Antipyretics for children are prescribed by a pediatrician. But there are situations of emergency care for fever, when the child needs to give the medicine immediately. Then the parents take responsibility and apply antipyretic drugs. What is allowed to give to infants? How can you bring down the temperature in older children? Which medications are the safest?
Operation of electrical substations and switchgears Krasnik V. V.
2.2.4. Installation and maintenance of cooling systems for oil transformers
The process of transferring heat generated in windings, magnetic circuit and steel parts of a working transformer into the environment can be divided into the following two stages:
transfer of heat from windings and magnetic circuit to cooling oil
and the transfer of heat from the oil to the environment.
At the first stage, the transfer of heat is determined by the excess of the temperature of the windings and magnetic circuit above the temperature of the cooling oil; at the second stage - exceeding the temperature of the oil above the ambient temperature.
On this basis, it is conventionally accepted that the oil transformer cooling device consists of two systems: an internal cooling system that provides heat transfer in the first cooling stage and an external cooling system that provides heat transfer in the second stage.
Elements of the internal cooling system are vertical and horizontal channels in the windings and magnetic circuit, as well as special pipes and insulating panels, creating a directed circulation of oil through the channels. All these elements are located inside the transformer tank, which makes it impossible to visual control them.
The external cooling system includes oil coolers, filters, pumps, fans and other equipment located outside the transformer. The work of this equipment is systematically monitored.
Transformers with cooling systems are used at the substation M, D, DC and C.
Natural oil cooling system (M) is performed for low-power transformers (up to 16 MVA) with voltage, as a rule, up to 35 kV. In such transformers, the heat released in the windings and magnetic circuit is transferred to the oil circulating through the tank and radiators, and then to the surrounding air. Tanks of such transformers are smooth with cooling tubes or hinged tubular radiators (coolers). To better deliver heat to the environment, the transformer tank is supplied with fins, cooling pipes or radiators, depending on the power. Each radiator is a separate unit, connected by its branch pipes to the nozzles of the tank. Between the flanges of the nozzles are built flat cranes, overlapping the access of oil to the radiator. The natural movement of heated and cold oil layers in the transformer is due to their different density, that is, due to gravitational forces. In the environment, heat is transferred by convection air flows at the surface of the tank and radiators, as well as by radiation. At the nominal load of the transformer in accordance with the requirements of the PTE, the oil temperature in the upper, most heated layers should not exceed +95 ° C.
Cooling system D (oil cooling with blowing and natural circulation of oil) is used for more powerful transformers with voltage of 35, 110 and 220 kV. Cooling is based on the use of hinged radiators, blown by fans, which are installed on welded to the wall of the tank consoles. The fan sucks the air from the bottom and blows the heated upper part of the pipes. Each fan consists of a drive asynchronous motor and an impeller of the MC series. The fans start and stop automatically depending on the load and oil heating temperature. The fans motors are switched on and off automatically using thermometric signaling devices of the TC-100 type and manually. The impeller hub has a keyway on the motor shaft, which prevents the impeller from jumping off during operation.
Transformers with this cooling can operate with a fully de-energized blow if the load does not exceed 100% of the nominal and the temperature of the upper oil layers is not more than 55 ° C, and also regardless of the load at negative ambient temperatures and oil temperatures not exceeding 45 ° C. The maximum permissible oil temperature in the upper layers when the transformer is operating at rated load is 95 ° C.
In Fig. 2.1 shows the power supply for the fan motors.
