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Technological Advance in Relay Protection: Dangerous Tendencies
1.1 Issues of Philosophy in Relay Protection
Philosophy beginning with the ancient Greeks is literally âa love of wisdomâ and deals with the most general issues of reality. The Wikipedia terms philosophy as a science which studies everything. Logic and critical analysis are the pillars of philosophic thinking. So why donât we use these attributes of philosophy to analyze the situation around relay protection (RP)? It appears that such analysis may result in counterintuitive findings (Figure 1.1).
The life of a modern person is closely related to the use of complex and interconnected systems such as cellular communication, television (TV), radio, and electric systems. All these systems can be visualized as a so-called âconsumer chainâ that consists of series of links. The last link in this chain, that is, the one that directly interacts with a person, would be a certain apparatus (terminal): cellular phone, TV, radio receiver, refrigerator, washing machine, etc. The aspiration to improve the last link (in other words, the one that actually interacts with a person) and make it perfect, even though all other links may be far away from perfection, is clear and justified. A special design of a TV set, its user-friendliness, and special functions (such as record and playback telecasts according to a specific schedule, playback CDs, and split screen that allows having a main screen and a series of auxiliary screens, making it possible to watch several channels simultaneously) add significant value to such a TV set from the standpoint of the consumer, regardless the fact that this TV set is only a final link in a long chain called television. It does not mean that the quality of TV programs or the quality of broadcasting will be of the same quality (perfect) as the final link. However, this doesnât prevent a rich consumer from investing in an expensive (perfect) final link. Likewise, poorer consumers do not stop dreaming about this perfect final link. Thus, the final link in different consumer chains has a special status, and certain requirements and attention are accorded to it by both consumers and manufacturers. On the other hand, regardless of the perfection of the final link, it cannot influence the quality or reliability of the chain in general. Indeed, a broken TV set in one of the rooms in the consumerâs house will not influence the operation of TV sets in other rooms or the neighborsâ TV sets.
FIGURE 1.1
Philosophy in RP.
Another feature of the final link of the aforementioned consumer chains is the applying of customer requirements to functionality and design beyond the requirements of reliability and longevity. This is conditioned by modern trends, when substitution of one final link by the other has not much to do with malfunctioning or breakage, but with technological obsolescence and the emergence on the market of new models with better functions and improved design.
Now, let us compare this situation with what happens in RP, which is the most important component of a consumer power supply circuit that consists of a series of links called production, transmission, and distribution of electric energy. Where is the place of RP in this circuit? Surprisingly, there is no such link in this chain! Indeed, RP neither participates nor influences the operation of the circuit under normal mode of consumer chain operation. RP does not influence the amount of produced energy. Nor does it influence the capacity of energy transmitting lines or the process of energy distribution. RP can even be disconnected from energy supply circuit, and there will be no effect on the circuitâs operation. So what is RP and where is its place in energy transmission and distribution circuit? Visually RP can be depicted in this chain as a set of separate auxiliary links installed in the places of connection of main links of the energy supply circuit, that is, production, transmission, and distribution of electric energy (Figure 1.2).
FIGURE 1.2
Visualization of a consumer chain of power supply equipped with RP.
Functionally, these places of connection are formed by high-voltage (HV) switches, the condition of which is determined by RP. In other words, even though RP is not a series link in the power supply circuit, it can influence the connectors between the links (by circuit breakers) by cutting the ties between all the links of this chain. This is a fundamental difference of RP from other links in consumer chains.
If RP does not influence the power supply circuit under its normal mode of operation, does it have any effect under the emergency mode? It is widely perceived that this influence consists in the prevention of emergency modes in the power supply circuit. Is this really so? To answer this question, we need to understand what RP is and what its functions are. Let us review publication [1], which provides a detailed analysis of this issue based on which we obtain such concepts as âprotective relayâ and âRPâ:
Protective relay is a device, the purpose of which is to detect the emergency mode of the object being protected and send a command to a power control element, which eliminates this mode.
A system of relay protection is an aggregate of related devices, which ensure detect of the emergency mode in the operation of electric equipment and its elimination.
These definitions show that regardless of the widespread opinion that an RP cannot prevent the emergency mode in a power supply circuit, it can limit the scale of its effect on this circuit in time and space, in other words, limit the material damage from the breakdown and nothing more.
