How to Choose Pad Mounted Transformer?
Table of Contents Selecting the right pad-mounted transformer requires careful consideration of several critical factors,
ELECTRIC, WITH AN EDGE
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The transformer should be operated in an environment with suitable temperature and humidity. The damping of the transformer will seriously affect the service life of the transformer. The damping of the transformer is mainly caused by the poor quality of the insulating oil or the reduction of the oil level. This paper analyzes the damage of the transformer and the moisture-proof measures. Look up.
The fault of the transformer wet is mainly caused by the poor quality of insulating oil or the decrease of oil level.
1. Before the transformer is put into operation, moisture invades and dampens the insulation, or the transformer is in a humid place or a rainy area, and the humidity is too high.
How to prevent transformer oil from deteriorating?
2. Improper maintenance during storage, transportation, and operation, moisture, impurities or other oil stains are mixed into the oil, which greatly reduces the insulation strength.
3. During manufacture, the inner layer of the winding is impervious to paint, and the drying is not complete. The welding of the winding lead joints and the incomplete insulation lead to short circuits between turns and layers.
The damaged part of the distribution transformer winding occurs on the primary side, mainly due to inter-turn, inter-layer short circuit or winding-to-ground. When reaching or approaching the service life, the insulation will naturally wither and become black, and the insulation will be lost.
4. Insulation aging or oil level reduction Some old transformers that have been in disrepair for a long time have reduced oil level due to various reasons, and the contact area between insulating oil and air increases, which accelerates the entry of moisture in the air into the oil surface and reduces the insulation strength.
When the insulation decreases to a certain value, a short circuit occurs. Therefore, the distribution transformers in operation must regularly carry out oil level detection and grease testing, and find problems and deal with them in time.
Transformers cannot be affected by moisture, so what harm will the transformer be affected by moisture?
If the transformer is wet for a long time but not treated in time, the insulation capacity of the transformer will be drastically reduced, causing serious consequences such as inter-turn short circuit and coil burnout.
Safety measures to prevent moisture and air from entering the transformer
Professional teams should be invited to remove the moisture in the transformer oil, and the transformer oil should be replaced when the discharge is serious.
After the transformer is damp, the main insulation will be aged and the insulation level will be reduced; the breakdown voltage of the transformer oil is low;
Or caused by the expansion of other faults, such as when the winding has an inter-turn short circuit or a ground fault, due to the arc and the molten copper (aluminum) particles scattered and splashed, the accident spread and expanded and developed into a phase-to-phase short circuit.
Or due to poor internal welding of the wire, blown due to overheating or blown due to inter-turn short circuit, and winding breakage caused by short-circuit stress.
Therefore, once it is found that the transformer installation environment is relatively humid, it is necessary to carry out moisture-proof treatment on the transformer, so as to prevent faults and accidents caused by the transformer being damp.
1. After the transformer is purchased, the power supply bureau should be immediately requested to do the handover test;
2. Immediately install a moisture absorber, and all transformers with a capacity of 100 kVA and above are equipped with a moisture absorber. As soon as the transformer is transported to the site, a moisture absorber should be installed immediately to prevent the internal body from getting wet.
3. Monitor the silica gel in the dehumidifier and replace it immediately after getting wet. The silica gel in the moisture absorber absorbs moisture and protects the transformer. After the moisture is fully absorbed, the color of the silica gel changes, and a new dry silica gel needs to be replaced at this time.
4. When ordering, it should be noted that the storage time of the transformer before power transmission should be minimized. After the transformer is manufactured, it is very easy to get wet during storage. The longer the storage time, the more serious the moisture will be. Therefore, the plan should be arranged to shorten the storage time as much as possible.
