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The Ultimate Guide To What Is A Dry Type Transformer

Views: 1000     Author: Site Editor     Publish Time: 2023-07-14      Origin: Site


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1.What is a dry-type transformer?

2.Application overview of dry-type transformers:

3.What industries are dry-type transformers used in?

4.What is the difference between indoor and outdoor use of dry-type transformers?

5.What are the structures of dry-type transformers?

6.What are the classifications of dry-type transformers?

7.Characteristics of SCB cast resin dry-type transformer and SGB H-class immersed dry-type transformer:

8.What is the difference between SGB (VPI) and SCB dry-type transformers?

9.hat is the production process and composition of dry-type transformers?

   Production process of dry-type transformer:

   Composition of dry-type transformer:

10.What are the factors affecting the price of dry-type transformers?

11.What are the advantages of dry-type transformers?

12.What are the disadvantages of dry-type transformers?

13.Comparison of dry-type transformers and oil-immersed transformers:

14.What are the factors that affect the life of dry-type transformers?

15.What are the inspection and maintenance of dry-type transformers?

    What places do dry-type transformers need to check when leaving the factory?

    What are the tests and experiments of dry-type transformers?

16.What are the protections for dry-type transformers?

17.Fault judgment method and solution of cast resin dry-type transformer.

     What are the reasons for the abnormal sound of dry-type transformers?

    Dry-type transformer fault judgment method and solution:

18.How to debug dry-type transformers:

1.What is a dry type transformer?

• The definition of a dry-type transformer is that its core and winding are not filled with any liquid medium to meet the insulation and cooling requirements of the transformer. Its coils are generally composed of gaseous or dry insulating media. In contrast, liquid-filled transformers need to be filled with a liquid medium for insulation and cooling of the transformer.

2. Application overview of dry-type transformers:

• Dry type transformer is a type of distribution transformer that can meet the distribution requirements of various industries below 35kV. Due to its safety, stability, and environmental benefits, it can operate under harsh conditions such as high humidity, fire risk, and earthquake events. In order to minimize environmental pollution, avoid fire hazards, and ensure that there is no harm to human or property during the operation of the transformer, Dry type transformers are usually used in densely populated areas and sensitive ecosystems.

3.What industries are dry-type transformers used in?

Mineral Mining:Mineral mining involves highly flammable and explosive minerals (coal, oil, natural gas) that require high safety for transformers. Therefore, safety is the primary consideration, followed by whether transformers can operate, cool, and maintain normally in harsh environments (high and low temperatures, high temperatures, and dust)

Energy - Power Generation:After the power station generates electricity, it has to go through a long distance to transport the electricity to various regions for supply. During transmission, the high current creates a high heating effect, which melts the wire and causes increased resistive losses. At this time, the current needs to be transmitted through the step-up transformer to increase the voltage and reduce the current, keeping the power constant. High-voltage transmission has higher efficiency and saves operating costs.Choosing a prefabricated compact substation is a good solution.

solar energy generation:Environmental factors must first be considered. For example, when photovoltaic power generation is carried out in the desert, in order to avoid the dry-type transformer being completely exposed outdoors, it will be affected by environmental factors such as high temperature, drought, and dust,Equipped with metal housing according to protection level.

Wind power generation:Fully considering the harsh climate and environmental conditions during operation in the wind turbine cabin, as well as the limitations of cabin size, dry type transformers that are easy to install, reliable, maintenance free, corrosion resistant, and vibration resistant are the primary considerations

Hydroelectric power:Due to the fact that dry-type transformers can operate in humid environments, we need to consider waterproofing, moisture resistance, air circulation, and other aspects of the transformer. In order to avoid direct contact with the transformer by personnel in humid working environments, a transformer shell must be equipped.

Vehicle charging:Electric Car EV Charging Station Dry Type Transformer :In addition to considering the environment, it is also necessary to consider issues such as temperature, life, loss, impact, maintenance, etc.Low ‘No-load losses’ for efficiency during long idling period meeting、Long-term reliability and long-life expectancy.

Transportation Industry:The transportation industry generally includes Rail transport, Road transport, Water transport, and Air freight. Due to different usage environments, dry type transformers should be selected according to different environments and meet the requirements of different protection levels (vibration, dust, humidity, high voltage).