Cooling system DC (oil cooling with blowing and forced circulation of oil through air coolers) is used to cool external transformers with a capacity of 63 MVA and more than 110 kV and higher. This system is based on the use of oil-air coolers with forced circulation of oil and forced air cooling of finned tubes of air coolers. Coolers consist of thin ribbed tubes blown from the outside by a fan, and are equipped with sealless centrifugal pumps of the ECT series and slow-moving fans of the type NAP-7,4. Electropumps built into the oil lines create a continuous forced circulation of the oil through the coolers. Due to the high oil circulation speed, large cooling surface and intensive blowing, the coolers have a high heat dissipation and compactness. Such a cooling system can significantly reduce the overall dimensions of the transformers. Coolers can be installed together with the transformer on the same foundation or on separate foundations next to the transformer tank. In order to increase the efficiency of heat transfer in large transformers, oil is fed through special pipes to certain parts of the windings, as a result of which a directed circulation of oil through the cooling channels is created. For cooling devices with directional circulation of oil through the windings of transformers, pumps with a shielded stator of ECTEC type are used. Cooling control is automatic and manual. The automatic control circuit provides for the inclusion of the main group of coolers when the transformers are switched on, increasing the cooling intensity by switching on an additional cooler when the nominal load or the specified oil temperature in the transformer is reached, switching on the backup cooler in case of emergency shutdown of any worker, switching off the blowing fans without stopping the circulation pumps. Cooling control cabinets are equipped with a permanent alarm on stopping oil circulation, stopping the blast fans, turning on the backup cooler, switching the power supply of the cooling system engines from the backup source when the voltage is gone or when it is lowered in the network.
Cooling system C (oil-water cooling of transformers with forced oil circulation) is used for transformers of external and internal installation. This system is basically structured in the same way as the cooling system DC, but unlike the latter, the coolers in this system consist of tubes through which water circulates, and oil flows between the tubes. The oil temperature at the oil cooler inlet must not exceed 70 ° C. This system is compact and because of the greater intensity of heat transfer from oil to water than from oil to air, it has high reliability and thermal efficiency. However, the application of cooling C It is possible only if there is a powerful source of water supply. For outdoor transformers, the coolers are placed in a room with a positive temperature. In winter, measures are also envisaged to prevent freezing of water in oil coolers, pumps, waterways, for example, draining water from coolers when the transformer is disconnected, heating the coolers, etc. In order to prevent water from sucking into the oil when leakage and cracks form in the pipes, on which water circulates, oil pumps are installed in front of oil coolers. For the same purpose, the excess oil pressure in the oil cooler is maintained above the water pressure by at least 0.2 MPa (2 N / cm 2). In cooling systems C There are devices for monitoring the temperature, flow and pressure of oil and water, for cleaning oil and water, as well as cooling control equipment and various signaling devices. This cooling system is efficient, but has a complex design and is therefore used for powerful transformers (160 MVA and higher).
With manual control, the cooling system is switched on after the transformer is plugged into the mains in the following sequence: first the oil pump is started up and the oil circulation in the oil cooler is checked, then the cooling water is supplied and the ratio of the water and oil pressures is checked. If necessary, adjust the water pressure. Oil coolers in the oil-water cooling system reduce the oil temperature by 10-15 ° C and are able to maintain the temperature of the upper oil layers at a level of 50-55 ° C. Therefore, the cooling water is supplied to the oil coolers at a temperature of at least 15 ° C. Circulation of water is stopped when the oil temperature drops to 10 ° C. Disconnect the oil-water cooling after the transformer is disconnected from the mains in the following sequence: first stop the water access to the oil cooler and then switch off the oil pump.
In accordance with the requirements of the PTE, at the rated load of the transformer, the temperature of the upper oil layers should not be higher (if the manufacturer's factory instructions do not specify other temperatures):
transformers with oil cooling system with blowing and forced circulation of oil ( DC) - 75 ° C;
with oil cooling systems ( M) and oil cooling with blowing ( D) - 95 ° C;
transformers with oil cooling system with forced circulation of oil through the water cooler ( C) the oil temperature at the inlet to the oil cooler must not be higher than 70 ° C.
On transformers and reactors with oil cooling systems DC, directed circulation of oil in windings ( NDC), C, directed circulation of oil in the windings and forced through the water cooler ( NC) the cooling devices must be automatically switched on (switched off) at the same time as the transformer (reactor) is switched on (off).
For rated load, the inclusion of transformers is allowed:
with cooling systems M and D - at any negative air temperature;
with cooling systems DC and C - at an ambient temperature of minus 25 ° C. At lower temperatures, the transformer must first be preheated with a load of up to 0.5 nominal without triggering an oil circulation system, which must be activated only after the temperature of the upper oil layers has increased to minus 25 ° C.
In emergency modes, the transformers can be switched on to full load regardless of the ambient temperature (transformers with cooling systems NDC, NC - in accordance with the factory instructions).
