Analysis of the statistics of failures of relay protection devices and automation, which is maintained at the enterprise.

Analysis of URZA failure statistics at an enterprise in our country, relay protection of power systems in most cases is still performed on the basis of relays, mostly electromechanical. The transition to a more modern element base – microcircuits of an average level of integration and microprocessor technology is taking place slowly. According to ORGRES [1], by 2002, 98.5% of electromechanical devices (including devices with microelectronic elements and semiconductor-based devices) and 1.5% of microelectronic devices, including microprocessor ones, were in operation in the power systems of Russia. In accordance with [2], the number of microprocessor relay protection devices is about 0.12% of the total. Thus, it can be stated that the transition to a modern element base, the need for which has been discussed for a long time, has not yet taken place. The situation is further complicated by the fact that the ultimate goal of such a transition – a significant increase in the efficiency of functioning – as a rule is not achieved. Technical excellence has improved markedly. Microprocessor terminals and relay protection panels based on microcircuits of an average level of integration are much easier to configure, they provide fairly complete information about an accident that has occurred, they can change their settings, if necessary, on command from the control room, etc. But the percentage of incorrect actions of modern relay protection panels and cabinets often turns out to be significantly higher than for old protections made on electromechanical relays. There were some kind of “champions” in terms of the number of failures. Thus, according to the ORGRES company [3], in 1994, the percentage of incorrect operation of the differential protection of blocks based on the DZT-21 relay was 62.5%. In subsequent years, the figures fluctuated around this figure. Differential protection of transformers with relays DZT-21 and DZT-23 did not work correctly in 30.3% of cases, differential protection of tires with braking – in 24.1%, etc. These results can hardly be called satisfactory. Consider one of the reasons for such unpleasant statistics. The value for protected objects such as power transformers and busbars is very small. For example, power transformers are damaged on average once every 15 … 40 years (with such damage, it becomes necessary to operate their protection), busbars are damaged a little more often (the frequency of their damage depends on the voltage and the number of connections). At the same time, short circuits outside the protection zone occur several times a year. If at least a small part of these external short circuits leads to excessive operations, then the value in accordance with (1) will be dangerously large. As an example, consider the differential protection of a power transformer. We conditionally assume that excessive protection trips occur once per 200 external short circuits, and other failures in the functioning of the protection in question do not occur at all. Let us apply the protection under consideration on a power transformer, on which damage occurs on average once every fifteen years, i.e. =0.067 1/year. Suppose that external short circuits occur on average 4 times a year (which is quite likely with several lines electrically connected to this transformer). Then =0.02 1/year, a = 23%. If the same protection is installed on a power transformer that is damaged once every forty years, then = 0.025 1/year, a = 44.4%. Thus, it turns out that, despite the seemingly satisfactory characteristics of the protection itself, a high percentage of its incorrect actions is due to the low damageability of the protected object, and by installing the same protection on different protected objects, we obtain different values of the percentage of incorrect actions. For objects that are damaged relatively often (for example, for power lines), the failure statistics are much more favorable. For example, in accordance with [7] in 1997, the current protection against earth fault on power lines 500 … 750 kV type PDE-2002 had 7.1% of incorrect operations, remote protection ShDE-2800 – 2.3%, directional high-frequency protection PDE -2802 – 3.2% false positives, etc. All the protection devices described above are made on a microelectronic element base (mainly using microcircuits of an average level of integration). At the same time, as noted above, a large number of relay protection devices based on old electromechanical relays are still in operation in the Russian power systems. The percentage of their incorrect actions averages 0.4 … 0.5%. In fairness, it should be noted that in the developed countries of the West, the transition to a modern element base, associated, as a rule, with the complication of the circuit and design of relay protection devices and panels, was also accompanied by a significant increase in the number of failures in operation. In accordance with the data [4] in the West at the end of the last century, the percentage of incorrect actions of relay protection devices performed on electromechanical relays was 0.1% (in Russia for similar equipment – 0.4 … 0.6%), for relays on based on integrated circuits – 0.3% (in Russia for various cabinets and panels 2.3 … 10%), for protection based on microprocessors – 5% (in recent years in Russia [1] the first, although not very representative, data have appeared by the percentage of incorrect actions of such devices – 