Operation maintenance and accident treatment of th

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Transformer operation and maintenance and accident handling

check whether the upper oil temperature of the transformer exceeds the allowable range. Since each transformer in China is a large plastic production and consumption country in the world, the transformer load, cooling conditions and seasons are different. The transformer in operation cannot be based on the upper oil temperature not exceeding the allowable value, but also on the previous operation experience and the comparison with the last oil temperature under the above conditions. If the oil temperature rises suddenly, check whether the cooling device is normal and whether the oil circulation is damaged to judge whether there is a fault inside the transformer

1. Abnormal phenomena during transformer operation

(1) during transformer operation, such as oil leakage, high or low oil level, abnormal temperature, abnormal sound and abnormal cooling system, should be eliminated as soon as possible

(2) when the load of the transformer exceeds the allowable normal overload value, the load of the transformer shall be reduced as required

(3) the sound inside the transformer is very large, very abnormal, with popping sound; The temperature is abnormal and rising; The oil conservator or safety air passage is sprayed with oil; Serious oil leakage makes the oil level drop below the indication limit of the oil level gauge; The oil color changes too fast, and carbon appears in the oil; In case of serious damage and discharge of the bushing, the power shall be cut off immediately for repair

(4) when it is found that the oil temperature of the transformer is high and the oil level corresponding to the oil temperature is significantly reduced, oil should be added immediately. Observe the regulations when refueling. If the oil level drops rapidly due to a large amount of oil leakage, the gas protection should be changed to a variety of competitive materials tested by the antenna partition strip of Xiaomi 4 mobile phone, so that it only acts on the signal, and the measures to plug the oil leakage must be taken quickly and refuel immediately

(5) when the oil level of the transformer rises gradually due to the temperature rise, if the oil level at the highest temperature may be higher than the oil level indicator, the oil should be drained to reduce the oil level to an appropriate height to avoid oil overflow

2. Inspection during transformer operation

(1) check whether the upper oil temperature of the transformer exceeds the allowable range. Due to the different load size, cooling conditions and seasons of each transformer, the transformer in operation cannot be based on the upper oil temperature not exceeding the allowable value, but also on the previous operation experience and the comparison with the last oil temperature under the above conditions. If the oil temperature rises suddenly, check whether the cooling device is normal and whether the oil circulation is damaged to judge whether there is a fault inside the transformer

(2) check the oil quality, which should be transparent and slightly yellow, so as to judge the quality of the oil. The oil level should meet the standard line of ambient temperature. If the oil level is too low, check whether the transformer leaks oil, etc. If the oil level is too high, check the service condition of the cooling device and whether there is internal fault

(3) the sound of the transformer should be normal. In normal operation, there is usually a uniform buzzing electromagnetic sound. If the sound changes, it should be carefully checked, and promptly reported to the dispatcher on duty and asked the maintenance unit to deal with it

(4) check whether the bushing is clean, whether there are cracks and discharge traces, and the cooling device should be normal. The working and standby power supply and oil pump shall meet the operation requirements, etc

(5) when the weather changes, special inspections should be focused on. In case of strong wind, check whether the lead wire swings violently, and there should be no sundries at the top cover of the transformer and the lead wire of the bushing; In heavy snow days, all contacts should not melt or discharge immediately after falling snow; Whether there is spark discharge in all parts in heavy fog, etc

3. Accident handling of transformer

in order to correctly handle the accident, we should master the following conditions: ① system operation mode, load state, load type; ② The upper oil temperature, temperature rise and voltage of the transformer; ③ Weather conditions at the time of the accident; ④ Whether there is maintenance and other work around the transformer; ⑤ Whether the operators operate; ⑥ Whether the system operates; ⑦ What kind of protection action, accident phenomenon, etc

the common faults of transformer in operation are the faults of winding, bushing and voltage tap changer, while the faults of iron core, oil tank and other accessories are less. Several common main faults are described as follows:

3.1 winding faults

mainly include inter turn short circuit, winding grounding, phase to phase short circuit, wire breakage and joint open welding. The causes of these faults are as follows:

