TERMINATING
THEORY & PRODUCTS
TERMINATING
THEORY & PRODUCTS
Caution: Working around energized high-voltage systems may
cause serious injury or death. Installation should be performed by
personnel familiar with good safety practice in handling high
voltage electrical equipment. De-energize and ground all electrical
systems before installing product.
CLASS 1 TERMINATION
(IEEE Standard 48)
• Electric Stress Control
for the Cable Shield Terminus
• External Leakage Insulation
between H.V. Conductor and Ground
(Tracking Protection)
• A Seal
to the External Environment
I. STRESS CONTROL
For the Cable Shield Terminus
Semi-conducting Shield Layer
NO STRESS CONTROL
Traditional
GEOMETRIC STRESS CONE
DIELECTRIC (HIGH-K) STRESS CONTROL
High-K (high dielectric constant) material is used
to reduce stress at the shield discontinuity by
field refraction due to different K values of
two adjacent dielectric layers.
HI-K STRESS CONTROL
EXAMPLE: Snell’s Law of Refraction
TRADITIONAL HIGH-K
STRESS CONE STRESS CONTROL
TERMINATION TERMINATION
II. EXTERNAL LEAKAGE INSULATION
Between Conductor & Ground
FLASHOVER PROTECTION TRACKING PROTECTION
BIL per (IEEE 48)
THE
INSULATOR
TRACKING
Three Conditions Must Exist:
• CONTAMINATION • MOISTURE
- Dust - Humidity
- Chemicals - Fog
- Salt - Condensation
- Other Airborne Particles - Mist
- Snow
• VOLTAGE - Rain
- Surface Stress (V/mil)
DISCHARGE
FORMATION Surface Resistance
Reduced When Wet
DRY BANDS
(Areas of Higher
Surface Resistance)
ELECTRICAL
&
DISCHARGES
Concentrated
Voltage Gradient (Generated in
Dry Band Areas)
Ways To
CONTROL TRACKING
1. Increase Distance from HV to Ground
2. Rain Shed (Insulator Skirts)
3. Track Resistant Materials
- Porcelain
- Inorganic Fillers in Rubber
- Inorganic Fillers in EVA (Heat Shrink)
- Silicone Rubber
Advantages of Silicone Rubber as
INSULATOR MATERIAL
1. Silicone is Hydrophobic
2. Silicone Can Recover Its Hydrophobicity
3. Silicone is Inherently UV-Stable
4. Silicone is Mostly Inorganic --
(No Conducting Carbon Path)
5. Silicone Has a Smooth Surface
Examples
HYDROPHOBIC & HYDROPHILIC
SILICONE RUBBER PORCELAIN
Hydrophobic Hydrophilic
(Water “Balls-up”) (Surface “Wets”)
HYDROPHOBIC
VS
HYDROPHILIC
HYDROPHOBIC HYDROPHILIC
Contact Angle
Water “balls” up Surface “wets” out
Energy from leakage current can cause
insulator surfaces to become hydrophilic
Recovery of Contact Angle for
SILICONE RUBBER TERMINATIONS
90 Deg. Recovery
24 Hrs. (Recovered)
Recovery of Contact Angle
(Based on study performed in
cooperation with Arizona State University)
SILICONE RUBBER INSULATOR
Coated with ASTM D-2132 Contaminant
Surface remains “Hydrophobic”
EPDM INSULATOR
UV Damage
SUMMARY and CONCLUSIONS
• Silicone Insulators are superior to EPDM, EVA and
porcelain insulators
• Silicone is more hydrophobic than other polymers or
porcelain
• Silicone has the ability to regenerate its hydrophobicity
in the event that high-leakage current changes its state
• Silicone Insulators are inherently stable to UV due to
its high backbone bond energy
• 3M™ Silicone Rubber Terminations - In use 30+ years