Forced circulation of oil in cooling systems must be continuous regardless of the load of the transformer.
Number of chillers for main and standby cooling systems to be switched on and off DC (NDC), C (NC), operating conditions of the transformers with the cooling system switched off D are determined by factory instructions.
Operation of transformers and reactors with forced circulation of oil is allowed only when the alarm system is activated to stop the circulation of oil, cooling water and the operation of fans for cooling the coolers.
When the oil-water cooling system is turned on C (NC) first of all an oil pump must be started. Then, at the temperature of the upper oil layers above 15 ° C, a water pump is turned on. The water pump is switched off when the temperature of the upper oil layers drops to 10 ° C, unless otherwise specified by the factory documentation.
The oil pressure in the oil coolers must exceed the circulating water pressure by at least 10 kPa (0.1 kgf / cm 2) with the minimum oil level in the transformer expander.
Measures should be provided to prevent the freezing of oil coolers, pumps, waterways.
For transformers with cooling systems, if all fans are switched off accidentally, the rated load may be operated depending on the ambient temperature for the next time:
For transformers with cooling systems DC and TS, it is allowed:
at the end of artificial cooling operation with a nominal load for 10 minutes or idle (XX) for 30 minutes, if after the specified time the temperature of the upper oil layers did not reach 80 ° C; for transformers with a capacity of over 250 MVA, it is allowed to work with a rated load up to the specified temperature, but not more than 1 hour;
with full or partial deactivation of the fans or when the circulation of water ceases while maintaining the circulation of the oil, continuous operation with reduced load at the temperature of the upper oil layers is not higher than 45 ° C.
These requirements are valid unless otherwise specified in the manufacturer's instructions.
On transformers with a cooling system, the fan motors must be systematically switched on at an oil temperature of 55 ° C or a current equal to the nominal, regardless of the oil temperature. The fan motors are switched off when the temperature of the upper oil layers drops to 50 ° C, if the load current is less than the rated current.
The main tasks of servicing cooling systems are monitoring and technical maintenance of cooling system equipment.
Inspection The cooling system is manufactured simultaneously with the inspection of the transformer. Upon inspection, the integrity of the entire cooling system is checked, that is, no leakage of oil; the work of radiators (the degree of their heating is determined by touch); cooling system operation DC by their heating and by the readings of manometers installed near the nozzles of oil-pumping pumps; work adsorption filters - palpation of the hand; the condition of the fastenings of pipelines, coolers, pumps and fans; the work of the fans is due to the absence of vibrations, rattling and rupture of the impellers behind the casing.
When inspecting the cabinets of automatic cooling control, the absence of heating and corrosion of contacts, as well as damage to insulation of live parts of equipment, sealing the bottoms and doors of cabinets against penetration of dust and moisture into them is checked.
An extraordinary inspection of the circuit-breakers in the cabinets should be performed after each short-circuit trip. Also it is necessary to inspect the contacts of switching equipment after automatic switching-off of electric motors of fans and pumps.
Technical Care for cooling system devices includes the elimination of malfunctions detected during inspection, replacement of worn parts (pump blades, fan blades, bearings), cleaning of coolers and fans, lubrication of bearings, monitoring of insulation resistance of electric motors.
When taking care of the coolants of the cooling system C periodic cleaning of pipes and water chambers from silt and other deposits on cooling surfaces is performed.
The correctness of the power supply circuits for the cooling engines and the operation of the ATS are checked on a schedule at least once a month.
The efficiency of cooling systems as a whole is checked by the temperature of the upper oil layers in the transformer. With good cooling, the maximum oil temperatures should not exceed in transformers:
with cooling M and D - 95 ° C;
with cooling DC at power up to 250 MVA inclusive - 80 ° C and at a power above 250 MVA - 75 ° C;
with cooling C the oil temperature at the inlet to the oil coolers is 70 ° C.
For the maximum oil temperature in this case, the oil temperature under the tank lid is taken, measured with the transformer operating at rated load for 10-12 h for transformers with cooling M and D, and for 6-8 hours - for transformers with cooling DC with a constant cooling air temperature of 40 ° C.
