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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 7. Electrical equipment of special installations Electrothermal installations. General requirements
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 7.5.8. The category of electrical receivers of the main equipment and auxiliary mechanisms, as well as the volume of redundancy of the electrical part, must be determined taking into account the characteristics of the electrical installation and the requirements imposed by the current standards, norms and rules for the equipment of the electrical installation, systems for supplying it with water, gases, compressed air, creating and maintaining pressure in the working chambers or rarefaction. It is recommended to include ECU electrical receivers in workshops and non-serial production areas in category III: forging, stamping, pressing, mechanical, mechanical assembly and painting; workshops and sections (departments and workshops) of tool, welding, prefabricated reinforced concrete, woodworking and woodworking, experimental, repair, as well as laboratories, testing stations, garages, depots, administrative buildings. 7.5.9. These units, in which electrical energy is converted into heat using direct current, alternating current of low, high-medium high or ultra-high frequency, are recommended to be equipped with converters connected to general-purpose power supply networks directly or through independent furnace (power, converter) transformers. It is also recommended to equip industrial frequency ETS with arc furnaces (regardless of their voltage and power) and installations with furnaces with furnace (power) transformers or autotransformers1) induction and resistance furnaces operating at a voltage different from the voltage of the general-purpose electrical network, or with single-phase induction and resistance furnaces with a unit power of 0,4 MW or more, three-phase - 1,6 MW or more. Converters and furnace (converter) transformers (autotransformers), as a rule, must have a secondary voltage in accordance with the requirements of the technological process, and the primary voltage of the ETU must be selected taking into account technical and economic feasibility. Furnace transformers (autotransformers) and converters, as a rule, must be equipped with devices for voltage regulation when this is necessary under the conditions of the technological process. 1. Here and further in Chap. 7.5, in addition to electric furnaces, we also mean electric heating devices. 7.5.10. The primary circuit of each ECU, as a rule, must contain the following switching and protective devices, depending on the voltage of the power supply network of industrial frequency:
To connect an electrothermal device with a power of less than 1 kW to an electrical network up to 1 kV, it is allowed to use plug-in detachable contact connections at the input, connected to a line (main or radial), the protection device of which is installed in a power (lighting) point or panel. In the primary circuits of ETS with voltages up to 1 kV, it is allowed to use switches without arc-extinguishing contacts as input switching devices, provided that switching by them is carried out without load. Switches with voltages above 1 kV for operational and protective purposes in electrical installations, as a rule, must perform operations of turning on and off electrothermal equipment (furnaces or devices), determined by the operational features of its operation, and protection against short circuits and abnormal operating conditions. Operational switches with voltages above 1 kV ETU must perform operational and part of the protective functions, the scope of which is determined during a specific design, but they should not be provided with short-circuit protection (except for operational short-circuits that cannot be eliminated in the event of a malfunction of the furnace automatic control system), which must be provided by safety switches. Operational protective and operational switches with voltages above 1 kV can be installed both at furnace substations and in workshop (factory, etc.) distribution devices. It is allowed to install one safety switch to protect a group of electrothermal installations. 7.5.11. In electrical circuits with voltages above 1 kV with an average number of switching operations of five on-off cycles per day or more, special switches with increased mechanical and electrical wear resistance must be used that meet the requirements of current standards. 