A.5   Operation and Maintenance Procedures

The HVDC technology proposed for the Project is highly reliable and requires minimal operation and maintenance. The 2 converter stations, at the ends of the cable route in San Francisco and Pittsburg, would normally operate with a minimal staff and/or be remotely operated. Personnel would support the stations by performing periodic inspections and routine maintenance.

At the commencement of system commercial operation, operation and maintenance procedures and critical spare parts would be in place to ensure that reasonably foreseeable problems with the cable or converter stations could be remedied quickly.

A.5.1   Operation

Operating parameters  would be adjusted to maintain system operation within input settings supplied by the CAISO. A fiber optic communications cable would be installed with the HVDC cable to allow dedicated communication for the computer control systems operating at both of the converter stations. This would allow rapid response to changes in the AC transmission grid, converter station equipment, and/or the cable. The computer systems would alert an on-call operator on detection of an event requiring attention.

A.5.1.1   California Independent System Operator (CAISO)

The Project would transmit electrical power via a dedicated HVDC connection between Pittsburg and San Francisco. The cable system would be placed in service and operated under the direction of the CAISO. The proposed Project would provide the CAISO with the capability to better support electric power demand and stability requirements on the northern part of the San Francisco Peninsula.

A.5.2   Routine Maintenance

A.5.2.1   Converter Stations

The proposed electrical equipment and electronic controls at the converter stations would be expected to require a minimal amount of routine maintenance on a periodic basis. Planned routine maintenance activities include a general visual inspection for signs of external damage, leakage, or overheating, checks of insulating fluids levels and properties, lubrication of cooling fans, and electrical checks that are beyond those performed automatically by the station computer systems. Some of the proposed equipment would be expected to operate indefinitely, without maintenance, while other components have limited life expectancies and would require periodic service or replacement. Approximately 5 scheduled outage days would be required every year.

The station control systems would be designed to automatically alert on-call personnel if problems were detected with the cable or converter stations. The converter stations would be designed with redundant components and stocked with critical spare parts. Contractual arrangements would be in place for specialized services that may be required on short notice.

A.5.2.2   Cable Repair

With the exception of periodic cleaning of outdoor insulators, the proposed transmission cable would be expected to require no scheduled maintenance for the life of the Project. Specialized personnel and equipment would be required to repair any damage to the cable. Generally, the repair would require a new section of cable to be added by splicing.

A spare length of cable would be kept on hand to allow timely splicing and replacement of a damaged section of cable. The spare cable would be stowed directly on a boat or barge moored at Pittsburg Marina or other suitable local facility, or in a nearby onshore storage area, specifically for making emergency repairs. Contractual arrangements would be in place for specialized services that may be required.

A.5.3   Reliability and Availability

The HVDC system consists of 2 main systems: 1) the submarine cable system; and 2) the converter system.

Submarine electric cable technology is well established and has a long service record. The cable and main circuit equipment are all passive, reliable, and well-proven technologies. The converters are supplemented with well-proven electronics for control and protection, and standard motors for cooling, ventilation, etc.

A.5.3.1   Submarine Cable System

A.   Insulation. Aging of HVDC insulation is slower than for HVAC due to lower operating temperature. It was reported in 1994 that no sign of aging insulation was observed for the Gotland cable or the Skagerrak 1 and 2 cables after 20 years of operation.

A.   Erosion/Abrasion. The buried HVDC cable would be protected from erosion/abrasion due to wave action and water currents. In those areas where burial was not feasible, the cable would be protected by mattresses.

A.   Corrosion. The HVDC cable is designed to impair corrosion, using bitumen and zinc coating of the armoring wires. Burial reduces exposure to oxygen which is necessary for corrosion to occur. Further, the cable would be expected to operate satisfactorily even if the armoring were to break down.

A.5.3.2   Converter Stations

Converters would use proven AC/DC conversion technology of thyristor valves, allowing the rapid control of power transfers and a fast response to changing system conditions.

All critical auxiliary equipment, controls, protections, metering, and communications would use redundant systems to maximize system availability and reliability.

The overall energy availability of both converter stations including scheduled outages and the related forced outage rate would be in accordance with the definitions given in CIGRE-Report 14-97 WG04, "Protocol for Reporting the Operational Performance of HVDC Transmission Systems" and is based on the following assumptions for the operation of the stations:

A.5.3.3   Redundancy in Systems

The proposed design includes redundancies of key components and systems to minimize outages in key components/systems, including:

A.5.3.4   Availability of Spares of Major Equipment

A.   Converter Transformer. One spare converter transformer is foreseen for each converter station. In the event of a transformer fault, a transformer can be replaced with the spare within approximately 4 or 5 days.

A.   Smoothing Reactor. One spare smoothing reactor coil is foreseen for each converter station, as well as 1 insulator stack of the support insulators.

A.   Circuit Breakers, Disconnects, and Ground Switches. One spare of each switch/breaker is foreseen for each converter station, as well as motor operated mechanisms and wearing parts.

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