One, protection box type transformer configuration technology:
1, the installation of lightning arrester protection, to prevent lightning overvoltage: lightning protection transformer, using the installation of no gap metal oxide lightning arrester as overvoltage protection, in order to prevent the high and low voltage line intrusion of high voltage lightning waves caused by the transformer internal insulation breakdown, resulting in short circuit, to prevent the occurrence of lightning damage accident. When the lightning arrester is used to protect the transformer,
First, it is necessary to purchase qualified products through normal channels, and then put them into operation after strict tests before installation and operation.
Second, preventive tests are carried out regularly on the equipment in operation, and the unqualified products whose leakage current value exceeds the standard value are replaced in time;
Three is to regularly carry out the transformer grounding resistance testing, for 100KVA and above the box transformer grounding resistance must be within 4 ω, for 100KVA box transformer below, grounding resistance must be within 10 ω. If the test value is not within the specified range, extend the grounding wire, add the grounding body, and take physical and chemical measures to reach the specified value. Retest the grounding resistance twice in April and July every year to prevent the grounding resistance from exceeding the standard due to unwelding of the welding points, environment, and other factors. If the grounding resistance of the transformer exceeds the standard, the lightning current can not flow into the earth when the lightning strike, but through the grounding line will be added to the lightning voltage at the low voltage side of the box transformer and then reverse boost to high voltage, the transformer will be burned;
Four is installation location should be appropriate choice, box-type transformer high voltage lightning arrester installed in the lead by the distribution transformer hv bushing recently, minimize directly caused by lightning intruded into the match opportunity, low voltage surge arrester with recent changeable loading on low pressure casing, to ensure the correctness of thunder electric wave invasion with former changeable actions, according to the standards required to install electrical equipment installation specification, Prevent blind installation and lose the meaning of protection.
2, the box transformer is equipped with speed break, over-current protection, to ensure the selective removal of fault line: transformer short circuit protection and overload protection by installed in the transformer fuse high voltage side and low voltage side of the leakage protection (the device has leakage protection and transformer low voltage over-current protection) to achieve. In order to protect the transformer effectively, the melt (fuse, fuse, etc.) of the fuse and the protection value of low voltage and over current must be selected correctly. The fuse on the high voltage side should be selected to ensure that it is fused in case of short circuit in the transformer internal or external bushing. Fuse selection principle:
(1) For the transformer with a capacity of 100kVA and below, the high voltage fuse should be selected according to the rated current of 2 ~ 2.5 times;
(2) For transformer with capacity above 100kVA, high voltage fuse should be selected according to 1.5 ~ 2 times rated current. Low sliding sideways electricity protector had always flow value with low voltage side changeable rating of 1.3 times, with low voltage changeable each branch circuit overcurrent protection setting value should not be greater than the total protection of a flow value, its value should be less than with low voltage side changeable rated current, generally by the conductor maximum carrying capacity selection flow, ensure that occur at each outlet loop short circuit or output load is too large, In case of excessive load caused by the distribution change, it can act in time, cut off the load and the fault line, and realize the purpose of protecting the distribution change. At the same time, it meets the selective requirements of all levels of protection. When the low voltage branch circuit is short circuit fault, the branch circuit will operate, and the leakage general protector will not operate under the overcurrent protection. When the low voltage side total circuit fault or short circuit, the leakage general protector on the low voltage side will operate under the overcurrent protection, and the melt on the high voltage side shall not be fused. When the transformer is short-circuited due to internal fault, the melt of the high-voltage side is fused, and the high-voltage line protection device of the next-level substation should not operate and trip, so as to ensure the protection device of the distribution network operates correctly and in different grades. The melt protection material on the high pressure side of the transformer must be provided as standard, and the replacement of fuse melt with copper, aluminum and other metal conductors should be strictly prohibited.
Two, box transformer daily operation management:
1. Strengthen routine inspection, maintenance and regular testing of box-type transformers:
(1) Carry out daily maintenance, timely clean and erase the oil and dust on the high and low pressure bushing, in order to prevent the pollution flash discharge when the climate is wet or rainy, resulting in short circuit between the bushing, the high voltage fuse fuse, the transformer can not operate normally;
(2) with the oil level and oil color changeable timely observation, regularly test the oil temperature, especially the load change is big, big temperature difference, harsh weather should increase patrol frequency, box of oil-immersed transformer running top oil temperature is not higher than 95 ℃, the temperature rise shall not exceed 55 ℃, in order to prevent the deterioration of winding and oil tachycardia, top oil temperature rise is often more than 45 ℃;
(3) Shake the insulation resistance of the transformer, check whether the lead is firm, pay special attention to the low voltage outlet connection is good contact, temperature is abnormal;
(4) Strengthen the measurement of power load, in the peak of power consumption, strengthen the load measurement of each transformer, increase the measurement times when necessary, timely adjust the three-phase current imbalance box transformer, prevent the neutral line current is too large to burn the lead, causing damage to user equipment, transformer damage. The connection group is Yyn0 distribution transformer, the three-phase load should be balanced as far as possible, not only one or two phase power supply, neutral line current should not exceed 25% of the rated current of the low voltage side, and strive to make the distribution transformer not overload, unbiased load operation;
2, prevent box transformer from external damage:
(1) The reasonable choice of the installation site of the transformer, transformer installation should not only meet the requirements of the user voltage, but also try to avoid the installation in the wild mountains, easy to be struck by lightning, can not be installed in a place far away from residential areas, to prevent illegal theft. The installation location is too remote is not conducive to the regular maintenance of the operation personnel, not convenient for the management of the staff;
(2) Avoid installing low-voltage meter box on box-type transformer, because the glass of meter box or low-voltage pile head of transformer can not be replaced in time due to long time operation, which will cause the electricity meter to be burned out and the transformer to be damaged due to rain and other reasons;
(3) It is not allowed to adjust the tap switch privately, in case that the tap switch is not adjusted in place and inter-phase short circuit occurs, resulting in the burning of the box-type transformer;
(4) install insulation cover at the high and low voltage end of the transformer to prevent natural disasters and external damage. Install high and low voltage insulation cover in the narrow road area and the forest area with frequent animal access to prevent the box transformer wiring pile from falling things so that the low voltage short circuit and burning the transformer;
(5) Regularly inspect the line, cut down the line channel, to prevent branches from touching the wire and causing low-voltage short circuit to burn the box-type transformer accident.
To sum up: in order to make the box transformer to maintain long-term safe and reliable operation, in addition to strengthening the level of protection configuration technology, in the daily operation management is also very important.
As the management personnel of distribution transformer operation, we must do frequent inspection, maintenance and measurement, find problems and deal with them timely, and take various measures to strengthen the protection of box-type transformer to prevent faults or accidents, so as to ensure the safe, stable and reliable operation of distribution network.