Urban Ecology and Construction、Civil:In urban ecological construction, dry type transformers with low loss, low noise, obvious energy-saving effects, maintenance free, good heat dissipation, and environmental protection should be selected to reduce energy consumption and environmental pollution, and avoid fire and other hazards that may harm human safety and property.

Sourceway engineers have 40 years of experience in the transformer industry and have accumulated a wealth of experience in participating in different projects in various countries. Based on project cooperation cases, Sourceway can help you analyze the types of transformers you need in project construction and provide complete power distribution and other solutions.

4.What is the difference between indoor and outdoor use of dry-type transformers?

1. The difference between temperature rise and heat dissipation, especially for transformers with natural heat dissipation.

2. Insulation requirements: Considering the poor outdoor insulation environment (pollution level), the requirements for the external insulation performance of transformers will be higher.

3. Protection level: Considering the differences in outdoor safety performance, the protection level of transformers will be slightly higher.

4. Environment: Rain, dust, and dirt prevention should be considered. It is not suitable for indoor use, but heat dissipation should be considered.

5. Wiring method: The wiring method for outdoor transformers can be cable wiring or copper busbar wiring. Indoor transformers rarely use cable wiring.

6. Most outdoor transformers are oil immersed, and dry type transformers without bushings can only be used indoors.

5.What are the structures of dry-type transformers?

The structure of dry-type transformers is divided into three parts: open type, closed type, and pouring type.

1. Open type: It is a commonly used form. Its body will be in direct contact with the atmosphere. It is usually used in a clean room without dust influence. (When the ambient temperature is 20 degrees, the relative humidity should not exceed 90%). Generally, there are Air self-cooling and air-cooling two cooling methods.

2. Closed type: the dry-type transformer is enclosed by a casing, and does not directly contact the external environment. Usually, the corresponding casing is equipped according to the protection level.

3. Casting type: cast with epoxy resin. After casting, the overall mechanical strength of the casting coil is good, and the ability to withstand short circuit is strong.

6.What are the classifications of dry-type transformers?

• Dry-type transformers are divided into single-phase and three-phase according to the number of phases.

• Dry-type transformers can be divided into power transformers and distribution transformers according to the voltage.

• Dry-type transformers are divided into SCB cast resin dry-type transformers and SGB H-class immersed dry-type transformers according to the production process.

7. Characteristics of SCB cast resin dry-type transformer and SGB H-class immersed dry-type transformer:

SCB cast resin dry type transformer :

• Coil is using epoxy resin totally enclosed pouring. Coil is not moisture absorption, non-pollution, high mechanical strength, good dielectric strength, strong resistance short circuit impact ability; excellent flame retardancy, explosionproof, disaster prevention outstanding performance.

SGB Level H immersion type dry type transformer:

• It has a long thermal life and strong overload operation ability, can be under 120% rated capacity long-term overload running, can long-term full load running under no forced air cooling; with strong thermal shock resistance ability, can fill up load immediately at -50P;Have a high security and flame retardant property.under the 800P high temperature combustion for a long time without smog; After finished its duty can easily separate the insulation materials and copper wire and recycle, non-pollution.

8.What is the difference between SGB (VPI) and SCB dry-type transformers?

1. In terms of coil winding: SGB is a non-encapsulated dry-type transformer, and the low-voltage coil of SCB dry-type transformer is wound with foil.

2. Winding structure: Copper foil is used for single-layer winding, and the interlayer material contains epoxy resin with latent curing agent and lower-level composite foil.

3. Winding material: Oxygen-free copper with good conductivity is used, and its copper content is 99.99%. The low-voltage coil of SGB dry-type transformer is wire-wound.

4. Winding structure: cylindrical coil, multiple flat copper wires covered with ordinary glass fiber.

5. SGB type dry-type transformer has stronger short-circuit resistance than SCB type dry-type transformer.

6. In terms of heat dissipation: SCB type dry-type transformers are better than SGB type transformers.

7. In terms of load loss: SCB type transformers are lower than SGB type dry-type transformers.

8. In terms of temperature rise: the heat dissipation of SCB type transformers is better than that of SGB type dry-type transformers.

9. Installation environment: SCB dry transformer can be installed near the load to reduce line loss and installation cost; while SGB must be installed in a specific environment.

9.hat is the production process and composition of dry-type transformers?