In operation at the rated load of the transformer, the temperature of the upper oil layers rarely reaches a maximum value.
The following reasons are possible for increasing the heating of the oil for cooling systems M and D:
closed or not fully open flat radiator taps; from the upper radiator collectors the air is not released when the radiators are filled with oil;
the external surfaces of the radiators are heavily soiled.
For cooling D besides the listed above, the following reasons are possible:
not all fans are in operation,
fan impellers rotate in the opposite direction.
For cooling system DC the following reasons are typical:
the impeller of the pump rotates in the opposite direction;
insufficient number of working fans;
fan impellers rotate in the opposite direction;
the surfaces of the fins of the coolant tubes are heavily soiled, etc.
If the external inspection does not reveal a malfunction in the operation of the cooling system, hence the cause of excessive heat may be a malfunction of the transformer itself.
In accordance with the requirements of the PUE, each oil transformer should be installed in a separate chamber located on the first floor. It is allowed to install oil transformers on the second floor, and also below the floor level of the first floor by 1 m in non-flooded areas, provided that it is possible to transport outside and remove oil in emergency situations.
It is allowed to install two oil transformers in the common chamber with an oil volume of up to 3 tons each, having a general purpose, control, protection and considered as one unit.
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From the book Carving on wood [Techniques, receptions, products] author Podolsky Yuri Fedorovich From the book Commodity: Crib author author unknownChapter 2.1. POWER TRANSFORMERS AND REACTORS
2.1.1. Installation of transformers and reactors should be carried out in accordance with the rules for the installation of electrical installations and standards for technological design of substations.
Transportation, unloading, storage, installation and commissioning of transformers and reactors must be carried out in accordance with the guidelines (instructions) of the manufacturing plants.
2.1.2. When using power transformers (autotransformers) and shunt oil reactors, their reliable operation must be ensured. Loads, voltage level, temperature, oil characteristics and insulation parameters must be within the established norms; devices for cooling, voltage regulation, protection, oil facilities and other elements should be kept in good order.
2.1.3. Transformers (reactors) equipped with gas protection devices must be installed so that the lid (removable part of the tank) has a rise to at least 1% towards the gas relay. At the same time, the oil line to the expander must have a slope of at least 2%.
2.1.4. The oil level in the expander of a non-working transformer (reactor) should be at the mark corresponding to the oil temperature of the transformer (reactor) at the moment.
The service personnel should monitor the temperature of the upper layers of the oil by means of thermosignals and thermometers, which are equipped with transformers with an expander, as well as for readings of manometers for sealed transformers, for which, when the pressure in the tank is raised above 50 kPa (0.5 kgf / cm2), the load must be reduced.
2.1.5. The air cavity of the protective tube of the transformer (reactor) must be connected to the air cavity of the expander.
The level of the membrane of the safety pipe must be higher than the level of the expander.
The exhaust pipe membrane, if damaged, can only be replaced with an identical factory one.
2.1.6. Stationary fire extinguishing installations should be in a state of readiness for use in emergency situations and subject to inspections on an approved schedule.
2.1.7. Gravel backfilling of oil receivers of transformers (reactors) should be kept in a clean condition and washed at least once a year.
When contaminating gravel backfilling (dust, sand, etc.) or gravel packing, it should be flushed, as a rule, in spring and autumn.
When gravel deposits are formed on solid deposits from oil products thicker than 3 mm, the appearance of vegetation or the impossibility of washing it should be replaced by gravel.
2.1.8. On the tanks of the three-phase transformers of the outdoor installation, substation numbers must be indicated. On the groups of single-phase transformers and reactors, the substation number is indicated in the middle phase. The colors of the phases are applied to the tanks of the group of single-phase transformers and reactors.
Transformers and reactors of the outdoor installation are painted in light colors with a paint resistant to weathering and the effects of transformer oil.
2.1.9. On the doors of transformer points and chambers from the outside and inside, substation numbers of transformers must be indicated, and also warning signs should be on the outside. Doors must be permanently locked.
2.1.10. Inspection and maintenance of highly located elements of transformers and reactors (more than 3 m) should be performed from stationary staircases with railings and platforms at the top with safety rules.
