APPENDIX A DETAILED PROJECT DESCRIPTION

A.3   Project Component Design

A.3.1   Overview

The proposed Project is made up of the following primary components:

Table A.3-1 provides a list of major equipment for the proposed Trans Bay Cable Project.

A.3.2   Transmission Systems

All the proposed submarine and underground cable systems have a primary conductor and numerous layers of electrical insulation and other materials to ensure that the cable surface voltage remains at zero, protect the cable against water infiltration, and provide physical protection against breakage of the cable.

A.3.2.1   HVDC Transmission Cable

The power transmission capacity of the proposed Project is 400 MW. The proposed HVDC transmission cable system between the San Francisco and Pittsburg converter stations will consist of 1- 400 kV HVDC transmission cable, 1- 12 kV MVDC metallic return cable, and a fiber optic communication cable to be laid in a bundle. The transmission cable is estimated to be 4.5 inches in diameter and the return cable is estimated to be 3.5 inches in diameter. The combined cable system bundle is estimated to be 10 inches in diameter. A cross-sectional diagram of the proposed HVDC cable system bundle is presented on Figure A.2-2.

TABLE A.3-1
SUMMARY OF PROPOSED PROJECT COMPONENTS
AND MAJOR EQUIPMENT


Submarine Cable System (HVDC, MVDC, and Fiber Optic)

  • HVDC voltage: 400 kilovolt (kV)
  • HVDC conductor: single-circuit, 2,467 kcmil (1,000 circular mil), copper conductor; outer diameter: 114 mm (4.5 inches)
  • MVDC return voltage: 12 kV
  • MVDC conductor: single-circuit, 2,171 kcmil copper; outer diameter: 86 mm (3.4 inches)
  • Fiber optic: 1-inch diameter for communication

HVDC Underground Cable (Onshore)

  • HVDC voltage: 400 kV
  • HVDC conductor: single-circuit, 2,467 kmil copper conductor; outer diameter: 102 mm (4.0-inch diameter)

MVDC Underground Cable/Fiber Optic Bundle (Onshore)

  • Voltage: 12 kV
  • Conductor: single-circuit, 2,171 kcmil, copper conductor; outer diameter: 86 mm (3.4 inches)
  • Fiber optic: 1-inch diameter for communication

115 kV AC Underground Transmission Cable (Onshore; San Francisco Only)

  • Voltage: 115 kV
  • Conductors: double-circuit, 2,368 kcmil, Milliken copper conductor, XLPE; outer diameter: 91 mm (3.6 inches), each circuit consisting of 3 cable phases (6 cables total)
  • Conduit type: PE or PVC
  • Minimum depth: 30 inches to top of duct
  • Splice vaults: reinforced concrete, 30 feet long x 20 feet wide x 10 feet deep (outside dimensions); 6 splices per vault
  • Total number of splice vaults: 0 to 1 (depending on final design)

115 kV AC Overhead Transmission Line (Onshore Alternative to Underground; San Francisco Only)

  • Voltage: 115 kV
  • Conductors: double-circuit, 715.5 kcmil ACSR each circuit with 3 phases; conductor diameter: 21 mm (0.84 inches)
  • Structure type: self-supporting tubular steel poles
  • Structure height: approximately 75 feet (exclusive of any EMF reduction measures that may be required)
  • Approximate distance between structures: 350 to 700 feet

230 kV AC Submarine Transmission Cable (Applies to Proposed Standard Oil Converter Station Site Only)

  • Voltage: 230 kV

  • Conductors: single-circuit, 2,763 kcmil, copper conductor, XLPE; outer diameter: 125 mm (4.9 inches), the circuit consisting of 3 cable phases (3 cables total)

230 kV AC Underground Transmission Cable (Onshore; Pittsburg Only)

  • Voltage: 230 kV

  • Conductors: single-circuit, 2,371 kcmil, copper conductor, XLPE; outer diameter: 112 mm (4.4 inches), the circuit comprising 3 cable phases (3 cables total)

  • Cable directly buried or installed in conduit (typically PVC or PE)

  • Minimum depth: 36 inches to top of conduit
  • Splice vaults: reinforced concrete, 30 feet long x 10 feet wide x 10 feet deep (outside dimensions); 3 splices per vault

  • Total number of splice vaults: 0 to 3 (depending on final design)

