Summary of Basic Knowledge of Dry-type Transformers

Dry-type transformers are widely used in local lighting, high-rise buildings, airports, terminal CNC machinery equipment and other places. Simply put, dry-type transformers refer to transformers whose cores and windings are not immersed in insulating oil.
Cooling methods are divided into natural air cooling (AN) and forced air cooling (AF).
When natural air cooling, the transformer can run continuously for a long time under the rated capacity.
When forced air cooling, the output capacity of the transformer can be increased by 50%.
It is suitable for intermittent overload operation or emergency accident overload operation; due to the large increase in load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be kept in continuous overload operation for a long time.

1. Structure type
Construction performance
⑴Solid insulation encapsulated winding
⑵No enveloping winding
Of the two windings, the higher voltage is the high voltage winding, and the lower is the low voltage winding
From the relative position of the high and low voltage windings, the high voltage can be divided into concentric type and overlapping type
The concentric winding is simple and convenient to manufacture, and this structure is adopted.
Overlap type, mainly used for special transformers.
Dry-type transformers are widely used in local lighting, high-rise buildings, airports, terminal CNC machinery equipment and other places. Simply put, dry-type transformers refer to transformers whose cores and windings are not immersed in insulating oil.
Cooling methods are divided into natural air cooling (AN) and forced air cooling (AF).
When natural air cooling, the transformer can run continuously for a long time under the rated capacity.
When forced air cooling, the output capacity of the transformer can be increased by 50%.
It is suitable for intermittent overload operation or emergency accident overload operation; due to the large increase in load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be kept in continuous overload operation for a long time.

1. Structure type
Construction performance
⑴Solid insulation encapsulated winding
⑵No enveloping winding
Of the two windings, the higher voltage is the high voltage winding, and the lower is the low voltage winding
From the relative position of the high and low voltage windings, the high voltage can be divided into concentric type and overlapping type
The concentric winding is simple and convenient to manufacture, and this structure is adopted.
Overlap type, mainly used for special transformers.

2. Structural features
1. It is safe, fireproof, pollution-free, and can be directly operated in the load center;
2. Using domestic advanced technology, high mechanical strength, strong short-circuit resistance, small partial discharge, good thermal stability, high reliability and long service life;
3. Low loss, low noise, obvious energy saving effect, maintenance-free;
4. Good heat dissipation performance, strong overload capacity, and capacity operation can be increased when forced air cooling;
5. Good moisture-proof performance, adapt to high humidity and other harsh environments;
6. Dry-type transformers can be equipped with a complete temperature detection and protection system. Using intelligent signal temperature control system, it can automatically detect and circulate display the respective operating temperatures of the three-phase windings, can automatically start and stop the fan, and have functions such as alarms and trips;
7. Small size, light weight, less space and low installation cost.
Iron core
The high-quality cold-rolled grain-oriented silicon steel sheet is used, and the iron core silicon steel sheet adopts a 45-degree full oblique seam, so that the magnetic flux passes along the seam direction of the silicon steel sheet.

Winding form
⑴ Winding;
⑵ Epoxy resin and quartz sand filling and pouring;
⑶ glass fiber reinforced epoxy resin casting (that is, thin insulating structure);
⑷Multi-strand glass fiber impregnated epoxy resin winding type (generally 3 is used because it can effectively prevent the pouring resin from cracking and improve the reliability of the equipment).
High voltage winding
Generally adopt multi-layer cylindrical or multi-layer segmented structure.

3. Form
⒈Open type: It is a commonly used form. Its body is in direct contact with the atmosphere. It is suitable for a relatively dry and clean room (when the ambient temperature is 20 degrees, the relative humidity should not exceed 85%). Generally, there is air cooling Two cooling methods are air-cooled.
⒉Closed type: The body of the device is in a closed shell and does not directly contact the atmosphere (due to the sealing and poor heat dissipation conditions, it is mainly used for mining and belongs to the explosion-proof type).
⒊Pouring type: epoxy resin or other resin is used as the main insulation. It has a simple structure and small volume, which is suitable for transformers with smaller capacity.

4. Technical parameters
1. Frequency of use: 50 / 60HZ;
2. No-load current: <4 %;
3. Compressive strength: 2000V/min without breakdown; test instrument: YZ1802 withstand voltage tester (20mA);
4. Insulation grade: F grade (special grade can be customized);
5. Insulation resistance: ≥2M ohm test instrument: ZC25B-4 type megohmmeter <1000 V);
6. Connection mode: Y/Y, △/Y0, Yo/△, auto-coupling (optional);
7. Allowable temperature rise of coil: I00K;
8. Heat dissipation method: natural air cooling or temperature control automatic heat dissipation;
9. Noise coefficient: ≤30dB.

