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POWER ENGINEERS SUPPORTING TRUTH
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BASIC WEAKNESSES IN THE TRANSMISSION SYSTEM on AUGUST 14, 2003 VOLTAGE SUPPORT Prepared by F. Delea, R.M. Maliszewski, J.A. Casazza, and G. Loehr Members Power Engineers Supporting Truth January 6, 2004 The Interim Report on the Blackout alleges that cascading of the transmission system was not a classic case of voltage collapse (page 63), but nevertheless, the report cites many references to low voltages and operator actions to correct this situation (pages 18, 19, 23, 24). In fact, the action at the Eastlake #5 to increase reactive output to support low voltages resulted in its trip-out, further exacerbating a sagging voltage condition in the First Energy load area (page 24). The report also states that voltage was a factor in some of the events that led to the ultimate cascading of the system in Ohio (page 63). The trip-out of Eastlake #5 increased MW line flows on the heavily loaded transmission lines into the Cleveland - Akron load area, increased reactive power flows into this area from other parts of the system and further aggravated an already deteriorating voltage situation in this area. This deteriorating condition was further exacerbated by the subsequent tripping of the 345-kV transmission lines serving the northern Ohio load area and contributed to the subsequent tripping of the many 138-kV transmission lines in northern Ohio due to the operation of 3rd zone relaying (page 50). Notwithstanding the basic contention in the Interim Report that voltage was not a root cause of the blackout, all evidence available strongly suggests that deteriorating voltage conditions were a major contributor to the many events leading up to the cascading of the transmission system in northern Ohio and the ultimate blackout in many areas. This raises a serious concern as to whether the importance of adequate reactive supply and good voltage support is adequately being addressed by the industry, the reliability councils and the regulator. Reactive power supply too often has been given little attention in the design and operation of the transmission system in the goal to maximize the use of transmission for the transfer of power (MW). It must be recognized in the operation of any transmission network that there is an intrinsic relationship between the ability of the network to transfer power (MW) and reactive supply located throughout the network so that adequate voltage levels can be maintained under all expected operating conditions. It is in view of these concerns, that the authors believe any final report on the August 14 Blackout must address the crucial issue of providing adequate voltage support on the transmission network. In this regard, the following points should be considered A. The industry needs to establish a coordinated and consistent voltage criteria for the operation of the transmission grid reflecting the transmission and generation facilities in service and the power transfers expected. The criteria should include the allowable voltage gradient across the grid as well as allowable voltage drops at any transmission station following a contingency. The industry also should address the requirement for maintaining adequate reactive reserves in the event of unanticipated outages. B. Reactive power cannot be efficiently transmitted across the transmission system without causing reduced voltages. Therefore sufficient reactive supply needs to be installed throughout the system and especially near customer load centers to minimize the flow of reactive power across the transmission system at the required levels of real power transfer. C. In planning the reactive supply to maintain adequate voltage levels during all expected operating conditions, systems should give consideration to the installation of automatic under-voltage load shedding to provide a means of controlling voltages for unexpected extreme system emergencies. D. It must be recognized that the true rating of any piece of transmission equipment is its current carrying capability and that ratings in terms of MW or MVA can give a false indication of the true capability due to the influence of voltage. Therefore, transmission line ratings should be expressed and monitored in terms of amperes. E. Acceptable voltage at key transmission stations should be specified by every transmission operator and communicated to all affected operational entities. F. The daily and hourly security analyses of the transmission system carried out at the control center and ISO/RTO are usually based on simplified linear load flow techniques. These analyses should be expanded to explicitly consider voltage conditions on the system. In addition, such security analyses should take into account the de-rating or unavailability of reactive sources. G. An industry wide effort should be made to better define the load power factor (reactive power component of the load) used in planning and operational analysis studies. This effort should include regular benchmarking of system models to actual system conditions. H. Generator MVAR capabilities should be regularly audited and be available to both the operators on duty and used in the operational studies to establish safe operating limits. I. Information on actual generator MVAR capabilities versus MW loading levels should be available to the operators at the control centers as well as the ISO/RTO or Regional Reliability Coordinator. J. Approval of IPP contracts by responsible authorities should require that the contract contain specific directions regarding the supply of reactive power by the IPP in the event of an emergency condition on the transmission system. K. Operator responses to low system voltage should be pre-determined and provision made at control centers to rapidly implement any corrective actions. Such information should also be available to the RTO. |
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To participate in Pest activities contact: Jack Casazza |