Pilot and Non-Pilot Protection of Transmission Lines - Essay Example

Pilot and Non-Pilot Protection of Transmission Lines al Affiliation Introduction Engineers have already identified the drawbacks related to non-pilot protection. As a remedy, there has been the development of pilot protection measures. The pilot system operate by sending information using communication tools linked to the remote relay terminal on one side and to the local rely terminal on the other side. The use of the pilot system will allow fault tripping at high speeds and with a 100% guarantee of the used line (Taylor, 1927). In this research paper I would not want to dwell much on the differences between the pilot and non-pilot system but rather on the circumstance under which the pilot system should be used in the protection of the transmission line. This is of course in addition to today’s independent systems. It is important to note that the emphasis in this paper is not on the pilot scheme to be used but rather on whether a pilot system would be necessary. This follows the realization that a typical pilot terminal would cost $150K more compared with a non-pilot terminal. The question in this case is why would someone spend so much on a pilot scheme rather than just take up a non-pilot system which is less costly? The answers to this question serve as the justifications for the pilot scheme. Taylor (1927) says that the pilot scheme come in with additional benefits such as improved resistive coverage, high speed reclosing, and improved sustainability compared with the non-pilot system. In addition, the pilot scheme comes with alternatives to protection including fall back strategies, extensions to Zone 1, and inverse time over current. The pilot system also provides extended considerations mainly used in the determination of the system’s redundancy usually dependent on a number of factors including security, reliability, and dependability. The pilot system is also preferred because of its free interactions with the regulatory issues (Taylor, 1927). 2. Circuit Diagram and Operation The protection of a transmission line has been a unique concept in the sense that, the system’s zone limit will have to separate geographical locations. This is contrary to the concepts in other systems such as buses, capacitors, and transformers. The idea behind the transmission line protection system is the alignment of the system elements and the input devices in one location and provides room for the instantaneous configuration of tripping. With the pilot scheme, this is usually done with very little coordination problems (Kim, 1996). Following the alignment of the system elements and input sources, all terminals will be interconnected for easy communication with each other allowing easy communication and 100% tripping at very high speeds in the transmission line. The above is a diagram showing a step distance protection scheme. This is a form of pilot protection with line terminals and directional units. 2.1 Selectivity of the Protective Pilot System According to Kim (1996) the selectivity of the pilot system shown here above is based on the measurement and evaluation of the signals at one or all boundaries. The dependent factor in this case is the alignment of protective relays with the aim of identifying the discrimination factor between faults categorized as either out-of-zone or in-of-zone. For the case of our pilot system scheme here above there has been the implementation of a scheme with a time controlled stepped distance with the work of providing clearances of up to 62% of faults found internally. This however comes with the assumption that the average Zone 1 setting takes up to 75% of the transmission line. The remaining 38% of the faults will be eliminated through a protected time delay, usually done in a period between 0.3 and 0.6 seconds (Kim, 1996). 2.2 High Speed Fault Clearing The high speed fault clearing characteristic is one of the major advantages of the pilot scheme. Going through the pilot scheme shown in the diagram above, it is clear that the high speed clearing fault is provided in the entire line (Kim, 1996). The only delays expected with such a scheme are only those related to the data of communication from one terminal to the other. In many transmission schemes, the delay will not go past two cycles, which is typically close to zero. Here, the pilot scheme calls for the introduction of a communication medium in the case of geographical dispersion of the zone boundaries. The communication medium will help in the bringing together of all measurements taken from terminals in all lines. Since the strength of the used communication channel may be inhibited by the applied scheme of communication-aided protection, there will be the use of exchangeable signals. The exchangeable signals used can either be binary or analogue, based on the specific type of pilot system used (Kim, 1996). 2.3 Use of the “Unit Protection Scheme” According to Fernando (1997) the unit protection scheme is a practice where a system uses continuous or analog signals in transmission. The process also includes a form of a pilot current differential where there is the integration with a microprocessor or given analogue scheme on a digital communication platform. A system using discrete or binary signal is on the other hand referred to as a “pilot assisted scheme” or a “non-unit protection scheme”. The operation of the analog system is that there is the use analog information that is later interpreted to binary digits for easy interpretation and communication to the boundary in the remote zone. The communication in this process is usually conducted through the help of a signal that is single in binary. At this point, the pilot scheme will need a “permissive scheme” that will assist in the reporting of the faults present in the in-zone. The pilot system in this case may also call for a “blocking scheme” that will assist in reporting cases of “no faults” or cases of “out-of zone faults” (Fernando, 1997). 