1.4%. Apparently, through frequent automatic diagnostic checks, the period between which in some cases approaches several hours, it was possible to prevent the transition of most defects into accidents). The service life of electromechanical relays in the West at that time was 30 years or more, the rest – 20 years or more. Recently, information has appeared that the service life of relay protection systems, for example, in the USA has approached 5-7 years. The rapid progress in the development of new microprocessor-based protections there leads to frequent updating of the applied technology. In [1], it is noted that 38% of relay protection devices in Russia have worked for more than 25 years, are morally and physically obsolete and require replacement. The number of failures in the functioning associated with the aging of equipment is growing from year to year. The situation is similar with protection objects – many elements of the power circuit of the power system (generators, transformers, etc.) have already worked much longer than their standard period, which leads to an increase in the number of failures and, in turn, increases the requirements for relay protection. As before, about 60% of failures in the functioning of RPA devices are associated with human errors [1]. The aging of the relay protection fleet and a large number of failures due to the fault of the operating personnel lead to the need for the widespread use of automatic and semi-automatic diagnostic devices, the main purpose of which is to quickly identify defects that occur in the relay protection circuits and enable personnel to eliminate them before they turn into accidents (if occurrence of short circuits or other disturbances in the system). In many countries abroad, a technology for servicing protection devices has been adopted that does not require the participation of maintenance personnel of relay protection services of power stations, distribution substations and industrial enterprises in checks, adjustments and setting changes. All this is done by specially trained personnel of enterprises – manufacturers and suppliers of protection devices. The volume of checks is many times less than on our traditional equipment, since most of the checks are performed automatically by diagnostic devices built into the relay protection devices themselves. For example, some microprocessor terminals check themselves every few hours, and in the event of a malfunction, they immediately inform the operating personnel about this. This approach made it possible not only to increase reliability by several times, but also to significantly (up to two times) reduce the staff of electrical laboratories. Most experts agree that the transition to the microprocessor element base of relay protection in Russia is inevitable, although it will be associated with great difficulties. For example, in [5], the following main reasons hindering such a transition are listed: lack of qualified service personnel, low reliability of relay protection devices based on microprocessors, high cost, poor electromagnetic compatibility with the conditions that actually exist in most substations, etc. In [5] it is said: “In Russian conditions, it is easier to demolish substations with a bulldozer and build new ones in their place. You can give an example of Kazakhstan. They received a foreign loan and chose the concept of a clean field, up to the fact that new substations will be built in parallel with the existing ones.” As a temporary measure, in [5] it is proposed, when installing new microprocessor sets of relay protection, to duplicate them with Russian electromechanical devices. Many times in recent years, specialists ordering modern microprocessor-based imported relay protection devices have become convinced that expensive imported devices do not always work correctly in Russian conditions. This is due to a number of reasons: 1. Imported microprocessor terminals in most cases impose increased requirements on the parameters of the ground loop, in particular, they require a low impulse resistance of this loop. In the West, it is customary for such devices to mount their own ground loop. In Russian conditions, many failures in the functioning of such protections are associated with impulse noise induced in the ground loop. 2. Microprocessor terminals are affected by electromagnetic interference coming “out of thin air” through control current circuits, voltage circuits and current transformers. There have been cases of false alarm protection, for example, when you turn on a mobile phone next to it. 3. Modern protection devices often cannot be satisfactorily “coupled” with domestic current transformers, which have unacceptably large errors for Western terminals, both in steady state and, especially, in transient modes. 4. Often imported protections do not take into account the peculiarities of domestic equipment, in particular, protected objects. 5. The very “ideology” of building imported RPA devices usually does not correspond to the domestic one. In particular, in the West there are practically no such concepts as AChR, SAON, AR is performed in a different way, etc. All this requires domestic customers to carefully analyze the whole range of problems as a whole even before ordering certain modern relay protection devices. Practice shows that this is not always the case, and operators identify many shortcomings of protection already in the process of their practical work, accompanied by failures in the functioning of protection.

Section 2

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