Underground System Design

TADP 547

History and Background

Presentation 1.1

Instructor: George R. MattoRegional Engineer

The Okonite Co.

INSULATED CONDUCTOR HISTORY

• Invention of Telegraph and telephone triggered the

need for insulated communication cables.

• While Edison was still perfecting the electric light

bulb, he committed to lighting lower Manhattan -

necessitating the development of insulated

electrical power cables.

How Did We Get From This to This?

Types of Insulation 1812 - 1852

India Rubber

Jute and Pitch

Cotton Shellac/Lead

Cotton Rosin Sealed in Wood with Pitch

Jute Pitch and Rubber

Gutta-percha/Tape Tar Covering

Successes and Failures

Early successes were soon met by failure. Just as it

was thought that an installation of underground

telegraph cable was a success the system started

failing in two years or less.

This is a familiar cycle of discovering what does not

work and holding on to those elements that do work.

DID YOU KNOW…?

The first practical use of an "insulated conductor"

transmitting electricity is believed to have occurred in

1812, when it was used to detonate an underwater

mine in the Neva River in St. Petersburg, Russia.

The Edison Tube (Cable) 1879

Edison needed to place his electric light system

underground due to the plethora of telegraph wires.

Successful versions of insulated telegraph wire were

scarce - except for Gutta-percha which deformed when

heated.

Edison Cable: Two to three copper rods rods wrapped

with jute in an iron pipe — heavy bituminous

compound repelled water. Some still in service in 1931.

George Westinghouse A-C System - 1886

Required overhead lines — prohibited in Chicago and

Washington, DC

AC underground wires performed poorly

All combinations of materials failed

National Electric Light Assn. ―…no wire found to last

two years at 2000 V…‖ 1888

NY Subway adopts rubber/lead cable

Paper insulated cable followed.

Cable Components

Conductors: Copper (tinned) or Aluminum

Stranding: Solid, Class B or C/Round or Shaped

Insulation: Rubber or Paper

Shields and Sheaths: Copper Tape, Cotton Braid,

Lead Sheaths

Coverings-Jackets: Lead, Plastic and Rubber

Problems to Overcome

Moisture Ingress

Oxidation of Insulation

Electrical Degradation of Insulation

DID YOU KNOW…?

By 2006, there were only 60 customers using DC

service, and on November 14, 2007, the last direct-

current distribution by Con Edison (N.Y) was shut

down. Customers still using DC were provided with

on-site AC to DC rectifiers.

From Wikipedia, the free encyclopedia

PAPER vs. RUBBER (Both Lead Sheathed)

PAPER INSULATION

1884 Lapped Paper Tape

Vacuum Drying,

Pressure Impregnation

10 kV in 1897/20‟ mains

lasted to 1933

RUBBER INSULATION

Unvulcanized = short

life

1855 Goodyear Patent

on vulcanization

1900 Rubber at 25 kV

1895 “Engineering News “… (cable) evenly divided between

paper insulated and rubber-insulated cables, both in lead…”

IONIZATION?

Damaging electrical stress can take place at

2000 V

Two Insulating Materials

Up River Fine Para RubberFine Wood Pulp Paper Tape

EARLY TO MID 1900‟S - BANBURY MIXER

Two Insulating Processes

RUBBER STRIP PROCESSAPPLYING PAPER TO

CONDUCTOR

SHIELDS -- AN ACCIDENTAL INVENTION??

Even though lead coverings were not called shields,

when applied over an insulated conductor, lead if

properly grounded confines voltage stress to the

insulation… (see purpose of shields Okonite

Engineering Publication - EHB)

Two Pressurized Cables

Hollow core-

liquid filled

Pipe Cable

(3 per pipe)

1900‟s — Demand for Transmission Cables & Reliability/Capacity Solutions

Paper Insulation Fully Entrenched

Higher voltages required better vacuum drying

Drying and degasifying

Improve oil impregnation

Better Temperature and Pressure Control

Shielding by Martin Hochstadter

British and American progress

CIRCA 1955 CHART OF CABLE TYPE / VOLTAGE

CIRCA 1967 CHART OF CABLE TYPE / VOLTAGE

From Instrument Level to 555 kV

15 kV to 138 kV Paper Insulated

Pipe Type Cable

XLPE/LEAD/JACKETED HV CABLE

Post WW II to Present - Medium Voltage Cable

EPR – Ethylene Propylene Rubber

HMWPE – High Molecular Weight Polyethylene

XLPE – Cross Linked Polyethylene

TR-XLPE – Tree retardant Cross Linked Polyethylene

Polyethylene Insulation Performance

What is causing these failures?

Water Tree

Can progress into

an “electrical tree”

“Cost of a Failure”

Okonite „92

To Summarize:

Insulated power cable followed insulated telegraph wire.

Successful insulations/jackets were hard won.

Moisture, ionization (electrical breakdown) and oxidation

continue to be a challenge for cable engineers.

EPR, XLPE and paper insulation are current choices for

medium and high voltage insulation. Each must deal with

the above “triad” of degrading forces.

One manufacturer has capitalized on “sameness” concept

in their insulation system of “all” EPR.

Research continues on elusive “best” XLPE formulation.

Transmission voltage continue to be pushed to ever higher

levels.

Pressure was the “secret” of laminated HV Cable success.