Underground System Design

TADP 547

Terminations, Splices, andLink Boxes

Presentation 3.2

Instructor: George R. Matto

Shields, Splices, and Link Boxes

Cable shields avoid unwanted consequence

of increasing conductor voltage level.

A uniform electrical stress provided by the

shield is disrupted by cable splicing and

terminations, but is required to connect

cables.

Link boxes provide a convenient means for

transposing shields of HV cable.

Terminology

Splices and Terminations:

Stress Cones, Pot Heads, Slip-on, Heat and

Cold Shrink, Elbows, Modular – Bushing,

Shield Adaptors, Dead Break or Load Break,

Separable Connectors, moles and current

limiters, low and medium voltage networks.

Types of Splices and Terminations

Early splices and terminations utilized cloth in the

form of strips saturated with pitch and tar, and later

varnished cambric.

Hand wrapped tapes were then utilized with at least

one supplier shaping the tape in a long triangle,

much like a pennant flag. Wrapping the wide side

first formed a perfect stress cone.

Although internal taping still used (HV applications),

preformed devices have replaced tape at medium

voltage levels.

Shielded or Non-shielded?

Electrical Stress

Outside Cable

Electrical Stress

Confined to Insulation

Two Methods of Stress Grading

Geometric

Impedance

600 V Network Connections - Moles

A Mole is a device

that provides multiple

connections in a small

reliable package.

Circuit redundancy

makes an outage

almost impossible.

600 V Network Mole

Components of a 600 V

termination called a

Mole:

• Socket

• Compression Nut

• Compression

Cone

600 Volt Network

Older Network Vault Multi “Moles” Serving

Loads with Reliable

Power

Parts and Pieces

Excellent web site to reference cable

accessories. Other manufacturers have

similar products.

www.zangagency.com/pdf/ZANG_Elastimold_Cable_

Accessories.pdf

200 Amp Elbow T - Tap

3 X 1/C,

1000 kcmil

to 3 X 1/0

15 kV EPR

1/3 neutral

cable ,

Network Vault Deep Enough to Coil Cable – all ends tagged

PILC Trifurcating to EPR

3/C Paper Insulated

Lead Sheath

PILC to 3 x 1/C EPR Flat

Strap Shield Jacketed

Singles.

Solution: Heat Shrink

Splicing, Trifurcating - PILC, EPR, XLPE

Simplest splice is a single conductor to a

single cable of same type.

Three conductor to single conductors in

EPR, or a combination with XLPE can be a

challenge.

Trifurcating PILC is a learned art.

Ultimate may be Elbow tapping a 15 kV,

three conductor, PILC Cable

Elbow Tap PILC to EPR

Left Side Stress Relief

BoltedRight Side PILC

Termination Preparation

High Pressure Gas (Nitrogen) or HPFF (Fluid Filled)

Typical 69 kV - 345 kV Pipe Type Cable

115 kV Bus Access Ports

Pipe type cable can

terminate directly

into gas insulated

substations.

Short terminations

make almost seam-

less transition.

HPGF Pothead

Pothead similar to other Pipe

Type Cable Terminations.

Common elements are outer

Ceramic shell, internal paper

insulation roll build-up.

An HPOF version would

include an internal porcelain

stress control insulator.

HPGF or HPOF 1/C Splice

One of three conductors of a 3/C splice

HV Pipe Cable Splice Housing

Termination Structure

Structure can accommodate

any HV cable discussed

thus far.

Underground Trifurcate

would result in singles that

could be terminated here.

EPR - Triple Solid Dielectric Cable

EPR insulated 69 kV to 138 kV terminated in

similar fashion to other solid insulations.

Cable preparation somewhat different since

extruded semicon easily peeled back.

Pothead similar to paper insulated.

Splices utilize pre-molded rubber half-shells

or EPR tapes that are vulcanized in field

EPR, 115 – 138 kV Cable Term. Prep.

Clean stripping EPR semicon

from red EPR Insulation

EPR, 115 – 138 kV

Silicone filled potheads

on stand-off insulators,

grounded at one end to

avoid circulating current

and de-rating.

Circuit Length - 550 ft.

Switch Cabinet

Tight quartersBarely enough room

to terminate

Landing Lugs Back-to-Back

Not a good idea on

Primary - Why?Secondary-Common

Practice

Design makes cable installation and termination difficult.

Solution:

Placing cabinet over a

shallow vault will

allow proper bend

radius of cable and

easier termination

URD Switch Cabinet

This type of installation is versatile, secure

and easy to maintain.