5. Working environment
1.0-40 (℃ ), relative humidity <70%;
2. Altitude: not more than 2500 meters;
3. Avoid rain, humidity, high temperature, high heat or direct sunlight. The distance between the heat dissipation and ventilation holes and the surrounding objects should not be less than 1000px;
4. Prevent working in places where there are more corrosive liquids, or gases, dust, conductive fibers or metal fines;
5. Prevent working in places with vibration or electromagnetic interference;
6. Avoid long-term storage and transportation upside down, and avoid strong impact.

6. Product selection-product definition
The distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10⑹kV or 35kV network voltage to the 230/400V bus voltage used by the user. This type of product is suitable for AC 50 (60) Hz, three-phase maximum rated capacity 2500kVA (single-phase maximum rated capacity 833kVA, generally not recommended to use single-phase transformer)
1) When there are a large number of primary or secondary loads, two or more transformers should be installed. When any one of the transformers is disconnected, the capacity of the remaining transformers can meet the power consumption of primary and secondary loads. The primary and secondary loads should be concentrated as much as possible, and should not be too scattered.
2) When the seasonal load capacity is large, a special transformer should be installed. Such as large-scale civil S4270D27-29 27 2005.7.29, 3:24 AM building air conditioning chiller load, heating electric heating load, etc.
3) When the concentrated load is large, a special transformer should be installed. Such as large heating equipment, large X-ray machine, electric arc furnace, etc.
4) When the lighting load is large or the power and lighting use a shared transformer, which seriously affects the lighting quality and bulb life, a special lighting transformer can be installed. Under normal circumstances, power and lighting share a transformer.
Product selection-choose a transformer according to the use environment

1) Under normal media conditions, oil-immersed transformers or dry-type transformers can be selected, such as independent or attached substations for industrial and mining enterprises, agriculture, and independent substations for residential communities, etc. The available transformers are S8, S9, S10, SC(B)9, SC(B)10 and so on.
2) In multi-story or high-rise main buildings, non-combustible or non-combustible transformers should be used, such as SC(B)9, SC(B)10, SCZ(B)9, SCZ(B)10, etc.
3) In places where dusty or corrosive gas seriously affects the safe operation of the transformer, a closed or sealed transformer should be selected, such as B S 9, S9-, S10-, SH12-M, etc.
4) High and low power distribution devices without combustible oil and non-oil-immersed distribution transformers can be installed in the same room. At this time, the transformer should be equipped with an IP2X protective enclosure for safety.
Product selection-choose a transformer according to the electrical load
1) The capacity of the distribution transformer should be integrated with the facility capacity of various electrical equipment to calculate the calculated load (generally excluding the fire-fighting load). The apparent capacity after compensation is the basis for selecting the capacity and number of transformers. The load rate of a general transformer is about 85%. This method is relatively simple and can be used to estimate capacity.
2) In GB/T17468-1998 “Guidelines for Selection of Power Transformers”, it is recommended that the capacity selection of distribution transformers should be determined according to GB/T17211-1998 “Guidelines for Dry-Type Power Transformer Loads” and the calculated load. The above two guidelines provide computer programs and normal cycle load diagrams to determine the capacity of distribution transformers.

7. Installation points
Distribution transformers are important components of substations. Dry-type transformers without shells are installed directly on the ground, with protective barriers around them; dry-type transformers with shells are installed directly on the ground. For its installation, please refer to the National Building Standard Design Atlas. 03D201-4 10/0.4kV transformer room layout and installation of common equipment components in substations.
8. Type selection-temperature control system
The safe operation and service life of dry-type transformers largely depend on the safety and reliability of the transformer winding insulation. The winding temperature exceeds the insulation withstand temperature and the insulation is damaged, which is one of the main reasons that the transformer can not work normally. Therefore, the monitoring of the transformer’s operating temperature and its alarm control are very important.