5. Small transformers with a capacity of 100 kVA and below, without a moisture absorber device. The oil in the oil pillow is easily damp, and the oil pillow accumulates water. If it has been stored for more than six months without power transmission, or has been put into operation for more than one year, the oil in the transformer oil pillow has been seriously damp. If you want to carry out lifting and transportation, maintenance and refueling, oil valve draining, lifting core, etc., you should first drain the dirty oil in the oil pillow through the oil drain plug under the oil pillow, and wipe it with a dry cloth and seal it well to avoid Let the dirty oil in the oil pillow enter the oil tank.
6. During the operation of the transformer, always pay attention to the changes of oil level, oil temperature, voltage and current. If there is any abnormal situation, it should be analyzed and dealt with in time.
7.When installing the transformer, it is strictly forbidden to use aluminum stranded wire, aluminum row, etc. to connect with the copper guide rod of the transformer to avoid corrosion of the guide rod.
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How to deal with the wet distribution transformer? In the continuous rainy temperature or extremely hot temperature, the distribution transformer is very easy to return to moisture, and the power distribution transformer that returns to the moisture is very prone to some problems such as short-circuit failure.
The power distribution transformers that have returned to the tide must be solved in a centralized manner, and there must be a way to solve them, so that the power distribution transformers can reduce common faults and reduce hazards.
Maintenance Procedures for Pad Mounted Transformers
How should the solution be carried out in the whole process of the solution of the specific power distribution transformer damping? The following are five common treatment processes for everyone to carry out reference:
The key to the heating method of magnetic induction is to place the entire body of the toroidal distribution transformer in the fuel tank of the car, and the external winding resistance electromagnetic coil can withstand the amount of DC current.
Then use the wear of the vortex on the inner wall of the automobile fuel tank to dry and heat the toroidal distribution transformer. At this time, the temperature of the inner wall of the tank should not exceed 115℃-120℃, and the temperature of the body should not exceed 90℃. In the middle of -95°C, in order to facilitate the winding of the electromagnetic coil, the number of turns of the electromagnetic coil should be reduced as much as possible, or the amount of current should be smaller.
Under normal circumstances, the current should be 150A, and the transmission line should be 35-50mm2. Multiple rock wool and glass magnesium strips can be placed on the wall of the car fuel tank, and then the transmission line is coiled on the rock wool and glass magnesium strips.
The method of warm air drying is to place the body of the toroidal transformer outdoors, or dry it according to the warm air, and the temperature of the imported warm air should increase slowly.
However, the temperature cannot exceed 95 °C, and a filter device should be installed at the air inlet of the warm air. The key is to prevent dust and sparks from entering the toroidal transformer. There are also warm air that cannot be blown against the body immediately. , as far as possible from the underside of the toroidal transformer body to blow in different directions evenly, so that the moisture can go out from the vent of the cover.
This is the common way to deal with the damping of the transformer. For everyone’s reference, if the transformer also has other common faults, please consult Daelim or establish contact with Daelim’s professional technicians to deal with it.
The moisture absorber is also called “respirator”, which is used to remove and dry the impurities and moisture in the air entering the oil conservator due to the temperature change of the transformer, so as to ensure the insulation strength of the transformer oil.
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According to the structure, the moisture absorber is divided into two types: hanging type and seat type.
It is installed under the oil storage pipe through the connecting pipe. The moisture absorber is equipped with 2.7-7mm granular silica gel (also available with activated alumina), and the lower part has an oil container, which is used to filter and remove impurities and moisture in the inhaled air. The silica gel is damp To a certain extent, pink is generated from blue.
The method of drying the silica gel after it is wet is: drying at a high temperature of 120-140 ℃ for 4-6 hours, so that the water evaporates and becomes blue.
The moisture absorber is used according to the capacity of filling silica gel and according to the weight of the transformer.
According to the different capacity and structure of the transformer, the method of heating and heating up the transformer during drying on site can be carried out by the method of oil tank iron loss or short-circuit iron loss and hot oil spraying. There are two types of moisture removal methods: vacuuming and no vacuuming.
