The distribution transformer is a kind of static electrical appliance in the distribution system that transforms AC voltage and current according to the law of electromagnetic induction and transmits AC electrical energy. Usually installed in utility poles, benches, or power distribution stations, generally the voltage of 6 to 10 kV is reduced to about 400 volts for input users. The normal operation of the transformer directly affects the user's electricity production and life, and relates to the safety of electrical equipment. In order to ensure that users use high-quality, safe electricity, we must ensure that the distribution transformer is operating normally. Therefore, we need to talk about the protection measures of distribution transformers and their precautions from the perspectives of protection configuration technology and daily operation and management.
First, the protection configuration technology 1, installed arrester protection, to prevent lightning overvoltage: lightning protection with distribution, the use of installation of gapless metal oxide arrester as overvoltage protection, to prevent high-voltage and low-voltage lines invade the high-voltage lightning waves The resulting internal insulation breakdown of the transformer causes a short circuit and prevents lightning damage accidents. When lightning arresters are used to protect distribution transformers, the first one is to purchase qualified products through normal channels. After installation and operation, rigorous tests are performed to achieve operational requirements and then put into operation. Second, periodic preventive tests are performed on the equipment in operation, and the leakage current exceeds the value. The standard value of the unqualified product shall be replaced in time. The third is the transformer earthing resistance test. The distribution resistance of 100KVA and above distribution transformers must be within 4Ω. For the distribution transformer below 100KVA, the grounding resistance must be within 10Ω. . If the test value is not within the specified range, extend the grounding wire, increase the grounding body and physical and chemical measures to achieve the specified value, conduct two retests of the grounding resistance in April and July every year, to prevent the welding point off , environment and other factors lead to excessive grounding resistance. If the transformer grounding resistance exceeds the standard, the lightning current can not flow into the earth during lightning strike. Instead, the lightning voltage is added to the low voltage side of the distribution transformer through the grounding line and then reversed to boost the voltage to high voltage, and the distribution transformer will be burned. Fourth, the installation location should be selected properly. The high-voltage arrester is installed at the nearest lead wire of the transformer high-voltage bushing to minimize the opportunity for lightning to directly invade the transformer. The low-voltage arrester is installed at the low-voltage bushing that is closest to the transformer to ensure that the lightning wave intrudes correctly before the distribution transformer. Action, according to the installation requirements of electrical equipment installation standards, to prevent blind installation and lose the meaning of protection.
2. Install quick-break and over-current protection to ensure the selective removal of faulty lines: short-circuit protection and overload protection of transformers are provided by the fuses installed on the transformer high-voltage side and the total leakage protector on the low-voltage side (the device has Earth leakage protection and distribution transformer low-voltage over-current protection). In order to effectively protect the distribution transformer, the fuse (fuse, fuse, etc.) and the low-voltage over-current protection setting of the fuse must be correctly selected. The selection of high-side fuses should ensure that they are blown when a short circuit occurs inside or outside the transformer. Fuse selection principle: (1) Distribution with capacity of 100kVA and below, high voltage fuse with 2～2.5 times rated current; (2) Distribution with capacity above 100kVA, high voltage fuse with 1.5～2 times rated current select. The over-current leakage protection total-protector over-current action value is taken to be 1.3 times the rated value of the low-voltage side breaker. The value of the over-current protection over-current protection branch circuit should not be greater than the over-current protection value of the total protection, and its value should be less than the distribution transformer voltage. The rated current on the side is generally selected as the overcurrent value of the maximum current carrying capacity of the conductor to ensure that a short circuit occurs in each outlet circuit or that the output load is too large. When the distribution transformer is overloaded, it can act in time to remove the load and the faulty line to achieve the purpose of protecting the distribution transformer. . At the same time meet the selective requirements of all levels of protection. When the low-voltage branch circuit short-circuit fault occurs, the branch circuit operates, and the total leakage protector over-current protection does not operate. When the low-voltage side total circuit fails or is short-circuited, the low-side leakage total protection over-current protection action, the high-pressure side melt shall not be broken; the transformer When the internal fault is short-circuited, the high-pressure-side melt blows, and the upper-level substation high-voltage line protection device should not be tripped to ensure the correct classification action of the distribution network protection device. The transformer high-pressure side melt protection material must be equipped according to the standard, and resolutely eliminate the use of copper, aluminum and other metal conductors to replace the fuse melt.
