CHINA Oil Distribution transformers are one of the important equipment in the power supply and distribution systems of industrial and mining enterprises and civil buildings. They reduce the network voltage of 10 (6) kV or 35kV to the 230/400V bus voltage used by users. This product is suitable for AC 50 (60) Hz, three-phase maximum Nameplate capacity 2500kVA (single-phase maximum Nameplate capacity 833kVA, single-phase transformer is generally not recommended), and can be used indoors (outdoors). When the capacity is 315kVA or less, it can be installed on the pole. The ambient temperature is not higher than 40 ℃, not lower than -25 ℃, the maximum daily average temperature is 30 ℃, the maximum annual average temperature is 20 ℃, and the relative humidity is not more than 90% (ambient temperature is 25 ℃), The altitude shall not exceed 1000m. If it does not comply with the above usage conditions, appropriate quota adjustments should be made in accordance with the relevant provisions of GB6450-86.
development history
Transformer oil is a petroleum based liquid that has the potential for combustion and has environmental drawbacks. However, due to the excellent performance and low price of transformer oil, the vast majority of power transformers still use transformer oil as insulation and cooling medium.
At the end of the 19th century, transformers began to use transformer oil as insulation and cooling medium, leading to the emergence of oil immersed transformers. In addition to abundant natural storage and low prices, transformer oil has been widely used due to its following characteristics.
1) When used in conjunction with fiber materials, the insulation performance is good, which can reduce insulation distance and reduce costs.
2) Transformer oil has low viscosity and good heat transfer performance.
3) It can effectively protect the iron core and winding from the influence of moisture in the air.
4) Protect insulation paper and cardboard from the action of oxygen, reduce the aging of insulation materials, and extend the service life of transformers.
Except for some special purpose small and medium-sized transformers and gas transformers, the vast majority of large and medium-sized transformers still use transformer oil as a cooling and insulation medium.
The insulation of transformers impregnated with transformer oil has a heat resistance grade of A and a long-term operating temperature of 105 ℃.
classification
Phase differentiation
It can be divided into three-phase transformers and single-phase transformers. In three-phase power systems, three-phase transformers are generally used. When the capacity is too large and limited by transportation conditions, three single-phase transformers can also be used in three-phase power systems to form transformer groups.
Winding differentiation
It can be divided into dual winding transformers and triple winding transformers. Usually, transformers are double winding transformers, which have two windings on the iron core, one is the original winding and the other is the secondary winding. A three winding transformer is a transformer with a larger capacity (above 5600 kVA) used to connect three different voltage transmission lines. In special cases, there are also Satons transformers that use more windings.
Structural classification
It can be divided into core type transformers and shell type transformers. If the winding is wrapped around the iron core, it is an iron core transformer; If the iron core is wrapped around the periphery of the winding, it is an iron shell transformer. The two are only slightly different in structure and have no essential difference in principle. Power transformers are all iron core type.
The transformer mainly consists of an iron core, winding, oil tank, conservator, insulating sleeve, tap changer, and gas relay.
1. Iron core
The iron core is the magnetic circuit part of a transformer. During operation, hysteresis loss and eddy current loss are generated to generate heat. To reduce heating loss and reduce volume and weight, the iron core is composed of cold rolled grain oriented silicon steel sheets with a high magnetic conductivity coefficient of less than 0.35mm. According to the arrangement of the winding in the iron core, there are two types: core type and shell type.
In large capacity transformers, in order to ensure that the heat generated by the loss of the iron core can be fully carried away by the insulating oil during circulation, in order to achieve good cooling effect, cooling oil channels are often installed in the iron core.
2. Winding
The winding and iron core are both core components of the transformer. Due to the resistance of the winding itself or the contact resistance at the joints, it is known from Joule's law that heat is generated. Therefore, the winding cannot pass a current higher than the rated current for a long time. In addition, when passing short-circuit current, a significant electromagnetic force will be generated on the winding and damage the transformer. There are two basic types of windings: concentric and overlapping.
The main faults of transformer windings are inter turn short circuits and short circuits to the casing. Interturn short circuits are mainly caused by insulation aging, or mechanical damage to the insulation during transformer overload and through short circuits. When the oil level inside the transformer drops, causing the winding to expose the oil level, inter turn short circuits can also occur; In addition, when there is a through short circuit, due to the effect of overcurrent, the winding deforms, causing mechanical damage to the insulation, and also causing inter turn short circuits. When there is an inter turn short circuit, the current inside the short-circuit winding may exceed the rated value, but the entire winding current may not exceed the rated value. In this case, the gas protection will act, and in severe cases, the differential protection device will also act. The cause of short circuit to the casing is also due to insulation aging, oil moisture, oil level drop, or lightning and overvoltage during operation. In addition, when a through short circuit occurs, the deformation of the winding due to overcurrent can also cause a short circuit to the casing. When there is a short circuit to the casing, it is generally the action of the gas protection device and the grounding protection action.