However, this drying treatment is easily limited by site conditions, is often difficult to implement, requires a long power outage, and is likely to cause abnormal aging of the transformer insulation.
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The no-load loss and load loss generated during the normal operation of the transformer are used as the heat source for the drying process of the transformer.
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The moisture in the transformer insulating paper gradually penetrates into the transformer oil, and the online oil filter device is used to remove the moisture in the transformer oil, and then the transformer oil passes through
The inlet filter enters the vacuum container, and the transformer oil is sprayed out by the vacuum pressure nozzle, and the gas and water vapor in the oil film are transferred to the air by the pressure nozzle, so as to complete the degassing and dehydration process of the insulating oil.
The purified oil is collected at the bottom of the container, filtered by the filter element and re-injected into the transformer.
During operation, a container and corresponding valve should be installed at the lower part of the oil return filter to detect and discharge air bubbles to prevent gas from entering the transformer.
This treatment method has the characteristics of short power outage time, uniform heating, and not easy to cause transformer insulation damage.
Under the circumstance that the safety measures are fully in place, it can avoid the gas protection malfunction of the transformer being treated.
The quality of transformer insulation and safe operation level directly affect the reliability of power supply of the entire power system.
In the preventive test, focus on detecting several data related to whether the transformer is damp, such as insulation resistance, absorption ratio, polarization index, dielectric loss, winding leakage current, micro-water analysis in oil, etc.
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When the insulation of the transformer is detected to be damped by certain technical means, offline and online methods can be used to deal with the damping of the transformer.
The basic method of offline treatment of transformer drying: heating and moisture removal, depending on the capacity and structure of the transformer. The method of heating and heating when drying the transformer on site can use the iron loss of the oil tank or the short-circuit iron loss and hot oil spraying. method to proceed.
There are two types of moisture removal methods: vacuuming and no vacuuming. However, off-line drying treatment is easily limited by on-site conditions, and is often difficult to implement. The power outage time is long, and it is easy to cause abnormal aging of transformer insulation.
The method of dealing with moisture in the transformer online: using the no-load loss and load loss generated during the normal operation of the transformer as the heat source for the drying process of the transformer, the moisture in the transformer insulating paper gradually penetrates into the transformer oil, and the online oil filter device is used to remove the transformer oil. Then the transformer oil enters the vacuum container through the inlet filter, and the transformer oil is sprayed out by the vacuum pressure nozzle, and the gas and water vapor in the oil film are transferred to the air by the pressure nozzle, so as to complete the insulation oil. Degassing and dehydration process.
The purified oil is collected at the bottom of the container, filtered by the filter element and re-injected into the transformer. During operation, a container and corresponding valve should be installed at the lower part of the oil return filter to detect and discharge air bubbles to prevent gas from entering the transformer.
The method for dealing with moisture on the transformer body on-line has the characteristics of short power failure time, uniform heating, and not easy to cause transformer insulation damage. When the safety measures are fully in place, it can avoid the gas protection malfunction of the transformer being processed.
The rated capacity of the transformer is different, so its volume is different, but no matter what kind of transformer, its structure is basically the same.
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The insulating enameled wire is wound into two wire wraps, one is a high-voltage wire wrap, and the other is a low-voltage wire wrap. Finally, the high and low-voltage wires are wrapped around the iron core of the silicon steel sheet, and immersed in insulating varnish for moisture-proof treatment and can be used after drying. .
When the transformer is immersed in water or damp in use, the surface of the enameled wire is exposed to water or moisture. Due to the presence of corrosive substances in the water, the enameled wire becomes moldy and deteriorated and the insulating paint falls off or the degree of insulation decreases. Electrical breakdown occurs between turns, resulting in inter-turn short circuit or inter-layer short circuit.
When the above fault occurs in the transformer, a large short-circuit current is generated in the short-circuit circuit, which makes the transformer heat up quickly until it burns out.
Under normal circumstances, it is first to heat up, and then to smoke, so when the transformer has a strange smell, you should immediately cut off the power to check the cause.
