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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 3. Protection and automation Relay protection. General requirements
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 3.2.2. Electrical installations must be equipped with relay protection devices designed for: a) automatic disconnection of the damaged element from the rest, undamaged part of the electrical system (electrical installation) using switches; if the damage (for example, earth fault in networks with isolated neutral) does not directly disrupt the operation of the electrical system, the relay protection is allowed to act only on the signal. b) response to dangerous, abnormal modes of operation of the elements of the electrical system (for example, overload, voltage increase in the stator winding of the hydro generator); Depending on the operating mode and operating conditions of the electrical installation, relay protection must be performed with an action on the signal or on the shutdown of those elements that, if left in operation, can lead to damage. 3.2.3. In order to reduce the cost of electrical installations, instead of circuit breakers and relay protection, fuses or open fuses should be used if they:
When using fuses or open fuses, depending on the level of unbalance in open-phase mode and the nature of the supplied load, it is necessary to consider the need to install protection against open-phase mode at the receiving substation. 3.2.4. Relay protection devices should provide the shortest possible short-circuit disconnection time in order to maintain uninterrupted operation of the undamaged part of the system (stable operation of the electrical system and electrical installations of consumers, ensuring the possibility of restoring normal operation through the successful operation of automatic reclosure and automatic transfer, self-starting of electric motors, retraction into synchronism, etc.) and restrictions on the area and degree of damage to the element. 3.2.5. Relay protection acting on shutdown, as a rule, must provide selectivity of action, so that if any element of the electrical installation is damaged, only this damaged element is switched off. A non-selective protection action is allowed (corrected by a subsequent AR or ATS action): a) to ensure, if necessary, the acceleration of the tripping of the short circuit (see 3.2.4); b) when using simplified main electrical circuits with separators in the circuits of lines or transformers that disconnect the damaged element during a dead time. 3.2.6. Relay protection devices with time delays that ensure the selectivity of the action are allowed to be performed if: when a short circuit is disconnected with time delays, the requirements of 3.2.4 are met; protection acts as a backup (see 3.2.15). 3.2.7. Reliability of functioning of relay protection (triggering when conditions for triggering and non-operating in their absence) must be ensured by the use of devices that, in terms of their parameters and design, correspond to their intended purpose, as well as by proper maintenance of these devices. If necessary, special measures should be used to improve the reliability of operation, in particular circuit redundancy, continuous or periodic monitoring of the state, etc. The probability of erroneous actions of maintenance personnel when performing the necessary operations with relay protection should also be taken into account. 3.2.8. In the presence of relay protection having voltage circuits, devices should be provided:
3.2.9. When installing high-speed relay protection on power lines with tubular arresters, it must be provided for detuning it from the operation of arresters, for which:
3.2.10. For relay protections with time delays, in each specific case, it is necessary to consider the feasibility of providing protection from the initial value of current or resistance during a short circuit in order to exclude failures of protection operation (due to attenuation of short circuit currents in time, as a result of oscillations, the appearance of an arc at the fault site and etc.). 3.2.11. Protections in electrical networks of 110 kV and above must have devices that block their action during swings or asynchronous running, if such swings or asynchronous running are possible in these networks, in which the protections can operate unnecessarily. It is allowed to use similar devices for lines below 110 kV, interconnecting power supplies (based on the likelihood of oscillations or asynchronous running and the possible consequences of excessive shutdowns). It is allowed to perform protection without blocking during swings, if the protection against swings is adjusted in time (protection time delay is about 1,5-2 s). 3.2.12. The action of relay protection should be recorded by indicator relays, operation indicators built into the relay, operation counters or other devices to the extent necessary to account for and analyze the operation of protections. 3.2.13. Devices that record the action of relay protection for shutdown should be installed so that the operation of each protection is signaled, and in case of complex protection, its individual parts (different levels of protection, separate sets of protection against different types of damage, etc.). 