3. Fuel tank
The body (winding and iron core) of an oil immersed transformer is installed in a tank filled with transformer oil, which is welded with steel plates. The oil tank of medium and small transformers consists of a box shell and a box cover. The transformer body is placed inside the box shell, and the box cover can be opened to lift out the body for maintenance.
Insulation cooling classification
It can be divided into oil immersed transformers and dry type transformers. In order to enhance insulation and cooling conditions, the iron core and winding of the transformer are immersed together in the oil tank filled with transformer oil. In special situations, such as street lamps and mine lighting, dry transformers are also used.
Oil immersed type
1. Non enclosed oil immersed transformers: mainly including S8, S9, S10 and other series products, widely used in industrial and mining enterprises, agriculture, and civil buildings.
2. Closed oil immersed transformers: mainly including S9, S9-M, S10-M and other series of products, commonly used in places with high oil pollution and chemical substances in the petroleum and chemical industries.
3. Sealed oil immersed transformers: mainly available in BS9, S9-, S10-, S11-MR, SH, SH12-M and other series of products, can be used for power distribution in various places such as industrial and mining enterprises, agriculture, and civil buildings.
In addition, there are various special transformers for specific purposes. For example, high-voltage transformers for testing, transformers for electric furnaces, transformers for welding and transformers for thyristor circuits, Voltage transformer and current transformers for measuring instruments.
Performance characteristics
a. The low-voltage winding of oil immersed transformers generally adopts a cylindrical structure with copper foil winding, except for small capacity copper wires; The high-voltage winding adopts a multi-layer cylindrical structure, ensuring a balanced distribution of ampere turns, low magnetic leakage, high mechanical strength, and strong short-circuit resistance.
b. The iron core and winding each adopt fastening measures, and the fastening parts such as the height and low-voltage leads of the device are equipped with self-locking anti loosening nuts. They adopt a non hanging core structure and can withstand transportation bumps.
c. The coil and iron core are vacuum dried, and the transformer oil is filtered and injected using a vacuum process to minimize moisture inside the transformer.
d. The oil tank adopts corrugated plates, which have breathing function to compensate for the volume change of oil caused by temperature changes. Therefore, this product does not have an oil storage tank, which obviously reduces the height of the transformer.
e. Due to the replacement of the oil storage tank with corrugated sheets, the transformer oil is isolated from the outside, effectively preventing the entry of oxygen and water, which can lead to a decrease in insulation performance.
f. Based on the above five performance points, it ensures that the oil immersed transformer does not require oil replacement during normal operation, greatly reducing the maintenance cost of the transformer and extending its service life.
Key selection points
Load nature
1) When there is a large number of primary or secondary loads, it is advisable to install two or more transformers. When either transformer is disconnected, the capacity of the remaining transformers can meet the electricity consumption of primary and secondary loads. 1, The secondary load should be concentrated as much as possible and should not be too dispersed.
2) When the seasonal load capacity is large, special transformers should be installed. For example, the load of air conditioners and freezers in large civil buildings, and the load of heating electric heating.
3) When the concentrated load is large, special transformers should be installed. Such as large heating equipment, large X-ray machines, electric arc furnaces, etc.
4) When the lighting load is large or the use of a shared transformer for power and lighting seriously affects the lighting quality and bulb life, a dedicated lighting transformer can be installed. In general, power and lighting share a transformer.
Usage environment
Under normal medium conditions, oil immersed transformers or dry-type transformers can be selected, such as independent or attached Electrical substation for industrial and mining enterprises, agriculture, and independent Electrical substation for residential areas. The transformers available for selection include S8, S9, S10, SC (B) 9, SC (B) 10, etc.
Temperature environment
① Maintain long-term stability at a temperature of 220 ℃
② Capable of withstanding short-term operation at a temperature of 350 ℃
③ Maintain stable performance over a wide range of temperature and humidity
④ At a temperature of 250 ℃, it will not melt, flow, or support combustion
⑤ No toxic or corrosive gases will be released at a temperature of 750 ℃
Installation requirements
1. The transformer foundation track should be horizontal, and the oil conservator should have a slope of 1-1.5%.
2. Transformers should be reinforced.
3. The primary and secondary leads of the transformer should not cause stress on the bushing.
The transformer shell is firmly connected to the neutral point and grounding device to form a trinity 800KVA (install gas relay).
characteristic
advantage
1. Transformer oil has good insulation and thermal conductivity, while transformer oil is cheap.
2. It can solve the problem of high capacity heat dissipation and high voltage insulation in transformers.
disadvantage
1. Transformer oil has flammability and may burn and explode when encountering flames
2. Transformer oil is harmful to human health
3. Transformer oil needs to be regularly inspected
4. The sealing performance of oil immersed transformers is poor and should be aged, resulting in severe oil leakage in the operating site, which affects the safe operation of equipment and also affects the environment
5. The insulation level of oil-immersed transformers is low, and they are designed and manufactured according to Class A insulation
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