7.5.12. It is recommended that the electrical load of several single-phase electrical receivers connected to a general-purpose electrical network be distributed between the three phases of the network in such a way that, in all possible operating modes, the voltage asymmetry caused by their load, as a rule, does not exceed the values allowed by the current standard. In cases where such a condition at the selected point of connection to the general purpose network of single-phase electrical receivers ETU is not met and at the same time it is inappropriate (according to technical and economic indicators) to connect these electrical receivers to a more powerful electrical network (i.e. to a network point with a higher short-circuit power ), it is recommended to equip the ECU with a balun device or a parametric current source, or install switching devices, with the help of which it is possible to redistribute the load of single-phase electrical receivers between the phases of a three-phase network (if asymmetry occurs infrequently during operation). 7.5.13. The electrical load of the ETS, as a rule, should not cause non-sinusoidal voltage curves in general-purpose electrical networks, in which the requirement of the current standard is not met. If necessary, it is recommended to equip furnace step-down or converter substations or workshop (factory) transformer substations supplying them with filters for higher and, in some cases, lower harmonics, or to take other measures to reduce the distortion of the voltage waveform of the electrical network. 7.5.14. The power factor of ETS connected to general-purpose electrical networks, as a rule, must be no lower than 0,98. ETS with a unit power of 0,4 MW or more, the natural power factor of which is lower than the specified value, are recommended to be equipped with individual compensating devices, which should not be included in ETS if technical and economic calculations reveal clear advantages of group compensation. 7.5.15. For ETS connected to general-purpose electrical networks, for which capacitor banks are used as a compensating device, the circuit for connecting capacitors (in parallel or in series with electrothermal equipment), as a rule, should be selected based on technical and economic calculations, the nature of the change in the inductive load of the installation and the shape of the voltage curve, determined by the composition of higher harmonics. 7.5.16. Voltage of furnace (including converter) substations, including intra-shop ones, the number, power of transformers, autotransformers, converters or reactors installed in them, both dry and oil-filled or filled with environmentally friendly non-flammable liquid, the height (mark) of their location in relation to the floor of the first floors of the building, the distance between chambers with oil-filled equipment of different substations is not limited, provided that only two chambers (two rooms) with oil-filled equipment of furnace transformer or converter substations can be located nearby, separated by a wall with a fire resistance limit specified in 7.5.22 for load-bearing walls ; distance to similar two located in the same row with them1) cells (rooms) with a total number of up to six must be at least 1,5 m; with a larger number, a passage of at least 4 m wide should be arranged after every six cells (rooms). 1. Or one with their total number of three or five. 7.5.17. Under the oil-filled equipment of furnace substations, the following should be built:
The oil collection tank must be underground and located outside buildings at a distance of at least 9 m from walls of I-II degrees of fire resistance and at least 12 m from walls of III-IV degrees of fire resistance according to SNiP 21-01-97 "Fire safety of buildings and structures." The oil receiver should be covered with a metal grate, on top of which a layer of washed sifted gravel or non-porous crushed stone with particles from 30 to 70 mm should be poured, at least 250 mm thick. 7.5.18. Under devices for receiving oil, it is not allowed to place rooms with a permanent presence of people. Below them, the ETU control panel can only be located in a separate room with a protective waterproofed ceiling that prevents oil from entering the control room even if there is a low probability of leakage from any oil receiving devices. It should be possible to systematically inspect the waterproofing of the ceiling, its fire resistance limit is at least 0,75 hours. 7.5.19. The capacity of the underground collection tank must be no less than the total volume of oil in the equipment installed in the chamber, and when several chambers are connected to the collection tank, no less than the largest total volume of oil in one of the chambers. 7.5.20. The internal diameter of the oil drain pipes connecting the oil receivers to the underground holding tank is determined by the formula
