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HomeMy WebLinkAbout1996-09-16 City Council (36)City of Palo Alto City Manager’s Report HONORABLE CITY COUNCIL FROM:CITY MANAGER DEPARTMENT:UTILITIES AGENDA DATE: SEPTEMBER 16, 1996 CMR:398:96 SUBJECT:PG&E SERVICE RELIABILITY RECOMMENDATIONS This report is informational only and requires no action from the City Council at this time. EXECUTIVE SUMMARY The attached informational report was included in the Utilities Advisory Commission’s September 4, 1996 meeting packet, describing events that occurred on PG&E’s system causing disturbances and service interruption during July and August 1996. The report describes the western power grid, how the system reacts to outages, an analysis of the effects on the City of Palo Alto and the actions taken since the August 12th outage. Subsequently, meetings between Palo Alto and PG&E were held and several joint actions have been outlined with the goal of increasing PG&E’s level of service reliability to Palo Alto. ATTACHMENTS Attachment A: Informational Report to the UAC Prepared by: Larry Start, Assistant Director, Engine, Department Head Approval: and Operations D City Manager Approval: FLEMING Manager CMR:398:96 Page 1 of 1 TO: FROM: UTILITIES ADVISORY COMMISSION UTILITIES DEPARTMENT AGENDA DATE: SUBJECT: September 4, 1996 Staff Report to UAC on PG&E Service Reliability RECOMMENDATIONS This report is informational only and requires no Utilities Advisory Commission (UAC) action. BACKGROUND This is an informational report to the UAC describing events that have occurred on PG&E’s system that have affected service reliability in the City of Palo Alto. The events described are as follows: 1) system disturbances on July 2 and August 10, 2) service interruption to the City of Palo Alto on August 12, and 3) voluntary load curtailments on August 13, 1996. Also included in this report is a description of the western power grid, a discussion of the how the system reacts to outages, an analysis of the effects on the City of Palo Alto, and a discussion of the actions taken since the August 12,1996 outage. DISCUSSION City of Palo Alto’s Electrical Interconnection The electrical interconnection between the City of Palo Alto and PG&E occurs between PG&E’s Palo Alto Switching Station and the City’s Colorado Power Station (Attachment A). This interconnection is made with 115 kV lines. The voltage is then stepped down to 60 kV within Colorado Power Station by three 115/60 kV transformers. The system is configured so that the loss of any of the interconnecting lines or transformers at Colorado Power Station will not cause an outage to the City. At PG&E’s Palo Alto Switching Station there are two separate 115 kV buses to provide redundant sources of power to the City’s Colorado Power Station. Palo Alto Switching Station is interconnected to two different substations, Ravenswood and Cooley Landing Substations, through subtransmission line interconnections. These substations are connected to PG&E’s wide area transmission grid at San Mateo and Newark Substations. These stations are connected into PG&E’s area transmission system which is connected to Western Power Grid. This interconnection provides fully redundant sources within both PG&E’s and the City of Palo Alto’s system. Western Power Grid System Operation A power system is different from other forms of energy delivery systems because electricity must be produced at essentially the same time it is being used. To keep an electrical system functioning, the system, operators must constantly balance the generation of electricity with electrical load. The balancing of load and generation occurs daily and in most cases without incident. However, during outages that interrupt large blocks of generation or main transmission routes, the balancing act between load and generation is disrupted and the system can become unstable. This instability is the result of location of the system load in relation to the generation during an outage. Two different instability conditions can occur after an outage, synchronous and voltage. During synchronous instability, the generators on the system begin running at different speeds as they try to synchronize with each other. When a generators control system is unable to adjust fast enough to correct its speed to match system frequency the generator is shut off to avoid permanently damaging the unit. Voltage instability or voltage collapse is a condition where small changes in the power delivered on the system causes a large change in the voltage. During an outage, a change in the power causes the voltage to decay rapidly. This occurs because the motors on the system begin drawing additional current to offset the reduced voltage. The additional current causes the system voltage to drop further thus causing the motors to use even more current. If left unchecked, the system voltage completely collapses. To stop voltage collapse after it starts, the system is separated into large blocks or islands to allow system stability to be regained. It should be noted that voltage collapse can be initiated without large changes in system frequency. When an initiating event occurs, the system automatically takes corrective action to reestablish stability of the system to prevent a complete shutdown or catastrophic damage to the electrical system. In areas of excess generation, where system frequency accelerates, the load is balanced with the generation by removing generators from the system. While in the areas where there is a generation deficit that causes the frequency to drop, the system decreases electrical load to reestablish the balance with the generation. The western