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Transformer burnout cause

In the power system, the low-voltage transformer is often the failure of burning down. With the implementation of rural power grid construction and renovation project and the deepening reform of power system, the property right of distribution transformers belongs to the power supply department. However, the burning of distribution transformers will not only result in a large-scale power outage in the region, but even more serious will make the power supply department promised to the society that the reliability of power supply will not be fully guaranteed and the power image will be affected.

Transformer burned reason:

1. Core multi-point grounding.
(1) l0kV distribution transformer core multi-point grounding is not easy to find and test, mainly because the transformer core is grounded in the interior with a thin purple copper one clip between the core (silicon steel) between , The other end is pressed on the core plywood and transformer housing directly connected.
(2) Between the core silicon steel coated with insulating paint, but its insulation resistance is very small, can only cut off the eddy current and can not stop the high voltage induction current. If the surface of the insulating sheet of silicon steel due to natural aging, will have a great eddy current loss, increase the core of the local overheating, damage to the transformer.

2. When the distribution transformer low voltage side of the earth, short circuit between the phase, it will produce a higher than the rated current of 20-30 times the short-circuit current, such a large current in the high-voltage winding, the coil will have a lot of mechanical stress, This mechanical stress will cause the coil to compress. After the short-circuit fault is relieved, the stress will disappear. If the coil is repeatedly subjected to mechanical stress, the insulating glue beads, pads, etc. will loosen and fall off, and the iron core clamp screws will also relax slightly. High-voltage coil distortion or cracking. In addition will also produce higher than the allowable temperature rise several times the temperature, causing the transformer to burn in a very short period of time.
3. Man-made damage.
(1) The lead-out of the transformer is a copper screw, and overhead lines are generally more aluminum core rubber line, so in the air between the copper and aluminum is very prone to electrochemical corrosion, under the action of ionization, forming an oxide film between the copper and aluminum , So that the contact resistance increases, the lead screw, nut and lead burned or fused together.
(2) Casing flashover discharge is also one of the common appearance anomalies of transformers. Conductive metal dust in the air attached to the surface of the casing, in case of rain and snow wet weather, grid system resonance, subjected to lightning over-voltage occurs when the casing flashover discharge or explosion.
(3) When tightening or loosening the lead nut of the transformer, make the conductive screw rotate with the uneven force, causing the short circuit caused by the soft copper of the lead wire of the high-voltage coil in the transformer being twisted or pulled out by the low voltage.
(4) In the maintenance of the hanging core, it is not carried out according to the maintenance procedures and the technical standards. Inadvertently, the insulation at the coils, lead wires, tap changers or the like is forgotten or the tools are forgotten in the transformer, Short circuit to ground, damage transformer. The company is located in:
       (5) distribution transformer high and low voltage on both sides without insurance. Although some have been fitted with flip-type fuses and claw insurance, but the fuse is replaced by aluminum or copper wire, resulting in low-voltage short circuit or overload, the fuse can not be properly blown and burned the transformer.

5. Distribution transformer high and low fuse configuration properly. Fuse on the transformer is generally the phenomenon of configuration is too large, resulting in a serious overload distribution transformer, the transformer burned.
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6. Due to the large rural lighting lines, most of them are single-phase power supply, coupled with the jumper in the construction of randomness and management is not in place, resulting in the distribution transformer with partial phase operation. Long-term use, resulting in a phase coil insulation burn and burn transformer.
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7. Tap changer.
(1) Individually adjust the tap-changer. Due to the large difference between the electricity load in winter and summer, the voltage level changes greatly. Therefore, some rural areas and enterprises do not have to adjust the tap-changers without trial adjustment by the electric power remediation department, resulting in the tap changers not in place and the poor contact and burning.
(2) The quality of the tap changer is poor, the structure is not reasonable, the pressure is not enough, the contact is not reliable, the position of the external character wheel is not exactly the same as the internal actual position, which causes the position of the star moving contact to be in incomplete contact, So that the insulation distance between the two taps becomes smaller and shorts or discharges to the ground under the potential between the two taps, the short circuit current will soon burn the tap wire and even cause the entire winding to be damaged.

8. Oil leakage is the most common appearance of the transformer anomalies. As the transformer body is full of oil, the joints have glue beads, pads to prevent oil leakage. After a long period of operation, some plastic beads and pads in the transformer will crack and cause oil leakage. As a result, the performance will drop after discharge and the discharge will be short-circuited and the transformer will be destroyed.
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9. The distribution transformer high and low voltage lines are mostly introduced by the overhead lines, due to the arrester is put into operation in time or not installed 10kV arrester, causing the transformer burned when the lightning strike.

10. Some distribution transformers are not equipped with a level of protection or configured with a level of protection but their maneuverability, low reliability, and some do not even act at all.
In summary, the distribution transformer burned for many reasons, some are caused by nature, while others are caused by man-made.
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Precaution:
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1. In the new construction, should promptly install high-voltage fuses and low-voltage insurance. In the transformer operation, found that the fuse burned or stolen should be promptly replaced.
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2. High and low voltage fuses should be properly configured.
(1) Transformers with capacities above 100kVA are to be equipped with (1.5 ~ 2.0) rated current fuses.
(2) Transformers with capacities above 100kVA are to be equipped with (2.0 ~ 3.0) rated current fuses.
(3) low-voltage side fuse should be slightly larger rated current point of choice.

3. Strengthen the power load measurement work, at the dawn of the advent of a clamp-type ammeter with each variable load conditions measured, adjust the load reasonable to avoid the three-phase unbalanced load with partial load operation.
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4 switch. When adjusting the tap-changer, it should be tested and adjusted by the technician in charge of repair.
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5. Regularly check whether the three-phase current balance or exceed the rated value, such as the three load current serious imbalance, measures should be taken to promptly adjust; regularly check the distribution transformer oil level is normal, with or without leakage, found that timely replenishment , To avoid tap changer, coil dew in the air damp.
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6. In the annual thunderstorm season before, all the arresters on the distribution transformers should be sent to the electric repair department for testing, qualified and timely installation.
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7. Distribution transformer must be installed a protection, put into operation before the following testing should be done:
   (1) with load, switch three times, shall not be mistaken.
(2) test button test three times, should be the correct action.
(3) Each test resistance grounding test three times, should be the correct action.
   (4) test hop once a week, should be the correct action.
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8. Regularly clean the surface of the distribution transformer casing dirt: Check the casing for flashover traces, grounding is good, the grounding wire used for breaking, desoldering, breaking phenomenon; with the megger test ground resistance shall not be greater than 4Ω.

9. Rational use of low-voltage side of the wire wiring, wiring board or steel with aluminum transition clamp and other special equipment, and cast conductive paste, increase the contact area, to prevent oxidation.

10. Strengthen personnel management, regularly organize technical and managerial personnel to conduct scientific and technological training activities, conscientiously study professional and technical knowledge such as "safety rules and regulations" and "technical regulations", and increase the inspection of distribution transformers.
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In short, the operation of distribution transformers and management is inextricably linked. In the work, as long as managers do diligence, diligence, diligence and diligence, it will be able to effectively avoid the occurrence of distribution transformer burnout, thus greatly ensuring the reliability of regional power supply.