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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 3. Protection and automation Relay protection. Protection of overhead lines in networks with a voltage of 110-500 kV with an effectively grounded neutral
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 3.2.106. For lines in 110-500 kV networks with an effectively grounded neutral, relay protection devices against multiphase faults and ground faults must be provided. 3.2.107. Protections must be equipped with devices that block their action during swings, if swings or asynchronous movement are possible in the network, during which excessive protection operations are likely. It is allowed to perform protection without blocking devices if it is adjusted against swings in time (about 1,5-2 s). 3.2.108. For lines of 330 kV and above, protection must be provided as the main one, acting without delay during a short circuit at any point in the protected area. For lines with a voltage of 110-220 kV, the question of the type of main protection, including the need to use protection that acts without delay during a short circuit at any point in the protected area, must be resolved primarily taking into account the requirement to maintain the stability of the power system. Moreover, if, according to calculations of the stability of the power system operation, other, more stringent requirements are not imposed, it can be accepted that the specified requirement, as a rule, is satisfied when three-phase short circuits, in which the residual voltage on the buses of power plants and substations is below 0,6-0,7, 0,6 Unom, switches off without time delay. A lower residual voltage value (110 Unom) can be allowed for 220 kV lines, less critical 220 kV lines (in highly branched networks where power to consumers is reliably provided from several sides), as well as for more critical XNUMX kV lines in cases where when the short circuit in question does not lead to significant load shedding. When choosing the type of protection installed on 110-220 kV lines, in addition to the requirement to maintain the stability of the power system, the following must be taken into account: 1. On lines of 110 kV and higher extending from the nuclear power plant, as well as on all elements of the adjacent network, on which, during multi-phase short circuits, the positive sequence residual voltage on the higher voltage side of the nuclear power plant units can decrease to more than 0,45 of the nominal value, redundancy of high-speed protections with a time delay not exceeding 1,5 s taking into account the action of the breaker failure. 2. Faults, the shutdown of which with a time delay can lead to disruption of the work of critical consumers, must be switched off without a time delay (for example, faults in which the residual voltage on the buses of power plants and substations will be below 0,6 Unom, if their shutdown with a time delay can lead to self-discharge due to a voltage avalanche, or damage with a residual voltage of 0,6 Un or more, if disconnecting them with a time delay can lead to disruption of the technology). 3. If it is necessary to carry out high-speed automatic reclosure, a high-speed protection must be installed on the line, ensuring that the damaged line is disconnected without a time delay on both sides. 4. When disconnecting with a time delay of faults with currents several times higher than the rated current, unacceptable overheating of the conductors is possible. It is allowed to use high-speed protection in complex networks and in the absence of the conditions stated above, if this is necessary to ensure selectivity. 3.2.109. When assessing the provision of stability requirements, based on the residual stress values according to 3.2.108, it is necessary to be guided by the following: 1. For a single connection between power plants or power systems, the residual voltage specified in 3.2.108 must be checked on the buses of substations and power plants included in this connection, with a short circuit on the lines extending from these buses, except for the lines forming the connection; for a single connection containing part of the sections with parallel lines - also with a short circuit on each of these parallel lines. 2. If there are several connections between power plants or power systems, the value of the residual voltage specified in 3.2.108 must be checked on the buses of only those substations or power plants where these connections are connected, in case of a short circuit on the connections and on other lines powered from these buses, as well as on lines powered by communication substation buses. 3. The residual voltage must be checked during a short circuit at the end of the zone covered by the first stage of protection in the cascade fault tripping mode, i.e. after tripping the circuit breaker from the opposite end of the line by protection without a time delay. 3.2.110. On single lines with one-way power supply from polyphase faults, step current protection or step current and voltage protection should be installed. If such protections do not meet the requirements of sensitivity or speed of fault shutdown (see 3.2.108), for example, in the head sections, or if this is advisable based on the condition of coordinating the protection of adjacent sections with the protection of the section in question, stepwise distance protection should be provided. In the latter case, it is recommended to use current cut-off without a time delay as additional protection. As a rule, step current directional or non-directional zero sequence protection should be provided against ground faults. Protection should be installed, as a rule, only on those sides from which power can be supplied. For lines consisting of several consecutive sections, for the purpose of simplification, it is allowed to use non-selective stepwise current and voltage protection (against multiphase faults) and stepwise zero-sequence current protection (against ground faults) in combination with sequential reclosure devices. 3.2.111. On single lines with power from two or more sides (the latter on lines with branches), both with and without bypass connections, as well as on lines included in a ring network with one power point, there must be protection against multiphase short circuits distance protection is applied (mostly three-stage), used as a backup or primary (the latter - only on 110-220 kV lines). As additional protection, it is recommended to use a current cut-off without a time delay. In some cases, it is allowed to use a current cutoff to act in the event of an erroneous connection to a three-phase short circuit at the place where the protection is installed, when the current cutoff performed for operation in other modes does not satisfy the sensitivity requirement (see 3.2.26). As a rule, step current directional or non-directional zero sequence protection should be provided against ground faults. 