230 kV AC Overhead Transmission Line (Applies to Standard Oil Converter Station Site Only; Pittsburg)

  • Voltage: 230 kV
  • Conductors: single-circuit, 954 kcmil ACSS each circuit with 3 phases; conductor diameter: 30 mm (1.196 inches)
  • Structure type: self-supporting tubular steel poles
  • Structure height: approximately 75 feet (exclusive of any EMF reduction measures that may be required)
  • Approximate distance between structures: 700 to 1,500 feet

Converter Stations (Common to Both Stations)

  • Control building: 64 feet tall, 4,550 square feet
  • Valve hall: 9,750 square feet
  • DC hall: 7,500 square feet
  • AC switchyard: high voltage AC circuit breakers, horizontal- or center-break line disconnect switch, vertical-break feeder disconnect switch
  • AC filters, capacitor banks: 3 banks – additional filtering or reactive power demand may be required as determined by PG&E Facilities Impact Study.
  • Converter transformers: oil-insulated
  • DC smoothing reactor: air-insulated
  • Emergency diesel generator: 900 kW rated output (1,350 hp driver)
  • Two diesel-driven fire pumps: 1,500 gpm each (268 hp drivers)

Note: The above data may vary based on final engineering.


A.3.2.2   AC Transmission Cable

The proposed 115 kV and 230 kV AC transmission cables consist of an inner copper conductor, surrounded with XLPE insulation. The 230 kV and 115 kV underground cables have aluminum or lead alloy sheaths. The 230 kV submarine cable has a copper wire armor.

A.3.3   Fiber Optic Communications Cable

A fiber optic communications cable will be installed to ensure reliable communications and control between the San Francisco and Pittsburg converter stations. The Project proposes to bundle an armored, multi-strand fiber optic cable with the HVDC and MVDC cables in a single installation (refer to Figure A.2-2).

A.3.4   HVDC Converter Stations

The 2 proposed converter stations (San Francisco and Pittsburg) consist of various key components with multiple functions associated with the conversion of electrical current between HVDC and HVAC.

A.3.4.1   San Francisco Converter Station

The proposed San Francisco Converter Station would occupy approximately 5.6 acres of a 6.8-acre site at the HWC property site on 23rd Street, located between the shore of the Bay and Illinois Street, north of 24th Street. The existing buildings on the site are considered to be potentially eligible for listing on the National Register of Historic Places; the existing buildings on the site (refer to Figure A.3-1) would need to be removed in order for the proposed San Francisco Converter Station to be constructed.

The proposed valve hall would be approximately 64 feet high with an adjoining DC hall and a control building occupying approximately 23,000 square feet. Transformers, AC and DC switchgear, AC filters and a closed loop valve cooling system would occupy the balance of the site. A perimeter barrier would surround the site in order to prevent unauthorized access. The proposed HWC Converter Station layout is shown on Figure A.3-2 and Figure A.3-3 presents an elevation view of the proposed HWC Converter Station.

Photosimulations of the proposed HWC Converter Station are shown from 2 different viewing locations on Figures A.3-4 and A.3-5.

The buildings would be designed to blend in with surroundings and to complement existing architecture of the area.

A.3.4.2   Pittsburg Converter Station

The proposed Pittsburg Converter Station at the location referred to as the Standard Oil site would occupy an approximately 7.5-acre site. Utilization of this site would require the existing structures (e.g., abandoned wastewater storage tanks, small dilapidated building, and the surrounding berm) be removed (refer to Figure A.3-6).

Proposed structures are the same as described in Section A.3.4.1 of this Appendix for the proposed San Francisco Converter Station. The proposed Pittsburg Converter Station layout is shown on Figure A.3-7, and Figure A.3-8 presents an elevation view of the proposed Standard Oil Converter Station.

A photosimulation of the proposed Pittsburg Converter Station from the Pittsburg-Antioch Highway is presented on Figure A.3-9.

The buildings would be designed to blend in with surroundings and to complement existing architecture of the area.

A.3.5   HVAC Interconnections to PG&E Switchyards

The proposed Project is designed to deliver electric power from the PG&E Pittsburg substation to the PG&E Potrero substation. The existing PG&E Pittsburg Substation interconnects with a number of other substations in Northern California. It is also fed by several nearby existing power plant facilities in Contra Costa County capable of producing over 3,000 MW. The existing PG&E Potrero Substation is at the northern end of PG&E's transmission system on the San Francisco Peninsula.