3.2.14. On each of the elements of the electrical installation, the main protection should be provided, designed to operate in case of damage within the entire protected element with a time shorter than that of other protections installed on this element. 3.2.15. For action in case of failure of protections or switches of adjacent elements, back-up protection should be provided, designed to provide long-range back-up action. If the main protection of the element has absolute selectivity (for example, high-frequency protection, longitudinal and transverse differential protection), then a backup protection must be installed on this element, which performs the functions of not only long-range, but also short-range redundancy, i.e., acting in case of failure of the main protection this element or removing it from work. For example, if differential-phase protection is used as the main protection against short circuits between phases, then three-stage distance protection can be used as a backup. If the main line protection of 110 kV and above has relative selectivity (for example, step protection with time delays), then:
3.2.16. For power transmission lines of 35 kV and above, in order to increase the reliability of fault disconnection at the beginning of the line, current cutoff without time delay can be provided as additional protection, provided that the requirements of 3.2.26 are met. 3.2.17. If the full provision of long-range redundancy is associated with a significant complication of protection or is technically impossible, it is allowed: 1) do not reserve short-circuit disconnections behind transformers, on reacted lines, lines of 110 kV and above in the presence of near redundancy, at the end of a long adjacent section of the 6-35 kV line; 2) have a long-range redundancy only for the most common types of damage, without taking into account rare operating modes and taking into account the cascade action of protection; 3) provide for non-selective action of protection in case of short circuit on adjacent elements (with long-range backup action) with the possibility of de-energizing in some cases substations; at the same time, it should be possible to ensure that these non-selective trips are corrected by the action of automatic reclosure or automatic reclosure. 3.2.18. Redundancy devices in case of failure of circuit breakers (RPF) should be provided in electrical installations of 110-500 kV. It is allowed not to provide for breaker failure in electrical installations of 110-220 kV, subject to the following conditions: 1) the required sensitivity and the disconnection times from long-range backup devices acceptable under the conditions of stability are provided; 2) when back-up protections are in operation, there is no loss of additional elements due to disconnection of circuit breakers that are not directly adjacent to the failed circuit breaker (for example, there are no partitioned buses, branch lines). At power plants with generators having direct cooling of stator winding conductors, in order to prevent damage to generators in the event of failures of 110-500 kV circuit breakers, breaker failure should be provided, regardless of other conditions. In case of failure of one of the switches of the damaged element (line, transformer, busbars) of the electrical installation, the breaker failure must act to turn off the switches adjacent to the failed one. If the protections are connected to remote current transformers, then the breaker failure should also operate in the event of a short circuit in the zone between these current transformers and the circuit breaker. It is allowed to use simplified breakers that operate in case of short circuit with circuit breaker failures not on all elements (for example, only in case of short circuit on lines); at a voltage of 35-220 kV, in addition, it is allowed to use devices that act only to turn off the bus-connecting (sectional) switch. When the effectiveness of long-range redundancy is insufficient, the need to increase the reliability of short-range redundancy in addition to breaker failure should be considered. 3.2.19. When performing backup protection as a separate set, it should be carried out, as a rule, in such a way that it is possible to separately check or repair the main or backup protection while the element is operating. In this case, the main and backup protection should be powered, as a rule, from different secondary windings of current transformers. The power supply of the main and backup protections of power transmission lines of 220 kV and above should be carried out, as a rule, from different automatic circuit breakers of the operational direct current. 3.2.20. The assessment of the sensitivity of the main types of relay protection should be carried out using a sensitivity coefficient determined by:
The calculated values of the quantities should be established based on the most unfavorable types of damage, but for a realistically possible mode of operation of the electrical system. 3.2.21. When assessing the sensitivity of the main protections, it is necessary to proceed from the fact that the following minimum coefficients of their sensitivity should be provided: 1. Overcurrent protections with and without voltage start, directional and non-directional, as well as current single-stage directional and non-directional protections, included in the negative or zero sequence components:
For the maximum current protection of transformers with a low voltage of 0,23-0,4 kV, the smallest sensitivity coefficient can be about 1,5. 2. Step current or current and voltage protection, directional and non-directional, connected to full currents and voltages or zero sequence components:
3. Remote protection against multi-phase short circuits:
4. Longitudinal differential protection of generators, transformers, lines and other elements, as well as full differential protection of tires - about 2,0; for the current starting body of the incomplete differential distance protection of the generator voltage buses, the sensitivity should be about 2,0, and for the first stage of the incomplete differential current protection of the generator voltage buses, made in the form of a cut-off, it should be about 1,5 (with a short circuit on the tires). For differential protection of generators and transformers, the sensitivity should be checked for short circuits at the terminals. In this case, regardless of the values of the sensitivity factor for hydro generators and turbo generators with direct cooling of the winding conductors, the protection operation current should be taken less than the rated current of the generator (see 3.2.36). For autotransformers and step-up transformers with a capacity of 63 MVA and more, it is recommended to take the operation current, excluding braking, less than the nominal one (for autotransformers - less than the current corresponding to the typical power). For other transformers with a capacity of 25 MVA and more, the operation current without braking is recommended to take no more than 1,5 of the rated current of the transformer. It is allowed to reduce the sensitivity factor for the differential protection of a transformer or a generator-transformer unit to a value of about 1,5 in the following cases (in which providing a sensitivity factor of about 2,0 is associated with a significant complication of protection or is technically impossible):
For the mode of supplying voltage to damaged tires by turning on one of the supply elements, it is allowed to reduce the sensitivity coefficient for the differential protection of tires to a value of about 1,5. The specified coefficient of 1,5 also applies to the differential protection of the transformer in case of a short circuit after the reactor, installed on the low voltage side of the transformer and entering the zone of its differential protection. If there are other protections covering the reactor and meeting the requirements for sensitivity in case of a short circuit after the reactor, the sensitivity of the differential protection of the transformer in case of a short circuit at this point may not be provided. 5. Transverse differential directional protection of parallel lines:
6. Directional protections with high frequency blocking:
7. Differential-phase high-frequency protection:
8. Current cutoffs without time delay, installed on generators with a power of up to 1 MW and transformers, with a short circuit at the place of protection installation - about 2,0. 9. Protection against earth faults on cable lines in networks with isolated neutral (acting on a signal or on shutdown):
10. Protection against earth faults on overhead lines in networks with isolated neutral, acting on a signal or on a shutdown - about 1,5. 3.2.22. When determining the sensitivity factors specified in 3.2.21, paragraphs 1, 2. 5 and 7, the following must be taken into account: 1. The power sensitivity of the inductive power direction relay is checked only when it is turned on for the components of currents and voltages of the reverse and zero sequences. 2. The sensitivity of the power direction relay, made according to the comparison circuit (absolute values or phases), is checked: when turned on for full current and voltage - by current; when connected to the components of currents and voltages of the reverse and zero sequences - by current and voltage. 3.2.23. For generators operating on busbars, the sensitivity of the current protection against earth faults in the stator winding, acting to trip, is determined by its trip current, which should not exceed 5 A. An increase in trip current up to 5,5 A is allowed as an exception. For generators operating in a block with a transformer, the sensitivity factor of protection against single-phase earth faults, covering the entire stator winding, must be at least 2,0; for zero-sequence voltage protection that does not cover the entire stator winding, the response voltage must be no more than 15 V. 3.2.24. The sensitivity of protections on alternating operating current, performed according to the scheme with deshunting of tripping electromagnets, should be checked taking into account the actual current error of current transformers after deshunting. In this case, the minimum value of the sensitivity coefficient of the tripping electromagnets, determined for the condition of their reliable operation, should be approximately 20% higher than that accepted for the corresponding protections (see 3.2.21). 3.2.25. The smallest sensitivity factors for back-up protection in case of a fault at the end of an adjacent element or the most distant of several consecutive elements included in the redundancy zone should be (see also 3.2.17):