When the rated power of the transformer does not match the load power, increase the load of the transformer at will to make it overloaded;
The temperature of the working environment is too high; the cooling equipment of the transformer is damaged or the ventilation openings are blocked, the transformer is too close to the heat source, etc.
There are many places where transformers are used in electrical equipment, so during its operation, it should be strictly waterproof and immersed in the transformer or placed in a humid environment for a long time.
When the transformer is immersed in water, drying measures should be taken in time. If the transformer is used in a humid environment, ventilation should be strengthened to minimize the degree of humidity.
When the transformer is not used for a long time, it should also be energized and dehumidified regularly to keep the interior dry.
The quality of transformer insulation and safe operation level will directly affect the reliability of power supply of the entire power system.
In the preventive test, focus on detecting several data related to whether the transformer is damp, such as insulation resistance, absorption ratio, polarization index, dielectric loss, winding leakage current, micro-water analysis in oil, etc.
When the insulation of the transformer is detected to be damped by certain technical means, offline and online methods can be used to deal with the damping of the transformer.
Heating heating and moisture removal are determined according to the transformer capacity and structure.
The method of heating and heating during transformer drying on site can be carried out by the method of oil tank iron loss or short-circuit iron loss and hot oil spraying.
There are two types of moisture removal methods: vacuuming and no vacuuming.
However, off-line drying treatment is easily limited by on-site conditions, and is often difficult to implement.
The power outage time is long, and it is easy to cause abnormal aging of transformer insulation.
The no-load loss and load loss generated during the normal operation of the transformer are used as the heat source for the drying process of the transformer.
The moisture in the transformer insulating paper gradually penetrates into the transformer oil, and the online oil filter device is used to remove the moisture in the transformer oil, and then the transformer oil passes through The inlet filter enters the vacuum container, and the transformer oil is sprayed out by the vacuum pressure nozzle, and the gas and water vapor in the oil film are transferred to the air by the pressure nozzle, so as to complete the degassing and dehydration process of the insulating oil.
The purified oil is collected at the bottom of the container, filtered by the filter element and re-injected into the transformer.
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During operation, a container and corresponding valve should be installed at the lower part of the oil return filter to detect and discharge air bubbles to prevent gas from entering the transformer.
The method for dealing with moisture on the transformer body on-line has the characteristics of short power failure time, uniform heating, and not easy to cause transformer insulation damage. When the safety measures are fully in place, it can avoid the gas protection malfunction of the transformer being processed.
The rated capacity of the transformer is different, so its volume is different, but no matter what kind of transformer, its structure is basically the same.
The insulating enameled wire is wound into two wire wraps, one is a high-voltage wire wrap, and the other is a low-voltage wire wrap. Finally, the high and low-voltage wires are wrapped around the iron core of the silicon steel sheet, and immersed in insulating varnish for moisture-proof treatment and can be used after drying. .
When the transformer is immersed in water or damp in use, the surface of the enameled wire is exposed to water or moisture. Due to the presence of corrosive substances in the water, the enameled wire becomes moldy and deteriorated and the insulating paint falls off or the degree of insulation decreases. Electrical breakdown occurs between turns, resulting in inter-turn short circuit or inter-layer short circuit.
When the above fault occurs in the transformer, a large short-circuit current is generated in the short-circuit circuit, which makes the transformer heat up quickly until it burns out.
Under normal circumstances, it is first to heat up, and then to smoke, so when the transformer has a strange smell, you should immediately cut off the power to check the cause.
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When the rated power of the transformer does not match the load power, increase the load of the transformer at will to make it overloaded;
The temperature of the working environment is too high; the cooling equipment of the transformer is damaged or the ventilation openings are blocked, the transformer is too close to the heat source, etc.
There are many places where transformers are used in electrical equipment, so during its operation, it should be strictly waterproof and immersed in the transformer or placed in a humid environment for a long time.
