What faults can occur in dry-type transformers? Do you know the cause of the failure

Dry-type transformer is one of the transformers. It has the advantages of small size and convenient maintenance. However, at the same time, there are still many problems in the use of the system, such as winding failure, switch failure and iron core failure, etc., which affect its normal operation.

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1. The temperature of the transformer rises abnormally
The abnormal operation of dry-type transformers is mainly manifested in temperature and noise.
If the temperature is abnormally high, the specific treatment measures and steps are as follows:
1. Check whether the thermostat and thermometer are malfunctioning
Check whether the air blowing device and indoor ventilation are normal;
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:
Short circuit between partial layers or turns of transformer windings, loose internal contacts, increased contact resistance, short circuits on the secondary circuit, etc.;
Partial short-circuit of the transformer core, damage to the insulation of the core screw used for clamping the core;
Long-term overload operation or accident overload;
Deterioration of heat dissipation conditions, etc.
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 changes in strength with the size of the load; when the transformer has an abnormal sound, first analyze and determine whether the sound is inside or outside the transformer.
If it is internal, the possible parts are:
1. If the iron core is not tightly clamped and loosened, it will make a “dingdong” and “huhu” sound;
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 “squeak” and “crack” sounds, which will increase with the increase of load;
4. The hissing sound will be heard when the oil pollution on the surface of the casing is serious.
If it is external, the possible parts are:
1. A heavy “buzzing” will be emitted during overload operation;
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 power grid system, the transformer will emit noise with uneven thickness;
5. When there is a short circuit or grounding on the low-voltage side, the transformer will make a huge “boom” sound;
6. When the external connection is loose, there is arc or spark.
7. Simple handling of temperature control failure
3. Low insulation resistance of iron core to ground
The main reason is that the humidity of the ambient air is relatively high, and the dry-type transformer is damp, resulting in low insulation resistance.
Solution:
Place the iodine tungsten lamp under the low-voltage coil for continuous baking for 12 hours. As long as the insulation resistance of the iron core and high and low voltage coils is low due to moisture, the insulation resistance value will be increased accordingly.
4, 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 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 the 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 should be paid attention to when powering on site?
Generally, the power supply bureau sends power 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 there is condensation on the body of the device; check whether there are holes in the shell that can allow small animals to enter (especially the cable entry part); whether there is discharge sound during power transmission.
6. When the power transmission shocks, 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.
Solution:
Use a 2500MΩ shake meter to break down the insulation of the board or scrape off 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 discharge sound during the handover test?
There are several possibilities. The pull plate is positioned at the tensioned part of the clamp to discharge. You can use a blunderbus here to make the pull plate and the clamp conduct good conduction; the cushion block creepage, especially the high voltage product (35kV) has caused this Phenomenon, it is necessary to strengthen the insulation treatment of the spacer; the high-voltage cable and the connection point or the close insulation distance with the breakout board and the corner connection tube will also produce discharge sound. The insulation distance needs to be increased, the bolts should be tightened, and the high-voltage coils should be checked. Whether there are dust particles on the inner wall, because the particles absorb moisture, the insulation may be reduced and discharge may occur.
8. Common faults of thermostat operation
Common faults and treatment methods of temperature control during operation.
9, common faults in fan operation
Common faults and treatment methods of fans during operation
10. The unbalance rate of DC resistance exceeds the standard
In the user’s handover test, loose tap bolts or test method problems will cause the DC resistance unbalance rate to exceed the standard.
Check item:
Whether there is resin in each tap;
Whether the bolt connection is tight, especially the connection bolt of the low-voltage copper bar;
Whether there is paint or other foreign matter on the contact surface, for example, use sandpaper to smooth the contact surface of the joint.
11. Abnormal travel switch
The travel switch is a device that protects the operator when the transformer is powered on. For example, when the transformer is powered on, the contact of the travel switch should be closed immediately when any shell door is opened, so that the alarm circuit is turned on and an alarm is issued.
Common faults: No alarm after opening the door, but still alarm after closing the door.
Possible reasons: Poor connection of the travel switch, poor fixing or malfunction of the travel switch.
Solution:
1) Check the wiring and wiring terminals to make them in good contact.
2) Replace the travel switch.
3) Check and tighten the positioning bolts.
12. The corner connection pipe is burnt out
Check carefully the black parts of the high-voltage coil and scrape off the darkest part with a knife or iron sheet. If the carbon black is removed and the red color is leaked, it means that the insulation inside the coil is not damaged and the coil is mostly in good condition. Judge whether the coil is short-circuited by measuring the transformation ratio. If the test transformation ratio is normal, it means that the fault is caused by an external short circuit and the angle adapter is burned out.


Post time: Sep-11-2021