Article Summary and Analysis: A Mal-Trip in the Peruvian Power System
Article Summary and Analysis: A Mal-Trip in the Peruvian Power System
Distance transmission line protection is important in the modern environment where extra high transmissions are commonplace. Distance relays are vital in securing these transmissions. Much consideration is required when designing and installing transmission line protection systems to avoid possible mishaps similar to the case of Peru by Jacome and Henville (2001). This paper presents a summary and an analysis of this case.
In his informative and educative article, Jacome and Henville (2001) observed that distance delays are vital in transmission line protection and may be set on the simple but often sufficient approach of percentages of the line impedances. They vary in type from mho to quadrilateral among others, both requiring additional care for varied reasons. Where parallel lines feature, they complicate the situation as well and necessitate additional considerations in the relay setting.
The Peruvian power System experienced a mal-trip of a distance relay in a poorly designed setting. Jacome and Henville (2001) observed that a single fault to ground in a sub-transmission line L-111 in the system, which employed two protection mechanisms: mho and ground distance relay. A distance relay of the circuit L-2215, constituting a line that forms a major connection between North and South-Center Peru, detected the fault. As a consequence, the North area experienced a blackout.
A time delay in this transmission line prolonged the clearing of the single phase-to-ground fault by the protection of line L-111. The reason was that the mho characteristic of the affected distance relay was not sensitive enough. A test re-energizing of circuit L-1111 after the disturbance revealed that a power swing emanating from the fault that was not cleared in time and together with certain flow conditions through the near stability-limit line L-2215 led to the operation of Zone 1 of the protection relay at Paramonga L-2255 Southern Sub-station. Additionally, a failure to simulate resistance faults in Chimbote Substation, which are necessary to validate the appropriateness of the percentages of the impedance approach that was in use also contributed to the mishap.
A maximum allowable resistive reach of 94Ω was determined using various power flow scenarios to first establish the maximum power flow through the lines and using it to compute the minimum load impedance, and then deriving the maximum allowable resistive reach as a percentage of the minimum load. Using the Warrington Formulation, the maximum allowable resistive reach was checked with the resistive reach under different arch resistance levels. A simulation that involved Zone 1 reaction time, phase-to-phase and phase-to-ground fault showed that a 35Ω resistive reach for phase-to-phase faults sensitive enough. Like other parallel lines, the settings of the phase-to-ground elements in the case were influenced mutual coupling determined through formulas. A simulation of a fault in Chimbote Sub-station under different states of the parallel line was conducted to check the reactive reach of the Zone 1 ground distance. This result favored a reduction of Zone 1 to 84Ω.
A reduction in time and resistive reach of Zone 2 was necessary to avoid an operating fault in Chimbote 138kV with the parallel lines out of service. This necessitated the creation of Zone 3 to foster dependence on the setting by detecting faults that Zone 2 would not due to the reduced. A tele-protection Zone within Zone 3 was also instituted to improve dependence. Jacome and Henville concluded that software tools are important in transmission line protection and engineers should use all the options they offer to validate settings. Settings based on percentages of the line should necessarily be checked by simulating faults. The various options of power system protection available are equally viable and can be very helpful if collectively considered.
Power system protection is vital in this era of ever extra high voltage transmission due to the ever growing demand for power across the globe. It is essential to ensure that transmission lines are secure and provide a stable supply of power that can be depended on. The role of power protection systems is underscored in the Peruvian case discussed by Jacome and Henville (2001). Engineers should strive to install robust power protection systems that can be relied upon in both aspects of security and stability of supply. Many issues revolve around these two elements of a robust power protection system as discussed to different extends in Jacome and Henville’s work.