The proposed locations of the San Francisco and Pittsburg Converter Stations were chosen to fit in with surrounding land uses, provide direct land-to-sea cable access and minimize the length of AC transmission inter-ties to the PG&E substations. The interconnection of the Project to the PG&E substations at Potrero and Pittsburg does not increase the land area of the substations, and does not increase the voltage of the substations above the voltage for which those substations were previously rated. No permit to construct is required for the substation work or the interconnections under CPUC General Order No. 131-D, Section III.

A.3.5.1   San Francisco

The proposed HVAC interconnection in San Francisco consists of a 3-phase, double-circuit 115 kV underground or overhead transmission line that would deliver AC power from the proposed San Francisco Converter Station to the existing PG&E Potrero Substation.

A.3.5.2   Pittsburg

The proposed HVAC interconnection in Pittsburg consists of a 3-phase, single-circuit 230kV submarine and buried onshore transmission cable that would deliver AC power from the PG&E Pittsburg Substation to the Pittsburg Converter Station.

A.3.6   Electromagnetic Fields (EMF)

The following information indicates that no established electric or magnetic field standards would be exceeded by the Project. Refer to Appendix K for further information regarding EMF.

A.3.6.1   Transmission Lines

A.3.6.1.1   Submarine Transmission Cable. External electric fields for both HVDC and HVAC submarine cable systems would be practically absent due to their shielded design. The electric field is confined within the insulation. The cable shields (metallic sheath and armor) would be directly grounded at both ends. Continuous grounding along the entire length of the cable would be achieved due to direct contact with water. Therefore, the cable would be at zero potential with respect to the surrounding earth.

The HVDC and MVDC cables to be buried in the floor of the bay and for short onshore sections in San Francisco and Pittsburg would develop low-intensity, static magnetic fields approximately equal to the earth's natural magnetic fields. The magnetic fields of the main and return cables would be substantially cancelled due to the fact that the 2 cables would be bundled closely together. The current flowing in the 2 cables would be equal but flow in opposite directions. As a result, the total magnetic field on the bay floor would be within or near background levels. Figure A.3-10 depicts the predicted magnetic field along a profile crossing the 400 kV HVDC monopole system laid at a depth of approximately 5 feet (1.5 meters) beneath the bottom of the bay.

A.3.6.1.2   Underground AC Transmission Cable. External electric fields for the HVAC cable system would be zero due to their shielded design. The proposed configuration for the buried double-circuit 115 kV HVAC cable system (in pre-installed conduit) interconnecting the San Francisco Converter Station with the Potrero substation is shown on Figure A.3-11. An alternate configuration for the buried double-circuit 115 kV HVAC cable system (in duct bank) is shown on Figure A.3-12. The graph on Figure A.3-13 shows typical magnetic field levels along a profile crossing the 115 kV HVAC cable system as configured on Figure A.3‑11 and Figure A.3-14 shows typical magnetic field levels along a profile crossing the 115 kV HVAC cable system as configured on Figure A.3-12.

Figure A.3-15 shows the trefoil arrangement for the single-circuit 230 kV HVAC route at Pittsburg, and Figure A.3-16 shows the typical magnetic field values at 3 heights above ground level along a profile that crosses perpendicular to the cable system. The proposed configuration for the buried single-circuit 230 kV HVAC, 400 kV HVDC, and MVDC is shown on Figure A.3-17. The external magnetic fields resulting from this configuration are shown on Figures A.3-18, A.3-19, and A.3-20.

A.3.6.1.3   Overhead AC Transmission Line Option. The proposed Project includes a buried HVAC cable system between the converter stations and the PG&E substations. Another option under consideration in San Francisco would be to employ an overhead transmission line. The proposed configuration for the double-circuit 115 kV HVAC overhead transmission line option for interconnecting the San Francisco Converter Station with the PG&E Potrero Substation is shown on Figure A.3-21. This is an alternate configuration if the underground configuration is not used. Typical electric field levels for aboveground 115 kV transmission lines are 1.0 kV/m under the transmission towers, 0.5 kV/m at 50 feet, and 0.07 kV/m at 100 feet (EMF-Link Information, Ventures, Inc, 1995). Typical magnetic field levels for aboveground 115 kV transmission lines are 29.7 milligauss (mG) under the transmission towers, 6.5 mG at 50 feet, and 1.7 mG at 100 feet.