⑴Automatic control of the fan: The temperature signal is measured by the Pt100 thermistor that is embedded in the hottest part of the low-voltage winding. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110°C, the system automatically starts the fan cooling; when the winding temperature drops to 90°C, the system automatically stops the fan.
⑵Over-temperature alarm and trip: Collect winding or iron core temperature signals through PTC non-linear thermistor embedded in the low-voltage winding. When the transformer winding temperature continues to rise, if it reaches 155°C, the system will output an over-temperature alarm signal; if the temperature continues to rise to 170°C, the transformer cannot continue to operate, and an over-temperature trip signal must be sent to the secondary protection circuit, and the transformer should be used Tripped quickly.
⑶Temperature display system: The temperature change value is measured by the Pt100 thermistor embedded in the low-voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and the highest temperature in history can be recorded). The temperature is output by 4-20mA analog quantity, if it needs to be transmitted to a remote computer (distance up to 1200m)
Selection-protection method
IP20 protective housing is usually used to prevent solid foreign objects with a diameter greater than 12mm and small animals such as rats, snakes, cats, and birds from entering, causing malignant failures such as short-circuit power failures, and providing a safety barrier for live parts. If you need to install the transformer outdoors, you can choose an IP23 protective enclosure. In addition to the above IP20 protective function, it can also prevent water droplets within a 60° angle to the vertical. However, the IP23 shell will reduce the cooling capacity of the transformer, so pay attention to the reduction of its operating capacity when selecting.
Selection-overload capacity
The overload capacity of a dry-type transformer is related to the ambient temperature, the load condition before overload (initial load), the insulation and heat dissipation of the transformer, and the heating time constant. If necessary, the overload curve of the dry-type transformer can be obtained from the manufacturer.

How to use its overload capacity?
⑴When choosing to calculate the capacity of the transformer, it can be appropriately reduced: Fully consider the possibility of short-term impact overload of certain steel rolling, welding and other equipment-try to use the strong overload capacity of the dry-type transformer to reduce the transformer capacity; Evenly-loaded places, such as residential areas mainly for night lighting, cultural and entertainment facilities, and shopping malls mainly for air conditioning and daytime lighting, can make full use of their overload capacity, appropriately reduce the transformer capacity, and make the main operating time at full load Or short-term overload.
9. Check
⒈ Whether there is abnormal sound and vibration.
⒉Whether there is local overheating, harmful gas corrosion and other discoloration caused by creepage traces and carbonization on the insulating surface.
⒊Whether the air-cooling device of the transformer is operating normally.
⒋There should be no overheating of the high and low voltage joints. There should be no leakage and creepage at the cable head.
⒌The temperature rise of the winding should be based on the insulation material grade adopted by the transformer, and the monitored temperature rise shall not exceed the specified value.
⒍The supporting porcelain bottle should be free of cracks and discharge traces.
⒎Check whether the winding pressure piece is loose.
⒏Indoor ventilation, iron core air ducts should be free of dust and debris, and iron cores should be free from rust or corrosion.

10. Difference
Inverter: It can be adjusted to achieve the required power frequency (50hz, 60hz, etc.) to meet our special needs for electricity.
Transformer: Generally, it is a “step-down device”, which is commonly found near communities or factories. Its function is to reduce the ultra-high voltage to the normal voltage of our residents to meet people’s daily electricity consumption.
Dry-type transformers and oil-immersed transformers are the two most commonly used transformers. Compared with oil-immersed transformers, dry-type transformers have better fire protection performance, and are mostly used in places with higher fire protection requirements, such as hospitals, airports, stations, etc. Places, but the price is relatively high, and there are certain requirements for the environment, such as not being too humid, not having too much dust and dirt, etc.

2. Structural features
1. It is safe, fireproof, pollution-free, and can be directly operated in the load center;
2. Using domestic advanced technology, high mechanical strength, strong short-circuit resistance, small partial discharge, good thermal stability, high reliability and long service life;
3. Low loss, low noise, obvious energy saving effect, maintenance-free;
4. Good heat dissipation performance, strong overload capacity, and capacity operation can be increased when forced air cooling;
5. Good moisture-proof performance, adapt to high humidity and other harsh environments;
6. Dry-type transformers can be equipped with a complete temperature detection and protection system. Using intelligent signal temperature control system, it can automatically detect and circulate display the respective operating temperatures of the three-phase windings, can automatically start and stop the fan, and have functions such as alarms and trips;
7. Small size, light weight, less space and low installation cost.
Iron core
The high-quality cold-rolled grain-oriented silicon steel sheet is used, and the iron core silicon steel sheet adopts a 45-degree full oblique seam, so that the magnetic flux passes along the seam direction of the silicon steel sheet.
Winding form

