Abstrect-Emergency conditions arising due to generatingUFLS is common practice for electric utilities around power deficiency and the consequent drop in power sys-the world [l-51. WL!I uses under-frequency relays tem frequency can lead to system collapse and a large (sometimes equipped with time delays) to drop loads as the scale loss of load. Underfrequency load shedding (UFLS) frequency drops. Depending on the philosophy and the needs is a globally accepted practice to handle this situation. of the power company, the: number of frequ,ency steps varies Most UFLS schemes use pre-specified step sizes based from two to f&een [6]. Tlzis basic technique has not appreupon frequency measurements. This paper presents an ciably changed since its inception more that 50 years ago. adaptive scheme which uses both frequency and rate-ofFor an UFLS system to be most effeclive, the location change of frequency measurements to dynamically set and magnitude of all generation and loads is needed. Unfor-UFLS relays if more than one generation outage is experi-tunately, there is not enough time to obtain this information enced. It then proposes a technique for coordinating in an underfrequency emergency 271. Both generation and UFLS and the activation of spinning reserves through load profiles are constantly changing (due io load shedding, localized governor control. Recent developments in com-changing generator set points, and generator outages) yet puter based frequency and rate-of-change of frequency underfrequency relays have a single set point for all scenarrelays makes this scheme both feasible and attractive.ios. A need exists to develop an adaptive UFLS system which can customize underfrequency relay set points in response to Recent efforts to improve UFLS use the rate of change A sudden loss of generation, causing a mismatch be-of frequency, dydt, as an additional control variable [6-91. tween energy supplied and energy demanded, will result in a These methods shed load when dydt is greater than a pre-set system frequency drop. If governor action cannot activate value. Anderson et. al. [SI1 presents a more sophisticated apspinning reserve quickly enough to restore the system to its proach which determines the amount of load to be shed based normal operating frequency, underfrequency load shedding on frequency, df/ddt, and ihe inertia constant system. These (UnS) serves as a last-resort tool to prevent the system from methods are a more advanced approach to UFLS but do not collapse. account for the constantly changing generatiodload characteristics of the system. For example, the inertia constant is perpetually changing as the amount of load connected to each UFLS relay varies from hour to hour. A recent paper [9] sug- 96A paper recommended and approved by the IEEE Power system Engineering Committee of the IEEE Power Engineering 25, 1996, Baltimore, MD. Manuscript submitted July 31, 1995; made plants using power flow results. This paper and others [loavailable for printing January 15, 1996. ll] show that UFLS can be improved...
Paper considers development trends and perspectives for widespread implementation of distributed generation, based on renewable energy sources (RES) in the Baltic States. The main issue of the research is integration of RES into the power grid and electricity markets. Paper provides an overview of legislative statements and main rules, which regulates formal relationships between power producers using RES and network operators. Major problems and barriers that limit intensive development of RES are identified and possible solutions to overcome them are proposed. Index Terms--renewable energy sources (RES), distributed generation (DG), distributed energy sources (DER), grid and market integration.
Paper considers common issues of emergency automation preventing power system stability disturbance. Emergency automation operating on new principle during real emergency time calculates the value of necessary power impact dose on power system to prevent the stability disturbance. As a result improves the control efficiency of emergency conditions. In paper some examples of emergency conditions under different modes of disturbances and location of emergency control are performed.
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