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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 4. Switchgears and substations Switchgears and substations with voltages above 1 kV. Protection of rotating electrical machines against lightning surges
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 4.2.160. Overhead lines on metal and reinforced concrete supports can be directly connected to generators (synchronous compensators) with a capacity of up to 50 MW (up to 50 MB·A) and the corresponding switchgear. Overhead lines on wooden supports may be connected to generators (synchronous compensators) with a capacity of up to 25 MW (up to 25 MVA) and the corresponding switchgear. Connection of overhead lines to generators (synchronous compensators) with a capacity of more than 50 MW (more than 50 MVA) should be carried out only through a transformer. To protect block transformers connected to generators with a capacity of 100 MW and more, on the side of the HV, a RH of at least Group II or the corresponding surge arresters should be installed. 4.2.161. To protect generators and synchronous compensators, as well as electric motors with a power of more than 3 MW, connected to common busbars by overhead lines or current conductors, group I RS or surge arresters with the corresponding remaining lightning current and capacitance voltage of at least 0,5 μF per phase must be installed. When choosing RTS or surge arresters with lower values of the remaining voltages, it is allowed to install capacitances of less than 0,5 microfarads per phase. In addition, the protection of overhead lines approaches to the switchgear of power plants, substations and current conductors to machines must be performed with a lightning resistance level of at least 50 kA. Valve arresters or surge arresters should be installed to protect: generators (synchronous compensators) with a capacity of more than 15 MW (more than 15 MVA) - at the connection of each generator (synchronous compensator); 15 MW or less (15 MVA or less) - on tires (bus sections) of generator voltage; electric motors with a power of more than 3 MW - on the busbars of the switchgear. When protecting generators (synchronous compensators) with a withdrawn neutral that do not have turn insulation (machines with a rod winding) with a power of 25 MW or more (25 MVA or more), instead of capacitances of 0,5 μF per phase, a RT or arrester can be used in generator neutral (synchronous compensator) to the rated voltage of the machine. The installation of protective capacitances is not required if the total capacitance of cable sections up to 100 m long connected to generators (synchronous compensators) is 0,5 μF or more per phase. 4.2.162. If rotating machines and overhead lines are connected to the common busbars of the switchgear of power plants or substations, then the approaches of these overhead lines must be protected from lightning effects in compliance with the following requirements: 1) the approach of overhead lines with metal and reinforced concrete supports must be protected by a cable for at least 300 m; The grounding resistance of the RV or surge arrester should not exceed 4.2.20 ohms, and the grounding resistance of the supports on the cable section should not exceed 3 ohms. It is recommended to use wooden traverses with a distance of at least 10 m along the tree from the point of attachment of the insulator string to the support post. On the approaches of overhead lines with wooden poles, in addition to the protective equipment used on overhead lines with reinforced concrete poles, a set of RW of group IV or the corresponding surge arresters should be installed at a distance of 150 m from the beginning of the cable approach towards the line (Fig. 4.2.20, 'b'). The grounding resistance of the arresters should be no more than 3 ohms. It is allowed to install RT at the beginning of the approach. The grounding resistance of such arresters should not exceed 5 ohms; 2) on overhead lines connected to power plants and substations with cable inserts up to 0,5 km long, the approach protection must be performed in the same way as on overhead lines without cable inserts (see clause 1) and an additional RV2 set of group IV must be installed or corresponding surge arresters at the point of connection of the overhead line to the cable. The grounded terminal of the protective device should be connected in the shortest way to the armor, the metal sheath of the cable and to the ground electrode (Fig. 4.2.20, 'c', 'd'). The grounding resistance of the apparatus must not exceed 5 ohms; 3) if the overhead line approach at a length of at least 300 m is protected from direct lightning strikes by buildings, trees or other tall objects and is located in their protection zone, then the cable suspension at the overhead line approach is not required. At the same time, at the beginning of the protected section of the overhead line (from the side of the line), a set of РВ1 of group IV (Fig. 4.2.20, 'e') or the corresponding surge arresters should be installed. The grounding resistance of the arrester must not exceed 3 ohms. PB1 grounding slopes should be connected in the shortest way to the ground loop of the substation (power plant); 4) if there is a current-limiting reactor at the overhead line connection, the approach at a length of 100-150 m must be protected from direct lightning strikes by a lightning rod (Fig. 4.2.20, 'a'). At the beginning of the approach, protected by a lightning rod, as well as at the reactor, sets of PB1 and PB2 of group IV (Fig. 4.2.20, 'a') or corresponding surge arresters should be installed. The grounding resistance of the apparatus installed at the beginning of the approach from the side of the line should be no more than 3 ohms; 5) when connecting an overhead line to the busbars of a switchgear with rotating machines through a current-limiting reactor and a cable insert longer than 50 m, protection of the overhead line approach from direct lightning strikes is not required. At the point of connection of the overhead line to the cable and in front of the reactor, sets of PB1 and PB2 of group IV or surge arresters with a grounding resistance of not more than 3 Ohm should be installed (Fig. 4.2.20, 'g'); 6) on overhead lines connected to the busbars of the switchgear with rotating machines with a power of less than 3 MW (less than 3 MB A), the approaches of which for a length of at least 0,5 km are made on reinforced concrete or metal supports with a ground resistance of not more than 5 Ohm, should be a set of RV group IV or the corresponding surge arresters is installed at a distance of 100-150 m from the substation (power plant) (Fig. 4.2.20, 'h'). Grounding resistance of protective devices should be no more than 3 ohms. At the same time, protection of the overhead line approach with a cable is not required.