2. Routine Operation and Management 1. Strengthen daily inspections, maintenance and periodic tests: (1) Perform routine maintenance and timely clean and erase dust from distribution oil and high- and low-pressure bushings to prevent the weather from getting wet or rainy. Flash discharge, resulting in short-circuit between the bushing phase, high-voltage fuse blown, distribution transformer can not be normal operation;
2) Observe the oil level and oil color of the transformer in time, and regularly check the oil temperature, especially the weather with heavy load, large temperature difference and bad weather, increase the number of inspections, and the top oil temperature in the operation of oil-immersed distribution transformers. It must not be higher than 95°C and the temperature rise must not exceed 55°C. To prevent the windings and oil from deteriorating too quickly, the temperature rise of the top oil should not exceed 45°C. (3) Measure the insulation resistance of the distribution transformer and check whether the leads are firm. Special attention shall be paid to whether the contact at the low-voltage outlet connection is good and whether the temperature is abnormal. (4) To strengthen the measurement of the electricity load, in the peak period of electricity consumption, to strengthen the load measurement for each distribution transformer, if necessary, increase the number of measurements, The distribution transformer with unbalanced three-phase currents is adjusted in time to prevent excessive blowout of the neutral conductor current, causing damage to the user equipment and damage to the distribution transformer. The connection group is Yyn0's distribution transformer. The three-phase load should be balanced as much as possible. It is not allowed to use only one or two-phase power supply. The neutral current should not exceed 25% of the rated current of the low-voltage side, so that the distribution transformer is not overloaded or unbalanced. run;
2, to prevent external damage: (1) a reasonable choice of distribution transformer installation site, distribution transformer installation must meet the user voltage requirements, but also try to avoid its installation in wild mountains and mountains, easy to be struck by lightning, can not be installed away from residents Districts to prevent lawbreakers from stealing. If the installation location is too remote, it is not conducive to the regular maintenance of the operating personnel, which is inconvenient for the management of the staff; (2) Avoid installing the low-pressure metering box on the distribution transformer. Because of long-time operation, the glass of the metering box is damaged or the low-voltage pile head is damaged. Can not be replaced in time, resulting in damage due to rain and other causes of power meter damage distribution; (3) not allowed to adjust the tap switch, in order to prevent the adjustment of the tap switch is not in place, resulting in phase-to-phase short circuit caused by the distribution transformer; ( 4) Insulation cover is installed at the high and low voltage side of the distribution transformer to prevent natural disasters and damage to foreign objects. High- and low-voltage insulation covers are installed in the narrow roads and in the forest areas where animals enter and exit frequently to prevent the distribution transformer from getting out of the wiring piles. Low-voltage short-circuit and burn the distribution transformer; (5) regularly inspect the line, cut the line channel, to prevent the branches touching the wire caused by low-voltage short circuit burnout distribution transformer accident.
To sum up: To ensure long-term safe and reliable operation of distribution transformers, in addition to strengthening the technical level of protection configuration, it is also very important in daily operation and management. As distribution and operation management personnel, it is necessary to do diligent inspections, ground maintenance, and ground measurement, promptly identify problems and deal with them in a timely manner, and take various measures to strengthen the protection of distribution transformers to prevent malfunctions or accidents and ensure the safety of distribution networks. , stable and reliable operation.
First, the protection configuration technology 1, installed arrester protection, to prevent lightning overvoltage: lightning protection with distribution, the use of installation of gapless metal oxide arrester as overvoltage protection, to prevent high-voltage and low-voltage lines invade the high-voltage lightning waves The resulting internal insulation breakdown of the transformer causes a short circuit and prevents lightning damage accidents. When lightning arresters are used to protect distribution transformers, the first one is to purchase qualified products through normal channels. After installation and operation, rigorous tests are performed to achieve operational requirements and then put into operation. Second, periodic preventive tests are performed on the equipment in operation, and the leakage current exceeds the value. The standard value of the unqualified product shall be replaced in time. The third is the transformer earthing resistance test. The distribution resistance of 100KVA and above distribution transformers must be within 4Ω. For the distribution transformer below 100KVA, the grounding resistance must be within 10Ω. . If the test value is not within the specified range, extend the grounding wire, increase the grounding body and physical and chemical measures to achieve the specified value, conduct two retests of the grounding resistance in April and July every year, to prevent the welding point off , environment and other factors lead to excessive grounding resistance. If the transformer grounding resistance exceeds the standard, the lightning current can not flow into the earth during lightning strike. Instead, the lightning voltage is added to the low voltage side of the distribution transformer through the grounding line and then reversed to boost the voltage to high voltage, and the distribution transformer will be burned. Fourth, the installation location should be selected properly. The high-voltage arrester is installed at the nearest lead wire of the transformer high-voltage bushing to minimize the opportunity for lightning to directly invade the transformer. The low-voltage arrester is installed at the low-voltage bushing that is closest to the transformer to ensure that the lightning wave intrudes correctly before the distribution transformer. Action, according to the installation requirements of electrical equipment installation standards, to prevent blind installation and lose the meaning of protection.