① during manufacturing or maintenance, local insulation is damaged, leaving defects. ② During operation, due to poor heat dissipation or long-term overload, sundries fall into the winding, resulting in excessive temperature and aging insulation. ③ The manufacturing process is poor, the pressing is not tight, and the mechanical strength cannot withstand the impact of short circuit, which will deform the winding and damage the insulation. ④ The winding is damp, and the insulation expansion blocks the oil passage, causing local overheating. ⑤ The insulation oil is degraded by mixing water, or the contact area with the air is too large, so that the acid value of the oil is too high, the insulation level is reduced, or the oil level is too low, and some windings are exposed in the air and cannot be treated in time

due to the above reasons, once insulation breakdown occurs during operation, it will cause short circuit or grounding fault of winding. The fault phenomenon during inter turn short circuit is that the transformer is overheated, the oil temperature increases, the current at the power side increases slightly, the DC resistance of each phase is unbalanced, and sometimes there is a squeak and bubbling sound in the oil. Slight inter turn short circuit can cause gas protection action; In serious cases, the differential protection or overcurrent protection on the power side will also act. If inter turn short circuit is found, it should be handled in time, because the inter turn short circuit of winding often causes more serious faults, such as phase grounding or phase to phase short circuit

3.2 casing failure

this kind of failure is commonly caused by explosion, flash and oil leakage. The reasons are:

(1) poor sealing and insulation damp ratio

(2) the respirator is improperly configured or the inhaled water is not handled in time

3.3 tap changer fault

common faults are surface melting and burning, interphase contact discharge or each connector discharge. The main reasons are:

(1) the connecting screws are loose

(2) the load adjustment device is poor and improperly adjusted

(3) poor insulation of tap insulation board

(4) insufficient soldering tin, poor contact, poor manufacturing process, insufficient spring pressure

(5) the acid value of the oil is too high, causing the contact surface of the tap changer to be corroded

3.4 core failure

most of the core failure is caused by the insulation damage of the through core screw of the core column or the clamping screw of the iron wheel. The consequences may cause the through core screw to connect with the core lamination at two points, and the circulation may cause local heating, and even cause local melting of the core. It may also cause local short circuit of iron core laminations, produce eddy current overheating, cause damage to the insulation layer between laminations, increase the no-load loss of transformer and degrade the insulating oil

after the transformer fails in operation, if it is identified that it is the winding or iron core fault, the core should be lifted for inspection. First, measure and compare the DC resistance of each phase winding. If the difference is large, it is a winding fault. Then check the appearance of the iron core, and then measure the insulation resistance between the pieces by DC voltage and ammeter method. If the damage is not serious, paint the damaged part

3.5 gas protection fault

gas protection is the main protection of transformer. Light gas acts on the preheating of signal equipment. Because there are many electronic equipment in the electronic universal experimental machine, heavy gas acts on tripping. The causes and treatment methods of gas protection action are analyzed below:

(1) signal is sent after light gas protection action. The reason is: there is a slight fault inside the transformer; There is air inside the transformer; Secondary circuit fault, etc. The operator should check immediately. If no abnormality is found, gas sampling and analysis should be carried out

(2) when the gas protection action trips, there may be serious faults in the transformer, causing a large amount of gas to be decomposed from the oil, and there may also be secondary circuit faults. In case of gas protection action tripping, the standby transformer shall be put into operation first, and then the external inspection shall be carried out. Check whether the oil conservator explosion-proof door, each welding joint is cracked, and whether the transformer shell is deformed; Finally, check the flammability of the gas

when the transformer trips automatically, the protection action shall be found out and external inspection shall be carried out. If it is not caused by internal fault but by external fault (through fault) or personnel misoperation, power transmission can be put into operation without internal inspection. If the differential protection acts, all equipment within the protection range shall be checked

in addition, transformer fire is also a dangerous accident. Because there are many combustible substances in the transformer, if it is not handled in time, it may explode or expand the fire. The main reasons for the ignition of the transformer are: the bushing is damaged and flashed, and the oil flows out under the pressure of the conservator and burns on the top cover; The internal fault of the transformer breaks the shell or radiator, and the burning transformer oil overflows. In case of such accidents, the transformer protection shall act to disconnect the circuit breaker. If the circuit breaker is not disconnected for some reason, manually disconnect the circuit breaker immediately, open the disconnector that may lead to the power supply of the transformer, stop the cooling equipment, and put out the fire. When extinguishing the fire of transformer, it is best to use foam fire extinguisher, and sand can be used to extinguish the fire if necessary

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