2.1.11. The inclusion of a transformer (reactor) into the network must be effected by a push to full voltage. Transformers operating in a block with a generator can be put into operation together with the generator by raising the voltage from zero.
2.1.12. For each electrical installation, depending on the load schedule, taking into account the reliability of consumer power supply and minimum losses, the number of simultaneously operating transformers must be determined.
In distributing electrical networks with voltage up to 20 kV inclusive, measurements of loads and voltages of transformers are made in the first year of operation at least 2 times during the period of maximum and minimum loads, then - if necessary.
2.1.13. Reserve transformers must be kept in a state of constant readiness to be put into operation.
2.1.14. Neutrals of windings with a voltage of 110 kV of transformers and reactors should work, as a rule, in the mode of blind earthing. Another mode of operation of neutral transformers with a voltage of 110 kV and ways to protect them is established by the power supply organization.
2.1.15. If the transformer (reactor) is automatically disconnected, the transformer (reactor) can be turned on only after inspection, testing, analysis of gas, oil and the elimination of detected defects (damage) by the action of internal damage protection.
If the transformer (reactor) is disconnected from the protection, the action of which is not related to its internal damage, it can be switched on again without checking.
2.1.16. When the gas relay triggers the signal, an external inspection of the transformer (reactor) and the removal of gas from the relay for analysis and checking for flammability should be carried out.
To ensure the safety of personnel when extracting gas from the gas relay and identifying the cause of its operation, the transformer (reactor) must be unloaded and disconnected as soon as possible.
If the gas in the relay is non-combustible and there are no signs of damage to the transformer, and its disconnection caused a shortage of electricity, it can be switched on until the cause of the gas relay's response to the signal is determined. The duration of the transformer in this case is determined by the person responsible for the electric power of the Consumer. Based on the analysis of gas from the gas relay, oil analysis and other measurements and tests, it is necessary to establish the cause of the operation of the gas relay on the signal, to determine the technical state of the transformer (reactor) and the possibility of its normal operation.
2.1.17. The oil in the expander of transformers (reactors), as well as in the tank or expander of the voltage regulation device under load (hereinafter referred to as the "on-load tap-changer") must be protected from contact with air. For transformers and reactors equipped with special devices that prevent the oil from humidifying, these devices must be constantly switched on, regardless of the mode of operation of the transformer (reactor). These devices must be operated in accordance with the manufacturer's instructions.
Transformers with a capacity of 1000 kVA and more must be operated with a continuous oil regeneration system in thermosyphon and adsorption filters.
Oil of oil-filled bushings of leak-tight design should be protected from oxidation and humidification.
2.1.18. If it is necessary to switch off the idle current disconnector of an unloaded transformer equipped with a on-load tap-changer, after switching off the load on the consumer side, the switch must be set to the position corresponding to the rated voltage.
2.1.19. The parallel operation of transformers (autotransformers) is allowed provided that none of the windings is loaded with a current exceeding the permissible current for this winding.
Parallel operation of transformers is permitted under the following conditions:
- groups of winding connections are identical;
- power ratio of transformers not more than 1: 3;
- the transformation coefficients differ by not more than +/- 0.5%;
- short-circuit voltage differ by not more than +/- 10%;
- phased transformers.
To equalize the load between parallel-acting transformers with different short-circuit voltages, a change in the transformation ratio by switching the tapping is allowed, provided that none of the transformers is overloaded.
2.1.20. For oil transformers and transformers with a liquid non-combustible dielectric, a continuous load of any winding by a current exceeding by 5% the rated branch current is permissible if the voltage does not exceed the rated voltage of the corresponding tap. In the autotransformer, the current in the common winding must not be higher than the longest permissible current of this winding.
Long-term permissible loads of dry transformers are established in the standards and technical conditions of specific groups and types of transformers.
For oil and dry transformers, as well as transformers with a liquid non-combustible dielectric, systematic overloads are allowed, the significance and duration of which are regulated by the instructions of the manufacturing plants.