2. Install quick-break and over-current protection to ensure the selective removal of faulty lines: short-circuit protection and overload protection of transformers are provided by the fuses installed on the transformer high-voltage side and the total leakage protector on the low-voltage side (the device has Earth leakage protection and distribution transformer low-voltage over-current protection). In order to effectively protect the distribution transformer, the fuse (fuse, fuse, etc.) and the low-voltage over-current protection setting of the fuse must be correctly selected. The selection of high-side fuses should ensure that they are blown when a short circuit occurs inside or outside the transformer. Fuse selection principle: (1) Distribution with capacity of 100kVA and below, high voltage fuse with 2～2.5 times rated current; (2) Distribution with capacity above 100kVA, high voltage fuse with 1.5～2 times rated current select. The over-current leakage protection total-protector over-current action value is taken to be 1.3 times the rated value of the low-voltage side breaker. The value of the over-current protection over-current protection branch circuit should not be greater than the over-current protection value of the total protection, and its value should be less than the distribution transformer voltage. The rated current on the side is generally selected as the overcurrent value of the maximum current carrying capacity of the conductor to ensure that a short circuit occurs in each outlet circuit or that the output load is too large. When the distribution transformer is overloaded, it can act in time to remove the load and the faulty line to achieve the purpose of protecting the distribution transformer. . At the same time meet the selective requirements of all levels of protection. When the low-voltage branch circuit short-circuit fault occurs, the branch circuit operates, and the total leakage protector over-current protection does not operate. When the low-voltage side total circuit fails or is short-circuited, the low-side leakage total protection over-current protection action, the high-pressure side melt shall not be broken; the transformer When the internal fault is short-circuited, the high-pressure-side melt blows, and the upper-level substation high-voltage line protection device should not be tripped to ensure the correct classification action of the distribution network protection device. The transformer high-pressure side melt protection material must be equipped according to the standard, and resolutely eliminate the use of copper, aluminum and other metal conductors to replace the fuse melt.
2. Routine Operation and Management 1. Strengthen daily inspections, maintenance and periodic tests: (1) Perform routine maintenance and timely clean and erase dust from distribution oil and high- and low-pressure bushings to prevent the weather from getting wet or rainy. Flash discharge, resulting in short-circuit between the bushing phase, high-voltage fuse blown, distribution transformer can not be normal operation;
2) Observe the oil level and oil color of the transformer in time, and regularly check the oil temperature, especially the weather with heavy load, large temperature difference and bad weather, increase the number of inspections, and the top oil temperature in the operation of oil-immersed distribution transformers. It must not be higher than 95°C and the temperature rise must not exceed 55°C. To prevent the windings and oil from deteriorating too quickly, the temperature rise of the top oil should not exceed 45°C. (3) Measure the insulation resistance of the distribution transformer and check whether the leads are firm. Special attention shall be paid to whether the contact at the low-voltage outlet connection is good and whether the temperature is abnormal. (4) To strengthen the measurement of the electricity load, in the peak period of electricity consumption, to strengthen the load measurement for each distribution transformer, if necessary, increase the number of measurements, The distribution transformer with unbalanced three-phase currents is adjusted in time to prevent excessive blowout of the neutral conductor current, causing damage to the user equipment and damage to the distribution transformer. The connection group is Yyn0's distribution transformer. The three-phase load should be balanced as much as possible. It is not allowed to use only one or two-phase power supply. The neutral current should not exceed 25% of the rated current of the low-voltage side, so that the distribution transformer is not overloaded or unbalanced. run;
2, to prevent external damage: (1) a reasonable choice of distribution transformer installation site, distribution transformer installation must meet the user voltage requirements, but also try to avoid its installation in wild mountains and mountains, easy to be struck by lightning, can not be installed away from residents Districts to prevent lawbreakers from stealing. If the installation location is too remote, it is not conducive to the regular maintenance of the operating personnel, which is inconvenient for the management of the staff; (2) Avoid installing the low-pressure metering box on the distribution transformer. Because of long-time operation, the glass of the metering box is damaged or the low-voltage pile head is damaged. Can not be replaced in time, resulting in damage due to rain and other causes of power meter damage distribution; (3) not allowed to adjust the tap switch, in order to prevent the adjustment of the tap switch is not in place, resulting in phase-to-phase short circuit caused by the distribution transformer; ( 4) Insulation cover is installed at the high and low voltage side of the distribution transformer to prevent natural disasters and damage to foreign objects. High- and low-voltage insulation covers are installed in the narrow roads and in the forest areas where animals enter and exit frequently to prevent the distribution transformer from getting out of the wiring piles. Low-voltage short-circuit and burn the distribution transformer; (5) regularly inspect the line, cut the line channel, to prevent the branches touching the wire caused by low-voltage short circuit burnout distribution transformer accident.
To sum up: To ensure long-term safe and reliable operation of distribution transformers, in addition to strengthening the technical level of protection configuration, it is also very important in daily operation and management. As distribution and operation management personnel, it is necessary to do diligent inspections, ground maintenance, and ground measurement, promptly identify problems and deal with them in a timely manner, and take various measures to strengthen the protection of distribution transformers to prevent malfunctions or accidents and ensure the safety of distribution networks. , stable and reliable operation.
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