where M is the mass of oil in the equipment located in the chamber (room) above this oil receiver, t; n is the number of pipes laid from the oil receiver to the underground holding tank. This diameter must be at least 100 mm. Oil drain pipes on the side of the oil receivers must be closed with removable meshes made of brass or stainless steel with mesh sizes of 3x3 mm. If it is necessary to turn the route, the bending radius of the pipe(s) must be at least five pipe diameters. In horizontal sections, the pipe must have a slope of at least 0,02 towards the holding tank. Under all conditions, the time for oil removal to the underground collection tank should be less than 0,75 hours. 7.5.21. Chambers (rooms) with oil-filled electrical equipment should be equipped with automatic fire extinguishing systems when the total amount of oil exceeds 10 tons - for cells (rooms) located at the first floor level and above, and 0,6 tons - for cells (rooms) located below the level first floor. These fire extinguishing systems must have, in addition to automatic, also manual start modes (local - for testing and remote - from the ETU control panel). If the total amount of oil in the specified chambers (rooms) is less than 10 and 0,6 tons, respectively, they must be equipped with a fire alarm. 7.5.22. When installing transformers, converters and other electrical equipment of the ECU in the chamber of an intra-shop furnace (including converter) substation or in another separate room (outside separate rooms - chambers - it is not allowed to install electrical equipment of the ECU with the amount of oil in it exceeding 60 kg, except for its location outside buildings in accordance with Chapter 4.2) its building structures, depending on the mass of oil in a given room, must have fire resistance limits of at least I degree according to SNiP 21-01-97. 7.5.23. ETU equipment, regardless of its rated voltage, is allowed to be placed directly in the production premises, if its design meets the environmental conditions in this room. At the same time, in explosion-, fire-hazardous and outdoor areas of premises, it is allowed to place only such ETS equipment that has levels and types of explosion protection standardized for a given environment or an appropriate degree of shell protection. The design and location of the equipment itself and fences must ensure the safety of personnel and exclude the possibility of mechanical damage to the equipment and accidental contact of personnel with live and rotating parts. If the length of an electric furnace, an electric heating device or a heated product is such that fencing the current-carrying parts causes a significant complication of the design or makes it difficult to service the equipment, it is allowed to install a fence around the furnace or the device as a whole with a height of at least 2 m with blocking, preventing the possibility of opening the doors until the installation is turned off. 7.5.24. Power electrical equipment with voltage up to 1,6 kV and higher, related to one ETU (furnace transformers, static converters, reactors, furnace switches, disconnectors, etc.), as well as auxiliary equipment for hydraulic drives and cooling systems of furnace transformers and converters (pumps closed water and oil-water cooling systems, heat exchangers, absorbers, fans, etc.) may be installed in a common chamber. The specified electrical equipment must have fencing for exposed live parts, and the operational control of the drives of the switching devices must be placed outside the chamber. In justified cases, it is recommended that the electrical equipment of several electrical installations be located in common electrical rooms, for example, in electrical machine rooms in compliance with the requirements of Chapter. 5.1. 7.5.25. Transformers, converting devices and ETU units (motor-generator and static - ion and electronic, including semiconductor devices and lamp generators) are recommended to be located at the minimum possible distance from the electric furnaces and electrothermal devices (apparatuses) connected to them. The minimum clear distances from the most protruding parts of the furnace transformer, located at a height of up to 1,9 m from the floor, to the walls of the transformer chambers in the absence of other equipment in the chambers are recommended to be taken:
When installing furnace transformers and other equipment together in a common chamber (in accordance with 7.5.24), the width of the passages and the distance between the equipment, as well as between the equipment and the walls of the chamber, are recommended to be 10-20% larger than the specified values. 7.5.26. These installations must be equipped with interlocks that ensure safe maintenance of electrical equipment and mechanisms of these installations, as well as the correct sequence of operational switching. Opening doors located outside the electrical rooms of cabinets, as well as doors of chambers (rooms) with live parts accessible to touch, should be possible only after removing the voltage from the installation; the doors must have a lock that acts to remove voltage from the installation without a time delay. 