1. Technical aspects of protective box transformer configuration:
1. Install lightning arrester protection to prevent lightning overvoltage: lightning protection for distribution transformers, use gapless metal oxide arresters as overvoltage protection to prevent the internal insulation of the transformer caused by high-voltage lightning waves invaded by high- and low-voltage lines Breakdown, cause short circuit, prevent lightning damage accident. When using a lightning arrester to protect the distribution transformer,
One is to purchase qualified products through normal channels, and go through rigorous tests to meet operational requirements before installation and operation;
The second is to regularly conduct preventive tests on the equipment in operation, and promptly replace unqualified products with leakage current values exceeding the standard value;
The third is to conduct regular transformer grounding resistance testing. For box-type transformers of 100KVA and above, the grounding resistance must be within 4Ω, and for box-type transformers 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 reach the specified value, and conduct two retests of the grounding resistance in April and July each year to prevent the solder joints from being unsoldered. , Environment and other factors cause the grounding resistance to exceed the standard. If the grounding resistance of the transformer exceeds the standard, the lightning current cannot flow into the earth during a lightning strike. Instead, the lightning voltage is applied to the low-voltage side of the box-type transformer through the grounding wire and then reversely boosted to a high voltage, which will burn the distribution transformer;
Fourth, the box-type transformer installation location should be selected appropriately. The high-voltage arrester should be installed at the nearest lead wire of the high-voltage bushing of the distribution transformer to minimize the chance of lightning directly invading the distribution transformer. The low-voltage arrester should be installed at the low-voltage bushing nearest the distribution transformer. , In order to ensure the correct action before the lightning wave invades the distribution transformer, install according to the electrical equipment installation specifications and standards, to prevent blind installation and lose the meaning of protection.
2. The box-type transformer is equipped with quick-break and over-current protection to ensure selective removal of fault lines: the short-circuit protection and overload protection of the distribution transformer consist of a fuse installed on the high-voltage side of the distribution transformer and a total leakage protector on the low-voltage side ( The device has leakage protection and distribution transformer low-voltage overcurrent protection) to achieve. In order to effectively protect the distribution transformer, the melt (fuse, fuse, etc.) of the fuse and the low-voltage overcurrent protection setting must be correctly selected. The fuse of the high-voltage side should be selected to ensure that it is fused when a short circuit occurs inside or outside the transformer bushing. Principles of fuse selection:
(1) For distribution transformers with a capacity of 100kVA and below, the high-voltage fuse should be selected at 2 to 2.5 times the rated current;
(2) For distribution transformers with a capacity above 100kVA, the high-voltage fuse should be selected at 1.5 to 2 times the rated current. The overcurrent action value of the low-voltage side leakage master protector is 1.3 times the rated value of the low-voltage side of the distribution transformer. The overcurrent protection value of each branch circuit of the low-voltage distribution transformer should not be greater than the overcurrent action value of the overall protection, and its value should be less than the low-voltage distribution transformer The rated current of the side is generally selected according to the maximum current carrying capacity of the wire to ensure that when each outgoing circuit is short-circuited or the output load is too large, it can act in time when the distribution transformer is overloaded, and the load and faulty lines can be removed to achieve the purpose of protecting the distribution transformer. . At the same time, it meets the selective requirements of all levels of protection. When the low-voltage branch circuit is short-circuited, the branch circuit will act, and the overcurrent protection of the main leakage protector will not operate. When the low-voltage side main circuit is faulty or short-circuited, the low-voltage side leakage main protector will operate, and the high-voltage side melt should not be fused; When the internal fault is short-circuited, the high-voltage side melt melts, and the high-voltage line protection device of the upper-level substation should not be tripped to ensure that the distribution network protection device is correctly classified. The high-voltage side melt protection material of the distribution transformer must be equipped according to the standard, and the use of copper, aluminum and other metal conductors to replace the fuse melt must be strictly prohibited.
2. Daily operation and management of box-type transformers:
1. Strengthen the daily inspection, maintenance and regular testing of box-type transformers:
(1) Carry out daily maintenance, clean and wipe off the oil pollution and dust on the high and low voltage bushings in time to prevent the pollution from flashing and discharging when the weather is humid or rainy, resulting in a short circuit between the bushings, the high-voltage fuse blows, and the distribution transformer cannot normal operation;
(2) Observe the oil level and oil color of the distribution transformer in time, and check the oil temperature regularly, especially in the weather with large load changes, large temperature differences, and bad weather. The number of inspections should be increased, and the top oil in the operation of oil-immersed box-type transformers should be increased. The temperature should not be higher than 95℃, and the temperature rise should not exceed 55℃. In order to prevent the winding and oil from deteriorating too quickly, the temperature rise of the top oil should not exceed 45℃ frequently;
(3) Measure the insulation resistance of the distribution transformer, check whether the leads are firm, and pay special attention to whether the low-voltage outlet connection is in good contact and whether the temperature is abnormal;
(4) Strengthen the measurement of electricity load. During the peak period of electricity use, strengthen the load measurement of each distribution transformer, increase the number of measurements if necessary, and make timely adjustments to the box-type transformers with unbalanced three-phase currents to prevent neutral lines. Excessive current burns the lead, causing damage to the user's equipment and damage to the distribution transformer. For the distribution transformer whose connection group is Yyn0, the three-phase load should be balanced as much as possible, and no one-phase or two-phase power supply should be used. The neutral line current should not exceed 25% of the low-voltage side rated current, and strive to ensure that the distribution transformer is not overloaded or unbiased. Run;
2, to prevent the box-type transformer from being damaged by external force:
(1) Choose the installation location of the distribution transformer reasonably. The installation of the distribution transformer should not only meet the voltage requirements of the user, but also try to avoid installing it in barren mountains and ridges, which are easy to be struck by lightning, and cannot be installed far away from residential areas. Criminals steal. The remote installation location is not conducive to the regular maintenance of the operators, and it is not convenient for the management of the staff;
(2) Avoid installing a low-voltage metering box on the box-type transformer. Due to long-term operation, the metering box glass is damaged or the low-voltage pile head of the distribution transformer is damaged and cannot be replaced in time, resulting in damage to the distribution transformer due to the burning of the electric meter due to rain and other reasons;
(3) It is not allowed to adjust the tap changer privately, in case that the tap changer is not adjusted in place and the interphase short circuit will cause the box-type transformer to burn out;
(4) Install insulating covers at the high and low voltage ends of the distribution transformer to prevent natural disasters and damage from foreign objects, and install high and low voltage insulating covers in narrow roads and forest areas with frequent animal access to prevent things from falling on the box-type transformer terminal posts. Short-circuit the low voltage and burn the distribution transformer;
(5) Regularly patrol the lines and cut down the line channels to prevent tree branches from hitting the wires and cause low-voltage short-circuit and burn out the box-type transformer.
To sum up: In order to keep the box-type transformer in long-term safe and reliable operation, in addition to strengthening and improving the technical level of protection configuration, it is also very important in daily operation management.
As a distribution transformer operation manager, you must perform frequent inspections, maintenance, and measurement, discover problems and deal with them in a timely manner, and take various measures to strengthen the protection of box-type transformers, prevent failures or accidents, and ensure the safety of the distribution network , Stable and reliable operation.
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