Operation And Maintenance Of Distribution Transformers

1. Overload operation of distribution transformers
Transformer overload operation means that the load current exceeds the rated current of the transformer. Under normal circumstances, when a transformer is operating at a small load, its insulating material cannot fully function. During continuous overload operation, the transformer will generate high temperatures, which will cause the insulation part of the winding to be burned and fall off, forming an inter-turn short circuit; at the same time, the transformer oil will produce Sludge accumulates on the tank plate, windings and core, causing poor heat dissipation of the transformer oil. This vicious cycle not only seriously affects the life of the transformer, but also causes accidents such as high-voltage breakdown and transformer burnout. Therefore, the three-phase load current should be observed frequently. The three-phase load current should be consistent. If there is any deviation, it should not exceed 10%.
2. Abnormal sounds from distribution transformers
When alternating current passes through the transformer winding, a normal and uniform "buzzing" sound will be produced due to the self-vibration of the core. If abnormal sound occurs, the cause needs to be found and reported to the relevant departments for handling in a timely manner. The sound of the transformer is different when it is no-load and when it is loaded. According to the abnormal sound characteristics and comparison with the past, the cause can be found out before it can be put into operation.
3. Inspection of distribution transformer temperature
The operating temperature of the transformer has a great relationship with its service life. When the transformer operates below the normal temperature of 95℃, its service life is 20 years; if the temperature rises to 110℃, the service life will be shortened to 7 years; if the temperature rises to 130℃, its life will be shortened to 2 years; if the transformer operates at 170℃, it continues to operate under high temperature, it will be scrapped in about 1 year. If the temperature exceeds the allowable value of the transformer, find out the cause and take countermeasures in time.
4. Is the oil level of the distribution transformer normal? Is there any leakage, oil leakage or abnormal oil color?
There are many reasons for a drop in oil level. Due to poor welding quality and sealing, heat pipes, valves, box edges, etc. are prone to seepage and oil leakage. When the oil level drops below the upper cover of the transformer, the contact surface between the oil and the air increases, and it is prone to oxidation and deterioration and absorption of moisture in the air, resulting in a reduction in the pressure resistance of the oil, thereby destroying the insulation performance of the winding. When the oil shortage is serious, the insulation between the conductive parts of the transformer and the ground and between each other is reduced, causing breakdown and discharge between phases or to the ground. If you continue to use it at this time, the transformer oil will not be able to circulate and convection normally, causing the temperature of the transformer oil to rise, shortening its life and even burning it out.
5. Whether the insulation bushing of the distribution transformer is damaged, cracked or discharged
If the insulating bushing has not been cleaned for a long time, or there are damage, cracks and traces of discharge, in rainy or foggy weather, the leakage current of the insulating bushing will increase due to the moisture in the air, the insulation will decrease, and a flashover to the ground will occur. In addition, serious scale accumulation on the insulating casing, as well as large fragments and cracks on the insulating casing can also cause flashover or explosion accidents. To solve this phenomenon, in addition to observing the insulation bushing itself, we must also pay attention to the dirt accumulation pattern of the bushing, such as wind direction, surrounding environment, etc., so that we can do a good job in cleaning.
6. Regular cleaning of distribution transformers
It is necessary to regularly clean the dirt on the distribution transformer, check whether there is flashover discharge in the bushing, whether the grounding is good, and whether there are any disconnections, desoldering, or fractures. The grounding resistance should be measured regularly, and the resistance value should not be greater than 4Ω (capacity 100kV·A and above) or 10Ω (capacity less than 100kV·A), or take anti-fouling measures and install casing anti-fouling caps. When connecting and removing the lead wires of the distribution transformer, the process must be strictly followed to avoid internal breakage of the lead wires.