Production process of dry-type transformer:

Raw material selection→iron core stacking→making clips and insulators→winding coils→casting using molds→dry-type transformer assembly→testing.

Composition of dry-type transformer:

1. Magnetic core: used to transmit magnetic field and store magnetic energy, the common ones are iron core, aluminum core, copper core and so on.

2. Winding: A coil made of wire or charged material used to transmit electrical energy and electrical signals.

3. Insulating materials: used for dry-type transformers to isolate windings and magnetic cores to prevent electric shocks and arcs. The common ones are insulating paper, insulating varnish, insulating glue, etc.

4. Cross-flow fans: The cooling system of dry-type transformers usually adopts natural cooling or forced air cooling to ensure that the temperature of the transformer does not exceed the specified limit value. In natural cooling, the transformer casing is usually equipped with heat sinks or heat sinks to increase the heat dissipation area; in forced air cooling, the transformer is equipped with fans and radiators to enhance the cooling effect.

5. Controller: used to monitor and control the operating status of the transformer, common ones include temperature controllers, protective relays, current transformers, etc.

6. Connectors: Used to connect windings and external circuits, common ones are wiring boards, plugs, sockets, etc.

7. Other accessories: such as dry-type transformer brackets, gaskets, screws, etc.

10.What are the factors affecting the price of dry-type transformers?

• Choice of insulating material:

Generally speaking, insulation classes F and H are used for the insulation of primary and secondary windings. This is due to the high temperature resistance of these classes i.e. 150°C for class F insulation and 180°C for class H insulation. Generally, varnish and polyester resin are used as the insulating material of the coil. In addition to its excellent temperature resistance and mechanical strength; dielectric strength and thermal shock resistance are the necessary capabilities of the insulation material selected for winding.

• Selection of winding material:

Typically, copper and aluminum are used to make windings or coils. Although copper is a better conductor of electricity, aluminum coil transformers are low cost and lightweight. For the same rated current, a copper conductor with a smaller cross-section is used as the winding material in the transformer. Copper coils have higher mechanical strength than aluminum coils.

• Select a core material with low hysteresis loss:

Core material selection is critical in transformer design. The core material must have high magnetic permeability and low hysteresis loss. Generally, silicon steel, CRGO, etc. are used to achieve the minimum hysteresis loss and high magnetic permeability. The iron loss (ie, no-load loss) of the new amorphous alloy transformer is 70-80% lower than that of traditional transformers that generally use silicon steel as the core. As the loss is reduced, the demand for power generation is also reduced, and the emission of greenhouse gases such as carbon dioxide is also reduced accordingly.

• The rest is the choice of accessories:

Other accessories include, cooling system (the shell is equipped with forced cooling cover, radiator for forced air cooling), controller (temperature controller, protective relay, current transformer), connector (terminal board, plug, socket), scattered accessories ( brackets, washers, screws, etc.).

11.What are the advantages of dry-type transformers?

• Safety: Since dry-type transformers do not contain flammable or toxic liquids that can leak or catch fire.

• Environmental protection: type power transformers do not use harmful liquids or liquids to work, so they will not release harmful gases into the environment causing greenhouse effect.

• Low noise: due to the use of laminated iron core technology and multiple layers of insulating paint on the outside of the iron core, the noise of the dry-type transformer is reduced.

• Low loss: dry-type transformer adopts higher grade silicon steel sheet, which belongs to high energy efficiency grade transformer, the no-load loss is 15% lower than SCB12 transformer, and the load loss is 10% lower than SCB12 transformer.

• Low installation cost: small size, light weight, less space occupation, no need for fire extinguishing system and low installation cost.

• Maintenance: Since the dry-type transformer does not use liquid for filling and the use of accessories, it requires almost no maintenance.

• Sustainability: Small partial discharge (usually below 10PC), high reliability, long-term safe operation can be guaranteed, and the service life can reach 30 years.

•  Recyclable: Casting epoxy resin dry-type transformers are mainly composed of silicon steel sheet, non-gold alloy iron core, copper aluminum, epoxy resin and other insulating materials, and most of its components can be recycled.

• Use environment: Due to the stable performance and excellent environmental adaptability of dry-type transformers, they can still maintain stable operation in harsh environments, so they can be used in various industries.

• Overload capacity: It has excellent overload capacity due to good heat dissipation and heat resistance.