When the transformer is immersed in water, drying measures should be taken in time. If the transformer is used in a humid environment, ventilation should be strengthened to minimize the degree of humidity.
When the transformer is not used for a long time, it should also be energized and dehumidified regularly to keep the interior dry.
The quality of transformer insulation and safe operation level will directly affect the reliability of power supply of the entire power system.
In the preventive test, focus on detecting several data related to whether the transformer is damp, such as insulation resistance, absorption ratio, polarization index, dielectric loss, winding leakage current, micro-water analysis in oil, etc.
When the insulation of the transformer is detected to be damped by certain technical means, offline and online methods can be used to deal with the damping of the transformer.
Heating heating and moisture removal are determined according to the transformer capacity and structure. The method of heating and heating during transformer drying on site can be carried out by the method of oil tank iron loss or short-circuit iron loss and hot oil spraying. There are two types of moisture removal methods: vacuuming and no vacuuming.
However, off-line drying treatment is easily limited by on-site conditions, and is often difficult to implement. The power outage time is long, and it is easy to cause abnormal aging of transformer insulation.
The no-load loss and load loss generated during the normal operation of the transformer are used as the heat source for the drying process of the transformer. The moisture in the transformer insulating paper gradually penetrates into the transformer oil, and the online oil filter device is used to remove the moisture in the transformer oil, and then the transformer oil passes through The inlet filter enters the vacuum container, and the transformer oil is sprayed out by the vacuum pressure nozzle, and the gas and water vapor in the oil film are transferred to the air by the pressure nozzle, so as to complete the degassing and dehydration process of the insulating oil.
The purified oil is collected at the bottom of the container, filtered by the filter element and re-injected into the transformer. During operation, a container and corresponding valve should be installed at the lower part of the oil return filter to detect and discharge air bubbles to prevent gas from entering the transformer.
The method for dealing with moisture on the transformer body on-line has the characteristics of short power failure time, uniform heating, and not easy to cause transformer insulation damage. When the safety measures are fully in place, it can avoid the gas protection malfunction of the transformer being processed.
Insulation accidents of power transformers due to water ingress and dampness occur continuously, accounting for about 20% of insulation accidents, posing a threat to the safe operation of the power grid.
First, the silicone of the oil pillow respirator does not work, and the moisture in the air enters the transformer through the oil pillow, and the probability of this happening is relatively small.
Second, the sealing performance of the high-voltage bushing of the transformer is relatively poor, and moisture flows into the transformer through the top of the high-voltage bushing.
The connection cap at the top of the high-voltage bushing of the transformer is not well sealed, and moisture enters the winding insulation along the lead wire, causing a breakdown accident.
The reason for the poor sealing of the connection cap on the top of the casing is the unreasonable structure and the incorrect installation of the rubber gasket.
The connection cap on the top of the casing is connected to the threaded lead lug.
This connection cap has the dual function of sealing and conducting, which brings many disadvantages.
First, the manufacturing tolerance of the fine thread screw is too large, and the poor contact causes heat; secondly, the copper pins for fixing the lead wires are too long, and the terminal board used for the connection cap must also match the connection of the external busbar, so that the gasket cannot be pressed tightly. A little loose will leak water inwards.
In an insulation accident, the burnt part of the winding is generally near the lead, which means that the water enters along the casing lead.
During the inspection of the main transformer casing, it was found that the top connecting cap of the domestic casing was poorly sealed. When the lead was blown by the strong wind, the sealing rubber ring would be squeezed to one side, and the other side would have a vacancy, which could not prevent rainwater from infiltrating.
In order to eliminate the hidden danger of this accident, it was decided to add a copper cap to the top of the casing.
Working principle: The joint on the winding lead is fixed on the copper cap by thread, and the copper cap is connected with the external lead, so that the joint on the winding lead will not be in contact with the outside, thus preventing the entry of rainwater.
