Transformer DC resistance tester maintenance skills

First, strengthen daily maintenance and regular testing
According to the division of labor of the management personnel in Taiwan, in addition to regular transformer work, I also required the management personnel to strengthen their daily work and assign responsibilities. Key checks include:
1. Observe the appearance. Check whether there is oil leakage, whether there is smoke or emissions of parts. The transformer shell is not tightly welded or the rubber pad is not firm, which may lead to transformer leakage. If the oil level is too low, the insulation protection will be lost, leading to the discharge between the conductive part or between the conductive part and the housing, and the transformer will be burned seriously. Therefore, the fault should be eliminated and the oil should be replenished in time to ensure that the oil level is maintained at 1/4 to 3/4 of the oil standard. For loose parts, poor contact or even discharge, should be timely cut off the transformer fall insurance, in order to eliminate hidden dangers.
2. Check the hygroscopic device. When the volume of transformer oil expands and contracts due to changes in load or ambient temperature, the gas in the oil storage cabinet is forced to breathe through the moisture absorption device to remove debris and moisture in the air, so as to maintain the insulation strength of transformer oil in the transformer.
3.Check the shell regularly. Casing is a component insulation, consisting of conductive pipe and casing insulation. In the case of a transformer, it is used to channel its internal windings into an electrical connection with a power system or electrical equipment.
1) Check whether the oil level of the casing is normal
2) Check whether the shell surface is clean, whether there are cracks, damage, discharge points and other phenomena.
3) Check whether the connection between the busbar and the busbar is loose.
4) Check whether the oil level of the grease paper capacitor sleeve is normal.
5) Check whether the cover of the oiled paper capacitor sleeve is loose.
4. Listen to sound. The normal operation of the transformer will produce a uniform and subtle humming sound, which will change when the transformer is faulty with different characteristics. In this case, take measures according to the actual situation to locate the fault.
5. To check the oil dust on the high and low pressure shell, clean and remove the greasy dust and dirt arc discharge in time. When the climate is humid or rainy, if it causes a short circuit between the shell and the high voltage fuse is broken, the matching is invalid. I want people to clean it at least once every two months.
6. Observe the oil color and check the oil temperature regularly, especially in the case of large load change, large temperature difference and bad weather, increase the number of times. The top layer oil temperature of the oil-immersed distribution transformer in operation should not be higher than 95℃.
7. Shake and measure the insulation resistance of the transformer, check whether the wire is firm, and pay special attention to whether the low-voltage socket connection is good and the temperature is abnormal.
8. Strengthen the measurement of power load. During the peak period of power consumption, strengthen the load measurement of each distribution transformer, increase the number of measurements when necessary, and adjust the distribution transformer with unbalanced three-phase current in time to prevent the neutral line current from burning the lead wire excessively and causing damage. Customer's equipment and distribution transformer. The connection group is Yyn0. Not only one or two phase power supply should be used, but also the three-phase load should be balanced as far as possible. The neutral line current should not exceed 25% of the rated current of the low-voltage side, in an attempt to make the distribution transformer run without load and without bias to load.
9. Check and replace a fuse or two regularly. Do not use aluminum wire to replace a fuse. It is well known that the primary fuse protects the system and the secondary fuse protects the transformer.

Second, prevent external damage

1. Reasonably select the installation location of the distribution transformer. The installation location should be as close to the load center as possible, and the radius of the power supply should be controlled within 0.5km. Also, try to avoid installing equipment in lightning or low-lying waters. As it is located in the county seat, there are many transformers at the intersection. In order to reduce the number of cars hitting the tower, anti-collision signs are pasted along the road.
2. Avoid installing a low-voltage instrument case on the distribution transformer. Due to long time operation, the glass of the meter box is damaged or the low-voltage pile head of the transformer can not be replaced in time. More than 95% of public distribution transformers are installed with JP cabinets, which play a very good role in protecting the safe operation of transformers.
3. Do not adjust the tap changer without permission. If the tap changer is not adjusted in place and a short circuit occurs between phases, the distribution transformer may be burned.
4. Install insulation covers at the high and low voltage ends of the distribution transformer to prevent natural disasters and external damage. High and low voltage insulating covers are installed in narrow residential areas and forest areas where animals are frequently moved in and out to prevent burning of distribution transformers by falling on the distribution transformer's wiring pile.

5. Periodically cut off the circuit channels to prevent the branches from contacting the wires and causing low voltage short circuit and burning the distribution transformer.

Three, the use of matters needing attention
1. Prevent transformer overload operation: if the overload operation for a long time, the coil will be heated, the insulation layer will gradually aging, and between the wire box, between the phase or between the ground will also occur short circuit as the decomposition of oil;
2. Prevent transformer core aging and damage: core insulation aging or clamping bolt sleeve damage will cause large eddy current core, core long-term heating will lead to insulation aging;
3, prevent careless maintenance insulation damage: transformer maintenance core, should be paid
Pay attention to the protection coil or insulation sleeve. If there is any abrasion, please deal with it in time.
4 transformer low voltage maximum unbalance current shall not exceed 25% of the rated value; The transformer supply voltage is allowed to vary by plus or minus 5% of the rated voltage.
5. Ensure good wire contact: poor contact between coil internal joints, poor contact between the connection points between the coil, resulting in high pressure and low pressure side of the casing contact point and poor contact between the fulcrum on the splice switch will lead to local overheating, insulation damage, short circuit or open circuit. At this time the high temperature arc will make the insulation oil decomposition, in the transformer to produce a lot of gas, pressure. An explosion occurs when the pressure exceeds the value protected by the gas circuit breaker without tripping.
6, maintain good grounding: for the use of zero voltage protection low voltage system, (test. The neutral point on the low-voltage side of the transformer should be directly grounded. When this current is too large and the contact resistance is too large, the junction will appear high temperature, igniting the surrounding combustibles.
7, prevent overheating: the transformer should be monitored when the working temperature changes. If the transformer coil wire is A class insulation, the insulation is mainly paper and cotton yarn, temperature has A great impact on the insulation and service life, the temperature increases by 8℃, the insulation life will be reduced by about 50%. The transformer works at room temperature (90℃) and its service life is about 20 years. If the temperature rises to 105℃, the service life is 7 years. If the temperature rises to 120℃, the life will be only two years. Therefore, good ventilation and cooling must be maintained when the transformer is in operation. If necessary, forced ventilation can be used to reduce the temperature rise of the transformer