2.1.21. In emergency modes, short-term overloading of transformers in excess of the rated current is allowed for all cooling systems, regardless of the duration and value of the preceding load and the temperature of the cooling medium within the following limits:
| Oil transformers: | |||||
| overcurrent,% | 30 | 45 | 60 | 75 | 100 |
| 120 | 80 | 45 | 20 | 10 | |
| Dry transformers: | |||||
| overcurrent,% | 20 | 30 | 40 | 50 | 60 |
| duration of overload, min. | 60 | 45 | 32 | 18 | 5 |
2.1.22. A continuous operation of the transformers (at a load not exceeding the rated power) is permissible with an increase in the voltage at any branch of any winding by 10% in excess of the nominal voltage of this branch. At the same time, the voltage on any of the windings should not be higher than the maximum operating voltage.
2.1.23. At the rated load of the transformer, the temperature of the upper oil layers should not be higher (unless the manufacturer specifies other temperatures in the factory instructions): transformers with an oil cooling system with blowing and forced circulation of oil (hereinafter - DC) - 75 degrees. C, with oil cooling systems (hereinafter - M) and oil cooling with blowing (hereinafter - D) - 95 degrees. FROM; for transformers with oil cooling system with forced circulation of oil through the water cooler (hereinafter - C), the oil temperature at the inlet to the oil cooler must not be more than 70 deg. FROM.
2.1.24. On transformers and reactors with oil cooling systems DC, directed oil circulating in the windings (hereinafter referred to as NDC), C, directed circulation of oil in the windings and forced - through the water cooler (hereinafter - NC), cooling devices should automatically turn on (turn off) simultaneously with the inclusion ( off) of the transformer (reactor).
For rated load, the inclusion of transformers is allowed:
- with cooling systems M and D - at any negative air temperature;
- with cooling systems DC and C - at an ambient temperature of at least minus 25 degrees. C. At lower temperatures, the transformer must first be preheated with a load of up to 0.5 nominal without starting the oil circulation system. The oil circulation system should be switched on only after increasing the temperature of the upper oil layers to minus 25 degrees. FROM.
In emergency conditions, the transformers can be switched on to full load regardless of the ambient temperature (transformers with NDC cooling systems, NC - in accordance with factory instructions).
2.1.25. Forced circulation of oil in cooling systems must be continuous regardless of the load of the transformer.
2.1.26. The number of switched on and off coolers of the main and reserve cooling systems of the DC (NDC), C (NC), operating conditions of the transformers with the blow-off of the cooling system D disconnected are determined by the factory instructions.
2.1.27. Operation of transformers and reactors with forced circulation of oil is allowed only when the alarm system is activated to stop the circulation of oil, cooling water and the operation of fans for cooling the coolers.
2.1.28. When switching on the oil and water cooling system, the oil pump must be started first. Then, at the temperature of the upper layers of the oil, it is above 15 deg. C turns on the water pump. The water pump is switched off when the temperature of the upper oil layers drops to 10 degrees. C, unless otherwise provided by the factory documentation.
The oil pressure in the oil coolers must exceed the circulating water pressure by at least 10 kPa (0.1 kgf / cm2) with the minimum oil level in the transformer expander.
Measures should be provided to prevent the freezing of oil coolers, pumps, waterways.
2.1.29. For transformers with cooling systems D, if all fans are switched off accidentally, the rated load may be operated depending on the ambient temperature for the following time:
For transformers with cooling systems DC and TS, it is allowed:
- a) with the termination of artificial cooling, work with a nominal load for 10 minutes. or idling for 30 minutes; if after the specified time the temperature of the upper oil layers did not reach 80 degrees. FROM; for transformers with a capacity exceeding 250 MVA, it is allowed to work with a rated load up to the specified temperature, but not more than 1 hour;
b) with full or partial deactivation of the fans or stopping the circulation of water while maintaining the circulation of the oil, continuous work with reduced load at the temperature of the upper oil layers is not higher than 45 deg. FROM.
The requirements of this clause are valid unless otherwise specified in the instructions of the manufacturing plants.
Transformers with directional circulation of oil in the windings (cooling system NC) are operated in accordance with the factory instruction.
2.1.30. On transformers with a cooling system, the fan motors must automatically switch on at an oil temperature of 55 ° C. C or current equal to the nominal, regardless of the oil temperature. The fan motors are switched off when the temperature of the upper oil layers drops to 50 deg. C, if the load current is less than the rated current.