4.2.163. When using open current conductors for connecting generators (synchronous compensators) with transformers, the current conductors must be included in the protection zones of lightning rods and structures of the substation (power plants). The place of connection of lightning rods to the grounding device of the substation (power plants) must be removed from the place of connection of the earthed conductor elements to it, counting along the grounding lines, by at least 20 m. If open conductors are not included in the protection zones of lightning rods of the outdoor switchgear, then they must be protected from direct lightning strikes by separate lightning rods or cables suspended on separate supports with a protective angle of not more than 20º. Grounding of stand-alone lightning rods and cable poles should be carried out by separate grounding conductors that do not have a connection to the grounding devices of the busbar supports, or by connecting to the grounding device of the switchgear at points remote from the place of connection of the grounded elements of the current duct to it at a distance of at least 20 m. The distance from free-standing lightning rods (cable supports) to current-carrying or grounded elements of the current duct through the air must be at least 5 m. The distance in the ground from a separate ground electrode and the underground part of the lightning rod to the ground electrodes and the underground part of the current duct must be at least 5 m. 4.2.164. When connecting an open current duct to the generator voltage switchgear through the reactor, a set of group IV RVs or a corresponding surge arrester must be installed in front of the reactor. To protect generators from lightning overvoltage waves incident on the conductor, and from induced overvoltages, group I RS or surge arresters and protective capacitances should be installed, the value of which for three phases at the rated voltage of the generators should be at least: at a voltage of 6 kV - 0,8 uF, at 10 kV - 0,5 uF and at 13,8-20 kV - 0,4 uF. Protective capacitances do not need to be installed if the total capacitance of the generator and the cable network on the generator voltage buses has the required value. When determining the capacity of the cable network, in this case, sections of cables over a length of up to 750 m are taken into account. If the SS switchgear is connected by open conductors to the generator voltage switchgear of the CHPP, which has generators with a capacity of up to 120 MW, then the protection of the current conductor against direct lightning strikes must be carried out as specified in 4.2.163. 4.2.165. It is allowed not to protect approaches from direct lightning strikes when connecting overhead lines or open conductors: 1) for electric motors up to 3 MW; 2) to generators of diesel power plants with a capacity of up to 1 MW, located in areas with an intensity of thunderstorm activity of up to 20 thunderstorm hours per year. At the same time, it is required to install on the approach of the overhead line two sets of RV group IV or the corresponding surge arresters at distances of 150 (RV2) and 250 m (RV1) from the busbars of the substation (Fig. 4.2.21, 'a'). Grounding resistance of protective devices should be no more than 3 ohms. Grounding slopes should be connected in the shortest possible way to the grounding device of the substation or power plant. If there is a cable insert of any length, a group IV RH or a corresponding surge arrester must be installed directly in front of the cable. Their grounding clamp must be connected in the shortest possible way to the metal sheaths of the cable and to the grounding conductor (Fig. 4.2.21, 'b'). On the buses that feed the electric motors through cable inserts, group I RW or the corresponding surge arresters and protective capacitances of at least 0,5 μF per phase must be installed. On the approaches of overhead lines or open current conductors with reinforced concrete or metal supports, the installation of RV is not required if the grounding resistance of each support of the approach over a length of at least 250 m is not more than 10 ohms.
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