POTENTIAL BENEFITS OF SHUNT REACTIVE COMPENSATION TO IMPROVE GENERATION STATION PERFORMANCE

摘要

With the increasing stress on powerrnsystems, generating stations in critical locations can findrntheir operation constrained due to heavy reactive powerrnloading. This paper describes the potential performancernbenefits that can be realized by the application of shuntrnreactive compensation in conjunction with a conventionalrngenerator, to allow the generator to increase its powerrnoutput.rnRapid change in system reactive power requirements,rnincluding the dynamic swings resulting from a systemrnupset, means that rapidly and continuously variable varrnsources are required. This means that the dynamic reactivernpower resources of the generators must be kept in reservernduring normal operating conditions, so that they arernavailable during and following system disturbances. Therernexists considerable opportunity to create this reserve,rnthereby improving network security and power transferrnlimits, by using mechanically-switched shunt capacitorsrn(MSCs) with automatic control.rnThe automatic control of MSCs can be made secure byrnrecognizing the temporal characteristics of the powerrnsystem after a severe contingency. There are two keyrnaspects to consider:rn1. Loads will initially decrease after a contingency duernto their inherent voltage sensitivity. The loads willrnrecover gradually over several tens of seconds asrnload-tap-changing voltage regulators perform theirrnfunctions.rn2. Generators inherently possess considerable overloadrncapability (as dictated by ANSI standard C50.13).rnWith proper control and protection, this overloadrncapacity can be relied upon to support the voltagernfor many tens of seconds after an event.rnBoth of these characteristics allow for many seconds inrnwhich to make decisions regarding capacitor switching.rnWhile too fast for reliable operator-actuated response, thisrnis a generous time for automatic control. Thus, the schemerncan be made very secure with proper design.rnFigure 1. shows the dynamic response of an example fromrnthe Tennessee Valley Authority (TVA) system. In thatrnfigure, the traces show key system variables from one unitrnof a critically important generating station following arndisturbance. The solid traces show the behavior of thernsystem when augmented with MSCs (which can be seen tornswitch at 1 and 5 seconds). This relatively simplernenhancement allows the system to meet specified voltagernresponse criteria, and allows an extra 20 MW to berndispatched from the station.rnRegardless of the nature of the active power outputrnconstraint, relieving those constraints can result in morerneconomic operation of the generator. The value of thernincreased power output will be a function of the marginalrnprice of that power, with higher marginal price providingrnbetter value for the investment in the shunt compensation.rnIn the example system, payback for the capital investment,rnon this basis alone, is one to two years.