2.1.31. Voltage regulation devices under load must be in operation, as a rule, in automatic mode. Their work should be monitored by the readings of the counters of the number of operations.
According to the decision of the consumer responsible for the electric power, remote switching of the on-load tap-changer from the control panel is allowed, if the voltage fluctuations in the network are within the limits that satisfy the requirements of the Consumers. Switching under voltage manually (using the handle) is not allowed.
The personnel of the Customer servicing the transformers are required to maintain a match between the mains voltage and the voltage set on the control branch.
2.1.32. Switching devices on the tap changers of transformers are allowed to be switched on at the temperature of the upper oil layers above minus 20 degrees. C (for external resistor RPN devices) and above minus 45 deg. C - for on-load tap-changers with current-limiting reactors, as well as for switching devices with a contactor located on the insulator outside the transformer tank and equipped with an artificial heating device. The operation of the on-load tap-changers must be arranged in accordance with the factory instructions.
2.1.33. On transformers equipped with tap changers for windings without excitation (hereinafter - PBW), the correct choice of the transformation ratio should be checked at least 2 times a year - before the winter maximum and the summer minimum load.
2.1.34. Inspection of transformers (reactors) without their disconnection should be carried out in the following terms:
- the main step-down transformers of substations with constant staff watch - once a day;
- other transformers of electrical installations with a constant and without a permanent duty of the personnel - once a month;
- at transformer points - at least 1 time per month.
Depending on the local conditions and the condition of the transformers (reactors), the specified dates can be changed by the technical manager (responsible for the electric power) of the Consumer.
Extraordinary inspections of transformers (reactors) are made:
- after adverse weather conditions (thunderstorm, abrupt temperature change, strong wind, etc.);
- when the gas protection is operating on the signal, and also when the transformer (reactor) is disconnected by gas or (and) differential protection.
2.1.35. Current repairs of transformers (reagents) are made as required. Periodicity of routine repairs is established by the technical manager of the Consumer.
2.1.36. Capital repairs (planned preventive measures - according to the standard nomenclature of works) should be carried out:
- transformers 110 kV and higher with a capacity of 125 MVA and more, as well as reactors - no later than 12 years after commissioning, taking into account the results of the diagnostic control, in the future - as necessary;
- other transformers - depending on their condition and the results of the diagnostic control.
2.1.37. Extraordinary repairs of transformers (reactors) must be carried out if a defect in some of their elements can lead to failure. The decision on the withdrawal of the transformer (reactor) in repair is taken by the Consumer's manager or responsible for the electric power.
2.1.38. A customer who has oil-filled equipment on his balance sheet must store a minimum reserve of insulating oil of at least 110% of the volume of the most capacious apparatus.
2.1.39. The testing of transformers and reactors and their components in service must be carried out in accordance with the electrical equipment test standards (Appendix 3) and factory instructions. The test results are documented in acts or protocols and stored together with documents for this equipment.
2.1.40. Periodicity of oil sampling of transformers and reactors of 110 and 220 kV for chromatographic analysis of gases dissolved in oil must comply with the guidelines for diagnosing developing defects from the results of chromatographic analysis of gases dissolved in transformer oil.
2.1.41. The transformer (reactor) must be disconnected from work when:
- strong uneven noise and crackling inside the transformer;
- abnormal and constantly increasing heating of the transformer at a load below the nominal and normal operation of the cooling devices;
- discharge of oil from the expander or rupture of the diaphragm of the exhaust pipe;
- oil leakage with a lowering of its level below the level of the oil glass.
Transformers are withdrawn from work also if it is necessary to immediately change the oil according to the results of laboratory tests.
2.1.42. At each 10 / 0.4 kV transformer substation (hereinafter referred to as "TP") located outside the territory of the Consumer, its name, address and telephone number of the owner shall be affixed.
Transformers with a liquid dielectric use insulation based on the cellulose / liquid system. The liquid serves, both as an insulating and as a cooling medium. In the manufacture of windings, certain shapes of the body (rectangular or cylindrical) are used, and gaps remain between the layers of the turns of the winding. These gaps are necessary for the liquid to pass between the layers of the winding, and to cool the winding and the magnetic circuit.