The high-voltage bushings of several transformers were reconstructed. After adding a copper cap to the top of the bushings, it was found that no rainwater leaked into the transformers through the bushings.
(1) The higher the temperature used to dry the transformer, the higher the saturated steam pressure, and the better the drying effect. However, the heat-resistant temperature of the insulation of the transformer itself is 105 °C. In order to prevent the insulation from aging, the temperature of the transformer body should be controlled at about 95 °C;
(2) When the transformer oil temperature increases by 10°C, the oxidation rate doubles. When drying in the oil, the temperature of the hot oil should be limited to about 85°C;
(3) Excessive drying of the insulating material will damage the internal structure of the insulating material. As long as the insulating property values specified in the standard are reached, the drying can be stopped;
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(4) The higher the vacuum degree when drying the transformer, the lower the boiling point of moisture, and the easier the moisture inside the insulation evaporates. However, when the transformer oil tank is used for drying, due to the limitation of the deformation of the oil tank (the elastic deformation is required not to exceed 4 times the thickness of the tank wall, and the permanent deformation does not exceed 1.5 times the thickness of the tank wall), the vacuum degree of the oil tank is specified as: 35kv and below transformers 51kPa; 60-UO LV transformer 67kPa; 154kv and above transformer 80KPa;
(5) When drying the transformer, if the top cover of the fuel tank is not well insulated, water vapor may condense under the top cover. Therefore, the fuel tank should have a good thermal insulation belt. When vacuuming, it should be on a sunny day, and the relative air humidity should not exceed 65%, or use dry filtered air, and put it in slowly to avoid a sharp drop in temperature;
(6) When the induction heating method is used for drying, the excitation winding should be as close as possible to the winding of the fuel tank wall to avoid the load power factor being too low. When winding the excitation winding, the oil stains on the fuel tank wall, insulation materials and winding windings should be removed first;
(7) The temperature of the transformer should be tested at any time during drying, including the top and bottom of the drying tank or the oil tank wall, the oil temperature at the inlet and outlet of the body, and the temperature of the inlet and outlet hot air. For the part where the excitation winding is densely wound and close to the tank wall (such as the arc part of the fuel tank), a glass thermometer should be installed, and the temperature should not exceed 120 °C. For the temperature measurement inside the fuel tank, a resistance temperature measurement or a signal thermometer should generally be used. Mercury thermometers are not allowed. Various thermometers should be calibrated before use. When drying the transformer, the temperature of the high-voltage winding can be used as the representative temperature of the body. If the winding temperature is calculated by the resistance method, the measurement must be accurate;
(8) When drying the transformer, there should be at least two people on duty in each shift, record temperature, vacuum, current, voltage, insulation resistance once every 462 hours, discharge condensate once, and conduct regular safety fire inspections.
(1) Transformer after replacing windings or dealing with insulation defects;
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(2) When it is proved by test that the insulation has been damped and not less than the specified value;
(3) There are signs of dampness in the fuel tank or on the device;
(4) If the body stays in the air for more than the specified time, it should be judged whether it needs to be dried according to the insulation performance test value before and after the overhaul and the specified value after the overhaul;
(5) When the newly installed transformer does not meet the conditions, it should be dried;
(6) If the body stays in the air for more than 48 hours, it can be slightly dried;
(7) Transformers of 110kv and above without oil conservator, regardless of whether they are transported with oil or not, if the oil tank is found to be poorly sealed, and no water traces are found in the interior;
(8) When the breakdown voltage of the residual oil of the transformer transported without oil is lower than the specified;
(9) When the insulation performance is slightly lower than the specified value;
(10) For transformers shipped without oil, oil has not been filled for more than 6 months (specified as oil filling within 3 months) from the date of delivery;
(11) For transformers transported with oil but without oil conservator, the oil conservator should be installed within 3 months from the date of delivery, and the oil should be filled with enough oil, otherwise it should be lightly dried in the oil.
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