• Impact resistance: The solid insulation composed of resin and glass fiber not only has good impact resistance, but also has a small partial discharge.

• Good mechanical strength: After curing, the resin, wire, and glass fiber are closely combined, and the high-strength mechanical properties determine that the wire-wound castable product has good short-circuit resistance.

• Short-circuit resistance: Due to its low impedance and high mechanical strength, it has a strong ability to withstand short-circuit currents.

• Good anti-cracking performance: the composite insulating material formed by solidification of resin and glass fiber eliminates the mechanical stress between the winding conductor and the insulating material caused by thermal expansion and contraction during transformer operation, and eliminates cracking from the root .

• Moisture-proof: Since the high and low-voltage of the dry-type transformer is poured with resin, and the iron core is also coated with resin, it has strong moisture-proof and anti-corrosion capabilities. When the air relative humidity is 100%, it can still run for a long time.

• Fireproof: With self-extinguishing properties, there is no fire hazard and will not produce any smoke or flames in the event of a malfunction.

Good heat dissipation effect: the composite insulation composed of pure resin and glass fiber has extremely high electrical strength, which improves the heat dissipation efficiency of the winding surface.

• Cooling: Dry-type transformers are cooled by natural air cooling and forced air circulation cooling. After forced air circulation cooling, dry-type transformers of 800 kVA and below can be increased by 40%, and dry-type transformers of 800 kVA and above can be increased by 50%. and can run continuously.

• Protection: Dry-type transformers are generally IP00-IP10 protected, and protective casings can be added according to the use environment and customer requirements.

We supply distribution transformers to several industries, including power distribution & power transmission units, manufacturing industries, wind farms, solar projects, mining industry, cement industry, construction industry, transportation industry, IT hubs, and several other commercial industries.

12.What are the disadvantages of dry-type transformers?

• High cost: Dry-type transformers are more expensive to purchase and operate.

• Difficult to maintain: It needs to be shut down for maintenance, and failure is equivalent to direct scrapping.

• Volume: With the same rated power and rated voltage, dry-type transformers are larger and heavier than oil-immersed transformers.

• Poor heat dissipation performance: Since the dry-type transformer is poured with epoxy resin, the heat dissipation performance is relatively poor, and the heat generated by loss must be controlled by the cooling system.

• High noise: If the noise reduction process is not used, the dry-type transformer will have high noise during operation, so the dry-type transformer is generally used indoors.

• Influence on ambient temperature: During operation, copper loss will become heat dissipation and the ambient temperature will continue to rise.

13.Comparison of dry-type transformers and oil-immersed transformers:

Application Scenario:

1. Oil-immersed transformer: suitable for high-voltage, large-capacity occasions, such as power substations, industrial electricity, etc. In high-load, high-voltage scenarios, oil-immersed transformers have better performance and stability.

2. Dry-type transformer: suitable for crowded places and places with high environmental protection requirements, such as commercial centers, hospitals, schools, etc. Due to their lower fire risk and environmental protection characteristics, dry-type transformers have great advantages in these scenarios.

performance comparison:

1. Heat dissipation performance: oil-immersed transformers have good heat dissipation performance and can operate stably under high load conditions; dry-type transformers have relatively weak heat dissipation performance.

2. Cost: Oil-immersed transformers have lower manufacturing costs, but higher operation and maintenance costs; dry-type transformers have higher manufacturing costs, but lower operation and maintenance costs.

3. Safety: Dry-type transformers have lower fire risks and are more suitable for crowded places; oil-immersed transformers have relatively higher fire risks.

4. Environmental protection: Dry-type transformers do not need to use insulating oil, and there is no leakage and environmental pollution problems; oil-immersed transformers may have a risk of leakage, which will have a certain impact on the environment.

14.What are the factors that affect the life of dry-type transformers?

There are two main factors affecting the life of dry-type transformers:

1. During long-term operation, the functions and components of the transformer gradually age (usually the life of dry-type transformers is 30 years). When the transformer is overloaded, the temperature rises, It will cause high temperature aging of the transformer.

2. External factors: such as environmental (high temperature, high humidity, oxygen, etc.) factors, human factors, etc. lead to a reduction or damage to the life of the transformer.

15.What are the inspection and maintenance of dry-type transformers?

What places do dry-type transformers need to check when leaving the factory?

