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1. General requirements for power transformer cooling devices

a. Install all cooling devices as specified by the manufacturer;

b. The cooling system with strong oil circulation must have two independent power sources and can be switched automatically. When the working power supply fails, it should be automatically put into the standby power supply and send out sound and light signals;

c. Strong oil circulation transformer, when cutting the fault cooler should send sound and light signals, and automatically (water cooling can be manually) into the standby cooler;

d. The attached motor of fan, water pump and oil pump should be protected from overload, short circuit and phase break; There should be a device to monitor the rotation direction of the oil pump motor;

e. The oil pump of the water cooler shall be installed on the oil inlet side of the cooler, and ensure that the oil pressure in the cooler is about 0.05MPa greater than the water pressure in any case (except otherwise specified by the manufacturer). The outlet side of the cooler should have a drain cock;

f. Transformer with strong oil circulating water cooling, check valve should be installed at the outlet of submersible oil pump of each cooler;

g. The transformer with strong oil circulation cooling shall be able to control the switching of the cooler according to temperature and/or load.

2. The role of transformer cooler

When the temperature difference between the upper oil temperature and the lower oil temperature of the transformer occurs, the oil temperature convection is formed through the cooler, which flows back to the tank after cooling by the cooler and plays the role of reducing the temperature of the transformer.

I. Cooling mode of transformer cooler

(1) oil-immersed natural air cooling method;

(2) oil-immersed air-cooled type;

(3) forced oil circulation water cooling type;

(4) forced oil circulation air-cooled type;

(5) forced oil circulation guided cooling mode.

In 500kV substation, the general large transformer adopts forced oil circulation air cooling, and the super large transformer adopts forced oil circulation guided cooling.

Two. The working principle of transformer cooler

Traditional power transformers are manually controlled fans, and each transformer has 6 groups of air-cooled motors that need to be controlled, and each group of fans is realized by relying on thermal relay. The circuit of fan power supply is controlled by contactor, and the fan is measured by transformer oil temperature and transformer overload process. Thus through logical judgment to determine the fan start and stop.

The mechanical contact is driven mainly by the artificial mechanical contact. In this way, traditional control can only be controlled by manual control. But its biggest disadvantage is that all the fans should start and stop at the same time, and the impact current generated when starting is relatively large, often cause damage to the components in the circuit, when the temperature is 45 to 55 degrees Celsius, often adopt the way of all work input, This will lead to a huge waste of energy and the maintenance of equipment will cause great difficulties.

The general cooling control system mainly uses components including relays, thermal relays and various contact logic circuit control systems. The control logic is very complex. In the actual process of operation, the contactor will contact and separate with the contact for many times and cause the burning phenomenon. And the fan also lacks some very necessary protection, such as overload, phase deficiency and overload, which will reduce the reliability of its operation and increase the cost of operation virtually in the actual operation process.

Three. Strong oil strong air cooling transformer cooler components

The cooler consists of heat exchanger, fan, motor, airway, oil flow indicator and so on. The cooling fan is used to expel the hot air emitted from the heat exchanger. The oil pump is installed in the lower part of the cooler, so that the top oil of the heat exchanger circulates downward. The oil flow indicator is installed in the lower part of the cooler in a more obvious position to facilitate the operator to observe the running state of the oil pump.

Iv. The role of the transformer's fuel tank and cooling device

The oil tank of the transformer is the shell of the transformer, which is equipped with the core, winding and transformer oil, and plays a certain role in heat dissipation.

The function of the transformer cooling device is that when the temperature difference of the upper oil temperature of the transformer is generated, the oil circulation is formed through the radiator, so that the oil flows back to the tank after being cooled by the radiator, and the transformer oil temperature is reduced. In order to improve the cooling effect, air cooling, strong oil air cooling or strong oil water cooling measures can be used.