7.5.27. ETU must be equipped with protection devices in accordance with Sec. 3.1 and 3.2. Protection of arc furnaces and resistance arc furnaces shall be carried out in accordance with the requirements set out in 7.5.46, induction - in 7.5.54 (see also 7.5.38). 7.5.28. EES, as a rule, must have automatic regulators of the electrical operating mode, with the exception of EES, in which their use is impractical for technological or technical and economic reasons. For installations where AC value must be taken into account for electrical control (or overload protection), current transformers (or other sensors) should generally be installed on the low voltage side. In ETUs with high current values in the secondary current leads, current transformers can be installed on the higher voltage side. In this case, if the furnace transformer has a variable transformation ratio, it is recommended to use matching devices. 7.5.29. Measuring instruments and protection devices, as well as ETD control devices, must be installed so that the possibility of their overheating (from thermal radiation and other causes) is excluded. Switchboards and control panels (devices) for EPPs should, as a rule, be located in places where it is possible to monitor the production operations carried out at the installations. The direction of movement of the handle of the oven tilt drive control device must correspond to the direction of tilt. If ETUs are of considerable dimensions and the view from the control panel is insufficient, it is recommended to provide optical, television or other devices for monitoring the process. If necessary, emergency buttons should be installed to remotely shut down the entire installation or its individual parts. 7.5.30. On the control panels of the electric power plant, signaling of the on and off positions of operational switching devices should be provided (see 7.5.10); in installations with a unit power of 0,4 MW or more, it is recommended to also provide signaling of the on position of the input switching devices. 7.5.31. When selecting the cross-sections of electrical power supply conductors for currents of more than 1,5 kA of industrial frequency and for any currents of high-medium, high and ultra-high frequencies, including in circuits of higher harmonic filters and circuits of a reactive power stabilizer (thyristor-reactor group - TRG), it must take into account the uneven distribution of current both over the cross section of the bus (cable) and between individual buses (cables). The design of ETS current conductors (in particular, secondary conductors - “short networks” of electric furnaces) must ensure:
There should be no closed metal contours around single buses and lines (in particular, when passing through reinforced concrete partitions and ceilings, as well as when installing metal support structures, protective screens, etc.). Current conductors for industrial frequency currents of more than 4 kA and for any currents of high-medium, high and ultra-high frequencies should not be laid near steel building elements of buildings and structures. If this cannot be avoided, then for the corresponding building elements it is necessary to use non-magnetic and low-magnetic materials and check by calculation the loss of electricity in them and the temperature of their heating. If necessary, it is recommended to provide screens. For AC current conductors with a frequency of 2,4 kHz, the use of fastening parts made of magnetic materials is not recommended, and with a frequency of 4 kHz or more, it is not allowed, with the exception of busbar connection points to water-cooled elements. Supporting structures and protective screens of such conductors (with the exception of the structure for coaxial conductors) must be made of non-magnetic or low-magnetic materials. The temperature of busbars and contact connections, taking into account heating by electric current and external thermal radiation, as a rule, should not exceed 90 ºС. In reconstructed installations for secondary current leads, in justified cases, a temperature of 140 ºС is allowed for copper busbars, and 120ºС for aluminum busbars, while the busbar connections should be made welded. The maximum busbar temperature at a given current load and environmental conditions must be checked by calculation. If necessary, forced air or water cooling should be provided. 