with excellent results
III. SEAL
To the External Environment
Top Seal Potting
(Conductor Seal) Compound
Bottom Seal
(Jacket Seal)
SEALING
with
TAPE
POTTING
with
RESIN
SEALING
with
HEAT SHRINK
SEALING
with
COLD SHRINK
HEAT SHRINK TERMINATION
Example of
HEAT SHRINK TERMINATION
Raychem HVT
Heat Shrink Termination
INSTALLATION
(1)
Stress Relief
Material
(Semi-con Step
Filler)
(2)
Stress Control
Tube
(Special Torch,
“Bushy” Flame)
(3)
Top Seal
(4)
Jacket
Seal
(5)
Separate
Insulator
Tube
Allow Tube
To Cool (6)
Before Separate Shrink
Proceeding Insulator Evenly
Skirts With no
Tilt or Sag
COMPLETED
TERMINATION(S)
Outdoor Termination
(with skirts)
Indoor Termination
(same, but without skirts)
COLD SHRINK TERMINATION
Examples of Silicone Rubber
COLD SHRINK TERMINATIONS
Joslyn JPT & 3M™ QT-II Termination 3M™ QT-III Termination
Plymouth/Bishop ColdTerm Integrated 1-Piece
Plymouth Joslyn
Silicone Silicone
Tape Tape
Top Seal Top Seal
Silicone
Silicone
Grease
Grease
Pull Tabs
Examples of Silicone Rubber
COLD APPLIED (Shrink) TERMINATIONS
Raychem TFT
“Holdout” Tube
VITAL STEP: Loosen
termination by twisting
until it moves on holdout
Twist & slide off of
holdout tube onto cable
Adjust into final
position if necessary
Use pull tabs to
position over jacket
Typical Cold Shrink Termination
INSTALLATION
Apply mastic
seal around jacket
& neutral wires
Apply silicone
grease to fill
semi-con step
Install termination
by removing
supporting core
Complete top seal
with application
of silicone rubber
tape
COMPLETED
TERMINATION(S)
Outdoor Termination
(With Skirts)
Indoor Termination
(Tubular, without Skirts)
BENEFITS of COLD SHRINK
• No Tools for Installation
• Low Installation Force
• Good Interfacial Pressure
• Live Seal
• Broad Application Range
• Environmentally Stable Materials
INTRODUCING: 3M™ QT-III Termination
IMPROVED SILICONE RUBBER
Cold Shrink Termination
• IMPROVED SILICONE RUBBER - Improved
Tracking Resistance
• BUILT-IN TOP SEAL - Eliminates taping of top seal
• BUILT-IN SEMI-CON FILLER - No silicone grease
• IMPROVED HIGH-K STRESS CONTROL - Improved
corona, 60 Hz and impulse withstand performances
• SMALLER SIZE - Easier mounting
3M™ QT-III Termination
Integrated 1-Piece Design
Silicone Sealing Silicone Rubber Stress Control
Compound Insulator Compound
High Dielectric Constant
Step Core
Stress Relief Tube
SIZE COMPARISON: 15 KV CLASS
3M ™ QT- II 3M ™ QT- III
Termination Termination
- More versatile for
mounting
- Accommodates
smaller space in
- Shorter cable
cabinets
prep distance
INVERTED
3M™ QT-III Outdoor Termination
BUILT-IN COMPOUNDS:
• HI-K SEALING COMPOUND
Eliminates silicone grease at
semi-con cut-back step
• SILICONE SEALING COMPOUND
No (inverted) bottom seal taping required
SUMMARY
This New Generation of Polymeric Terminations
Takes Advantage of:
• New Developments in Silicone Rubber Technology
• New Developments in Sealing Compounds
• Integrated 1-piece Designs
• Factory Assembled Quality - Reliability
• Cold Shrink Design for Easier Field Installation
“TECHNOLOGY AND THE HUMAN FACTOR”
TERMINATION WORKSHOP
Install 3M ™ QT-III Termination
