# Brief Analysis of Electric Control Circuit Diagram for Automatic Cooling of Power Transformer

The power transformer runs continuously in summer. When its own temperature exceeds 65°C, the automatic control fan motor starts to cool down the power transformer, so as to prevent the power transformer from overheating and burning out. First, you should find out which components are used in the figure according to the graphic symbols in the figure, relays and AC contactors with contacts, and carefully distinguish their contacts and their states (moving on or off).

The power transformer runs continuously in summer. When its own temperature exceeds 65°C, the automatic control fan motor starts to cool down the power transformer, so as to prevent the power transformer from overheating and burning out. First, you should find out which components are used in the figure according to the graphic symbols in the figure, relays and AC contactors with contacts, and carefully distinguish their contacts and their states (moving on or off).

In the figure, SA1 is a start switch. WJ1 and WJ2 are electrical contact thermometers, WJ1 is the upper limit contact of the electrical contact thermometer, and WJ2 is the lower limit contact. KA is a relay coil, which has a set of moving and breaking contacts. KM is an AC contactor coil, which has multiple sets of moving contacts KM1, KM2, and KM3. SA2 is an automatic and manual switch. KT is a thermal relay.

1. Manual state

When the contacts ① and ③ of the function switch SA2 are connected, the circuit is in the state of manually controlling the fan motor. At this time, pressing the SA1 self-locking button will cause the KM coil to be electrically pulled in, its moving contact KM2 will be closed and self-locking, and the KM3 moving contact will be closed, which will make the electric work of the fan motor and the power transformer. cool down.

2. Automatic state

When the ① and ② contacts of the function switch SA2 are connected, the circuit is in the state of automatically controlling the fan motor.

1. Fan start

When the transformer is running and its temperature rises to the upper limit, the upper limit contact of the WJ1 thermometer is closed, so that the KM AC contactor coil is electrically pulled in, and its KM1, KM2, KM3 moving contacts are closed, so that the fan starts to work. , to cool the power transformer.

2. The fan stops

When the fan starts to cool down the power transformer, once the temperature of the transformer drops to the lower limit, the lower limit contact of WJ2 will be closed, and then the KA coil will be energized and closed, so that the dynamic break contact will be disconnected, thereby cutting off the KM coil. The power supply of the fan will release the power supply, and its KM1~KM3 contacts will be disconnected, so that the fan motor will stop working. Once the temperature of the transformer rises to the upper limit value, the above-mentioned actions are repeated, and the circuit works over and over again.