⑴ Winding;
⑵ Epoxy resin and quartz sand filling and pouring;
⑶ glass fiber reinforced epoxy resin casting (that is, thin insulating structure);
⑷Multi-strand glass fiber impregnated epoxy resin winding type (generally 3 is used because it can effectively prevent the pouring resin from cracking and improve the reliability of the equipment).
High voltage winding
Generally adopt multi-layer cylindrical or multi-layer segmented structure.
3. Form
⒈Open type: It is a commonly used form. Its body is in direct contact with the atmosphere. It is suitable for a relatively dry and clean room (when the ambient temperature is 20 degrees, the relative humidity should not exceed 85%). Generally, there is air cooling Two cooling methods are air-cooled.
⒉Closed type: The body of the device is in a closed shell and does not directly contact the atmosphere (due to the sealing and poor heat dissipation conditions, it is mainly used for mining and belongs to the explosion-proof type).
⒊Pouring type: epoxy resin or other resin is used as the main insulation. It has a simple structure and small volume, which is suitable for transformers with smaller capacity.

4. Technical parameters
1. Frequency of use: 50 / 60HZ;
2. No-load current: <4 %;
3. Compressive strength: 2000V/min without breakdown; test instrument: YZ1802 withstand voltage tester (20mA);
4. Insulation grade: F grade (special grade can be customized);
5. Insulation resistance: ≥2M ohm test instrument: ZC25B-4 type megohmmeter <1000 V);
6. Connection mode: Y/Y, △/Y0, Yo/△, auto-coupling (optional);
7. Allowable temperature rise of coil: I00K;
8. Heat dissipation method: natural air cooling or temperature control automatic heat dissipation;
9. Noise coefficient: ≤30dB.

5. Working environment
1.0-40 (℃ ), relative humidity <70%;
2. Altitude: not more than 2500 meters;
3. Avoid rain, humidity, high temperature, high heat or direct sunlight. The distance between the heat dissipation and ventilation holes and the surrounding objects should not be less than 1000px;
4. Prevent working in places where there are more corrosive liquids, or gases, dust, conductive fibers or metal fines;
5. Prevent working in places with vibration or electromagnetic interference;
6. Avoid long-term storage and transportation upside down, and avoid strong impact.

6. Product selection-product definition
The distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10⑹kV or 35kV network voltage to the 230/400V bus voltage used by the user. This type of product is suitable for AC 50 (60) Hz, three-phase maximum rated capacity 2500kVA (single-phase maximum rated capacity 833kVA, generally not recommended to use single-phase transformer)
1) When there are a large number of primary or secondary loads, two or more transformers should be installed. When any one of the transformers is disconnected, the capacity of the remaining transformers can meet the power consumption of primary and secondary loads. The primary and secondary loads should be concentrated as much as possible, and should not be too scattered.
2) When the seasonal load capacity is large, a special transformer should be installed. Such as large-scale civil S4270D27-29 27 2005.7.29, 3:24 AM building air conditioning chiller load, heating electric heating load, etc.
3) When the concentrated load is large, a special transformer should be installed. Such as large heating equipment, large X-ray machine, electric arc furnace, etc.
4) When the lighting load is large or the power and lighting use a shared transformer, which seriously affects the lighting quality and bulb life, a special lighting transformer can be installed. Under normal circumstances, power and lighting share a transformer.
Product selection-choose a transformer according to the use environment

1) Under normal medium conditions, oil-immersed transformers or dry-type transformers can be used, such as independent or attached substations for industrial and mining enterprises, agriculture, and independent substations for residential communities, etc. The available transformers are S8, S9, S10, SC(B)9, SC(B)10 and so on.
2) In multi-story or high-rise main buildings, non-flammable or flame-retardant transformers, such as SC(B)9, SC(B)10, SCZ(B)9, SCZ(B)10, etc., should be used.
3) In places where dusty or corrosive gas seriously affects the safe operation of the transformer, a closed or sealed transformer should be selected, such as B S 9, S9-, S10-, SH12-M, etc.
4) High and low power distribution devices without combustible oil and non-oil-immersed distribution transformers can be installed in the same room. At this time, the transformer should be equipped with an IP2X protective enclosure for safety.

Product selection-choose a transformer according to the electrical load
1) The capacity of the distribution transformer should be integrated with the facility capacity of various electrical equipment to calculate the calculated load (generally excluding the fire load). The apparent capacity after compensation is the basis for selecting the capacity and number of transformers. The load rate of a general transformer is about 85%. This method is relatively simple and can be used to estimate capacity.
2) In GB/T17468-1998 “Guidelines for Selection of Power Transformers”, it is recommended that the capacity selection of distribution transformers should be determined according to GB/T17211-1998 “Guidelines for Dry-Type Power Transformer Loads” and the calculated load. The above two guidelines provide computer programs and normal cycle load diagrams to determine the capacity of distribution transformers.

