Analysis and Handling of Common Faults of Transformer

The transformer works on the principle of electromagnetic induction, Change the voltage, connect with the power grid, transmit and distribute the electricity; Power transformer is the core equipment of the substation, Complex structure, Poor operating environment, Fures and accidents have great impact on the reliability of power grid and power supply, Immediate measures need to be taken according to the specific circumstances; The analysis and discrimination of transformer faults involves many disciplines, To have electrician, high voltage, insulation materials and chemical analysis, Also familiar with automation, heat, etc.; There are many kinds of transformer faults, The forms of expression vary varied, Need to be familiar with the structural principle, familiar with the site operating conditions, familiar with the characteristics of each equipment, concrete issue, concrete analysis.

Chapter 1: Characteristics and Field Handling of Dominant Faults of Large Transformers

Explicit fault: refers to the characteristics and expression form of the fault is more intuitive and obvious fault, here, combined with the actual field, the cause and characteristics of the dominant fault of the large-scale transformer are described and analyzed, introduced the common processing methods on the site, but also some relatively simple methods.

1. Appearance Exception and Fault Type

When transformer abnormalities and faults occur in the process of operation, they are often accompanied by corresponding appearance characteristics. Through these simple external phenomena, some defects can be found and further analysis and treatment can be put forward for the abnormalities and faults. Moreover, the maintenance and test scheme can be determined for some more complex faults, and the following aspects can be analyzed and handled from several aspects:

1.1 Explosion-Proof Cylinder or Pressure Release Valve Film Is Damaged

When the transformer is not breathing freely, entering the air above the transformer oil pillow diaphragm, when the temperature rises, the pressure increases, with a large amount of transformer oil ejection; mainly for the following reasons and measures:

(1) The respirator is blocked due to more silicone gel or oil injection and foreign body in the pipeline. Silicone gel should account for 2 / 3 of the breathing apparatus, and there should be 1 / 3 of the oil in the oil seal. Nitrogen filling method can be used to check the pipeline.

(2) (oil pillow) installation and maintenance of the tight film bolt is too tight or the oil pillow flange is uneven, (pressure release valve) external force damage or personnel collision. Replace the damaged thin film or oil pillow.

(3) Short circuit fault occurs in the transformer, producing a large amount of gas. Generally accompanied by gas relay action: the gas sample can be taken from the gas relay first, if the ignition can be burned, the oil sample chromatographic analysis and electrical inspection to determine the nature of the fault, the cause of the fault has not been identified, the transformer can not be put into operation before the elimination of defects.

(4) The oil injection method of the diaphragm structure is improper during maintenance or installation, and the gas on the upper part of the oil pillow is not discharged according to the regulations. Fill the transformer oil with the oil pillow, and then put the transformer oil to the appropriate oil level height.

(5) The oil pillow of the capsule structure due to the low oil level, the capsule blocks the pipeline connection mouth between the oil pillow and the transformer body. Install a bracket at the pipeline joint port to prevent the capsule from directly blocking the joint port.

1.2 The Casing Flashover Discharge

Flashover discharge will cause heat and aging, causing short circuit accident at transformer outlet; the low voltage casing is especially serious: the main reasons and measures are:

(1) Dirty surface, in rainy and humid weather, due to the dirty conductivity and discharge. It is necessary to clean the casing of transformer power failure and apply RTV long-term coating to improve its anti-pollution flash performance.

(2) There are defects during installation, maintenance or manufacturing. During the test, the insulation index such as the medium loss angle exceeds the standard or the porcelain part is incomplete, so the casing should be replaced.

(3) During the design, the external creepage distance is small, and the transformer is running in the area with high filth level. Replace with casing with large creepage distance or casing insulated with silicone rubber or take anti-pollution measures such as silicone rubber skirt.

(4) Internal overvoltage and atmospheric overvoltage appear in the system. Test and check the casing and transformer, all qualified can be put into operation.

(5) The porcelain skirt on the casing surface: it can be picked out with the insulation rod.

(6) Rain and snow weather or ice cover, the transformer casing is the most likely to appear ice cover: stop running.

1.3 Leak Oil

Almost every transformer is a problem, every sealing point, even iron plate because of trachoma leakage. Oil seepage generally will not lead to the immediate shutdown of the transformer, but once the oil leakage is not handled in time, the heavy production will endanger the safe operation of the transformer. Because of the transformer sealing parts and various forms of various release, so the symbol of oil leakage is also different.

There are mainly the following reasons and measures:

(1) Sealant pad aging and fish crack, overdue replacement is not caused. Need to be replaced in combination with maintenance.

(2) The sealing point is not fastened in place, and the oil-free part will also accelerate the aging of the rubber pad, and the air will enter the transformer body. Keep it tight at any time.

(3) Valve manufacturing quality, poorly closed. Replace the valve with the oil release.

(4) Trachoma or poor welding quality. Can be welded with oil but must do a good job of fire prevention measures, the iron plate trachoma can also be welded on the surface of a certain area of iron plate to treat. The leakage oil of the transformer box cannot be welded without oil except for lifting the bell cover.