power grid consists of a series of interconnected transmission lines that transmit power throughout the Western United States. The Western Systems Coordinating Council (WSCC) is the organization charged with setting reliability standards in the western region (see Attachment B for more information). During large system outages where synchronous or voltage instability occurs, the grid is designed to separate into sections or islands. These islands are established to protect the system from damage and to enable the balance between generation and load to be reestablished. During the summer, California utilities purchase large blocks of power from the Northwest to reduce the cost of power. During a typical outage condition, the system has adequate backup capacity to maintain system stability. However, when multiple outages occur, the system can become unstable and experience synchronous and/or voltage instability. This can result in a complete separation of the connections to the Northwest. During the initial stages of the ~separation, Northern California typically would experience a shortage of generation within the region due to power imports. The generation shortage would initiate automatic underfrequency load shedding to reestablish the balance between load and generation. Underfrequency Load Shedding Underfrequency load shedding is a method of dropping load based on the drop in system frequency. Load shedding is staged into load blocks with the tripping of these blocks determined by the severity of the frequency drop. The more the frequency drops the greater the amount of load dropped from the system. The WSCC has established a schedule for underfrequency load shedding (Attachment C). This schedule is designed to reduce system load by 50% in 5 load blocks each representing 10 % of the load. Depending on the severity of an event, the underfrequency load shedding trips the required number of load blocks to reestablish the balance between load and generation. Once the frequency of the system recovers, through the addition of generation to the system or reconnection with the Northwest, the system automatically restores load in 10 blocks again initiated by system frequency. The City of Palo Alto, as a member of the WSCC and through contractual agreements with PG&E, has participated in the automatic underfrequency load shedding plan since the late 1970s. Palo Alto complied with the WSCC guidelines by installing underfrequency load shedding relays on each of its electrical substations and implementing a plan where between 40 and 50 % of its load was shed. In addition to our contractually required load shedding plan, PG&E implemented underfrequency load shedding on its service point at Palo Alto Switching Station. PG&E’s load shedding interrupts electrical service to the entire city in the last load shedding block. In addition to automatic underfrequency load shedding, PG&E also has installed a manual load. shedding scheme. The manual load shedding scheme is used in situations where the system is experiencing severe instability or is on the verge of voltage collapse. When the system is in one of these conditions manual interruption of load must be initiated to prevent complete system collapse or damage to the system. This system interrupts the City’s entire load by disconnecting service at Palo Alto Switching Station. July 2, 1996 On July 2, 1996 the system experienced an outage due to a tree in a 345 kV line and a subsequent misoperation on the relays on an adjacent line. This outage dropped generation capacity and caused voltage instability to develop and the system automatically separated into islands. When this occurred California had insufficient generation and the frequency began to drop. This initiated underfrequency load shedding on PG&E’s system. PG&E dropped their interruptible customers and some of its first underfrequency block. However the system frequency did not drop low enough to initiate tripping at 59.1 Hz and no load was dropped in Palo Alto. On July 3, 1996 the same outage occurred again because the tree condition had not been found. During this outage the operators at Idaho Power took corrective action by dropping load. This prevented the system voltage collapse from spreading as it had the prex;ious day and no outages occurred in California. August 10, 1996 On Saturday August 10, 1996 at 2:00 PM the events leading to system wide service interruptions began in the Pacific Northwest. The initial events were the result of trees contacting and interrupting the power transfers on two 500 kV lines. These interruptions were followed by an interruption of a third 500 kV line which in turn caused a 230 kV line to sag into a tree due to overload and trip. The cumulative effect of these outages was that system voltage began to collapse. In reaction to the impending voltage collapse, the Pacific Intertie was separated at the California border establishing an island in the Southwest. Subsequent to the intertie separation, PG&E and Southern California Edison separated leaving PG&E in a island by itself. Sometime during this sequence of events, PG&E’s Diablo Canyon Nuclear Power Plant tripped off line dropping 2000 MW of generation and automatic under’frequency load shedding for all the blocks was initiated when the frequency dropped below 58.3 Hz. This dropped approximately 50% of the load in PG&E’s territory. In the City of Palo Alto at approximately 3:55 PM alarms from our underfrequency relays were received from our substations. All of the City’s underfrequency relays operated and interrupted 40% of the City’s load. Subsequent to these interruptions, PG&E’s underfrequency relays operated at 58.3 Hz and