1. Causes of transformer burn-out
(1) There are no fuses on the high and low voltage sides of the distribution transformer. Some of them have been equipped with drop-type fuses and crocodile insurance, but most of their fuse-links are replaced with aluminum or copper wire, resulting in low-voltage short-circuit or overload, the fuse can not be properly blown and burned the transformer.
(2) Disposition of high and low voltage fuses of distribution transformers is not proper. The fuses on the transformer are generally oversized, and the transformer is burned when it is heavily overloaded.
(3) Due to the large number of rural lighting circuits, most of them use single-phase power supply, together with the arbitrariness of the jumpers in construction and lack of management, resulting in the phased operation of distribution transformer loads. The use of long-term, resulting in a phase coil insulation aging and burning the transformer.
(4) Tap changer: 1 If the tap changer is not adjusted automatically, the change-over tap changer is not in place, and the contact is bad and it is burned. 2 The quality of the tap switch is poor, resulting in incomplete contact of the star contact, short circuit or discharge to ground.
(5) Oil seepage is the most common appearance abnormality of the transformer. Because the transformer body is full of oil, each connection site has plastic beads and pads to prevent oil from leaking. After a long period of operation, some plastic beads and pads in the transformer will be cracked and cause oil leakage. As a result, the performance of the insulation deteriorates after it is wet, and the discharge is short-circuited and the transformer is burned.
(6) Most of the high and low voltage lines of distribution transformers are introduced by overhead lines, and 10 kV surge arresters are not installed in time because the arresters are not put into operation. Causes a lightning strike to burn the transformer.
(7) Multipoint grounding of the iron core.
(8) When the low-voltage side of the distribution transformer is earthed or phase short-circuited, a short-circuit current of 20 to 30 times the rated current will be generated. Such a large current will act on the high-voltage winding and the coil will have a large mechanical stress inside. This mechanical stress will cause the coil to compress. After the short-circuit fault is removed, the stress also disappears. If the coil is repeatedly subjected to mechanical stress, the insulating plastic beads and pads will loosen and fall off; the iron-cored splint will also loosen and the high-voltage coil will be distorted or cracked. In addition, high temperatures can also occur, causing the transformer to burn in a very short time.
(9) Man-made damage:
(1) The lead wire of the transformer is a copper screw, while the overhead wire is generally made of an aluminum core rubber wire, and the galvanic corrosion easily occurs between copper and aluminum. 2 bushing flashover discharge is also a common abnormal phenomenon of the transformer.
2. Measures to be solved (1) In the new construction, high and low voltage fuses should be installed in time. During the operation of the transformer, the fuse should be promptly replaced after it is found to have been burned or stolen.
(2) Reasonable disposition of high-voltage and low-voltage fuses: 1 The transformer with capacity above 100kVA should be equipped with (1.5-2.0) rated current fuses. 2 The transformer with the capacity below 100kVA should be equipped with (2.0-3.0) rated current fuses. 3 The low-voltage side fuses should be selected slightly larger than the rated current.
(3) Strengthen the electricity load measurement work, use the clamp-type ammeter at the peak period to measure the load of each distribution transformer, reasonably adjust the load, and avoid three-phase unbalanced operation of the distribution transformer.
(4) For the 10kV distribution transformer low voltage side voltage within +7% to -10% range, it is generally not allowed to adjust the tap changer. When adjusting the tap changer, it shall be tested and adjusted by the test technician.
(5) Check periodically whether the three-phase current is balanced or exceeds the rated value. If the three load currents are seriously out of balance, measures shall be taken to adjust them in time.
(6) Before the onset of the annual thunderstorm season, the arresters on all distribution transformers should be sent to the repairing department for inspection.
(7) The following inspection work should be done before putting into operation: 1 With load sharing and switching three times, it shall not be mis-operated. 2 Test three times with the test button and it should operate correctly. 3 Use the test resistor to earth test three times and it should operate correctly.
(8) Regularly clean the dirt on the surface of distribution transformer bushings: Check whether the bushings have flash traces, whether the grounding is good, and whether the leads used for grounding are broken, unplugged, or broken. Measured with a megohmmeter, the grounding resistance must not exceed 4Ω. In short, the operation of distribution transformers is inextricably linked with management. In the work, as long as the management personnel are meticulous in their work, they will surely be able to effectively avoid the occurrence of burnout accidents in distribution transformers.