2.4 Encoding Continuous Information A pilot scheme has the capability to monitor, measure, and encode continuous information, a practice that is not possible with other transmission protection measures. A pilot system uses binary signals in the evaluation and encoding of phase relays information attributed to the boundaries in the zones and current phases. Typically, there is usually a time coincidence in the binary signal emanating from the exchange between the relays of comparison in the interpretation of analog information, usually in an angular direction. Once this is done, there will be the development of a phase comparison scheme mainly defined as a “unit protection scheme” (Fernando, 1997). The pilot scheme shown in the diagram above takes into consideration a binary concept and an analog measurement that assist in the transmission of signals towards the measurement process. The same logic concept is used in the tripping of responses, mainly from the received and local measurements. The close coordination of the binary signal and the measurement process facilitates easy encoding. 2.5 Operation and Use of the Pilot Assisted Schemes The pilot assisted scheme come in three major classifications including a pilot-wire protection, a directional comparison, and a phase comparison. This is from a measurement viewpoint. If we move further to the trip and transmit log viewpoint, pilot assisted schemes would fall under the following categories; line current differential, under reaching transfer trip, both blocking and unblocking directional comparisons and other elements. Hybrid Combinations: When implementing hybrid combinations in our pilot scheme here above, the focus is on having the combinations in both the enhancements, logic and measurement parts. When referring to the enhancement part, the focus is on elements such as echo logic, weak feed, zone acceleration or current reversal. All these elements brought together promote the easier functioning of the transmission line (Waste Isolation Pilot Plant (N.M.), United States., Westinghouse, & USDOE Office of Nuclear Energy, Science and Technology (NE) (US), 2002). Having explained the operation of the pilot circuit diagram, the discussion will now shift to the examples on practical application. However, there are a few things that need to be noted before putting the pilot scheme to full applications. First relates to channel redundancy where the flexible the system, the higher the chances of success in protecting transmission line. Second is the desired response of the scheme, especially in the case of loss of channel. The response from the pilot circuit diagram will mainly be influenced by the initial processes and devices, hence the need to set the right scheme in the first place. Third is the communication path routing that will mainly influence the applicability of the pilot circuit device (Fernando, 1997). 3. Examples on Practical Applications Having explained the operation of a pilot scheme, it is now the time to explain how practically the scheme may be used in an organization setup. When examining the need for a pilot protection on a transmission line, there is the need to know the distinction between means and goals. Typically, improving stability can be seen as the goal, while the time taken in clearing a short fault comes out as the means of attaining that specific goal (In Arnaout, & In Slavin, 2013). His follows the understanding that a pilot scheme will not cut down the time taken to clear faults in transmissions in vain, but would cut down the time to either improve the quality of power, reduce the damage on equipments, and improve the stability of the specific operational device. 3.1 Generator Angular Stability in TRANSCO An angular stability is so much needed in the transmission of “real” power all over a power system. In TRANSCO’s power department angular stability, from a pilot protection scheme would be of great help in the transfer and saving of power through the following equation. With the use of a pilot protective scheme, it will be possible to add more transmitted power all over the entire power system by simply adjusting the equivalent sources from the sending end and the receiving end. The equation is primarily affected by two major influences including the angle and the voltage drop. In consideration of the strength of the sending and receiving end, there will be precedence in the voltage drop at the first 200 miles of line and the involved angle. In essence, the use a pilot protective scheme adds more stability to the power system compared with other transmission devices such as capacitors. In a well assembled pilot protective system the maximum that can be loaded in a transmission line is about 45 degrees. This represents the maximum across the line in consideration of the impedances in the sending and receiving terminal. The underlying argument in this case is that the transmission line will be loaded with up to 35 degrees in electrical. In the event that a fault in the system occurs, the system’s angle will increase, even to past 90 degrees. This is where the forces of restoration in a pilot system assist in bringing the power system to 90 degrees or below. The pilot system will also help protect unfaulted lines by monitoring to see whether it enters or do not enter the tripping zone. In the situation that the faulted line is tripped, the angle of the unfaulted line will increase as the voltage drops (In Arnaout, & In Slavin, 2013). 3.2 Cascading Purposes in a Sewage Plant Most sewerage firms are usually concerned of the result of cascading exercises in an effort to see to it that water being disposed cannot harm human beings or animals. To a sewerage firms, cascading is a process where water is poured rapidly and huge amounts. In the cascading process protected relays, usually marked by their “levels” work through the derivation of quantity going past the set threshold (In Arnaout, & In Slavin, 2013). The success of the process is usually highly determined by the functioning of the protected zones, found by calculating the fault level. The engineer’s experience and exposure to the surrounding of the power system also play a big role in the success of the cascading exercise. A tradeoff between sustainability and security is seen following the setting up of an open zone protection system. Various elements schemes of stepped distances are usually organized in a cascading style. This is important in the handling of risks related to cascading failures, and especially in situations where overreaching time coordinated distance zones are put to use. The underlying argument is that there is the likelihood of triggered chain of events following a fault on the power system. If such a fault is experienced, the overreaching distance elements will trip thus the contents cascading to big geographical areas leading to the failure of the power system. Where there are serious cascading issues, the organization may implement unique pilot schemes that are immune to power swings. Following the implementation of unique pilot schemes will be the justification of overloading tactic with differential overreaching schemes and relays (In Arnaout, & In Slavin, 2013). 