shut off service to the entire city. The City of Palo Alto dispatched its substation crews and stripped the distribution buses to prepare the system for service restoration. At 4:54, 5:47, 7:15, and 8:15 PM The City’s system operators contacted PG&E requesting the okay to begin service restoration. During each of these contacts we were told not to begin service restoration. At 5:54, without the okay from PG&E, the City initiated restoration of service to critical public safety facilities. Finally, at 8:43, nearly 5 hours after the initial trip, we were given permission to begin restoration of service to our customers. Final restoration of power was completed at approximately 11:37 PM. Some of the contributing factors in these events were: high electrical system demands throughout the West and the availability of large amounts of Northwest hydro generation in August. The impacts on the local business community, especially restaurants, was well documented in the local and regional media. Many other commercial and industrial customers had major impacts on their data processing systems, pharmaceutical operations and chip manufacturing processes. August 12, 1996 On August 12, 1996 at 12:05 PM the City of Palo Alto was interrupted again. The City’s operators immediately contacted PG&E’s operators at San Mateo Substation. PG&E’s operators ca3uld not verify the loss of power on their remote sensing equipment so crews were dispatched to Colorado Switching Station. In the meantime, City substation crews were dispatched to Colorado Switching Station and to the distribution substations to open the circuit breakers in preparation for a system restart. PG&E reported that power was restored at Colorado Substation at 12:45 PM. City of Palo Altos crews then began restoration of City’s substations. Power was restored to the entire city at approximately 1:26 PM. The same customers that were impacted on Saturday August 10 were impacted again. PG&E has attributed the outage to a misoperation of PG&E’s manual deep load shedding circuit. The exact cause of the failure is unknown but may have been caused by tones entering the telephone lease line circuit or an intermittent failure of the electronic gear. The deep load shedding scheme used at Palo Alto Switching Station is an older technology where telecommunications errors can occur. August 13, 1996 On August 13, 1996, PG&E called the City of Palo Alto and requested that we institute voluntary load curtailments. These curtailments were required because PG&E’s Pittsburg Power Plant and Diablo Canyon Nuclear Power Plant could not generate power, the Pacific Intertie load transfers were curtailed as a precautionary measure in response to the outage on Saturday August 10, 1996 and the system was experiencing record electrical demand. The City of Palo Alto complied with the request by having Utility Marketing Services contact Key and Major Account customers and request their assistance with voluntary load curtailment between noon and 6:00 p.m. While the exact level of customer participation and impact is difficult to quantify, the actions taken by these customers included: engaging backup generators, reducing lighting levels, resetting air conditioning controls to higher set points and shutdown of unneeded computer systems. Many of these customers were formally recognized and thanked in the Palo Alto Weekly (Wednesday, August 21, 1996, page 22) and included: Alza, Beckman, CPI, City of Palo Alto, Crystal Technology, Digital, Dow Jones, EPRI, Hewlett-Packard, Hyatt Hotels, IBM, Knight- Ridder, Lockheed Martin, Loral, Mercer Processing, Palo Alto Unified School District, Regional Water Quality Control Plant, Sandoz, Southwall, Stanford Health Services, Syntex/P, oche, SyStemix, VA Hospital, Varian Associates, Watkins Johnson, the law offices of Wilson, Sonsini, Goodrich & P, osati, and Xerox PARC. These recent events have raised several issues regarding PG&E’s service to the City and our joint operating procedures. These issues are as follows: PG&E has implemented underfrequency and deep load shedding on their system that is more stringent than what the WSCC guidelines and the NCPA Interconnection Agreement stipulates. As stated earlier, the WSCC requires that 50% of our load be shed during severe underfi’equency events. Due to PG&E’s underfrequency relays, 100 % ofPalo Alto’s load is shed. The deep load shedding scheme that PG&E installed at Colorado Switching Station does not have adequate security. Operators at San Mateo Substation were unable to determine the condition of Colorado Switching Station because the power for the monitoring equipment is supplied from the City’s Colorado Substation which had no power. Communications with PG&E’s operators at San Mateo Substation needs to be improved. Meeting with PG&E A meeting with PG&E was scheduled immediately after these events. The meeting occurred on August 15, 1996. At the meeting, Palo Alto attendees included: Ed Mrizek, Larry Start, Tom Auzenne and Tomm Marshall while PG&E had 12 representatives which included the local Division Manager and representatives from a variety of departments. At the meeting, the City of Palo Alto indicated that it was concerned with the level of service reliability that it was receiving from PG&E and identified the issues described above. In response to our concerns the following joint actions were agreed upon at the meeting: PG&E and the City of Palo Alto will meet to jointly discuss and revise the City ofPalo Alto’s participation in PG&E’s load shedding plan. This meeting will work out the load shedding plan changes required to remove the underfrequency tripping on PG&E’s equipment. Discussions will