What are the commonly used cooling methods for transformers
Время публикации: 2020-06-19 20:24:18
A transformer is a device that transforms AC voltage, current, and impedance. When an alternating current flows through the primary coil, an alternating magnetic flux is generated in the iron core (or magnetic core), which induces a voltage (or current) in the secondary coil. The transformer is composed of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power source is called a primary coil, and the remaining windings are called secondary coils. In the generator, whether the coil moves through the magnetic field or the magnetic field moves through the fixed coil, the electric potential can be induced in the coil. In both cases, the value of the magnetic flux is unchanged, but the amount of magnetic flux intersecting with the coil is Change, this is the principle of mutual induction. A transformer is a device that uses electromagnetic mutual induction to transform voltage, current, and impedance.
Commonly used cooling methods for transformers include oil-immersed self-cooling (ONAN), oil-immersed air cooling (ONAF), forced oil circulation air cooling (OFAF), forced oil circulation water cooling (OFWF), forced guided oil circulation air cooling (ODAF), Forced oil circulation water cooling ODWF). According to the requirements of transformer selection guidelines, the selection of cooling methods is recommended as follows:
1. Oil-immersed self-cooling
31500kVA and below, 35kV and below products;
Products of 50000kVA and below, 110kV.
2. Oil-immersed air cooling
12500kVA～63000kVA, 35kV～110kV products;
110kV products below 75000kVA;
40000kVA and below, 220kV products.
3. Forced oil circulation air cooling
50000-90000kVA, 220kV products.
4. Forced oil circulation water cooling
The booster transformers of general hydropower plants are used for 220kV and above, 60MVA and above.
5. Forced guided oil circulation air cooling or water cooling (ODAF or ODWF)
75000kVA and above, 110kV products;
120000kVA and above, 220kV products;
330kV and 500kV products.
When the strong oil air cooling method is selected, when the oil pump and the fan lose the power supply, the transformer cannot run for a long time. It can't run for a long time even without load. Therefore, two independent power supplies should be selected for the cooler. When the strong oil water cooling method is selected, the oil pump cooling water cannot run when it loses power. The power supply should select two independent power supplies.
The oil-invading self-cooling type has no special cooling equipment, it uses the natural convection effect of oil to bring the heat emitted by the winding and the iron core to the tank wall or the tube (chip) radiator, and then rely on the convection conduction of air to transfer the heat Distribute. This cooling method is often used in small-capacity transformers.
The oil-invaded air-cooled type is to install a cooling fan on the inside of the disassembled radiator of the transformer, and use the fan to blow the air to accelerate the cooling of the oil in the radiator. The same transformer, using air-cooled heat dissipation, can increase the capacity by 30-35%. Medium-capacity transformers generally use air-cooled heat dissipation.
Forced air cooling and strong oil water cooling are two methods of cooling the hot oil in the transformer oil tank, using an oil pump into the oil cooler, after cooling, return to the oil tank, cooling winding and oil tank. The oil cooler is made into a special shape that is easy to dissipate heat, and the heat in the oil is taken away by using a fan blowing or circulating water as a cooling medium. These two cooling methods have a strong cooling effect. Large-capacity transformers generally use these two cooling methods.
There are two cooling methods for dry-type transformers:
1. AN-air (circulation) natural cooling;
2. AF-air cooling. According to the technical requirements of the dry-type transformer, the transformer can meet the rated operation requirements under the cooling condition of AN. But dry-type transformers are usually equipped with fans, which are for emergency use by users. So strictly speaking, there is only one cooling method for dry-type transformers, which is natural air cooling.Тег: transformers