In order to ensure the normal operation of distribution transformers, it is necessary to strengthen the operation and management of the distribution transformers, do a good job in the operation and maintenance of the transformers, analyze the phenomenon according to the operation of the transformers, determine the causes and possible accidents, and take measures to eliminate hidden dangers. Safe operation of electricity and transformer operation.
The distribution transformer is the main power consumer of the power user. Its safe operation has a direct impact on the user's power reliability and safety. In order to ensure the normal operation of distribution transformers, it is necessary to strengthen the operation and management of the distribution transformers, monitor the operation of the transformers, analyze the abnormal phenomena occurring in the transformer operation, determine the causes and possible accidents, and take measures to prevent accidents. happened.
1The importance of doing a good job
Distribution transformers are the source of electricity for electric power users. Their operating conditions are directly related to whether electricity users can obtain reliable and continuous electricity. In the event of an accident in a transformer, the power failure will result in the suspension of production, inconvenience to life, and damage to facilities, and it will cause a chain reaction, causing large-scale power outages and huge direct and indirect economic losses. Therefore, strengthen the operation and management of transformers, monitor the operation of the transformers, ensure the healthy operation of the transformers, take abnormal measures, take measures, deal with them in a timely manner, and effectively prevent the transformation of fault conditions. Based on the operating data of the transformer, the operating status of the transformer Analysis is performed to determine the health status of the transformer, determine whether maintenance is needed, reduce or avoid losses caused by the development of the transformer fault, and improve the reliability of the power transformer operation. Secure power supply.
2 Pre-operational inspection
In order to ensure the safe operation of the distribution transformer, the transformer must be tested before it is put into operation. The main contents are as follows:
(1) Whether the oil level gauge on the oil pillow is in good condition and whether the oil level is clear and is in line with the ambient temperature oil level.
(2) Whether the cover plate, casing, oil level gauge, oil discharge valve, etc. are sealed well and there is no oil leakage.
(3) Whether the explosion-proof membrane of the explosion-proof tube (safety airway) is in good condition and whether the moisture absorption agent of the respirator fails.
(4) Whether the shell of the transformer and the neutral point of the low-voltage side are solid and reliable, and whether the grounding resistance meets the requirements.
(5) Whether the transformer first and second outlet bushings and the connection with the conductors are good and the phase contrast is correct.
(6) Measurement of the insulation resistance and DC resistance of the transformer shall comply with the relevant provisions of the "Electrical Apparatus Installation Engineering Electrical Equipment Transfer Test Standard".
If the above checks are all qualified, the transformer is first air-dropped (without load), check whether the electromagnetic sound is abnormal, and measure whether the secondary voltage is balanced. If the balance shows that the transformer turns normal, there is no turn-to-turn short circuit, and the transformer can carry normal load. run.
3 operation monitoring
3.1 Electrical parameters
The electrical parameters directly reflect the load and operating safety of the transformer. Especially during the peak period of power usage, monitoring must be strengthened. Distribution transformer should be designed distribution box, configure ammeter, voltmeter, etc., to facilitate the monitoring of electrical parameters, no ammeter, voltmeter, can be used in the low-voltage side clamp ammeter, multimeter measurement, in operation, must follow the safety regulations Requires to operate.
3.1.1 overload
During winter heating, cooling in summer and concentrated use of electricity in farm irrigation, transformers are often overloaded. At this time, the monitoring of the electrical parameters of the transformer must be strengthened and measures must be taken to properly allocate the time and load to limit the overload time. Within the scope of the operating procedures, otherwise, it will cause the insulation of the various components inside the transformer, coil, oil insulation affect the life of the transformer and increase the loss, and even make the transformer burned. A large part of the transformers we maintain is the long-term overload of the transformer, which causes the insulation to burn out. Therefore, if the transformer does not meet the load requirements, consider replacing large capacity or installing a transformer in parallel.
3.1.2 Three-phase electrical parameter imbalance
The main reason is that the three-phase load is unbalanced. We once checked the transformer of phase-A insulation aging breakdown caused by a phase imbalance due to load imbalance. The phase A insulation color is significantly deeper than the other two phases. At the same time, because the three-phase voltage is unbalanced, the three-phase load current generates a zero-sequence current component, which will generate zero-sequence magnetic flux in the transformer core and produce a zero-sequence voltage on the secondary side. Not only the load-side neutral point displacement, so that the neutral line Energized, leading to electric motor, household appliances shell charged, poses a threat to personal safety, while the zero-sequence magnetic flux generates a larger iron loss, intensified temperature rise, reduce the efficiency and service life of the transformer. Therefore, when running monitoring, carefully observe and measure whether the three-phase voltage and current are balanced. According to the percentage of the current exceeding the rated value, determine the time allowed for the overload to operate (specified by the transformer operating procedures) and balance the three-phase load current as much as possible.
