Distribution transformer protection measures - Solutions - Huaqiang Electronic Network

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

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The distribution transformer is a kind of static electric appliance that transmits AC electric energy according to the electromagnetic induction law to convert AC voltage and current according to the law of electromagnetic induction. Usually installed in poles, gantry or power distribution stations, generally reduce the voltage of 6 ~ 10 kV to about 400 volts input to the user. Whether the normal operation of the transformer directly affects the user's production and living electricity, and is related to the safety of the electrical equipment. In order to ensure that users use high-quality, safe electricity, it must be guaranteed that the distribution operation is normal. Therefore, it is necessary to talk about the protection measures of distribution transformers and their precautions from the perspective of protection configuration technology and daily operation management:
First, the protection configuration technology 1, the installation of lightning arrester protection, to prevent lightning overvoltage: lightning protection of the distribution, the use of gapless metal oxide arrester as overvoltage protection to prevent high-voltage lightning waves from high and low voltage lines The internal insulation breakdown of the transformer caused by it causes a short circuit and prevents lightning damage. When the arrester is used to protect the distribution transformer, the first is to purchase qualified products through normal channels. After the installation and commissioning, the rigorous test is carried out to meet the operational requirements and then put into operation. Second, the equipment in operation is regularly tested for preventive leakage. The standard value of the non-conforming product shall be replaced in time; the third is to periodically test the transformer grounding resistance. For the distribution transformer of 100KVA and above, the grounding resistance 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, the extension grounding wire should be taken to increase the grounding body and physical and chemical measures to achieve the specified value. The re-test of the grounding resistance is performed twice in April and July each year to prevent the welding spot from being desoldered. , environmental and other factors lead to excessive grounding resistance. If the grounding resistance of the transformer exceeds the standard, the lightning current cannot flow into the earth when lightning strikes. Instead, the lightning voltage is applied to the low-voltage side of the distribution transformer through the grounding wire and then boosted to a high voltage in reverse, and the transformer is burned. Fourth, the installation position should be properly selected. The high-voltage arrester is installed at the nearest lead of the high-voltage bushing to minimize the chance of lightning directly invading the distribution transformer. The low-voltage arrester is installed at the low-voltage bushing closest to the distribution transformer to ensure that the lightning wave is invaded correctly before the distribution. Actions, installed in accordance with the requirements of electrical equipment installation standards, to prevent blind installation and loss of protection.
2. Install quick-break and over-current protection to ensure selective removal of faulty lines: short-circuit protection and overload protection of the distribution transformer are provided by the fuses installed on the high-voltage side of the distribution transformer and the leakage total protection device on the low-voltage side (the device has Leakage protection and distribution transformer low voltage overcurrent protection). In order to effectively protect the distribution, the fuse (fuse, fuse, etc.) of the fuse and the low-voltage overcurrent protection setting must be correctly selected. The high-side fuse should be selected to ensure that it is blown when a short circuit occurs inside the transformer or at the outer bushing. Fuse selection principle: (1) distribution with capacity of 100kVA and below, high-voltage fuse selected by 2~2.5 times rated current; (2) distribution with capacity above 100kVA, high-voltage fuse with 1.5~2 times rated current select. The overcurrent action value of the low-voltage side leakage total protector is 1.3 times of the rated value of the low-voltage side. The over-current protection value of each branch line of the distribution transformer should not exceed the over-current action value of the total protection. The value should be less than the distribution voltage. The rated current of the side is generally selected according to the maximum current carrying capacity of the wire to ensure that the short circuit in each outgoing circuit or the output load is too large, causing the action to be timely when the distribution transformer is overloaded, and the load and the fault line are cut off to achieve the purpose of protection and distribution. . At the same time meet the selectivity requirements of all levels of protection. When the low-voltage branch circuit is short-circuited, the branch circuit operates, the overcurrent protection of the leakage total protector does not operate, and the low-voltage side main circuit fails or short-circuits, the low-voltage side leakage total protector over-current protection action, the high-pressure side melt should not be blown; When the internal fault is short-circuited, the high-pressure side melt is blown, and the high-voltage line protection device of the upper-level substation should not trip, ensuring the correct classification action of the distribution network protection device. The high-pressure side melt protection material of the distribution transformer must be equipped as standard, and the metal fuses such as copper and aluminum should be strictly prevented to replace the fuse melt.
Second, the daily operation management aspects 1, strengthen daily inspections, maintenance and regular testing: (1) carry out routine maintenance, timely cleaning and erasing the dust on the distribution oil and high and low pressure casing to prevent the weather from being wet or rainy Flash discharge, causing the phase-to-phase short circuit between the bushings, the high-voltage fuses are blown, the distribution transformer can not operate normally; (2) timely observe the oil level and oil color of the distribution transformer, and regularly check the oil temperature, especially the load change, the temperature difference is large, and the climate is bad. The weather should increase the number of inspections. The top oil temperature of the oil-immersed distribution transformer should not exceed 95 °C, and the temperature rise should not exceed 55 °C. To prevent the winding and oil from deteriorating, the temperature rise of the top oil should not be suitable. Frequently exceed 45 ° C; (3) shake the insulation resistance of the distribution transformer, check whether the leads are firm, especially pay attention to whether the contact at the low-voltage outlet connection is good, the temperature is abnormal; (4) to strengthen the measurement of the electrical load, During the peak period of power consumption, the load measurement of each distribution transformer is strengthened, and the number of measurements is increased when necessary, and the distribution transformer of the three-phase current unbalance is adjusted in time to prevent the neutral current. The connection group is the distribution of Yyn0. The three-phase load should be balanced as much as possible. It should not be powered by only one phase or two phases. The neutral current should not exceed 25% of the rated current of the low-voltage side, so as to ensure that the distribution is not overloaded or unbiased. run;
2, to prevent damage to external forces: (1) Reasonably choose the installation location of the transformer, the transformer installation must meet the requirements of the user's voltage, but also try to avoid installing it in the barren hills, easy to be struck by lightning, and can not be installed away from residents The place of the district to prevent the criminals from stealing. The installation location is too remote and is not conducive to the regular maintenance of the operating personnel, which is not convenient for the management of the staff; (2) Avoid installing the low-voltage metering box on the distribution transformer. Due to long-term operation, the glass of the measuring box is damaged or the low-pressure pile head is damaged. Can not be replaced in time, causing damage to the distribution transformer caused by rain or other reasons; (3) Do not allow the tap changer to be adjusted privately, in order to prevent the phase-to-phase short circuit caused by the adjustment of the tap changer, causing the distribution transformer to burn out; 4) Install an insulating cover at the high and low voltage end of the transformer to prevent natural disasters and foreign objects from being destroyed. Install high and low voltage insulation covers in the narrow forests and forest areas where animals enter and exit frequently to prevent the distribution transformers from dropping on the wiring piles. Low-voltage short-circuit and burn-in distribution; (5) Regular inspection of the line, cutting the line channel, preventing the branch from hitting the wire and causing a low-voltage short-circuit to burn the distribution transformer.
To sum up: in order to maintain the long-term safe and reliable operation of the distribution transformer, in addition to strengthening the level of protection and configuration technology, it is also very important in daily operation management. As a distribution operation manager, it is necessary to do diligent inspection, diligent maintenance, diligent measurement, timely detection of problems and timely treatment, and take various measures to strengthen the protection of distribution transformers to prevent malfunctions or accidents to ensure the safety of distribution networks. Stable, reliable operation.