Everything said earlier is related to a properly functioning RP and its correct operation. But as many other complex technical devices, RP can also malfunction. This creates an absolutely different situation, where a malfunctioning RP due to a so-called âunnecessary protection operationâ can send a faulty command to open a circuit breaker (in other words, break ties between the links of a power supply circuit), thus creating an artificial prevention of normal functioning of a power supply circuit, that is, its switching to an abnormal, emergency mode, leading to the disconnection of thousands of consumers and great damage.
This makes us conclude that RP cannot prevent an emergency mode of operation of a power supply circuit, but it can cause this mode.
Recently, significant qualitative changes have happened in the field of RP. Single-function electromechanical protection relays (EMRs) have been replaced by multifunctional digital protective relays (DPRs) with much higher qualitative characteristics and easily programmable logic. How does perfection of characteristics and improved functional capabilities of the new protection relays influence the operation of power supply circuit? As mentioned earlier, there is no influence under the normal mode of operation. However, in the case of emergency mode in the circuit, the DPR can efficiently limit its effect in time and space due to their improved characteristics; in other words, they are more effective in limiting the material damage than EMRs.
At the same time, it is known [2] that DPRs are less reliable than EMRs (we are talking about the best electromechanical relays manufactured by the leading Western companies). Their lifetime does not exceed 15â20 years. They are more susceptible to destructive external impacts, such as cyber attacks or intentional electromagnetic impact. A lot of functions in one terminal, some additional functions of DPR not specific to RP, and mistakes of staff during free programming of logics reduce reliability of RP even further and increase the probability of malfunctioning, that is, resulting in such impacts on the power supply network that lead to deterioration of its operation (emergency modes).
Thus, transition from EMRs to DPR results in reduction of equipment damage from accidental emergencies in the power supply network, but at the same time, it leads to an increase in the number of accidents (due to additional accidents caused by the malfunctioning of RP device itself) in the power system. To support this, let us quote [3], which provides a general picture of the situation:
Conventional electro-mechanic relay protection, like all domestic low-voltage equipment is reliable and long-lasting, which corresponds to the main principle of a renowned Austrian company of Paul Hertz: âAll types of electro-technical equipment must operate more than 50 years.â It is noteworthy that the unique power plant of Russia has been working without system outages for 50 years. In the course of reformation of electric power sector the philosophy of relay protection and automatics (RPA), where mostly electro-mechanical and microelectronic devices produced by Cheboksary Electric Apparatus Plant have been used, is reviewed now. Technical re-equipment of protection presupposes implementation of microprocessor RPA, produced mainly by foreign companies. This decision rests on the positive experience of implementation of microprocessor-based devices abroad. But it should be remembered that user friendly and multi-functional foreign equipment has its specific features. According to International power organization, which dates back to the time of full-fledged socialism (SIGRE) and the Soviet scientist Venikov V.A., system outages are regular in the power industry of many countries where equipment of companies sharing the Russian market has been used and is used now. Unlike the trouble-free operation of the Unified electric power system of Russia, which is protected by electro-mechanical relays, there were 13 major accidents abroad during the last two decades and 8 of them were in the USA. Power supply failures covered large territories, whereas Russian equipment continues functioning faultlessly in Egypt, Iran and Africa. There were neither breakdowns nor failures at power plants.
Taking this into consideration, we come to the conclusion that unlike consumer chains mentioned in the beginning of this chapter, reliability and longevity of RP in the power supply circuits should prevail beyond improved characteristics and expanded capacity and design.
1.2 Extrusion into the Historical Domain
For over a hundred years, all the tasks of RP have been performed by EMRs. The fact that EMRs are still widely used in many countries, including Russia (about 80% of all types of protective relays), proves that in general EMRs are capable of solving all the present problems of the RP. However, during the past 15â20 years, there has been a widespread displacement of EMR by DPR. DPR and various programmable logic controllers (PLCs) that control the operating modes of electrical equipment have become an integral part of our lives, and in many cases, there is no other device available to substitute for them to ensure the normal functioning of the power industry. This is not due to some unique features of microprocessor devices, this is rather a result of the costs of the fully automated production of DPR based on printed circuit boards compared with the production of high-precision m...
