History of relay protection

As far as we know, until the end of the nineteenth century there were neither relayers nor relay protection as such. But electric power and electrical engineering already existed at that time. And short circuits obviously happened periodically. What then protected the electrical equipment from electrical damage?

As is often done today, fuses were used. The exact date of the birth of the first fuses is still in question. Information about their widespread use comes to us from the 70s of the XIX century.

M.O. Dolivo-Dobrovolsky can rightly be considered the founding father of relay protection. It was he who, in the 90s of the XIX century, developed the first samples of a high-voltage circuit breaker – a completely integral part of the relay protection system, without which its existence would have been unthinkable. The first full-fledged relay for the purpose of relay protection and automation devices appeared in 1901. The same M.O. Dolivo-Dobrovolsky, but it was an electromechanical induction current relay.

All relay protection devices of early generations were performed on an electromechanical element base. Then, from the 30s, almost simultaneously, electronic relays began to appear both on lamps and on semiconductors. Then electronics gradually evolved into microelectronics. And as a result, already from the 60s microelectronic devices of relay protection and automation devices began to find application. The “pinnacle of progress” in the form of microprocessor-based protection was achieved only some 50 years ago. From then until now, newer generations of relay protection and automation devices have not yet been observed.

This is what the chronology of the development of relay protection technology looks like. However, it covers only generations of relay protection and automation devices according to their element base, which in itself is not very informative. By and large, all of this can be taken only that the relay protection technique is developing in step with the general scientific and technological progress. Of course, the element base of protection is very important, each generation has its own advantages and disadvantages that need to be known and taken into account in practice. But, for example, there is no fundamental difference between the digital current relay and the electromechanical current relay. Therefore, for completeness, it is interesting to consider the chronology of the development of relay protection itself, i.e. the evolution of its principles of action.

The principle of operation of the fuse is based on the fact that a short circuit is always accompanied by a significant increase in current. It is a large short circuit current that causes the fuse to burn out. Those. we can conclude that historically the first appeared protection, reacting to an increase in current. Incidentally, the basic requirements for relay protection, namely the requirements of selectivity, speed and sensitivity, were relevant even when there were only fuses. Induction relays that appeared at the very beginning of the 20th century also reacted to an increase in current during short-circuit. Very soon, already in 1905-1908. current differential protection appeared. Relay protection, together with additional current measurements, received a new property – absolute selectivity (whether the current cutoff that existed before was a protection of absolute selectivity is a rhetorical question). Then, voltage circuits were added to the current relays. So, from 1910, current directional protection began to be introduced, resistance relays appeared, which grew up to distance protection in the 20s. There was such a thing as a “relay with two input quantities.” In the 20s of the 20th century, the relay protection and automation equipment grew to such a level that generalizing scientific publications began to come to this subject. Then went a rapid improvement in the technical characteristics of relay protection and automation devices. Fundamentally new in terms of the principle of action were protection in symmetrical components, and then in the emergency components themselves. The latter are sometimes called adaptive defenses (there are also adaptive defenses that do not explicitly use emergency components). Symmetric components and emergency components proper (note: symmetric components of the reverse and zero sequence are also emergency components) is new information on the emergency process, which is extracted from currents and voltages, as compared to previously used ones. In the 50s, another type of protection appeared on a new principle – wave protection. Significant contribution to this direction was made by Soviet scientists from ENIN led by I.N. Popova. Several separate branches developed protection against earth faults and the protection of electrical machines. But these are separate stories.

If we trace the entire evolution of the principles of the operation of relay protection and automation devices, we can see that it is associated with the use of more and more information about the accident by the defense. At first, only current measurements were used, then currents from the other end of the protected object were added, then voltage measurements, etc. began to be used. By extrapolating this trend into the future, it can be predicted that new principles for the operation of relay protection and automation equipment will appear in the framework of the concept of “centralized protection”. Central protection here refers to that protection that most effectively uses all available emergency information. By the way, we can observe the first translations of this concept into life today. You don’t need to go far for examples, just drive the line “central protection” into any Internet search engine and view the search results. It should also be noted that all available information about the emergency has recently been widely used “retroactively”, including a priori information about the protected object. It is a question of using modern modeling systems with their amazing capabilities of reliable reproduction of electromagnetic and electromechanical transients in real time in the development and research of RPA. As a result of all this, with a competent approach, the relay protection system must inevitably go to a qualitatively new level of reliability. But there are still many pitfalls on this path, some of which are not yet visible.

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