-shrinkable wall enable the joint to follow the thermally induced dimensional changes of the cable insulation.