Before carrying out the dry-type transformer visual inspection test, it must be ensured that it is powered off and has stopped working. And before the power is connected, the inside of the transformer must be exhausted, drained and cleaned, and the inspection process must be ensured. Through the above inspection and test, the problems existing in the transformer can be found in time, the reliability of the transformer can be improved, and the occurrence of faults can be reduced.

1. Check the appearance of the transformer, including whether the machine casing, welding, connection, paint film, and signs are damaged, peeled off, dirty or deformed.

2. Check whether the transformer insulation materials, including partitions, grids, insulation pads, winding insulation, etc., are intact. If any problem is found, it needs to be replaced or repaired in time.

3. Check whether the wiring, screws, etc. are fastened reliably. If any looseness is found, it should be dealt with in time.

4. Check whether the circuit breaker, relay, thermometer and other equipment are normal. If any problem is found, it needs to be repaired or replaced.

5. Infrared thermometers are often used to test transformers. When serious dust accumulation or local high temperature is found, cleaning measures should be taken in time.

6. Check whether there are alarm lights on the machine, whether the temperature and humidity meter, LCD display and other instruments are working normally, so as to ensure the normal operation of the equipment.

What are the tests and experiments of dry-type transformers?

Usually, the dry-type transformer will undergo the following tests before leaving the factory:

insulation Resistance (Giga -OHM) Ratio Test Winding resistance measurement at Amb No Load Loss Load loss at tap(3) at Amb Temprature Separate source power frequency withstand test Induced over voltage withstand test Polarity tes9t Iron core insulation resistance measurement ⑪Vector Group (Dyn11) ⑫BDV Transformer oil BDV.

Preparation before the test: whether the assembly is completed as required, and whether there is a lack of accessories necessary for the test, such as transformer grounding and iron core grounding devices.

1. Insulation resistance test: Keep the insulation dry before testing. The insulation resistance depends on the temperature, and is usually measured according to the ambient temperature during operation. If the measurement is performed at a higher ambient temperature, it must be considered before determining the insulation resistance value Positive coefficient. The insulation resistance is measured between the high voltage winding and the low voltage winding, the high voltage winding to ground, and the low voltage winding to ground. All other parts of the transformer not tested are always grounded when the rest is tested.

2. Winding resistance test: Before the test, the static time of the dry-type transformer at a constant temperature should be no less than 3 hours. The influence of the self-inductance effect during the test should be minimized. The connection and welding position between the parts of the purpose Whether it is good, whether the resistance and resistivity of each winding are balanced.

3. Voltage ratio test: The voltage ratio is defined as the ratio of the primary voltage to the secondary voltage (VR). The voltage of the winding is proportional to the number of turns of the coil. It is carried out with a transformer turns ratio tester (TTR) for the purpose of Make sure the turns ratio of primary turns to secondary turns is correct.

4. Polarity test: ① Add polarity - the windings of two or more transformers are connected, then the voltages of the connected transformers are added together. ② Polarity subtraction - if the opposite windings are connected, polarity subtraction will occur. If If the transformers are connected in reverse polarity in parallel operation, it will cause accidents and cause damage to the system.

5. No-load loss test: No-load loss is to apply the rated voltage (main tap) of the sinusoidal waveform at the rated frequency to the selected winding, and the remaining windings are open, and the measured active power input to the transformer is called no-load loss. No-load loss It occurs in the iron core, and the loss caused by the change of the magnetic flux in the silicon steel sheet with the AC frequency is dissipated in the form of heat. In addition, the no-load current flowing through the winding will generate the resistance loss I2R of the no-load current in the winding, but the loss I2R is usually small and generally negligible.

6. No-load loss includes two aspects:

• Hysteresis loss: When the AC passes through the transformer, the direction and size of the magnetic field lines passing through the silicon steel sheet of the transformer change accordingly, causing the internal molecules of the silicon steel sheet to rub against each other and release heat energy, thus losing part of the electric energy.

• Eddy current loss: When the transformer is working, there are magnetic force lines passing through the iron core, and an induced current will be generated on a plane perpendicular to the magnetic force lines. Since this current forms a closed loop and forms a vortex, it is called eddy current. The existence of eddy current Heat the iron core and consume energy.