also be undertaken to see if the City of Palo Alto can be eliminated from the deep shedding plan or its participation in the plan reduced. In the interim, the City is requesting that the PG&E’s load shedding relays be disabled. The City of Palo Alto and PG&E will jointly develop a new operating agreement or update any existing one. This agreement will have measures to improve communications with San Mateo Switching Station and establish operating procedures during emergency conditions. The City of Palo Alto will install an additional phone line dedicated to communications with San Mateo Substation. PG&E will develop proposals to limit the possibility of accidental trip of the 115 kV system serving the City of Palo Alto. In the interim, the existing transfer trip system will be disabled. The City of Palo Alto and PG&E must agree to a system that has adequate security and will not trip the entire city. PG&E will initiate work to install firm power to its monitoring equipment at Colorado Switching Station so that in the event of a loss of power it can continue to monitor the electrical system. Utilities Staff will keep the Utilities Advisory Commission informed as details of the preceding issues are resolved with PG&E. ATTACHMENTS Attachment A: Attachment B: Attachment C: Palo Alto Interconnection Diagram Description of WSCC Relay Settings for Automatic Underfrequency Load Shedding and Underfrequency Protective Relaying ENVIRONMENTAL ASSESSMENT None required Prepared by: Tomm Marshall, Electrical Engineering Manager Reviewed by: Larry Starr, Assistant Director, Engineering and Operations Approved by: Director of Utilities Attachment A SAN bIATEO COOLEY LANDING BAIR () COLOR~ 0 II5KV/60KV POWER STATION PG&E CPA, 60KV () ()SWITCHING STATION PALO ALTO IISKV NEWARK RAVENSWOOD CITY OF PALO ALTO ELECTRICAL INTERCONNECTION DIAGRAM Attachment B Description of WSCC Western Systems Coordinating Council (WSCC) was formed with the signing of the WSCC Agreement on August 14, 1967 by 40 electric power systems. Those "charter members" represented the electric power systems engaged in bulk power generation and/or transmission serving all or part of the 14 Western States and British Columbia, Canada. Membership in WSCC is voluntary and open to major transmission utilities, transmission dependent utilities, and independent power producers/marketers. In addition, affiliate membership is available for power brokers, environmental organizations, state and federal regulatory agencies, and any organization having an interest in the reliability of interconnected system operation or coordinated planning. The WSCC region encompasses a vast area of nearly 1.8 million square miles. It is the largest and most diverse of the nine regional councils of the North American Electric Reliability Council (NERC). WSCC’s service territory extends from Canada to Mexico. It includes the provinces of Alberta and British Columbia, the northern portion of Baja California, Mexico, and all or portions of the 14 western states in between. Transmission lines span long distances connecting the verdant Pacific Northwest with its abundant hydroelectric resources to the arid Southwest with its large coal-fired and nuclear resources. Due to the vastness and diverse characteristics of the region, WSCC’s members face unique challenges in coordinating the day-to-day interconnected system operation and the long-range planning needed to provide reliable and affordable electric service to more than 59 million people in WSCC’s service territory. WSCC member systems have long recognized the many benefits of interconnected system operation. During the mid 1960s, expansion of interconnecting transmission lines among systems in the western United States and western Canada resulted in the complete interconnection of the entire WSCC region. As this expansion was taking place, systems generally adopted the Operating Guides of the North American Power Systems Interconnection Committee (NAPSIC) to promote consistent operating practices within the region. NAPSIC later became the NEKC Operating Committee. WSCC and the eight other regional reliability councils were formed due to national concern regarding the reliability of the interconnected bulk power systems, the ability to operate these systems without widespread failures in electric service, and the need to foster the preservation of reliability through a formal organization. Today, over 25 years later, WSCC continues to provide the forum for its member systems to enhance communication, coordination, and cooperation -- all vital ingredients in planning and operating a reliable interconnected electric system Attachment C Relay Settings for Automatic Load Shedding and Underfrequency Protective Relayinq i.Pacific Gas and Electric Company Underfrequency Shedding and Tie Tripping Schedule Load .Frequency I~lay Fr~:iuency Applicable Hz ~Hz Recloslnq Footmo~es A-18 Intlrrupdble 59.75 6 Manual (g) Customers I=t 5% Block of Load 59.10 6 59.90 AutomaUc (s)(b)(d) 2nd 5% Block of Load 59.10 6 59.85 AutomaUc (s)(b)(d) 3rd 5% Block of Load 58.90 6 59.80 Automatic (a)(b)(d) 4th 5% Block of L~ad 58,90 6 59.70 Automatic (a)(b)(d) 5th 5% Block of Load 58.70 6 59,65 AutomaUc (a)(b)(d) 6th 5% Block of Load 58.70 6 59.60 Automatic (a)(b)(d) 7th 5% Block of Load 58.50 6 59.55 AutomaUc (a)(b) 8th 5% Block of Load 58.50 6 59.50 Automatic (a)(b) ~ 5% Block of Load 58.30 20 59.40 Automatic (e)(d) 10th 5% Block of Load 58.30 26 ¯59.40 Automatic (e)(d) Round Mountain Tie 58.20 60 Manual By System (a) Lines Dispatcher Midway 13e Unes 58.20 6 Manual By System (a) Dispatcher Separate Thermal 55.00 30 Manual (f~ Plants cycles 57.00 1 minute 58.00 3 minutes