For cooling purposes, the liquid flows through the transformer through the channels around the winding, being inside a sealed enclosure in which the magnetic circuit and windings are enclosed. The removal of heat accumulated in the liquid is carried out through external tubes, usually having an elliptical cross-section that extend along the outer walls of the housing.
When the transformer class exceeds 5 MVA, additional heat removal means are required. Here radiators are used. They contain collectors protruding from the transformer housing from above and from below, and connected by rows of tubes. The transformer liquid, acting as a cooling medium, transfers heat collected from the magnetic circuit and windings into them. This heat is dissipated in the air with the help of external tubes.
The paper insulation used today in transformers with a liquid dielectric is thermally strengthened, assuming a 65 ° C average winding temperature as standard. In the devices of the 1960s, the temperature was 55 ° C as the standard.
Sometimes the transformer specification specifies a permissible temperature rise of 55 ° / 65 ° C. This provides an increase in operating performance by 12%, since this power class is based on the old standard of temperature increase of 55 ° C, although thermal kraft paper is used.
For both dry type transformers and liquid dielectric transformers, the key factor in transformer design is the amount of temperature rise that insulation can withstand. The decrease in the temperature rise of the transformer can be achieved in two ways. First, it is possible to increase the dimensions of the conductor in the winding (which will reduce its resistance and, consequently, reduce heat generation). Secondly, it is possible to lower the nominal value of the transformer, which allows a higher temperature rise. The second method should be used with caution, since if the percentage value of the transformer impedance is based on a higher permissible temperature rise, the short-circuit current passed and the switching current will be proportionally higher than the corresponding parameters of the applied transformer. As a result, equipment connected to the transformer must have higher current and interruption rates, and primary switches must have higher characteristics to cope with the switching current.
Transformers with a lower temperature rise, have larger physical dimensions, and therefore require more space for installation. A positive aspect here is a longer service life. New standards in the electrical industry recommend choosing transformers, based on optimization of losses in the absence of load, at partial load and at full load. At the same time, operational requirements and reliability requirements of the entire electrical system should not be at risk.
Temperature considerations of dry type transformers
Transformers of dry type are available in three main classes of insulation. The main purpose of insulation is to ensure the dielectric strength, and the ability to withstand certain temperature limits. Insulation refers to one of the classes: 220 ° C (class H), 185 ° C (class F), and 150 ° C (class B). The permissible temperature rise is based on the growth of the temperature at full load with respect to the average air temperature (usually 40 ° C above the average), and is 150 ° C (only for class H insulation), 115 ° C (for insulation classes H and F ), and 80 ° C (with insulation classes H, F, and B). For each class, the excess of 30 ° C at the hot spots of the winding is allowed.
Lower temperature increases of transformers are more effective, especially at loads of 50% or higher. Losses at full load for transformers with an allowable temperature of 115 ° C are approximately 30% less than for transformers with an allowable temperature of 150 ° C. And transformers with a temperature of 80 ° C have losses of about 15% less than transformers with a temperature of 115 ° C, and 40% less than transformers with a temperature of 150 ° C. Losses at full load for transformers with an allowable temperature of 150 ° C are in the range of 4% -5% for 30 kVA, and are reduced to 2% for 500 kVA and higher.
With continuous operation at 65% of full load, and more, for transformers with a temperature of 115 ° C, the self-repayment period is less for 2 years (or for one year, when working with a load of 90% of full load) compared with 150 ° C transformers. Transformers with an allowable temperature of 80 ° C, in comparison with transformers with a temperature of 150 ° C, pay off more quickly for 2 years with a load of at least 75% of the full load. At 100% load, they pay off more quickly for one year. If such a transformer will work continuously at a load of at least 80% of the full, then it will pay off two years faster than a transformer with a temperature of 115 ° C (or 1.25 years at full load).
It should be noted that when the load is below 50% of full load, there is no significant time-saving advantage for either the transformer from 115 ° or the transformer from 80 ° C over the transformer with a temperature of 150 ° C. In addition, if the load is less than 40%, a lower temperature rise will be less effective than transformers with a temperature of 150 ° C. That is, not only will there be a payoff in the payback time, but also annual operating costs will increase.
