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.