7.5.32. In installations of electric furnaces and electric heating devices with a quiet operating mode, including indirect arc, plasma, resistance arc heating (see 7.5.1), direct arc - vacuum arc (also skull), induction and dielectric heating, resistance direct and indirect heating, including ESR, ESL and ESHN, electron beam, ion and laser for rigid current conductors of secondary current leads, as a rule, busbars made of aluminum or aluminum alloys should be used. For the rigid part of the secondary current supply of electric furnace installations with shock loads, in particular steel and iron-smelting arc furnaces, it is recommended to use aluminum alloy busbars with increased mechanical and fatigue strength. It is recommended that the rigid conductor of the secondary current supply in alternating current circuits from multi-pole busbar packages be laminated with parallel alternating circuits of different phases or forward and reverse directions of current. Rigid single-phase current conductors of high-medium frequency are recommended to be used laminated and coaxial. In justified cases, it is allowed to manufacture rigid conductors of secondary current leads from copper. Flexible current conductor on moving elements of electric furnaces should be made with flexible copper cables or flexible copper tapes. For flexible current conductors for currents of 6 kA and more at industrial frequencies and for any currents of high medium and high frequencies, it is recommended to use water-cooled flexible cables. 7.5.33. Recommended permissible continuous currents are given at load: industrial frequency current of busbars from a laminated package of rectangular busbars - in table. 7.5.1 - 7.5.4, high-medium frequency current of current conductors from two rectangular busbars - in table. 7.5.5 - 7.5.6 and coaxial current conductors from two concentric pipes - in table. 7.5.7 - 7.5.8, ASG brand cables - in table. 7.5.9 and SG brands - in table. 7.5.10. The currents in the tables are taken taking into account the ambient air temperature of 25 ºС, rectangular busbars - 70 ºС, internal pipe - 75 ºС, cable cores - 80 ºС (correction factors for other ambient temperatures are given in Chapter 1.3 of the Electrical Installation Code). The recommended current density in water-cooled rigid and flexible industrial frequency conductors is: aluminum and aluminum alloys - up to 6 A/mm2, copper - up to 8 A/mm2. The optimal current density in such conductors, as well as in similar conductors of high-medium, high and ultra-high frequencies, should be selected at a minimum of reduced costs. For high-medium frequency lines, in addition to current conductors, it is recommended to use special coaxial cables (see also 7.5.53) Coaxial cable KVSP-M (rated voltage 2 kV) is designed for the following permissible currents:
Depending on the ambient temperature, the following load factors kn are established for the KVSP-M cable:
Table 7.5.1 Permissible long-term industrial frequency current of single-phase current conductors made from a laminated package of aluminum rectangular busbars 1), 2), 3)
1. In table. 7.5.1 - 7.5.4 currents are given for unpainted tires mounted on edge, with a gap between the tires of 30 mm for tires with a height of 300 mm and 20 mm for tires with a height of 250 mm or less. 2. Coefficients (k) of permissible long-term current load (to tables 7.5.1 and 7.5.3) of aluminum busbars painted with oil paint or enamel varnish:
3. Reduction factor for permissible long-term current load for busbars made of AD31T-0,94 alloy and AD31T-0,91 alloy. Table 7.5.2. Permissible long-term industrial frequency current of single-phase busbars made from a laminated package of rectangular copper busbars*
* See note to table. 7.5.1. Table 7.5.3. Permissible continuous current of industrial frequency of three-phase conductors from a laminated package of aluminum rectangular busbars*
*Cm. note to table. 7.5.1. Table 7.5.4. Permissible long-term industrial frequency current of three-phase busbars made from a laminated package of rectangular copper busbars*
*Cm. note to table. 7.5.1. Table 7.5.5. Permissible long-term high-medium frequency current of conductors made of two aluminum rectangular busbars 1), 2), 3)
1. In table. 7.5.5 and 7.5.6 currents are given for unpainted busbars with a calculated thickness equal to 1,2 current penetration depths, with a gap between the spikes of 20 mm when installing the busbars on the edge and laying them in a horizontal plane. 2. The thickness of busbars, the permissible long-term currents of which are given in table. 7.5.5 and 7.5.6, must be equal to or greater than the calculated value; it should be selected based on the requirements for the mechanical strength of tires, from the range given in the standards or technical specifications. 3. Current penetration depth h, with aluminum busbars depending on the frequency of alternating current f:
Table 7.5.6. Permissible long-term current of increased-medium frequency of conductors from two copper rectangular busbars 1)
1. Current penetration depth, h, with copper busbars depending on the alternating current frequency f:
2. See also notes 1 and 2 to the table. 7.5.5. Table 7.5.7. Permissible long-term current of high-medium frequency of conductors made of two aluminum concentric pipes 1)
