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Common problems of dry-type transformers

2020-09-29
Transformers can achieve the conversion of voltage levels in the power system, and are widely used in long-distance power transmission, effectively solving the energy loss in the process of power transmission.

Dry-type transformer is one of the transformers. It has the advantages of small size and convenient maintenance. At the same time, there are still many problems in the use of the system, such as winding faults, switch faults, and iron core faults, which affect it. normal operation. The transformer is the main component of the power system, and its operating quality is directly related to the operating quality of the power system. The iron core and windings of dry-type transformers do not need to be immersed in oil; secondly, dry-type transformers will not have hidden dangers such as explosion and pollution, and their applications are very wide.

Next, we mainly analyze the common faults of dry-type transformers, and give measures to solve the faults, hoping to provide suggestions and suggestions for the normal operation of dry-type transformers.

1. Abnormal temperature rise of transformer
The abnormal operation of dry-type transformers is mainly manifested in temperature and noise. If the temperature is abnormally high, the specific measures and steps are as follows:
1. Check whether the thermostat and thermometer are out of order;
2. Check whether the blowing device and indoor ventilation are normal;
3. Check the load condition of the transformer and the insertion of the thermostat probe to eliminate the malfunction of the thermostat and the blowing device. Under normal load conditions, the temperature continues to rise. It should be confirmed that there is a fault inside the transformer, and the operation should be stopped and repaired.

The reasons for the abnormal temperature rise are:
1. There is a short circuit between partial layers or turns of transformer windings, internal contacts are loose, contact resistance increases, and there is a short circuit on the secondary circuit, etc.;
2. Partial short circuit of the transformer core, damage to the insulation of the core screw used for clamping the core;
3. Long-term overload operation or accident overload;
4. Deterioration of heat dissipation conditions.

2. Treatment of abnormal sound of transformer
Transformer sounds are divided into normal sounds and abnormal sounds. The normal sound is the "buzzing" sound generated by the excitation of the transformer, which varies with the magnitude of the load; when the transformer has an abnormal sound, first analyze and determine whether the sound is inside or outside the transformer.
A. If it is internal, the possible parts are:
1. If the iron core is not tightly clamped and loosened, it will sound "ding" and "whooping";
2. If the iron core is not grounded, there will be a slight discharge sound of "peeling" and "peeling";
3. Poor contact of the switch will cause "creaking" and "crackling" sounds, which will increase with the increase of load;
4. The hissing sound will be heard when the oil pollution on the casing surface is serious.

B. If it is external, the possible parts are:
1. A heavy "buzz" will be emitted when overloaded;
2. The voltage is too high, the transformer is loud and sharp;
3. When the phase is missing, the sound of the transformer is sharper than usual;
4. When magnetic resonance occurs in the grid system, the transformer will emit noise with uneven thickness;
5. When the low-voltage side is short-circuited or grounded, the transformer will make a huge "boom" sound;
6. When the external connection is loose, there is arc or spark.
5. Simple handling of temperature control failures

3. Low insulation resistance of iron core to ground
Mainly because the ambient air humidity is relatively high, the dry-type transformer is damp and the insulation resistance is low.
Solution: Place an iodine tungsten lamp under the low-voltage coil for continuous baking for 12 hours. As long as the core and high- and low-voltage coils have low insulation resistance due to moisture, the insulation resistance will be increased accordingly.

Fourth, the core-to-ground insulation resistance is zero
It shows that the solid connection between metals may be caused by burrs, metal wires, etc., which are brought into the iron core by the paint, and the two ends are overlapped between the iron core and the clip; the insulation of the foot is damaged and the iron core is connected to the foot; there is metal falling Into the low voltage coil, causing the pull plate to be connected to the iron core.
Solution: Use a lead wire to poke down the channel between the core stages of the low-voltage coil. After confirming that there is no foreign matter, check the insulation of the feet.

5. What matters should be paid attention to when powering on site?
Generally, the power supply bureau sends power for 5 times, and there are also 3 times. Before sending power, check the bolt tightening and whether there are metal foreign objects on the iron core; whether the insulation distance meets the power transmission standard; whether the electrical function is operating normally; whether the connection is correct; Whether the insulation of each component meets the power transmission standard; check whether the body of the device has condensation; check whether the shell has holes that can allow small animals to enter (especially the cable entry part); whether there is discharge sound during power transmission.

6. When the power is transmitted, the shell and the subway slab discharge
It shows that the conduction between the shell (aluminum alloy) plates is not good enough, which is a poor grounding.
Method: Use a 2500MΩ shake meter to break down the insulation of the board or scrape the paint film of each connection part of the shell and connect it to the ground with a copper wire.

7. Why is there a sound of discharge during the handover test?
There are several possibilities. The pull plate is positioned at the tension of the clamp to discharge. You can use a blunderbus here to make the pull plate and the clamp conduct well, and the problem can be solved; the cushion creepage, especially for high-voltage products (35kV) ) This phenomenon has occurred, strengthen the insulation treatment to the spacer; the high-voltage cable and the connection point are virtually connected or the distance between the breakout board and the corner connection tube is also close to the discharge sound. Increase the insulation distance and re-tighten the bolts to solve the problem. Check whether there are dust particles on the inner wall of the high-voltage coil. As the particles absorb moisture, the insulation may decrease and discharge may occur.

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