The Peruvian case indicates the need to carefully plan and approach the processes involved in installing power protection systems, specifically distance relay systems. Potential hazards that can result from faults in distance transmission can be catastrophic. This calls for utmost care when dealing with the issue, which was is not evident in the case of the Peru fault. Jacome and Henville observed that there were conspicuous weaknesses in the setting that led to acute power shortages in North Peru (2001, p. 4). One major weakness was the failure to simulate the resistive faults in Chimbote 138kV to identify other factors that could affect the setting’s reliability (Jacome & Henville, p. 4). This is an important necessity of the installation process because a failure can be detrimental. Some of the devices used in the setting that was responsible for detecting the fault were not fit and compromised the entire relay setting. They noted that the mho element in the setting was not sensitive enough. This is probably due to the fact that the affected engineers did not carry out periodic checks on the distance relay setting to ensure that all elements were fit.
The improvements effected on the setting in the case study were quite effective. The use of three Zones, with a tele-protection Zone within the Zone 3 was rational. The reduction of the reach of Zone 1 to 84Ω from 94 Ω was important in avoiding non-selective tripping that would result from measurement error (ABB, 2008). By reducing Zone 2 reach as well, the setting was improved in the sense that it would then be able to avoid a trip in Chimbote 138kV with the parallel line out of service. The outcome, Zone 3, was very important because it would detect a fault that Zone 2 would not after the reduction. This ensured that the setting became dependable to a high degree. Equally important was the additional Zone 3 that acts as back up and can serve more than one purpose (cite). This is illustrated by the inclusion of the tele-zone in this Zone.
Structure analysis
Jacome and Henville (2001) presented their work in clearly labeled sections that include an abstract besides an introduction, a body section and a conclusion. In the abstract, they gave a succinct overview of the general idea discussed in the paper. This helps the reader to get a quick insight into the paper. In the introduction, he directly points out the possible audience for his work by referring to the educational perspective. The body is also organized into subsections that facilitate the understanding of the paper.
The ideas in the article have been organized in a coherent manner, chronologically exploring the events that happened in the case. Jacome and Henville (2001) begin by describing the problem that faced the Peruvian Power System in the first sub-section of the body before giving an account of the steps that were taken to solve the problem. This arrangement enhances a smooth flow of the main ideas, as well as their understanding. The second subsection of the body provides information regarding the measures that were taken after the problem had occurred, directed at solving it. The action steps are explored step-wise in the order in which they occurred and numbered successively. Jacome and Henville (2001) successively accounts for the processes undertaken in determining the best possible solution for every scenario.
The article also uses multiple graphs labeled sequentially to assist in presentation of ideas. These graphs are labeled clearly up to Figure 14 and appear next to the explanation regarding them. The labels and positioning make it easy to identify and link the graphs and text. The graphs offer the finer details of the processes and events that are otherwise not sufficiently provided verbally. The use of graphics also enhances the understanding of the information in the article. With the help of these graphics, Jacome and Henville (2001) were able to add a lot of information to his work but still remain precise.
The abstract and the introduction and a small section of the body are presented in prose. A larger part of the body and conclusion, on the contrary, are numbered. The numbering approach in the body and conclusion facilitate comprehension of the ideas and enable enabling the writer to be as precise as possible. The conclusion contains six different points to stress the main ideas encountered in the paper. This rap up encourages the reader to recall the informational and educational aspects of the paper as identified by the author. It would be challenging if every reader tried to infer the major points from the body of the paper had the author not given them outright.
The importance of a robust transmission line protection system has been underscored in Jacome and Henville work (2001), as well as the analysis above. Considerations for both the security aspect and the reliability factor should be incorporated in designing and implementing a relay setting up front. These are necessary proactive measures that can prevent possible hazards. Engineers should be committed to delivering viable settings that match the high power transmission demands of this era.
References
ABB (2008). Distance Protection. Ref 542plus. Retrieved from http://www05.abb.com/global/scot/scot229.nsf/veritydisplay/602e9601f9afb4f2c1257520002ca2d8/$file/appl_ref542plus_distance%20protection_756605_ena.pdf
Jacome, Y. & Henville, F. C. (2001). An Example Distance Protection Application with Complicating Factors. Western protective Relay Conference 2009.
