Underground System Design TADP 547

Transcription

1 Underground System Design TADP 547 History and Background Presentation 1.1 Instructor: George R. Matto Regional Engineer The Okonite Co.

2 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.

3 How Did We Get From This to This?

4 Types of Insulation India Rubber Jute and Pitch Cotton Shellac/Lead Cotton Rosin Sealed in Wood with Pitch Jute Pitch and Rubber Gutta-percha/Tape Tar Covering

5 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.

6 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.

7 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.

8 George Westinghouse A-C System 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.

9 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

10 Problems to Overcome Moisture Ingress Oxidation of Insulation Electrical Degradation of Insulation

11 DID YOU KNOW? By 2006, there were only 60 customers using DC service, and on November 14, 2007, the last directcurrent 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

12 PAPER vs. RUBBER (Both Lead Sheathed) PAPER INSULATION 1884 Lapped Paper Tape Vacuum Drying, Pressure Impregnation RUBBER INSULATION Unvulcanized = short life 1855 Goodyear Patent on vulcanization 10 kv in 1897/20 mains lasted to Rubber at 25 kv 1895 Engineering News (cable) evenly divided between paper insulated and rubber-insulated cables, both in lead

13 IONIZATION? Damaging electrical stress can take place at 2000 V

14 Two Insulating Materials Fine Wood Pulp Paper Tape Up River Fine Para Rubber

15 EARLY TO MID 1900 S - BANBURY MIXER

16 Two Insulating Processes APPLYING PAPER TO CONDUCTOR RUBBER STRIP PROCESS

17 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)

18 Two Pressurized Cables Pipe Cable (3 per pipe) Hollow coreliquid filled

19 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

20 CIRCA 1955 CHART OF CABLE TYPE / VOLTAGE

21 CIRCA 1967 CHART OF CABLE TYPE / VOLTAGE

22 From Instrument Level to 555 kv

23 15 kv to 138 kv Paper Insulated

24 Pipe Type Cable

25 XLPE/LEAD/JACKETED HV CABLE

26 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

27 Polyethylene Insulation Performance What is causing these failures?

28 Water Tree Can progress into an electrical tree Cost of a Failure Okonite 92

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30 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.