1. In the table. 7.5.7 and 7.5.8 current loads are given for unpainted pipes with a wall thickness of 10 mm. Table 7.5.8. Permissible long-term current of high-medium frequency of current conductors from two copper concentric pipes*
* See note to table. 7.5.7. Table 7.5.9. Permissible long-term high-medium frequency current of ASG brand cables for a voltage of 1 kV with a single-phase load 1)
1. Current loads are given based on the use: for three-core cables in the “forward” direction - one core, in the “reverse” direction - two, for four-core cables in the “forward” and “reverse” directions - two cores each, arranged crosswise. Table 7.5.10. Permissible long-term current of high-medium frequency cables of the SG brand for a voltage of 1 kV at a single-phase load *
* See note to table. 7.5.9. 7.5.34. The dynamic resistance at short-circuit currents of rigid ETS busducts with a rated current of 10 kA or more must be calculated taking into account the possible increase in electromagnetic forces in places of turns and intersections of busbars. When determining the distances between the supports of such a conductor, the possibility of partial or complete resonance must be checked. 7.5.35. For conductors of electrothermal installations, as insulating supports of busbar packages and gaskets between them in electrical circuits of direct and alternating current of industrial, low and high-medium frequencies with voltage up to 1 kV, it is recommended to use blocks or slabs (sheets) made of unimpregnated asbestos cement, in circuits with voltage from 1 up to 1,6 kV - from getinax, fiberglass or heat-resistant plastics. In justified cases, such insulating materials can be used at voltages up to 1 kV. For voltages up to 500 V, in dry and dust-free rooms, it is allowed to use impregnated (boiled in drying oil) beech or birch wood. For electric furnaces with abruptly changing shock loads, the supports (compresses, gaskets) must be vibration-resistant (at a frequency of oscillation of the effective current values of 0,5-20 Hz). It is recommended to use a bent U-shaped profile made of non-magnetic steel sheet as metal compression parts of the busbar package of current conductors for 1,5 kA or more alternating current of industrial frequency and for any currents of high-medium, high and ultra-high frequencies. It is also allowed to use welded profiles and silumin parts (except for clamps for heavy multi-strip bags). For compression, it is recommended to use bolts and studs made of non-magnetic chromium-nickel, copper-zinc (brass) alloys. For current conductors above 1,6 kV, porcelain or glass support insulators should be used as insulating supports, and at currents of 1,5 kA or more industrial frequency and for any currents of high-medium, high and ultra-high frequencies, the insulator reinforcement, as a rule, should be aluminum. The insulator fittings must be made of non-magnetic (low-magnetic) materials or protected by aluminum screens. The level of electrical insulation strength between busbars of different polarity (different phases) of busbar packages with rectangular or tubular conductors of secondary current leads of electrothermal installations located in production premises must comply with the standards and/or specifications for certain types (types) of electric furnaces or electric heating devices. If such data is not available, then when commissioning the installation, the parameters must be provided in accordance with Table. 7.5.11. As an additional measure to increase operational reliability and ensure the normalized value of insulation resistance, it is recommended to additionally insulate the busbars of secondary current leads in places of compression with insulating varnish or tape, and to attach insulating gaskets that are thermally and mechanically resistant between compensators of different phases (of different polarities). Table 7.5.11. Insulation resistance of conductors of secondary current leads
* Insulation resistance should be measured with a megohmmeter at a voltage of 1,0 or 2,5 kV with the conductor disconnected from the terminals of the transformer, converter, switching devices, resistance heaters, etc., with the electrodes and hoses of the water cooling system removed. 7.5.36. The clear distances between buses of different polarities (different phases) of a rigid DC or AC current conductor must be within the limits specified in Table. 7.5.12, and determined depending on the nominal value of its voltage, type of current and frequency. Table 7.5.12. Clear distance between busbars of secondary current lead1)