7. Installation points
Distribution transformers are important components of substations. Dry-type transformers without shells are installed directly on the ground, with protective barriers around them; dry-type transformers with shells are installed directly on the ground. For its installation, please refer to the National Building Standard Design Atlas. 03D201-4 10/0.4kV transformer room layout and installation of common equipment components in substations.

8. Type selection-temperature control system
The safe operation and service life of dry-type transformers largely depend on the safety and reliability of the transformer winding insulation. The winding temperature exceeds the insulation withstand temperature and the insulation is damaged, which is one of the main reasons that the transformer can not work normally. Therefore, the monitoring of the transformer’s operating temperature and its alarm control are very important.
⑴Automatic control of the fan: The temperature signal is measured by the Pt100 thermistor that is embedded in the hottest part of the low-voltage winding. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110°C, the system automatically starts the fan cooling; when the winding temperature drops to 90°C, the system automatically stops the fan.
⑵Over-temperature alarm and trip: Collect winding or iron core temperature signals through PTC non-linear thermistor embedded in the low-voltage winding. When the transformer winding temperature continues to rise, if it reaches 155°C, the system will output an over-temperature alarm signal; if the temperature continues to rise to 170°C, the transformer cannot continue to operate, and an over-temperature trip signal must be sent to the secondary protection circuit, and the transformer should be used Tripped quickly.
⑶Temperature display system: The temperature change value is measured by the Pt100 thermistor embedded in the low-voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and the highest temperature in history can be recorded). The temperature is output by 4-20mA analog quantity, if it needs to be transmitted to a remote computer (distance up to 1200m)
Selection-protection method
IP20 protective housing is usually used to prevent solid foreign objects with a diameter greater than 12mm and small animals such as rats, snakes, cats, and birds from entering, causing malignant failures such as short-circuit power failures, and providing a safety barrier for live parts. If you need to install the transformer outdoors, you can choose an IP23 protective enclosure. In addition to the above IP20 protective function, it can also prevent water droplets within a 60° angle to the vertical. However, the IP23 shell will reduce the cooling capacity of the transformer, so pay attention to the reduction of its operating capacity when selecting.
Selection-overload capacity
The overload capacity of a dry-type transformer is related to the ambient temperature, the load condition before overload (initial load), the insulation and heat dissipation of the transformer, and the heating time constant. If necessary, the overload curve of the dry-type transformer can be obtained from the manufacturer.

How to use its overload capacity?
⑴When choosing to calculate the capacity of the transformer, it can be appropriately reduced: Fully consider the possibility of short-term impact overload of certain steel rolling, welding and other equipment-try to use the strong overload capacity of the dry-type transformer to reduce the transformer capacity; Evenly-loaded places, such as residential areas mainly for night lighting, cultural and entertainment facilities, and shopping malls mainly for air conditioning and daytime lighting, can make full use of their overload capacity, appropriately reduce the transformer capacity, and make the main operating time at full load Or short-term overload.

9. Check
⒈ Whether there is abnormal sound and vibration.
⒉Whether there is local overheating, harmful gas corrosion and other discoloration caused by creepage traces and carbonization on the insulating surface.
⒊Whether the air-cooling device of the transformer is operating normally.
⒋There should be no overheating of the high and low voltage joints. There should be no leakage and creepage at the cable head.
⒌The temperature rise of the winding should be based on the insulation material grade adopted by the transformer, and the monitored temperature rise shall not exceed the specified value.
⒍The supporting porcelain bottle should be free of cracks and discharge traces.
⒎Check whether the winding pressure piece is loose.
⒏Indoor ventilation, iron core air ducts should be free of dust and debris, and iron cores should be free from rust or corrosion.

10. Difference
Inverter: It can be adjusted to achieve the required power frequency (50hz, 60hz, etc.) to meet our special needs for electricity.
Transformer: Generally, it is a “step-down device”, which is commonly found near communities or factories. Its function is to reduce the ultra-high voltage to the normal voltage of our residents to meet people’s daily electricity consumption.
Dry-type transformers and oil-immersed transformers are the two most commonly used transformers. Compared with oil-immersed transformers, dry-type transformers have better fire protection performance, and are mostly used in places with higher fire protection requirements, such as hospitals, airports, stations, etc. Places, but the price is relatively high, and there are certain requirements for the environment, such as not being too humid, not having too much dust and dirt, etc.