3.2.112. As the main protection against multiphase faults at the receiving end of the head sections of a ring network with one power point, it is recommended to use single-stage current directional protection; on other single lines (mainly 110 kV), in some cases it is allowed to use step current protection or step current and voltage protection, making them directional if necessary. Protection should generally be installed only on those sides from which power can be supplied. 3.2.113. On parallel lines fed from two or more sides, as well as on the supply end of parallel lines with one-sided supply, the same protections as on the corresponding single lines can be used (see 3.2.110 and 3.2.111). To speed up the disconnection of ground faults, and in some cases, faults between phases on lines with double-sided power supply, additional protection can be used to control the direction of power in a parallel line. This protection can be implemented in the form of a separate transverse current protection (with the inclusion of a relay for zero-sequence current or phase currents) or only in the form of an acceleration circuit of installed protections (zero-sequence current, maximum current, distance, etc.) with direction control power in parallel lines. In order to increase the sensitivity of zero-sequence protection, it is possible to provide for the removal of its individual stages from operation when the parallel line circuit breaker is disconnected. Transverse directional differential protection should generally be provided at the receiving end of two parallel single-ended feed lines. 3.2.114. If the protection according to 3.2.113 does not meet the speed requirements (see 3.2.108), as the main protection (when operating two parallel lines) at the supply end of two parallel 110-220 kV lines with one-way supply and at two parallel 110 kV lines with With two-way power supply, transverse differential directional protection can be used mainly in distribution networks. In this case, in the operating mode of one line, as well as as a backup when operating two lines, protection according to 3.2.110 and 3.2.111 is used. It is possible to turn on this protection or its individual stages for the sum of the currents of both lines (for example, the last stage of zero-sequence current protection) in order to increase its sensitivity to damage on adjacent elements. It is allowed to use transverse differential directional protection in addition to step current protection of parallel 110 kV lines to reduce the fault shutdown time on the protected lines in cases where, according to performance conditions (see 3.2.108), its use is not mandatory. 3.2.115. If the protection according to 3.2.111 - 3.2.113 does not satisfy the speed requirement (see 3.2.108), high-frequency and longitudinal differential protection should be provided as the main protection of single and parallel lines with double-sided power supply. For 110-220 kV lines, it is recommended to carry out basic protection using high-frequency blocking of distance and current directional zero-sequence protection, when this is appropriate due to sensitivity conditions (for example, on lines with branches) or simplification of protection. If it is necessary to lay a special cable, the use of longitudinal differential protection must be justified by a technical and economic calculation. To monitor the serviceability of auxiliary protection wires, special devices must be provided. On 330-350 kV lines, in addition to high-frequency protection, the use of a device for transmitting a tripping or permissive high-frequency signal (to accelerate the action of step backup protection) should be provided, if this device is provided for other purposes. On 500 kV lines it is allowed to install the specified device specifically for relay protection. It is allowed in cases where it is required by the conditions of speed (see 3.2.108) or sensitivity (for example, on lines with branches), the use of transmission of a tripping signal to accelerate the action of step protection of 110-220 kV lines. 3.2.116. When performing basic protection according to 3.2.115, the following should be used as backup:
In case of long-term deactivation of the main protection specified in 3.2.115, when this protection is installed according to the requirement of quickly disconnecting the fault (see 3.2.108), it is allowed to provide for non-selective acceleration of backup protection against faults between phases (for example, with control of the direct voltage value sequences). 3.2.117. The main protections, high-speed stages of backup protection against multiphase faults and the measuring elements of the automatic reclosure device for 330-350 kV lines must be of a special design that ensures their normal functioning (with the specified parameters) under conditions of intense transient electromagnetic processes and significant capacitive conductivity of the lines. For this purpose the following must be provided:
When switching on high-speed protection for the sum of the currents of two or more current transformers, if it is impossible to meet the requirements of 3.2.29, it is recommended to take special measures to prevent unnecessary operation of the protection in the event of external damage (for example, hardening of the protection) or install a separate set of current transformers in the line circuit to power the protection . In protections installed on 330-500 kV lines equipped with longitudinal capacitive compensation devices, measures must be taken to prevent excessive operation of the protection in the event of external damage caused by the influence of these devices. For example, negative sequence power direction relays or enable signal transmission may be used. 3.2.118. In the case of using OAPV, relay protection devices must be designed so that: 1) in case of ground faults of one phase, and in some cases also in case of faults between two phases, only one phase was disconnected (followed by its automatic reconnection); 2) in case of unsuccessful reconnection due to the damage specified in clause 1, one or three phases were disconnected, depending on whether a long-term, single-phase operation of the line was provided for or not; 3) in case of other types of damage, the protection acted on the disconnection of three phases.
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