7. Load loss test: The load loss U is the loss measured when one pair of windings of the transformer is short-circuited, the other winding is applied with voltage, and the rated current passes through. The rated frequency, sinusoidal The impedance when the winding on the other side of the rated current of the waveform is short-circuited is called the short-circuit impedance of the transformer, which is generally expressed as a percentage relative to a certain reference impedance. In the transformer load test, the load loss of the transformer and the short-circuit reactance of the transformer are measured in time.

8. High voltage test: ensure that the insulation performance of the transformer is sufficiently stable under rated electrical or overload conditions.

9. Dielectric test: Dielectric test is divided into three different types: applied potential test, induced potential test, pulse test (type test). The dielectric test ensures the overall insulation strength of the transformer and confirms that the transformer can withstand the conditions defined in the standard. test level. The full test voltage is applied for more than 60 seconds between the winding under test and all other windings, the transformer core, and the earthed case.

10. Partial discharge test: 

• Under the same electric field, bubbles and impurities with small dielectric constants bear higher electric field strength. Therefore, when the applied voltage reaches a certain value, these parts tend to discharge first. This is partial discharge.

• The cause of partial discharge: For the insulation structure of the transformer, there may be bubbles (air gaps), impurities, etc. inside, which are inevitable. Under the same electric field, bubbles and impurities with small dielectric constants withstand higher electric field strength.

• Purpose of the test: whether there are local defects in the insulating material used, whether air bubbles, moisture or various impurities are mixed in the insulating structure, whether there are bad links, and whether the electric field strength in individual areas is too high.

11. Magnetizing current test: The magnetizing current test ensures that the magnetic circuit has sufficient reluctance to establish flux in the core. It can indicate and locate defects in core construction, problems in tap changers, turn-to-turn insulation faults, winding displacements, and more. Measure the DC resistance before performing the test.

12. Power factor test: This test is to determine the power loss of the transformer insulation system. It indicates failure or degradation of transformer insulation and is the power angle between the applied AC voltage and the resulting current.

13. Wiring group test: The wiring group of the three-phase transformer and the polarity of the lead wire of the single-phase transformer should be consistent with the parameters on the transformer nameplate. It can judge whether the connection of the transformer winding is correct, so as to ensure the secondary protection circuit and measurement circuit Correctness of wiring.

14. Noise test: The noise of the dry-type transformer is caused by the hysteresis deformation of the iron core and the electromagnetic force in the winding and magnetic shielding. The noise generated by the magnetic field-induced vibration of the core laminations along the longitudinal direction is the main component of the transformer noise. The amplitude of the vibration is related to the magnetic flux density in the core laminations and the magnetic properties of the core material, but has little to do with the load current. In addition, the leakage magnetic field can also cause vibration of structural parts.

15. Climate test: The transformer is suitable for operation at an ambient temperature not lower than -5degrees celsius to -25degrees celsius, but the ambient temperature test during its transportation and storage.

16.Temperature rise test: The temperature rise value is determined by a combination of short-circuit test (providing load loss) and no-load test (providing load loss). It is suitable for non-closed, closed or fully enclosed thousand-type self-cooling AN or wind Cold AF Transformer.

17. Combustion performance test: F0 does not need to consider the fire hazard. Except for the characteristics inherent in the design of the transformer, no special measures are taken to limit its flammability, F2 flammability and the degree of toxic substances and opaque smoke released during combustion.

16.What are the protections for dry-type transformers?

1. Quick break protection:

It mainly protects the phase-to-phase short circuit of each phase of the transformer winding or lead wire, the ground short circuit of the large ground current system and the inter-turn short circuit of the winding. The protection schemes include voltage quick-break protection, current quick-break protection, and transformer differential quick-break protection.

2. Overcurrent protection:

Generally, electronic equipment has a rated current. If the rated current is exceeded, the equipment may burn out. Therefore, when the current exceeds the set current, the current protection module will automatically cut off the power to the equipment. It can protect equipment, back-up protection for gas protection and differential protection (or current quick-break protection).