(5) Leakage of oil from the oil pump. Some parts of the negative pressure in its operation does not leak oil, once stopped will leak, this situation will often bring the air into the transformer, causing gas transmission or even action off. It is difficult to find, and the oil pump must stop to check the discrimination and processing.

(6) The rubber pad is too large deformation, unreasonable sealing structure manufacturing and installation process, will also lead to oil leakage. It needs to be handled for specific reasons.

2. Color Changes and Odor Abnormalities

Many faults of transformers are often accompanied by heating phenomenon, causing the color, temperature change or special smell.

2.1 The External Clamp Connection Overoverheated

By the transformer casing lead clip itself or connecting lead fastening bolt screw loose, contact surface oxidation or area is not enough, for hot color dim luster, temperature measurement will find the temperature is more than 70 degrees, temperature sheet discoloration, surface paint black prevention of such defects can be combined with power outage test measurement including clip transformer winding DC resistance, with doubt can measure the contact resistance of the clip itself (generally not more than 500u Ω), processing combined with the specific situation open clip grinding contact surface and fastening: if necessary, check the load of the clip:

2.2 The Silicone of The Respirator Is Damp

The silica gel of the respirator is generally color-changing silica gel, its role is to adsorb the moisture into the transformer oil pillow, under normal circumstances is light blue color, if it becomes pink is failure, by normal breathing generally need to replace once a year on the silica gel; silica gel discoloration too fast reasons and measures:

(1) Poor sealing of silicone cylinder, such as aging rubber pad, loose screws, and cracked glass placement; rubber pad, tightening screw and glass placement should be replaced.

(2) The oil seal of the lower part of the silicone cylinder has no oil or low oil level, and the water in the oil seal, so that the air can directly enter the respirator without oil filter. Add an appropriate amount of transformer oil can be added.

(3) Rain and high humidity or water in the silicone tube can also accelerate the discoloration of the silica gel.

2.3 Transformer Light Gas Action, Gas Relay Oil Indoor Gas Collection.

Under normal circumstances, the transformer gas relay oil room is filled with transformer oil. Once the light gas action, the oil sample chromatography analysis should be checked and taken immediately to confirm the internal fault situation.

If the gas is colorless, tasteless and not combustible, it is air; causes and measures:

(1) After installation or maintenance, the new oil injection or oil filter takes the gas out repeatedly or the venting is not complete. Once the transformer is put into operation, the temperature rises, the gas expands and escapes into the gas relay; therefore, the transformer oil filling procedure and repeated venting shall be strictly enforced.

(2) If the oil pump is poorly sealed, bring the gas into the transformer body, and the oil pump should be checked one by one.

If the gas contains a peculiar smell, the transformer has an internal fault, and the operation inspection and test should be stopped immediately, generally manifested as:

(1) slightly yellow and non-combustible, internal insulation support and other wood materials overheating or burn out.

(2) Black, gray and combustible, bare metal overheating or insulation flashover to make the transformer oil decomposition.

(3) White and not easy to burn, which may be insulation breakdown or paper insulation burn loss. The above phenomenon, gas sample and oil sample chromatographic analysis, characteristic gas will exceed the standard, should be combined with the electrical test and characteristic gas content, according to the test procedures and chromatographic guidelines, comprehensive analysis, find out the cause, and then treatment.

The cooling pipeline setting is unreasonable, the cause of the submersible pump will cause heavy gas action, the old transformer is more common.

3. Sound and Temperature Failure

3.1 Abnormal Sound

When the transformer is in normal operation, under the action of the AC electromagnetic field, it will emit a continuous, uniform and slight "buzzing" sound. If the sound is uneven or there is a special sound, it is considered abnormal. The main reasons are:

(1) Overvoltage of the system.

(2) Transformer overload operation; the above shall be determined according to the nameplate parameters of the transformer.

(3) Internal clamps or core screws and pulls are loose, and the vibration of core silicon steel sheet increases with obvious noise; lifting cover is required.

(4) Electrostatic discharge of metal parts with poor contact or ungrounding and external insulation corona discharge; accompanied by "cracking" discharge sound.

(5) The nameplate, sign plate, fan motor and other external accessories will also sound abnormal sound because they are not fixed. According to the specific situation to processing.

3.2 Abnormal Temperature

Many faults of the transformer are often accompanied by temperature changes. Regulations stipulate that the upper oil temperature of the transformer shall not exceed 95℃ and the temperature rise shall not exceed 55℃. The main causes and measures for the transformer temperature abnormality are:

(1) Internal transformer faults such as multi-point grounding and bare metal overheating: they need to be screened and processed.

(2) After the new installation or overhaul, the radiator gate is not opened, and the heat dissipation cannot be circulated normally. Check the operation of the oil pump and the movement of the flow gauge and open the open door.

(3) Respiratory device blockage or serious oil leakage affects the heat dissipation.

(4) The transformer structure is unreasonable, due to the magnetic leakage caused by the box shell local overheating will sometimes reach baidu. The separation material can be installed in specific parts.

(5) The cooling device is not running normally, which affects the heat dissipation.