When the three-phase electrical parameters appear unbalanced, it is also necessary to pay attention to whether there is a “buzzing†air bubble escaping sound in the transformer. If so, this is another cause of unbalance. Stop the operation immediately, check and deal with it; otherwise, serious consequences will result. For example, in an enterprise in our power supply area, when an operator reads the meter, he finds that the three-phase voltage and current are unbalanced and he understands that the load on the transformer has not changed. He began to doubt the metering problem. At this time, he heard a noise inside the transformer. After a power failure check, a short circuit in the windings was found.
3.2 Sound
Seen from the above examples, the discrimination of transformer sound is very important. Through the sound, we can understand the safe operation of transformers and judge faults and hidden dangers. When the ambient noise is noisy and affects the discrimination effect, it can be performed in relatively quiet conditions such as early evening. Through the analysis of the actual situation, the following points are summarized:
3.2.1 louder
The normal sound is a slight and even “squeaking†electromagnetic sound. If the sound is loud, it is mainly due to the following reasons:
(1) The load is large. The sound increases with the increase of load, if the oil temperature, oil level change is not large and stable, the three-phase current increases and is more balanced, the three-phase voltage balances and slightly decreases, the louder sound is caused by the increase of the load. Pay attention to changes in the load.
(2) The system voltage increases. When the system voltage increases, it will also cause louder sound. At this time, the three-phase current is relatively balanced and slightly decreased. The three-phase voltage is obviously increased and exceeds the rated value. Attention should be paid to observation and resolution, and contact the power supply department to understand the reason.
3.2.2 Abnormal sound
When the following abnormal noise occurs in the distribution transformer, the operation shall be stopped and the transformer shall be inspected and treated. Otherwise, accidents may occur.
(1) The sound is loud and noisy. The indication of the instrument is normal. There is no major change in the color, temperature, and oil level of the insulating oil. It may be that the transformer core clamp or the screw that presses the core is loose.
(2) There is boiling sound of water in the sound, and the sound of “buzzing†bubbles escaping is mainly caused by a short circuit between the windings or poor contact of the tap-changer.
(3) There is an explosion in the sound, which is large and uneven. It may be that the insulation of the transformer body is broken down.
(4) There is a discharge “buzz†in the sound, which may be a partial discharge on the surface of the transformer body or casing. During inspection and maintenance, dirt on the surface of the casing should be cleaned, then painted with silicone oil or grease, or the distance between the grounding of the iron core and the live parts should be checked.
(5) There is a continuous, regular impact or friction sound in the sound, and there is no reaction between the various meter indications and the temperature. It may be that some parts of the transformer are mechanically contacted due to the vibration of the iron core, or because The abnormal sound caused by electrostatic discharge should be treated in a timely manner.
3.3 Transformer Oil
Under normal conditions, the transformer oil is transparent and yellowish, and the oil level of the oil level gauge matches the oil temperature mark. The transformer oil in operation is affected by the discharge, overheating, etc., and it will change, and it will be reflected by oil color and oil level. It should be carefully observed and analyzed. In addition, the transformer oil test and chromatographic analysis should be performed regularly to determine the health of the transformer.
3.3.1 Oil level
The oil level of the transformer depends on the operating temperature and the ambient temperature. The operating temperature, in turn, is related to the size of the load. The oil level of the general transformer changes in the range of -30 to 30 °C. If the oil level rises above the highest position indicated and continues to rise, and the sound is abnormal, the three-phase current and voltage are unbalanced, which indicates that the internal temperature of the transformer has abnormally increased. Short circuit fault. At this time, you should stop the operation and carry out a heart inspection. If the leakage of transformer oil is serious, or if it continuously leaks from the damaged part, the oil level is too low, and the bushing lead and the tap changer are exposed to the air, the insulation level will be greatly reduced, and the breakdown discharge will occur. The transformer should be stopped immediately. Run, fill leaks and refuel. Also pay attention to whether the color of the desiccant in the respirator has changed, if it has expired, replace it in time and find that the defect is eliminated in time to prevent the false oil level caused by the respirator plugging.
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