3. Overload protection:

When the dry-type transformer outlet, bushing and internal short-circuit fault, the instantaneous action of protection is to disconnect the circuit breaker on each side of the dry-type transformer. Generally, two protection methods are adopted: longitudinal differential protection and current quick-break protection

4. Zero sequence protection:

Zero-sequence protection means that the cable line adopts a special zero-sequence current transformer to realize grounding protection. After a ground fault occurs in the system, when a ground fault occurs, a large current will appear in the secondary coil of the zero-sequence transformer, which will cause the current relay to operate, thereby sending out signal or eliminate faults

5. Temperature protection:

The dry-type transformer measures the winding temperature through a temperature controller. When the temperature of the transformer is abnormal during operation, it will sound an alarm or trip.

6. Indoor and outdoor protection of dry-type transformers:

When the dry-type transformer is used outdoors, it needs to be equipped with a casing for protection, so as to avoid the influence and damage of the environment and organisms on the dry-type transformer.

17.Fault judgment method and solution of cast resin dry-type transformer.

What are the reasons for the abnormal sound of dry-type transformers?

1. When the tap changer is loose, the dry-type transformer will make a loud "chirp" sound. If the tap changer is not connected properly, there will be a slight "squeak" spark discharge sound, which will cause the transformer to work overloaded and may burn out. The contact of the tap changer is damaged. In severe cases, the high-voltage fuse is blown.

2. The iron core clamp is loose

3. The iron core is not grounded: When the iron core of the transformer is grounded and disconnected, the transformer will produce a slight discharge sound of "snapping and stripping"

4. Overload: When the transformer is seriously overloaded, it will emit a low "hum" sound like a heavy-duty airplane.

5. Too high voltage: When the power supply voltage is too high, the transformer will be over-excited, and the sound will increase and be sharp.

6. Short circuit in the winding: When the transformer winding is short-circuited between layers or turns and burns out, the transformer will make a "gurgling" sound of boiling water.

7. Fan failure: There is a sound of "crackling" metal impact. This is because there are foreign objects in the fan, and the foreign objects need to be cleaned at this time.

8. There are many stains on the surface of the shell, and there is a "hissing" sound.

Dry-type transformer fault judgment method and solution:

1. Resonance of components: The resonance of fans, casings, and other components will generate noise, which is generally mistaken for the noise of the transformer.

• Solution: Slightly press the insulating material on the fan, casing, and other components. If the sound changes, it means that there is resonance in this part.

• Solution: When the connection of accessories is loose, it needs to be tightened. If it is damaged, it needs to be replaced in time.

2. Installation problems: poor installation will aggravate the vibration of the transformer and amplify the noise of the transformer

Judgment method: Whether the installation foundation is flat or not.

Solution: Improve the installation method and install a shockproof rubber pad at the bottom

3. Operating environment problems: the operating environment affects the noise of the transformer, and the unfavorable environment increases the noise of the transformer

Judgment method: The room is empty but there is an echo. When it is close to the wall, the reflection noise and the transformer noise are superimposed, and the noise increases.

Solution: Absorbing materials can be installed indoors to reduce noise

4. The problem of vibration of the bus bridge: the side-by-side bus has a large current passing through, and the bus will vibrate due to the leakage magnetic field, and the vibration of the bus bridge will increase the noise of the transformer.

Judgment method: 1. The noise changes with the load. 2. Check whether the bus bar is fixed. 3. Open the bus bridge cover and check whether the bus bar is fixed.

Solution: Open the cover plate of the busbar bridge and fix the busbar. The low-voltage outgoing line adopts soft connection

5. Transformer core resonance: There is an electromagnetic attraction caused by magnetic leakage at the joints of silicon steel sheets and between the laminations.

Judgment method: The noise of the transformer is wavy, and multiple noises are superimposed.

Solution: Tighten the screws on the transformer, including the screws at both ends of the clip, the core-through screws, and the pad screw. Install a shock-proof rubber pad under the transformer.

6. Transformer core resonance: When a load current passes through the winding, the magnetic flux leakage generated by the load current causes the vibration of the winding.

Judgment method: The noise increases with the increase of the load, and the noise is relatively low.

Solution: Tighten the spacer pressure screw to increase the axial compression force of the coil.

7. Transformer core resonance: Distort the voltage waveform of the transformer (such as resonance phenomenon) and generate noise.

Judgment method: In addition to the noise of the transformer itself, the noise is also mixed with "clack" noise. Sometimes there is no.

Solution: Check whether there are rectification equipment and frequency conversion equipment in the load, and install a device to reduce harmonics.