When assessing the sensitivity of backup protection stages that provide short-range redundancy (see 3.2.15), one should proceed from the sensitivity factors given in 3.2.21 for the corresponding protections. 3.2.26. For current cutoffs without time delay, installed on the lines and performing the functions of additional protection, the sensitivity coefficient should be about 1,2 for short circuit at the place of protection installation in the most favorable mode according to the sensitivity condition. 3.2.27. If the action of the protection of the next element is possible due to a failure due to insufficient sensitivity of the protection of the previous element, then the sensitivity of these protections must be coordinated with each other. It is allowed not to coordinate the stages of these protections, intended for long-range redundancy, if the failure to disconnect the short circuit due to insufficient sensitivity of the protection of the subsequent element (for example, the protection of the negative sequence of generators, autotransformers) can lead to serious consequences. 3.2.28. In networks with a dead-earthed neutral, such a mode of grounding the neutrals of power transformers (i.e., placing transformers with a grounded neutral) should be selected based on the conditions of relay protection, in which the values of currents and voltages during ground faults ensure the operation of relay protection of network elements for all possible operating modes of the electrical system. For step-up transformers and transformers with two- and three-sided power supply (or significant feeding from synchronous electric motors or synchronous compensators) with incomplete winding insulation on the side of the neutral terminal, as a rule, the occurrence of an unacceptable operation mode for them with an isolated neutral on dedicated buses should be excluded or a section of a 110-220 kV network with an earth fault of one phase (see 3.2.63). 3.2.29. Current transformers designed to power the current circuits of relay protection devices against short circuit must meet the following requirements: 1. In order to prevent unnecessary operation of protection during short circuits outside the protected area, the error (total or current) of current transformers, as a rule, should not exceed 10%. Higher errors are allowed when using protections (for example, differential protection of tires with braking), the correct operation of which, with increased errors, is ensured by special measures. These requirements must be met:
For differential current protections (tires, transformers, generators, etc.), the total error must be taken into account, for the remaining protections - the current error, and when the latter are turned on for the sum of the currents of two or more current transformers and in the external short circuit mode - the total error. When calculating the allowable loads on current transformers, it is allowed to take the total error as the initial one. 2. The current error of current transformers in order to prevent protection failures in case of short circuit at the beginning of the protected zone should not exceed:
3. The voltage at the terminals of the secondary winding of the current transformers in case of short circuit in the protected area should not exceed the value allowed for the RPA device. 3.2.30. The current circuits of electrical measuring instruments (together with meters) and relay protection should be connected, as a rule, to different windings of current transformers. It is allowed to connect them to one winding of current transformers, provided that the requirements of 1.5.18 and 3.2.29 are met. At the same time, in the protection circuits, which, according to the principle of operation, may not work correctly if the current circuits are disturbed, the inclusion of electrical measuring instruments is allowed only through intermediate current transformers and provided that the current transformers meet the requirements of 3.2.29 with an open secondary circuit of the intermediate current transformers. 3.2.31. Protection using direct acting relays, both primary and secondary, and protection on alternating operational current is recommended to be used, if possible, and leads to a simplification and reduction in the cost of the electrical installation. 3.2.32. As a source of alternating current for protection against short circuits, as a rule, current transformers of the protected element should be used. It is also allowed to use voltage transformers or auxiliary transformers. Depending on the specific conditions, one of the following schemes must be applied: with deshunting of the circuit breaker opening electromagnets, using power supplies, using chargers with a capacitor. 3.2.33. Relay protection devices that are taken out of operation due to the conditions of the network mode, selectivity of action, or for other reasons, must have special devices for taking them out of operation by operational personnel. To ensure operational checks and tests, protection circuits should provide, where necessary, test blocks or test clamps.
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