3.3 Limiting Fault Damage in a Cement Factory Most factories need extensively high voltages to run their activities. With such high voltages a fault on the current will definitely lead to huge damages. The pilot protective scheme comes to offer a remedy in such situations. To start with, a pilot scheme comes in with tools to be used by the protection engineer in the determination of the type of protection needed to minimize or completely mitigate damage. A good example in this case is the transformer that has been provided in form of fault damage curve. This acts as a guide to protections regarding power transformers. At the same time, there is the representation of damage curves mainly used in thermal control and insulation in conductors (Geo-Frontiers & Alzamora, 2011). In the determination of the heating effect, an engineer will examine the proportionality in the time taken for the current to flow through a conductor (I-squared) and the current squared. From these results, engineers can draw a thermal damage curve for conductors. In addition, manufacturers may also use the time the current takes to flow through a conductor (I squared) in the development of insulation devices or any other component that may be used in the termination of conductors. It is important to note that short circuit conductor damage may occur in two different ways including annealing and burn-down (Geo-Frontiers & Alzamora, 2011).Annealing is seen as a process where a wire is completely weakened following the flow of short-circuits current. This leads to the damage of the entire wire, making the power operations of the cement factory impossible. The other way is the burn-down where a conductor breaks following the extended heating of the arc generated following the high resistance of the connection. The same case will also be seen in the situation where a poor splice is used leading to the increase in conductor damage in both duration and magnitude. In such a case, a pilot preventive scheme tends to clear faults thus reducing burn-downs. The common pilot scheme has also been built with large conductors, as opposed to small wires making the situation even better. Small wires tend to burn more readily than large conductors. 3.4 High Speed Reclosing AADC A company in the category of AADC will need an exaggeratedly high speed reclosing where, in the absence of faults, electrical power equates to the mechanical power. In the occurrence of a fault there will be an imbalance in the equilibrium and this will be transmitted to the acceleration of the synchronous machines. Following the acceleration, the acceleration power will be the same as the difference between mechanical power and the electrical power as shown in the equation here below. For the electrical angle, there will be direct proportionality between accelerating power and the electrical angle at the opposite side of the line which is being protected. The electrical angle at the opposite side of the line which is being protected will on the other hand be inversely proportional to the equivalent system’s inertia (Geo-Frontiers & Alzamora, 2011). From this observation an engineer at AADC may want to make conclusions from the change in the electrical angle in regard to the stability limit angle which will be used in the dictation of the critical fault. Having identified the critical fault, I will now be the time to determine the time needed for the clearing fault using the pilot protective scheme for the specific protected line. At this time, the pilot scheme will also be monitoring the reclosing speed purposely for synchronism in the seeking of a balance between the fault path and requirement needed in the de-ionization of the whole power system (Taylor, 1927). 4. Reflections and Feedback As explained here above, there are a number of issued that justify the implementation and use of a pilot scheme in the protection of a transmission line. Thinking creatively there is the realization that there are many technical reasons whereby transmission line out there needs high-speed clearing. An additional study and research is still needed in the causes and drivers of these issues as a way of determination the full-time need of the pilot protection scheme. The additional research should also accommodate the various considerations in the uses of communication paths as this will provide more justification for the permit and implementation of the pilot protection (Taylor, 1927). The implementation of the pilot scheme will not be the end of the road for research on the pilot scheme as there is need for the determination of other general requirements including the effect of relay and breaker maintenance on the pilot scheme and the operation of the line in the absence of pilot protection. A thorough analysis like the one done above on pilot protective scheme would not operate well without incorporating the economic implications in the mix. Including the economic implications in the mix will provide a unique platform where a comprehensive review of the protection of the transmission line can be done for both old and new transmissions (Taylor, 1927). The research will also help pre-determine the effect of upgrading the available transmission lines. References Fernando, I. T. (1997). Protection of transmission lines sharing the same right-of-way. Geo-Frontiers (Conference), Han, J., & Alzamora, D. A. (2011). Geo-Frontiers 2011: Advances in geotechnical engineering. Reston, VA: American Society of Civil Engineers. In Arnaout, S., & In Slavin, L. M. (2013). Pipelines 2013: Pipelines and Trenchless Construction and Renewals--A Global Perspective. Place of publication not identified: American Society of Civil Engineers. Kim, B. B. (1996). Current differential protection of transmission lines. Taylor, W. T. (1927). Overhead electric power transmission engineering: A treatise on design, construction, operation, protection, and maintenance of overhead electric transmission lines. London: Griffin. Waste Isolation Pilot Plant (N.M.), United States., Westinghouse, T. R. U. S. I., & USDOE Office of Nuclear Energy, Science and Technology (NE) (US). (2002). Waste Isolation Pilot Plant 2001 Site Environmental Report. Carlsbad, N.M: Waste Isolation Pilot Plant (N.M. Read More