18.How to debug dry-type transformers:

1. Open the box for inspection before installation

Check whether the packaging is in good condition. After the transformer is unpacked, check whether the data on the nameplate of the transformer meets the design requirements, whether the factory documents are complete, whether the transformer is in good condition, whether there is any sign of external damage, whether the parts are displaced and damaged, whether the electrical support parts or connecting wires are If there is damage, finally check whether there is any damage and shortage of spare parts.

2. Transformer installation:

First check the foundation of the transformer to check whether the pre-embedded steel plate is level. There should be no cavitation phenomenon under the steel plate to ensure that the foundation of the transformer has good shock resistance and sound absorption performance, otherwise the noise of the transformer after installation will increase. Then, use the roller to move the transformer to the installation position, remove the roller, and accurately adjust the transformer to the design position, and the installation level error meets the design requirements. Finally, four short channel steels are welded on the four corners close to the transformer base, that is, on the pre-embedded steel plate, so that the position of the transformer does not move during use.

3. Transformer wiring:

When wiring, the minimum distance between the electrified body and the electrified body to the ground should be ensured, especially the distance from the cable to the high-voltage coil. The high-current low-voltage busbar should be supported separately, and should not be directly connected to the transformer terminal to cause excessive mechanical tension and torque. When the current is greater than 1000A (such as the 2000A low-voltage busbar used in this project), the busbar and transformer There must be a soft connection between the terminals to compensate for the thermal expansion and contraction of the conductor and to isolate the vibration of the busbar and the transformer. The electrical connection at each connection point must maintain the necessary contact pressure. Elastic elements (such as disc-shaped plastic rings or spring washers) should be used. When tightening the connecting bolts, a torque wrench should be used.

4. Transformer grounding:

The grounding point of the transformer is on the base of the low-voltage side, and leads out to a special grounding bolt, which is marked with a grounding mark. The grounding of the transformer must be reliably connected to the protective grounding system through this point. When the transformer has a casing, the casing should be reliably connected to the grounding system. When the low-voltage side adopts a three-phase four-wire system, the neutral wire should be reliably connected to the grounding system.

5. Inspection before transformer operation:

Check whether all fasteners are loose, whether the electrical connection is correct and reliable, whether the insulation distance between the charged body and the charged body to the ground meets the regulations, there should be no foreign matter near the transformer, and the coil surface should be cleaned.

6. Debugging before transformer operation:

(1) .Check the transformation ratio and connection group of the transformer, measure the DC resistance of the high and low voltage windings, and compare the results with the factory test data provided by the manufacturer.

(2) .Check the insulation resistance between the coils and the coil to the ground. If the insulation resistance is significantly lower than the equipment factory measurement data, it indicates that the transformer is damp. When the insulation resistance is lower than 1000Ω/V (operating voltage), the transformer must be dried.

(3) .The test voltage of the withstand voltage test should comply with the regulations. When doing the low voltage withstand voltage test, the temperature sensor TP100 should be taken out, and the sensor should be returned to its place in time after the test is over.

(4) .When the transformer is equipped with a fan, the fan should be energized and operated to ensure its normal operation.

7. Trial run:

After the transformer has been carefully inspected before being put into operation, it can be energized for trial operation. During the test run, special attention must be paid to check the following points. Check for abnormal sounds, noises and vibrations. Is there any abnormal smell such as burnt smell? Whether there is discoloration caused by local overheating. Whether the ventilation is good. In addition, the following points should be noted.

First, although the dry-type transformer has strong moisture resistance, it is still prone to moisture because it is generally an open structure, especially the dry-type transformer produced in my country has a low insulation level (lower insulation level). Therefore, dry-type transformers can only obtain high reliability when the relative humidity is below 70%. Dry-type transformers should also avoid long-term outages to avoid severe damp. When the insulation resistance value is lower than 1000/V (operating voltage), it means that the transformer is seriously damp, and the test run should be stopped.

Second, the dry-type transformer used for step-up in the power station is different from the oil-immersed transformer. It is forbidden to open the low-voltage side to operate, so as to avoid the insulation breakdown of the dry-type transformer caused by the overvoltage on the grid side or the line being struck by lightning, resulting in overvoltage transmission. In order to prevent the danger of overvoltage transmission, a set of overvoltage protection arresters (such as Y5CS zinc oxide arresters) should be installed on the voltage bus side of the dry-type transformer.

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