1. With tire height up to 250 mm; at a higher height, the distance should be increased by 5-10 mm. 2. Dust is non-conductive. 7.5.37. Bridge, overhead, cantilever and other similar cranes and hoists used in rooms where there are installations of direct-acting electric resistance heaters, direct-heated arc furnaces and combined heating - arc resistance furnaces with bypassing self-sintering electrodes without shutting down the installations, must have insulating gaskets (providing three stages of isolation with a resistance of each stage of at least 0,5 MΩ), excluding the possibility of connecting to the ground (through a hook or cable of lifting and transport mechanisms) of the installation elements under voltage. 7.5.38. The incoming cooling system for equipment, apparatus and other elements of electrothermal installations must be designed taking into account the possibility of monitoring the condition of the cooling system. It is recommended to install the following relays: pressure, jet and temperature (the last two - at the outlet of water from the elements cooled by it) with their operation on a signal. In the event that stopping the flow or overheating of the cooling water can lead to emergency damage to the elements of the ECU, automatic shutdown of the installation must be ensured. The water cooling system - open (from the water supply network or from the enterprise's circulating water supply network) or closed (two-circuit with heat exchangers), individual or group - must be selected taking into account the requirements for water quality specified in the standards or technical specifications for the equipment of the electrothermal installation. Water-cooled elements of electrothermal installations with an open-loop cooling system must be designed for a maximum of 0,6 MPa and a minimum of 0,2 MPa of water pressure. If the standards or technical specifications for the equipment do not provide other standard values, the water quality must meet the requirements:
It is recommended to provide for the reuse of cooling water for other technological needs with a collection and pumping device. In cooling systems for elements of electrothermal installations that use water from the recycling water supply network, it is recommended to provide mechanical filters to reduce the content of suspended particles in the water. When choosing an individual closed water cooling system, it is recommended to provide a secondary water circulation circuit without a backup pump, so that if the operating pump fails, water from the water supply network is used for the time required for an emergency shutdown of the equipment. When using a group closed water cooling system, it is recommended to install one or two backup pumps with automatic switching on of the reserve. 7.5.39. When cooling elements of an electrothermal installation that may be energized with water through a flow or circulation system, insulating hoses (sleeves) must be provided to prevent the removal of potential through pipelines that is dangerous for operating personnel. The supply and drain ends of the hose must have metal pipes, which must be grounded if there is no fence to prevent personnel from touching them when the unit is turned on. The length of insulating water cooling hoses connecting elements of different polarities must be no less than specified in the technical documentation of the equipment manufacturers; in the absence of such data, it is recommended to take the length equal to: at rated voltage up to 1,6 kV, at least 1,5 m for hoses with an internal diameter of up to 25 mm and 2,5 m for hoses with a diameter of more than 25 mm; at rated voltage above 1,6 kV - 2,5 and 4 m, respectively. The length of the hoses is not standardized if there is a gap between the hose and the waste pipe and the stream of water falls freely into the funnel. 7.5.40. These equipment, the equipment of which requires prompt maintenance at a height of 2 m or more from the floor level of the room, must be equipped with working platforms, fenced with railings, with permanent stairs. The use of movable (for example, telescopic) ladders is not permitted. In an area where personnel may touch live parts of the equipment, platforms, fences and stairs must be made of non-combustible materials and coated with a dielectric material that does not propagate combustion. 7.5.41. Pump-battery and oil-pressure installations of hydraulic drive systems of electrothermal equipment containing 60 kg of oil or more must be located in rooms that provide emergency oil removal and compliance with the requirements of 7.5.17 - 7.5.22. 7.5.42. Vessels used in electrothermal installations operating under pressure above 70 kPa, devices using compressed gases, as well as compressor units must meet the requirements of the current rules approved by the Gosgortekhnadzor of Russia. 7.5.43. Gases from the exhaust of preliminary vacuum pumps, as a rule, must be removed outside; the release of these gases into production and similar premises is allowed only when the sanitary and hygienic requirements for air in the working area are not violated (SSBT GOST 12.1.005- 88).
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