The proposed configuration for the single-circuit 230 kV HVAC overhead transmission line that applies to a portion of the proposed cable route between the Standard Oil Converter Station site and New York Slough is shown on Figure A.3-22. Typical electric field levels for aboveground 230 kV transmission lines are 2.0 kV/m under the transmission tower, 1.5 kV/m at 50 feet, and 0.3 kV/m at 100 feet (EMF-Link Information Ventures, Inc., 1995). Typical magnetic field levels for aboveground 230 kV transmission lines are 57.5 mG under the transmission towers, 19.5 mG at 50 feet, and 7.1 mG at 100 feet.

A.3.6.2   Converter Stations

Currently, final design details are unavailable for the converter stations and the AC inter-ties to PG&E substations. However, preliminary estimates of electric and magnetic field levels, based on conceptual design, have been performed. The preliminary estimates indicate the AC and DC electric and magnetic fields are expected to be within established engineering standards.

The DC cable would enter the converter stations and end at a cable termination within the DC hall. The high-voltage conductor would be routed through a disconnect switch, current and voltage metering, a large smoothing reactor, and then on to the converter. Sufficient isolation of the high-voltage conductor would be maintained using post insulators. The spacing between conductors would result in electric and magnetic fields in some areas within the converter stations.

The proposed DC cable terminations and equipment are situated well within the proposed converter station facilities and all of the aforementioned equipment would be installed inside a building. Electric fields would be shielded by the building enclosure, and the magnetic fields would be reduced further because the buildings would be made of steel.

In the converter station AC filter area, lines run between the busbar and converter transformers, along with the interconnections to 3 AC filter banks, a shunt reactor and the underground inter-ties to the PG&E substations. Electric fields would occur beneath these conductors. Electric fields at the converter station fence lines would be negligible.

Preliminary estimates for the proposed San Francisco HWC Converter Station indicate the magnetic field along the fence line typically would be below 200 mG, with peak values along a relatively small portion of the southern fence line less than 300 mG (without consideration for attenuation by fencing). This southern fence line area is adjacent to the water and would not be accessible to the public. Electric fields at a distance of 1 foot from the fence line are estimated to be less than 1 kV/m, assuming a fence height of at least 13 feet (Siemens Preliminary EMF Estimation Potrero Converter Station 23 Nov 2005 [2005a]).

Preliminary estimates for the Pittsburg Standard Oil Converter Station indicate that the magnetic field along the fence line typically would be below 100 mG (without consideration for attenuation by fencing). Electric fields at a distance of 1 foot from the fence line are estimated to typically be less than 2 kV/m, assuming a fence height of at least 4.6 feet (Siemens Preliminary EMF Estimation Pittsburg Converter Station 23 Nov 2005 [2005b]).

A.3.6.2.1   Radio Interference. Corona effects would be limited to the air-insulated parts of the AC switchgear and the overhead line. The use of shielded, buried 230 kV and 115 kV AC cable would eliminate corona and field effects and thus radio interference related to these cables.

Radio frequency measurements taken near existing Siemens-designed HVDC converter stations show no disturbance to any radio, broadcast, or communication services. Measurements have shown, in all cases, that the radio frequency interference from the converter stations is reduced to a level so as to eliminate disturbances to such services. In most cases, the radio frequency levels are so low they cannot be distinguished from ambient levels.

A.3.6.2.2   Telephone Interference. The AC harmonic filters will be designed to limit the contribution to harmonic distortion in the PG&E AC grid to levels that would not influence the local telephone systems.

A.3.7   Audible Noise

The converter stations would be designed to conform to local ordinances, rules, and standards for the City and County of San Francisco and the City of Pittsburg. In addition, once the stations were operating, noise levels would be measured to ensure design goals were met. Major sources of noise from the converter stations include transformers, filters, HVAC units, circuit breakers, and the emergency diesel generator. Preliminary Audible Noise Studies have been performed and the predicted sound levels during operation are presented in Appendix H. Section 4.11 (Noise and Vibration) of this EIR presents a noise impact assessment for the proposed project and alternatives. Final measures for compliance with applicable regulations would be determined during detailed design.


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